Underfloor heating
Encyclopedia
Underfloor heating and cooling is a form of central heating and cooling which achieves indoor climate control for thermal comfort
using conduction, radiation
and convection
. The terms radiant heating and radiant cooling
are commonly used to describe this approach because radiation is responsible for a significant portion of the resulting thermal comfort but this usage is technically correct only when radiation composes more than 50% of the heat exchanged between the floor and the rest of the space.
periods. Archeological digs in Asia and the Aleutian islands of Alaska reveal how the inhabitants drafted smoke from fires through stone covered trenches which were excavated in the floors of their subterranean
dwellings. The hot smoke heated the floor stones which then radiated into the living spaces. These early forms have evolved into modern systems using fluid filled pipes or electrical cables and mats. Below is a chronological overview of under floor heating from around the world.
elements ("electric systems") or fluid flowing in pipes ("hydronic systems”) to heat the floor. Either type can be installed as the primary, whole-building heating system or as localized floor heating for thermal comfort. Electrical resistance can only be used for heating so when space cooling is also required, hydronic systems are used. Other applications for which either electric or hydronic systems are suited include snow/ice melting
for walks, driveways and landing pads, turf conditioning of football and soccer fields and frost prevention in freezers and skating rinks.
Electric heating elements or hydronic piping can be cast in a concrete floor slab ("poured floor system" or "wet system"). They can also be placed under the floor covering ("dry system") or attached directly to a wood sub floor ("sub floor system" or "dry system").
Some commercial buildings are designed to take advantage of thermal mass
which is heated or cooled during off peak hours when utility rates are lower. With the heating/cooling system turned off during the day, the concrete mass and room temperature drift up or down within the desired comfort range. Such systems are known as thermally activated building systems or TABS.
as the heat transfer fluid in a "closed loop" that is recirculated between the floor and the boiler.
Various types of pipes are available specifically for hydronic underfloor heating and cooling systems and are generally made from polyethylene
including PEX
, PEX-Al-PEX and PERT. Older materials such as Polybutylene
(PB) and copper or steel pipe are still used in some locales or for specialized applications.
Hydronic systems require skilled designers and tradespeople familiar with boilers, circulators, controls, fluid pressures and temperature. The use of modern factory assembled sub-stations, used primarily in district heating and cooling, can greatly simplify design requirements and reduce the installation and commissioning time of hydronic systems.
Hydronic systems can use a single source or combination of energy sources to help manage energy costs. Hydronic system energy source options are:
Electric systems are used only for heating and employ non-corrosive, flexible heating elements including cables, pre-formed cable mats, bronze mesh, and carbon films. Due to their low profile they can be installed in a thermal mass
or directly under floor finishes. Electric systems can also take advantage of time-of-use electricity metering
and are frequently used as carpet heaters, portable under area rug heaters, under laminate floor heaters, under tile heating, under wood floor heating, and floor warming systems, including under shower floor and seat heating. Large electric systems also require skilled designers and tradespeople but this is less so for small floor warming systems. Electric systems use fewer components and are simpler to install and commission than hydronic systems. Some electric systems use line voltage technology while others use low voltage technology. Power consumption of an electric system is not based on voltage but rather wattage output produced by the heating element.
is, “that condition of mind which expresses satisfaction with the thermal environment and is assessed by subjective evaluation.” Relating specifically to underfloor heating, thermal comfort is influenced by floor surface temperature and associated elements such as radiant asymmetry, mean radiant temperature
and operative temperature
. Research by Nevins, Rohles, Gagge, P. Ole Fanger
et al. show that humans at rest with clothing typical of light office and home wear, exchange over 50% of their sensible heat
via radiation
.
Underfloor heating influences the radiant exchange by thermally conditioning the interior surfaces with low temperature long wave radiation. The heating of the surfaces suppresses body heat loss resulting in a perception of heating comfort. This general sensation of comfort is further enhanced through conduction (feet on floor) and through convection
by the surface's influence on air density
. Underfloor cooling works by absorbing both short wave
and long wave radiation resulting in cool interior surfaces. These cool surfaces encourage the loss of body heat resulting in a perception of cooling comfort. Localized discomfort due to cold and warm floors wearing normal foot wear and stocking feet is addressed in the ISO 7730 and ASHRAE 55 standards and ASHRAE Fundamentals Handbooks and can be corrected or regulated with floor heating and cooling systems.
control, floor heating also establishes temperature conditions that are less favorable in supporting mold
, bacteria
, viruses and dust mites. By removing the sensible heat
ing load from the total HVAC
(Heating, Ventilating, and Air Conditioning) load, ventilation
, filtration and dehumidification of incoming air can be accomplished with dedicated outdoor air systems having less volumetric turnover to mitigate distribution of airborne contaminates. There is recognition from the medical community relating to the benefits of floor heating especially as it relates to allergens.
, entropy
, exergy
and efficacy
. When combined with high performance buildings, under floor systems operate with low temperatures in heating and high temperatures in cooling in the ranges found typically in geothermal
and solar thermal systems. When coupled with these non combustible, renewable
energy sources the sustainability
benefits include reduction or elimination of combustion and green house gases produced by boilers and power generation for heat pumps and chiller
s, as well as reduced demands for non renewables
and greater inventories for future generations. This has been supported through simulation evaluations and though research funded by the U.S. Department of Energy, Canada Mortgage and Housing Corporation, Fraunhofer Institute as well as ASHRAE.
hazards, nor is it a hazard for physical injuries due to accidental contact leading to tripping and falling. This has been referenced as a positive feature in healthcare facilities including those serving elderly clients and those with dementia
. Anecdotally, under similar environmental conditions, heated floors will speed evaporation of wetted floors (showering, cleaning, and spills). Additionally, underfloor heating with fluid filled pipes is useful in heating and cooling explosion proof environments where combustion and electrical equipment can be located remotely from the explosive environment.
systems except when pipes, cables or mats are embedded in the floor. Early trials (for example homes built by Levitt and Eichler, c. 1940-70’s) experienced failures in embedded copper and steel piping systems as well as failures assigned by the courts to Shell, Goodyear and others for polybutylene
and EPDM materials. There also have been a few publicized claims of failed electric heated gypsum panels from the mid 90’s.
Failures associated with most installations are attributable to job site neglect, installation errors and product mishandling such as exposure to ultraviolet radiation. Pre-pour pressure tests required by concrete installation standards and good practice guidelines for the design, construction, operation and repair of radiant heating and cooling systems mitigate problems resulting from improper installation and operation.
Fluid based systems using Cross-linked polyethylene (PE-x) a product developed in the 1930s and its various derivatives such as PE-rt, have demonstrated reliable long term performance in harsh cold-climate applications such as bridge decks, aircraft hangar aprons and landing pads. Since the materials are produced from polyethylene and its bonds are cross-linked, it is highly resistant to corrosion or the temperature and pressure stresses associated with typical fluid based HVAC systems.
Convective heat transfer with underfloor systems is much greater when the system is operating in a heating rather than cooling mode. Typically with underfloor heating the convective component is almost 50% of the total heat transfer and in underfloor cooling the convective component is less than 10%.
With underfloor cooling, condensation may collect on the surface of the floor. To prevent this, air humidity is kept low, below 50%, and floor temperatures are maintained above the dew point, 66°F(19°C).
Control system (see Hydronic heating systems
Underfloor heating and cooling systems can have several control points including the management of:
Modeling radiant piping (also tube or loop) patterns with finite element analysis (FEA) predicts the thermal diffusions and surface temperature quality or efficacy
of various loop layouts. The performance of the model (left image above) and image to the right are useful to gain an understanding in relationships between flooring resistances, conductivities of surrounding mass, tube spacing’s, depths and fluid temperatures. As with all FEA simulations, they depict a snap shot in time for a specific assembly and may not be representative of all floor assemblies nor for system that have been operative for considerable time in a steady state condition. The practical application of FEA for the engineer is being able to assess each design for fluid temperature, back losses and surface temperature quality. Through several iterations it is possible to optimize the design for the lowest fluid temperature in heating and the highest fluid temperature in cooling which enables combustion and compression equipment to achieve its maximum rated efficiency performance.
is a useful tool to see the actual thermal efficacy of an underfloor system from its start up (as shown) to its operating conditions. In a startup it is easy to identify the tube location but less so as the system moves into a steady state
condition. It is important to interpret thermographic images correctly. As is the case with finite element analysis (FEA), what is seen, reflects the conditions at the time of the image and may not represent the steady conditions. For example, the surfaces viewed in the images shown, may appear ‘hot’, but in reality are actually below the nominal temperature of the skin and core temperatures of the human body
and the ability to ‘see’ the pipes does not equate to ‘feel’ the pipes. Thermography can also point out flaws in the building enclosures (left image, corner intersection detail), thermal bridging (right image, studs) and the heat losses associated with exterior doors (center image).
, Asia
n and Europe
an communities. Consequently the market is more mature and systems relatively more affordable than North America
where market share for fluid based systems remains between 3% to 7% of HVAC systems (ref. Statistics Canada
and United States Census Bureau
).
In energy efficiency buildings such as Passive House
, R-2000
or Net Zero Energy, simple thermostatic radiator valve
s can be installed along with a single compact circulator and small condensing heater controlled without or with basic hot water reset
control. Economical electric resistant based systems also are useful in small zones such as bathrooms and kitchens, but also for entire buildings where heating loads are very low and preferably where photovoltaics, wind or hydro is the generating source of electricity. Larger structures will need more sophisticated systems
to deal with cooling and heating needs, and often requiring building management control systems
to regulate the energy use and control the overall indoor environment.
Low temperature radiant heating and high temperature radiant cooling systems lend themselves well to district energy
systems (community based systems) due to the temperature differentials between the plant and the buildings which allow small diameter insulated distribution networks and low pumping power requirements. The low return temperatures in heating and high return temperatures in cooling enable the district energy plant to achieve maximum efficiency. The principles behind district energy with underfloor systems can also be applied to stand alone multi story buildings with the same benefits. Additionally, underfloor radiant systems are ideally suited to renewable energy
sources including geothermal
and solar thermal systems or any system where waste heat is recoverable.
In the global drive for sustainability
, long term economics supports the need to eliminate where possible, compression
for cooling and combustion
for heating. It will then be necessary to use low quality heat sources for which radiant underfloor heating and cooling is well suited.
.
Though the efficiency of radiant systems is under constant debate with no shortage of anecdotal claims and scientific papers presenting both sides, the low return fluid temperatures in heating and high return fluid temperatures in cooling enable condensing boilers, chiller
s and heat pump
s to operate at or near their maximum engineered performance
. The greater efficiency of 'wire to water' versus 'wire to air' flow due to water's significantly greater heat capacity
favors fluid based systems over air based systems. Both field application and simulation research have demonstrated significant electrical energy savings with radiant cooling and dedicated outdoor air systems based in part on the previous noted principles.
In Passive House
s, R-2000 homes
or Net Zero Energy buildings the low temperatures of radiant heating and cooling systems present significant opportunities to exploit exergy
.
between the floor mass and occupants and other contents of the conditioned space. For example, carpeting has a greater resistance
or lower conductance
than tile. Thus carpeted floors need to operate at higher internal temperatures than tile which can create lower efficiencies for boilers and heat pumps. However, when the floor covering is known at the time the system is installed then the internal floor temperature required for a given covering can be achieved through proper tube spacing without sacrificing plant efficiency (though the higher internal floor temperatures may result in increased heat loss from the non-room surfaces of the floor).
The emissivity
, reflectivity
and absorptivity of a floor surface are critical determinants of its heat exchange with the occupants and room. Unpolished flooring surface materials and treatments have very high emissivity’s (0.85 to 0.95) and therefore make good heat radiators
.
With underfloor heating and cooling ("reversible floors") flooring surfaces with high absorbance and emissivity
and low reflectivity
are most desirable.
Thermal comfort
Thermal comfort is a term used by the American Society of Heating, Refrigerating and Air-Conditioning Engineers, an international body. It is defined as the state of mind in humans that expresses satisfaction with the surrounding environment...
using conduction, radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
and convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
. The terms radiant heating and radiant cooling
Radiant cooling
A radiant cooling system refers to a temperature-controlled surface that cools indoor temperatures by removing sensible heat and where more than half of heat transfer occurs through thermal radiation....
are commonly used to describe this approach because radiation is responsible for a significant portion of the resulting thermal comfort but this usage is technically correct only when radiation composes more than 50% of the heat exchanged between the floor and the rest of the space.
History
Underfloor heating has a long history extending back into the Neoglacial and NeolithicNeolithic
The Neolithic Age, Era, or Period, or New Stone Age, was a period in the development of human technology, beginning about 9500 BC in some parts of the Middle East, and later in other parts of the world. It is traditionally considered as the last part of the Stone Age...
periods. Archeological digs in Asia and the Aleutian islands of Alaska reveal how the inhabitants drafted smoke from fires through stone covered trenches which were excavated in the floors of their subterranean
Subterranea (geography)
Subterranea refers to underground structures, both natural and man-made . Some subterranea include:* Bunker* Casemate* Catacombs* Caves** Ice caves* Cave dwellings, Cave house* Cave temple* Cellar* Cenote* Dungeon...
dwellings. The hot smoke heated the floor stones which then radiated into the living spaces. These early forms have evolved into modern systems using fluid filled pipes or electrical cables and mats. Below is a chronological overview of under floor heating from around the world.
| Time period, c. BC | Description |
|---|---|
| 5,000 | Evidence of “baked floors” are found foreshadowing early forms of kang and dikang Kang bed-stove The Kang is a traditional long sleeping platform made of bricks or other forms of fired clay and more recently of concrete in some locations. Its interior cavity, leading to a flue, channels the exhaust from a wood or coal stove... “heated floor” later ondol Ondol An ondol, also called gudeul, in Korean traditional architecture, is underfloor heating which uses direct heat transfer from wood smoke to the underside of a thick masonry floor... meaning “warm stone” in Korea Korea Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the... and Manchu Manchu The Manchu people or Man are an ethnic minority of China who originated in Manchuria . During their rise in the 17th century, with the help of the Ming dynasty rebels , they came to power in China and founded the Qing Dynasty, which ruled China until the Xinhai Revolution of 1911, which... respectively. |
| 3,000 | Korean fire hearth, was used both as kitchen range and heating stove. |
| 1,000 | Ondol type system used in the Aleutian Islands, Alaska and in Unggi, Hamgyeongbuk-do Ondol An ondol, also called gudeul, in Korean traditional architecture, is underfloor heating which uses direct heat transfer from wood smoke to the underside of a thick masonry floor... (present-day North Korea). |
| 1,000 | More than two hearths were used in one dwelling; one hearth located at the center was used for heating, the others at the perimeter was used for cooking throughout the year. This perimeter hearth is the initial form of the budumak (meaning kitchen range), which composes combustion section of the traditional ondol in Korea. |
| 500 | Greeks Greeks The Greeks, also known as the Hellenes , are a nation and ethnic group native to Greece, Cyprus and neighboring regions. They also form a significant diaspora, with Greek communities established around the world.... and later Romans Ancient Rome Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world.... scale up the use of conditioned surfaces (floors and walls) with the hypocausts. |
| 200 | Central hearth developed into gudeul (meaning heat releasing section of ondol) and perimeter hearth for cooking became more developed and budumak was almost established in Korea. |
| 50 | China, Korea and Roman Empire Roman Empire The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean.... use kang, dikang/ondol and hypocaust respectively. |
| Time period, c. AD | Description |
|---|---|
| 500 | Asia continues to use conditioned surfaces but the application is lost in Europe where it is replaced by the open fire or rudimentary forms of the modern fireplace. Anecdotal literary reference to radiant cooling system in the Middle East Middle East The Middle East is a region that encompasses Western Asia and Northern Africa. It is often used as a synonym for Near East, in opposition to Far East... using snow packed wall cavities. |
| 700 | More sophisticated and developed gudeul was found in some palaces and living quarters of upper class people in Korea. Countries in the Mediterranean Basin Mediterranean Basin In biogeography, the Mediterranean Basin refers to the lands around the Mediterranean Sea that have a Mediterranean climate, with mild, rainy winters and hot, dry summers, which supports characteristic Mediterranean forests, woodlands, and scrub vegetation... (Iraq, Algeria, Turkey, Afghanistan et al.) use various forms of hypocaust type heating in public baths and homes (ref.: tabakhana, atishkhana, sandali) but also use heat from cooking (see:tandoor Tandoor A tandoor is a cylindrical clay oven used in cooking and baking. The tandoor is used for cooking in Azerbaijan, India, Turkey, Iran, Armenia, Georgia, Pakistan, Uzbekistan, Afghanistan, the Balkans, the Middle East, and Central Asia, as well as Burma and Bangladesh.The heat for a tandoor was... , also tanur) to heat the floors. |
| 1000 | Ondol continues to evolve in Asia. The most advanced true ondol system was established. The fire furnace was moved outside and the room was entirely floored with ondol in Korea. Europe uses various forms of the fireplace with the evolution of drafting combustion products with chimneys. |
| 1400 | Hypocaust type systems used to heat Turkish Baths of the Ottoman Empire Ottoman Empire The Ottoman EmpireIt was usually referred to as the "Ottoman Empire", the "Turkish Empire", the "Ottoman Caliphate" or more commonly "Turkey" by its contemporaries... . |
| 1500 | Attention to comfort and architecture in Europe evolves; China and Korea continue to apply floor heating with wide scale adoption. |
| 1600 | In France France The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France... , heated flues in floors and walls are used in greenhouses. |
| 1700 | Benjamin Franklin Benjamin Franklin Dr. Benjamin Franklin was one of the Founding Fathers of the United States. A noted polymath, Franklin was a leading author, printer, political theorist, politician, postmaster, scientist, musician, inventor, satirist, civic activist, statesman, and diplomat... studies the French and Asian cultures and makes note of their respective heating system leading to the development of the Franklin stove Franklin stove The Franklin stove is a metal-lined fireplace named after its inventor, Benjamin Franklin. It was invented in 1741.L.W. Labaree, W. Bell, W.B. Willcox, et al., eds., The Papers of Benjamin Franklin , vol. 2, page 419... . Steam based radiant pipes are used in France. Hypocaust type system used to heat public bath (Hammam Hammam A Turkish bath is the Turkish variant of a steam bath, sauna or Russian Bath, distinguished by a focus on water, as distinct from ambient steam.... ) in the citadel town of Erbil located in modern day Iraq. |
| 1800 | Beginnings of the European evolution of the modern water heater/boiler and water based piping systems including studies in thermal conductivities Conductivity, temperature, depth A CTD profiler is an essential instrument of physical and biological oceanographic field research. Operated from a ship, it greatly contributes to our understanding of ocean dynamics by gathering information on the distribution and variation of the ocean's properties... and specific heat of materials and emissivity Emissivity The emissivity of a material is the relative ability of its surface to emit energy by radiation. It is the ratio of energy radiated by a particular material to energy radiated by a black body at the same temperature... /reflectivity Reflectivity In optics and photometry, reflectivity is the fraction of incident radiation reflected by a surface. In general it must be treated as a directional property that is a function of the reflected direction, the incident direction, and the incident wavelength... of surfaces (Watt James Watt James Watt, FRS, FRSE was a Scottish inventor and mechanical engineer whose improvements to the Newcomen steam engine were fundamental to the changes brought by the Industrial Revolution in both his native Great Britain and the rest of the world.While working as an instrument maker at the... /Leslie John Leslie (physicist) Sir John Leslie was a Scottish mathematician and physicist best remembered for his research into heat.Leslie gave the first modern account of capillary action in 1802 and froze water using an air-pump in 1810, the first artificial production of ice.In 1804, he experimented with radiant heat using... /Rumford Benjamin Thompson Sir Benjamin Thompson, Count Rumford , FRS was an American-born British physicist and inventor whose challenges to established physical theory were part of the 19th century revolution in thermodynamics. He also served as a Lieutenant-Colonel in the Loyalist forces in America during the American... ). Reference to the use of small bore pipes used in the John Soane house and museum. |
| 1864 | Ondol type system used at Civil War American Civil War The American Civil War was a civil war fought in the United States of America. In response to the election of Abraham Lincoln as President of the United States, 11 southern slave states declared their secession from the United States and formed the Confederate States of America ; the other 25... hospital sites in America. Reichstag building Reichstag (building) The Reichstag building is a historical edifice in Berlin, Germany, constructed to house the Reichstag, parliament of the German Empire. It was opened in 1894 and housed the Reichstag until 1933, when it was severely damaged in a fire. During the Nazi era, the few meetings of members of the... in Germany uses the thermal mass of the building for cooling and heating. |
| 1899 | The earliest beginnings of polyethylene Polyethylene Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons... -based pipes occur when German scientist, Hans von Pechmann Hans von Pechmann Hans von Pechmann was a German chemist, renowned for his discovery of diazomethane in 1894. , Pechmann condensation and Pechmann pyrazole synthesis... , discovered a waxy residue at the bottom of a test tube, colleagues Eugen Bamberger and Friedrich Tschirner called it polymethylene but it was discarded as having no commercial use at the time. |
| 1904 | Liverpool Cathedral Liverpool Cathedral Liverpool Cathedral is the Church of England cathedral of the Diocese of Liverpool, built on St James's Mount in Liverpool and is the seat of the Bishop of Liverpool. Its official name is the Cathedral Church of Christ in Liverpool but it is dedicated to Christ and the Blessed Virgin... in England is heated with system based on the hypocaust principles. |
| 1905 | Frank Lloyd Wright Frank Lloyd Wright Frank Lloyd Wright was an American architect, interior designer, writer and educator, who designed more than 1,000 structures and completed 500 works. Wright believed in designing structures which were in harmony with humanity and its environment, a philosophy he called organic architecture... makes first trip to Japan, later incorporates various early forms of radiant heating in his projects. |
| 1907 | England, Prof. Barker granted Patent No. 28477 for panel warming using small pipes. Patents later sold to the Crittal Company who appointed representatives across Europe. A.M. Byers of America promotes radiant heating using small bore water pipes. Asia continues to use traditional ondol and kang—wood is used as the fuel, combustion gases sent under floor. |
| 1930 | Oscar Faber in England uses water pipes used to radiant heat and cool several large buildings. |
| 1933 | Explosion at England’s Imperial Chemical Industries Imperial Chemical Industries Imperial Chemical Industries was a British chemical company, taken over by AkzoNobel, a Dutch conglomerate, one of the largest chemical producers in the world. In its heyday, ICI was the largest manufacturing company in the British Empire, and commonly regarded as a "bellwether of the British... (ICI) laboratory during a high pressure experiment with ethylene gas Ethylene Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone... results in a wax like substance—later to become polyethylene and the re-beginnings of PEX pipe. |
| 1937 | Frank Lloyd Wright designs the radiant heated Herbert Jacobs house Herbert and Katherine Jacobs First House Herbert and Katherine Jacobs First House, commonly referred to as Jacobs I, is a single family home located in Madison, Wisconsin. Designed by noted American architect Frank Lloyd Wright, it was constructed in 1937 and is considered by most to be the first Usonian home.-History:Madison... , the first Usonian home. |
| 1939 | First small scale polyethylene plant built in America. |
| 1945 | American developer William Levitt William Levitt William Jaird Levitt was an American real-estate developer widely credited as the father of modern American suburbia. He came to symbolize the new suburban growth with his use of mass-production techniques to construct large developments of houses selling for under $10,000... builds large scale developments for returning GI’s. Water based (copper pipe) radiant heating used throughout thousands of homes. Poor building envelopes on all continents require excessive surface temperatures leading in some cases to health problems. Thermal comfort and health science research (using hot plates, thermal manikins and comfort laboratories) in Europe and America later establishes lower surface temperature limits and development of comfort standards. |
| 1950 | Korean War wipes out wood supplies for ondol, population forced to use coal. Developer Joseph Eichler Joseph Eichler Joseph Eichler was a 20th century post-war U.S. American real estate developer known for developing distinctive residential subdivisions of Mid-Century modern style Tract housing in California, United States. He was one of the influential advocates of bringing modern architecture from custom... in California begins the construction of thousands of radiant heated homes. |
| 1951 | Dr. J. Bjorksten of Bjorksten Research Laboratories in Madison, WI, announces first results of what is believed to be the first instance of testing three types of plastic tubing for radiant floor heating in America. Polyethylene, vinyl chloride copolymer, and vinylidene chloride were tested over three winters. |
| 1953 | The first Canadian polyethylene plant is built near Edmonton, Ab. |
| 1960 | NRC researcher from Canada installs underfloor heating in his home and later remarks, “Decades later it would be identified as a passive solar house. It incorporated innovative features such as the radiant heating system supplied with hot water from an automatically stoked anthracite furnace.” |
| 1965 | Thomas Engel patents method for stabilizing polyethylene by cross linking molecules Cross-link Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of... using peroxide (PEx-A) and in 1967 sells license options to a number of pipe producers. |
| 1970 | Evolution of Korean architecture leads to multistory housings, flue gases from coal based ondol results in many deaths leading to the removal of the home based flue gas system to a central water based heating plants. Oxygen permeation becomes corrosion issue in Europe leading to the development of barriered pipe and oxygen permeation standards. |
| 1980 | The first standards for floor heating are developed in Europe. Water-based ondol system is applied to almost all of residential buildings in Korea. |
| 1985 | Floor heating becomes a traditional heating systems in residential buildings in Middle Europe and Nordic countries Nordic countries The Nordic countries make up a region in Northern Europe and the North Atlantic which consists of Denmark, Finland, Iceland, Norway and Sweden and their associated territories, the Faroe Islands, Greenland and Åland... and increasing applications in non-residential buildings. |
| 1995 | The application of floor cooling and thermal active building systems (TABS) in residential and commercial buildings are widely introduced into the market. |
| 2000 | The use of embedded radiant cooling systems in middle of Europe becomes a standard system with many parts of the world applying radiant based HVAC systems as means of using low temperatures for heating and high temperatures for cooling. |
| 2010 | Radiant conditioned Pearl River Tower Pearl River Tower The Pearl River Tower is a clean technology skyscraper under construction at the junction of Jinsui Road/Zhujiang Avenue West, Tianhe District, Guangzhou, China. The tower's architecture and engineering were performed by Skidmore, Owings, and Merrill with Adrian D. Smith and Gordon Gill as... in Guangzhou, China, topped out at 71-stories. |
Description
Modern underfloor heating systems use either electrical resistanceElectrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
elements ("electric systems") or fluid flowing in pipes ("hydronic systems”) to heat the floor. Either type can be installed as the primary, whole-building heating system or as localized floor heating for thermal comfort. Electrical resistance can only be used for heating so when space cooling is also required, hydronic systems are used. Other applications for which either electric or hydronic systems are suited include snow/ice melting
Snowmelt system
A snowmelt system is used to remove snow and ice via embedded electric cables or hydronic tubing. Common areas for snowmelt systems are: driveways, walkways, parking areas, stairways, loading docks, and around car washes. A snowmelt system is usually installed during the original construction in...
for walks, driveways and landing pads, turf conditioning of football and soccer fields and frost prevention in freezers and skating rinks.
Electric heating elements or hydronic piping can be cast in a concrete floor slab ("poured floor system" or "wet system"). They can also be placed under the floor covering ("dry system") or attached directly to a wood sub floor ("sub floor system" or "dry system").
Some commercial buildings are designed to take advantage of thermal mass
Thermal mass
Thermal mass is a concept in building design which describes how the mass of the building provides "inertia" against temperature fluctuations, sometimes known as the thermal flywheel effect...
which is heated or cooled during off peak hours when utility rates are lower. With the heating/cooling system turned off during the day, the concrete mass and room temperature drift up or down within the desired comfort range. Such systems are known as thermally activated building systems or TABS.
Hydronic systems
Hydronic systems use water or a mix of water and anti-freeze such as propylene glycolPropylene glycol
Propylene glycol, also called 1,2-propanediol or propane-1,2-diol, is an organic compound with formula C3H8O2 or HO-CH2-CHOH-CH3...
as the heat transfer fluid in a "closed loop" that is recirculated between the floor and the boiler.
Various types of pipes are available specifically for hydronic underfloor heating and cooling systems and are generally made from polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
including PEX
PEX
Cross-linked polyethylene, commonly abbreviated PEX or XLPE, is a form of polyethylene with cross-links. It is formed into tubing, and is used predominantly in hydronic radiant heating systems, domestic water piping and insulation for high tension electrical cables...
, PEX-Al-PEX and PERT. Older materials such as Polybutylene
Polybutylene
Polybutylene is a polyolefin or saturated polymer with the chemical formula n. It should not be confused with polybutene, a low molecular weight oligomer with a different repeat unit....
(PB) and copper or steel pipe are still used in some locales or for specialized applications.
Hydronic systems require skilled designers and tradespeople familiar with boilers, circulators, controls, fluid pressures and temperature. The use of modern factory assembled sub-stations, used primarily in district heating and cooling, can greatly simplify design requirements and reduce the installation and commissioning time of hydronic systems.
Hydronic systems can use a single source or combination of energy sources to help manage energy costs. Hydronic system energy source options are:
- Boilers (heaters) including Combined heat and power plants(CHP) (see also micro CHP and fuel cellHome fuel cellA home fuel cell, also called micro combined heat and power and microgeneration, is a residential-scaled clean energy system. A home fuel cell is an alternative energy technology that increases efficiency by simultaneously generating power and heat from one unit, on-site within a home...
heated by: - Natural gasNatural gasNatural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
, coalCoalCoal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
, oilOilAn oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes vegetable oils, volatile essential oils, petrochemical oils, and synthetic oils....
or waste oil - ElectricityElectricityElectricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
- Solar thermal
- woodWoodWood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
or other biomassBiomassBiomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel.... - bio-fuels
- Heat pumpHeat pumpA heat pump is a machine or device that effectively "moves" thermal energy from one location called the "source," which is at a lower temperature, to another location called the "sink" or "heat sink", which is at a higher temperature. An air conditioner is a particular type of heat pump, but the...
s and chillerChillerA chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required.-Use in air conditioning:...
s powered by: - Electricity
- Natural gas
Electric systems
Thermal mass
Thermal mass is a concept in building design which describes how the mass of the building provides "inertia" against temperature fluctuations, sometimes known as the thermal flywheel effect...
or directly under floor finishes. Electric systems can also take advantage of time-of-use electricity metering
Electricity meter
An electricity meter or energy meter is a device that measures the amount of electric energy consumed by a residence, business, or an electrically powered device....
and are frequently used as carpet heaters, portable under area rug heaters, under laminate floor heaters, under tile heating, under wood floor heating, and floor warming systems, including under shower floor and seat heating. Large electric systems also require skilled designers and tradespeople but this is less so for small floor warming systems. Electric systems use fewer components and are simpler to install and commission than hydronic systems. Some electric systems use line voltage technology while others use low voltage technology. Power consumption of an electric system is not based on voltage but rather wattage output produced by the heating element.
Thermal comfort quality
As defined by ANSI/ASHRAE Standard 55 – Thermal Environmental Conditions for Human Occupancy, thermal comfortThermal comfort
Thermal comfort is a term used by the American Society of Heating, Refrigerating and Air-Conditioning Engineers, an international body. It is defined as the state of mind in humans that expresses satisfaction with the surrounding environment...
is, “that condition of mind which expresses satisfaction with the thermal environment and is assessed by subjective evaluation.” Relating specifically to underfloor heating, thermal comfort is influenced by floor surface temperature and associated elements such as radiant asymmetry, mean radiant temperature
Mean radiant temperature
The Mean Radiant Temperature is a concept arising from the fact that the net exchange of radiant energy between two objects is approximately proportional to their temperature difference multiplied by their ability to emit and absorb heat . Mean radiant temperature is simply the area weighted mean...
and operative temperature
Operative temperature
Operative temperature is defined as a uniform temperature of a radiantly black enclosure in which an occupant would exchange the same amount of heat by radiation plus convection as in the actual nonuniform environment. Some references also use the terms 'equivalent temperature" or 'effective...
. Research by Nevins, Rohles, Gagge, P. Ole Fanger
P. Ole Fanger
Povl Ole Fanger was an expert in the field of the health effects of indoor environments. He was a University Professor at Syracuse University when he died at the age of 72 from an abdominal aortic aneurysm. He was also a senior professor at the International Centre for Indoor Environment and...
et al. show that humans at rest with clothing typical of light office and home wear, exchange over 50% of their sensible heat
Sensible heat
Sensible heat is the energy exchanged by a thermodynamic system that has as its sole effect a change of temperature.The term is used in contrast to a latent heat, which is the amount of energy exchanged that is hidden, meaning it cannot be observed as a change of temperature...
via radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
.
Underfloor heating influences the radiant exchange by thermally conditioning the interior surfaces with low temperature long wave radiation. The heating of the surfaces suppresses body heat loss resulting in a perception of heating comfort. This general sensation of comfort is further enhanced through conduction (feet on floor) and through convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
by the surface's influence on air density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
. Underfloor cooling works by absorbing both short wave
Shortwave radiation
Shortwave radiation is a term used to describe radiant energy with wavelengths in the visible , near-ultraviolet , and near-infrared spectra....
and long wave radiation resulting in cool interior surfaces. These cool surfaces encourage the loss of body heat resulting in a perception of cooling comfort. Localized discomfort due to cold and warm floors wearing normal foot wear and stocking feet is addressed in the ISO 7730 and ASHRAE 55 standards and ASHRAE Fundamentals Handbooks and can be corrected or regulated with floor heating and cooling systems.
Indoor air quality
Underfloor heating can have a positive effect on the quality of indoor air by facilitating the choice of otherwise perceived cold flooring materials such as tile, slate, terrazzo and concrete. These masonry surfaces typically have very low VOC emissions (volatile organic compounds) in comparison to other flooring options. In conjunction with moistureMoisture
Humidity is the amount of moisture the air can hold before it rains. Moisture refers to the presence of a liquid, especially water, often in trace amounts...
control, floor heating also establishes temperature conditions that are less favorable in supporting mold
Mold
Molds are fungi that grow in the form of multicellular filaments called hyphae. Molds are not considered to be microbes but microscopic fungi that grow as single cells called yeasts...
, bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, viruses and dust mites. By removing the sensible heat
Sensible heat
Sensible heat is the energy exchanged by a thermodynamic system that has as its sole effect a change of temperature.The term is used in contrast to a latent heat, which is the amount of energy exchanged that is hidden, meaning it cannot be observed as a change of temperature...
ing load from the total HVAC
HVAC
HVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...
(Heating, Ventilating, and Air Conditioning) load, ventilation
Ventilation (architecture)
Ventilating is the process of "changing" or replacing air in any space to provide high indoor air quality...
, filtration and dehumidification of incoming air can be accomplished with dedicated outdoor air systems having less volumetric turnover to mitigate distribution of airborne contaminates. There is recognition from the medical community relating to the benefits of floor heating especially as it relates to allergens.
Sustainability—energy
Under floor radiant systems are evaluated for sustainability through the principles of efficiencyEfficiency
Efficiency in general describes the extent to which time or effort is well used for the intended task or purpose. It is often used with the specific purpose of relaying the capability of a specific application of effort to produce a specific outcome effectively with a minimum amount or quantity of...
, entropy
Entropy
Entropy is a thermodynamic property that can be used to determine the energy available for useful work in a thermodynamic process, such as in energy conversion devices, engines, or machines. Such devices can only be driven by convertible energy, and have a theoretical maximum efficiency when...
, exergy
Exergy
In thermodynamics, the exergy of a system is the maximum useful work possible during a process that brings the system into equilibrium with a heat reservoir. When the surroundings are the reservoir, exergy is the potential of a system to cause a change as it achieves equilibrium with its...
and efficacy
Efficacy
Efficacy is the capacity to produce an effect. It has different specific meanings in different fields. In medicine, it is the ability of an intervention or drug to reproduce a desired effect in expert hands and under ideal circumstances.- Healthcare :...
. When combined with high performance buildings, under floor systems operate with low temperatures in heating and high temperatures in cooling in the ranges found typically in geothermal
Geothermal
Geothermal is related to energy and may refer to:* The geothermal gradient and associated heat flows from within the Earth- Renewable technology :...
and solar thermal systems. When coupled with these non combustible, renewable
Renewable energy
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...
energy sources the sustainability
Sustainability
Sustainability is the capacity to endure. For humans, sustainability is the long-term maintenance of well being, which has environmental, economic, and social dimensions, and encompasses the concept of union, an interdependent relationship and mutual responsible position with all living and non...
benefits include reduction or elimination of combustion and green house gases produced by boilers and power generation for heat pumps and chiller
Chiller
A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required.-Use in air conditioning:...
s, as well as reduced demands for non renewables
Non-renewable resource
A non-renewable resource is a natural resource which cannot be produced, grown, generated, or used on a scale which can sustain its consumption rate, once depleted there is no more available for future needs. Also considered non-renewable are resources that are consumed much faster than nature...
and greater inventories for future generations. This has been supported through simulation evaluations and though research funded by the U.S. Department of Energy, Canada Mortgage and Housing Corporation, Fraunhofer Institute as well as ASHRAE.
Safety
Low temperature underfloor heating is embedded in the floor or placed under the floor covering. As such it occupies no wall space and creates no burnBurn
A burn is an injury to flesh caused by heat, electricity, chemicals, light, radiation, or friction.Burn may also refer to:*Combustion*Burn , type of watercourses so named in Scotland and north-eastern England...
hazards, nor is it a hazard for physical injuries due to accidental contact leading to tripping and falling. This has been referenced as a positive feature in healthcare facilities including those serving elderly clients and those with dementia
Dementia
Dementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...
. Anecdotally, under similar environmental conditions, heated floors will speed evaporation of wetted floors (showering, cleaning, and spills). Additionally, underfloor heating with fluid filled pipes is useful in heating and cooling explosion proof environments where combustion and electrical equipment can be located remotely from the explosive environment.
Longevity, maintenance and repair
Equipment maintenance and repair is the same as for other water or electrical based HVACHVAC
HVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...
systems except when pipes, cables or mats are embedded in the floor. Early trials (for example homes built by Levitt and Eichler, c. 1940-70’s) experienced failures in embedded copper and steel piping systems as well as failures assigned by the courts to Shell, Goodyear and others for polybutylene
Polybutylene
Polybutylene is a polyolefin or saturated polymer with the chemical formula n. It should not be confused with polybutene, a low molecular weight oligomer with a different repeat unit....
and EPDM materials. There also have been a few publicized claims of failed electric heated gypsum panels from the mid 90’s.
Failures associated with most installations are attributable to job site neglect, installation errors and product mishandling such as exposure to ultraviolet radiation. Pre-pour pressure tests required by concrete installation standards and good practice guidelines for the design, construction, operation and repair of radiant heating and cooling systems mitigate problems resulting from improper installation and operation.
Fluid based systems using Cross-linked polyethylene (PE-x) a product developed in the 1930s and its various derivatives such as PE-rt, have demonstrated reliable long term performance in harsh cold-climate applications such as bridge decks, aircraft hangar aprons and landing pads. Since the materials are produced from polyethylene and its bonds are cross-linked, it is highly resistant to corrosion or the temperature and pressure stresses associated with typical fluid based HVAC systems.
Typical installation details
Design and installation considerations
The engineering of underfloor cooling and heating systems is governed by industry standards and guidelines.A sample of design and installation standards:-
- Part 1: Determination of the design heating and cooling capacity
- Part 2: Design, dimensioning and installation
- Part 3: Optimizing for use of renewable energy sources, Brussels, Belgium.
- Part 1: Definitions and symbols
- Part 2: Floor heating: Prove methods for the determination of the thermal output using calculation and test methods
- Part 3: Dimensioning
- Part 4: Installation
- Part 5: Heating and cooling surfaces embedded in floors, ceilings and walls - Determination of the thermal output
- ISO TC 205/ WG 5, Indoor thermal environment
- ISO TC 205/ WG 8, Radiant heating and cooling systems
- ISO TC 205/ WG 8, Heating and cooling systems
Technical design
The amount of heat exchanged from or to an underfloor system is based on the combined radiant and convective heat transfer coefficients.- Radiant heat transfer is constant based on the Stefan–Boltzmann constant.
- Convective heat transfer changes over time depending on
- the air's density and thus its buoyancy. Air buoyancy changes according to surface temperaturesMean radiant temperatureThe Mean Radiant Temperature is a concept arising from the fact that the net exchange of radiant energy between two objects is approximately proportional to their temperature difference multiplied by their ability to emit and absorb heat . Mean radiant temperature is simply the area weighted mean...
and - forced air movement due to fans and the motion of people and objects in the space.
- the air's density and thus its buoyancy. Air buoyancy changes according to surface temperatures
Convective heat transfer with underfloor systems is much greater when the system is operating in a heating rather than cooling mode. Typically with underfloor heating the convective component is almost 50% of the total heat transfer and in underfloor cooling the convective component is less than 10%.
Heat and moisture considerations
When heated and cooled pipes or heating cables share the same spaces as other building components, parasitic heat transfer can occur between refrigeration appliances, cold storage areas, domestic cold water lines, air conditioning and ventilation ducts. To control this, the pipes, cables and other building components must all be well insulated.With underfloor cooling, condensation may collect on the surface of the floor. To prevent this, air humidity is kept low, below 50%, and floor temperatures are maintained above the dew point, 66°F(19°C).
Building systems and materials
- Heat losses to below grade
- The thermal conductivity of soilSoil thermal propertiesThe thermal properties of soil are a component of soil physics that has found important uses in engineering, climatology and agriculture. These properties influence how energy is partitioned in the soil profile...
will influence the conductive heat transfer between the ground and heated or cooled slab-on-gradeShallow foundationA shallow foundation is a type of foundation which transfers building loads to the earth very near the surface, rather than to a subsurface layer or a range of depths as does a deep foundation...
floors. - Soils with moisture contents greater than 20% can be as much as 15 times more conductive than soils with less than 4% moisture content.
- Water tableWater tableThe water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...
s and general soil conditionsGeotechnical engineeringGeotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. Geotechnical engineering is important in civil engineering, but is also used by military, mining, petroleum, or any other engineering concerned with construction on or in the ground...
should be evaluated. - Suitable underslab insulationBuilding insulation materialsBuilding insulation materials are thermal insulation used in the construction or retrofit of buildings.The materials are used to reduce heat transfer by conduction, radiation or convection and are employed in varying combinations to achieve the desired outcome .-Categories:Insulation may be...
such as rigid extruded or expanded polystyrenePolystyrenePolystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...
is required by Model National Energy CodesModel building codeA model building code is a building code that is developed and maintained by a standards organization independent of the jurisdiction responsible for enacting the building code. A local government can choose to adopt a model building code as their own. This saves local governments the expense and...
.
- Heat losses at the exterior floor framing
- The heated or cooled sub-floor increases the temperature difference between the outdoors and the conditioned floor.
- The cavities created by the framing timbers such as headers, trimmers and cantilevered sections must then be insulated with rigid, batt or spray type insulations of suitable value based on climate and building techniques.
- Masonry and other hard flooring considerations
- Concrete floors must accommodate shrinkage and expansion due to curing and changes in temperature.
- Curing times and temperatures for poured floors (concrete, lightweight toppings)must follow industry standards.
- Control and expansion joints and crack suppression techniques are required for all masonry type floors including;
-
-
-
- TileTileA tile is a manufactured piece of hard-wearing material such as ceramic, stone, metal, or even glass. Tiles are generally used for covering roofs, floors, walls, showers, or other objects such as tabletops...
- SlateSlateSlate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. The result is a foliated rock in which the foliation may not correspond to the original sedimentary layering...
- TerrazzoTerrazzoTerrazzo is a composite material poured in place or precast, which is used for floor and wall treatments. It consists of marble, quartz, granite, glass or other suitable chips, sprinkled or unsprinkled, and poured with a binder that is cementitious, chemical or a combination of both...
- StoneSTONeis a Japanese manga written and illustrated by Sin-Ichi Hiromoto. Kodansha released the two bound volumes of the manga on April 23, 2002 and August 23, 2002, respectively.The manga is licensed for an English-languague released in North America be Tokyopop...
- MarbleMarbleMarble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite.Geologists use the term "marble" to refer to metamorphosed limestone; however stonemasons use the term more broadly to encompass unmetamorphosed limestone.Marble is commonly used for...
- ConcreteConcreteConcrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
,stained, textured and stamped
- Tile
-
-
- Wood flooring
- The dimensional stability of wood is based primary on moisture content, however, other factors can mitigate the changes to wood as it is heated or cooled, including;
-
-
-
- Wood species
- Milling techniques, quarter sawn or plane sawnWood grainIn speaking of wood the term grain refers to the alternating regions of relatively darker and lighter wood resulting from the differing growth parameters occurring in different seasons . The term is used in several ways. Perhaps most important is that in woodworking techniques...
- Acclimation period
- Relative humidity within the space
-
-
- Piping standardsA sample of standards for pipes used in underfloor heating:
- ASTM F2623 - Standard Specification for Polyethylene of Raised Temperature (PE-RT) SDR 9 Tubing
- ASTM F2788 - Standard Specification for Crosslinked Polyethylene (PEX) Pipe
- ASTM F876 - Standard Specification for Crosslinked Polyethylene (PEX) Tubing
- ASTM F2657 - Standard Test Method for Outdoor Weathering Exposure of Crosslinked Polyethylene (PEX) Tubing
- CSA B137.5 - Crosslinked Polyethylene (PEX) Tubing Systems for Pressure Applications
- CSA C22.2 NO. 130, Requirements for Electrical Resistance Heating Cables and Heating Device Sets
- UL Standard 1673 – Electric Radiant Heating Cables
- UL Standard 1693 – Electric Radiant Heating Panels and Heating Panel Sets
Control system (see Hydronic heating systemsHydronicsHydronics is the use of water as the heat-transfer medium in heating and cooling systems.Some of the oldest and most common examples are steam and hot-water radiators. Historically, in large-scale commercial buildings such as high-rise and campus facilities, a hydronic system may include both a...
)
Underfloor heating and cooling systems can have several control points including the management of:
- Fluid temperatures in the heating and cooling plant (e.g. boilers, chillers, heat pumps).
- Influences the efficiency
- Fluid temperatures in distribution network between the plant and the radiant manifolds.
- Influences the capital and operating costs
- Fluid temperatures in the PE-x piping systems, which is based on;
- Heating and cooling demands
- Tube spacing
- Upward and downward losses
- Flooring characteristics
- Operative temperatureOperative temperatureOperative temperature is defined as a uniform temperature of a radiantly black enclosure in which an occupant would exchange the same amount of heat by radiation plus convection as in the actual nonuniform environment. Some references also use the terms 'equivalent temperature" or 'effective...
- Incorporates the mean radiantMean radiant temperatureThe Mean Radiant Temperature is a concept arising from the fact that the net exchange of radiant energy between two objects is approximately proportional to their temperature difference multiplied by their ability to emit and absorb heat . Mean radiant temperature is simply the area weighted mean...
and dry bulb - Surface temperatures for;
- Comfort
- Health and safety
- Material integrity
- Dew point (for floor cooling).
Sample - mechanical schematic
Illustrated is a simplified mechanical schematic of an underfloor heating and cooling system for thermal comfort quality with a separate air handling system for indoor air quality. In high performance residential homes of moderate size (e.g. under 3000 ft2 (278 m2) total conditioned floor area), this system using manufactured hydronic control appliances would take up about the same space as a three or four piece bathroom.Modeling piping patterns with finite element analysis
Modeling radiant piping (also tube or loop) patterns with finite element analysis (FEA) predicts the thermal diffusions and surface temperature quality or efficacy
Efficacy
Efficacy is the capacity to produce an effect. It has different specific meanings in different fields. In medicine, it is the ability of an intervention or drug to reproduce a desired effect in expert hands and under ideal circumstances.- Healthcare :...
of various loop layouts. The performance of the model (left image above) and image to the right are useful to gain an understanding in relationships between flooring resistances, conductivities of surrounding mass, tube spacing’s, depths and fluid temperatures. As with all FEA simulations, they depict a snap shot in time for a specific assembly and may not be representative of all floor assemblies nor for system that have been operative for considerable time in a steady state condition. The practical application of FEA for the engineer is being able to assess each design for fluid temperature, back losses and surface temperature quality. Through several iterations it is possible to optimize the design for the lowest fluid temperature in heating and the highest fluid temperature in cooling which enables combustion and compression equipment to achieve its maximum rated efficiency performance.
Using thermography to observe underfloor systems
ThermographyThermography
Infrared thermography, thermal imaging, and thermal video are examples of infrared imaging science. Thermal imaging cameras detect radiation in the infrared range of the electromagnetic spectrum and produce images of that radiation, called thermograms...
is a useful tool to see the actual thermal efficacy of an underfloor system from its start up (as shown) to its operating conditions. In a startup it is easy to identify the tube location but less so as the system moves into a steady state
Steady state
A system in a steady state has numerous properties that are unchanging in time. This implies that for any property p of the system, the partial derivative with respect to time is zero:...
condition. It is important to interpret thermographic images correctly. As is the case with finite element analysis (FEA), what is seen, reflects the conditions at the time of the image and may not represent the steady conditions. For example, the surfaces viewed in the images shown, may appear ‘hot’, but in reality are actually below the nominal temperature of the skin and core temperatures of the human body
Normal human body temperature
Normal human body temperature, also known as normothermia or euthermia, is a concept that depends upon the place in the body at which the measurement is made, and the time of day and level of activity of the person...
and the ability to ‘see’ the pipes does not equate to ‘feel’ the pipes. Thermography can also point out flaws in the building enclosures (left image, corner intersection detail), thermal bridging (right image, studs) and the heat losses associated with exterior doors (center image).
Economics
There is a wide range of pricing for underfloor systems based on regional differences, application and project complexity. It is widely adopted in the NordicNordic countries
The Nordic countries make up a region in Northern Europe and the North Atlantic which consists of Denmark, Finland, Iceland, Norway and Sweden and their associated territories, the Faroe Islands, Greenland and Åland...
, Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
n and Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
an communities. Consequently the market is more mature and systems relatively more affordable than North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
where market share for fluid based systems remains between 3% to 7% of HVAC systems (ref. Statistics Canada
Statistics Canada
Statistics Canada is the Canadian federal government agency commissioned with producing statistics to help better understand Canada, its population, resources, economy, society, and culture. Its headquarters is in Ottawa....
and United States Census Bureau
United States Census Bureau
The United States Census Bureau is the government agency that is responsible for the United States Census. It also gathers other national demographic and economic data...
).
In energy efficiency buildings such as Passive House
Passive house
The term passive house refers to the rigorous, voluntary, Passivhaus standard for energy efficiency in a building, reducing its ecological footprint. It results in ultra-low energy buildings that require little energy for space heating or cooling. A similar standard, MINERGIE-P, is used in...
, R-2000
R-2000 program
R-2000 is a Natural Resources Canada program that was developed in partnership with the Canadian Home Builders' Association in 1981, and formalized as a standard in 1982...
or Net Zero Energy, simple thermostatic radiator valve
Thermostatic Radiator Valve
A Thermostatic Radiator Valve is a self-regulating valve fitted to hot water heating system radiators. The TRV controls the temperature of a room by regulating the flow of hot water to the radiator...
s can be installed along with a single compact circulator and small condensing heater controlled without or with basic hot water reset
Hot water reset
Hot water reset is an energy-saving automatic control algorithm for hot water boilers that are typically fired with fuel oil or natural gas. A hot water reset control loop measures the outside air temperature; this information is used to estimate demand or heating load as the outdoor temperature...
control. Economical electric resistant based systems also are useful in small zones such as bathrooms and kitchens, but also for entire buildings where heating loads are very low and preferably where photovoltaics, wind or hydro is the generating source of electricity. Larger structures will need more sophisticated systems
Hydronics
Hydronics is the use of water as the heat-transfer medium in heating and cooling systems.Some of the oldest and most common examples are steam and hot-water radiators. Historically, in large-scale commercial buildings such as high-rise and campus facilities, a hydronic system may include both a...
to deal with cooling and heating needs, and often requiring building management control systems
Building Management System
A Building Management System is a computer-based control system installed in buildings that controls and monitors the building’s mechanical and electrical equipment such as ventilation, lighting, power systems, fire systems, and security systems...
to regulate the energy use and control the overall indoor environment.
Low temperature radiant heating and high temperature radiant cooling systems lend themselves well to district energy
District heating
District heating is a system for distributing heat generated in a centralized location for residential and commercial heating requirements such as space heating and water heating...
systems (community based systems) due to the temperature differentials between the plant and the buildings which allow small diameter insulated distribution networks and low pumping power requirements. The low return temperatures in heating and high return temperatures in cooling enable the district energy plant to achieve maximum efficiency. The principles behind district energy with underfloor systems can also be applied to stand alone multi story buildings with the same benefits. Additionally, underfloor radiant systems are ideally suited to renewable energy
Renewable energy
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...
sources including geothermal
Geothermal
Geothermal is related to energy and may refer to:* The geothermal gradient and associated heat flows from within the Earth- Renewable technology :...
and solar thermal systems or any system where waste heat is recoverable.
In the global drive for sustainability
Sustainability
Sustainability is the capacity to endure. For humans, sustainability is the long-term maintenance of well being, which has environmental, economic, and social dimensions, and encompasses the concept of union, an interdependent relationship and mutual responsible position with all living and non...
, long term economics supports the need to eliminate where possible, compression
Gas compressor
A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...
for cooling and combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...
for heating. It will then be necessary to use low quality heat sources for which radiant underfloor heating and cooling is well suited.
System efficiency
System efficiency and energy use analysis takes into account building enclosure performance, efficiency of the heating and cooling plant, system controls and the conductivities, surface characteristics, tube/element spacing and depth of the radiant panel, operating fluid temperatures and wire to water efficiency of the circulators. The efficiency in electric systems is analyzed by similar processes and includes the efficiency of electricity generationElectricity generation
Electricity generation is the process of generating electric energy from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...
.
Though the efficiency of radiant systems is under constant debate with no shortage of anecdotal claims and scientific papers presenting both sides, the low return fluid temperatures in heating and high return fluid temperatures in cooling enable condensing boilers, chiller
Chiller
A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required.-Use in air conditioning:...
s and heat pump
Heat pump
A heat pump is a machine or device that effectively "moves" thermal energy from one location called the "source," which is at a lower temperature, to another location called the "sink" or "heat sink", which is at a higher temperature. An air conditioner is a particular type of heat pump, but the...
s to operate at or near their maximum engineered performance
Thermal efficiency
In thermodynamics, the thermal efficiency is a dimensionless performance measure of a device that uses thermal energy, such as an internal combustion engine, a boiler, a furnace, or a refrigerator for example.-Overview:...
. The greater efficiency of 'wire to water' versus 'wire to air' flow due to water's significantly greater heat capacity
Heat capacity
Heat capacity , or thermal capacity, is the measurable physical quantity that characterizes the amount of heat required to change a substance's temperature by a given amount...
favors fluid based systems over air based systems. Both field application and simulation research have demonstrated significant electrical energy savings with radiant cooling and dedicated outdoor air systems based in part on the previous noted principles.
In Passive House
Passive house
The term passive house refers to the rigorous, voluntary, Passivhaus standard for energy efficiency in a building, reducing its ecological footprint. It results in ultra-low energy buildings that require little energy for space heating or cooling. A similar standard, MINERGIE-P, is used in...
s, R-2000 homes
R-2000 program
R-2000 is a Natural Resources Canada program that was developed in partnership with the Canadian Home Builders' Association in 1981, and formalized as a standard in 1982...
or Net Zero Energy buildings the low temperatures of radiant heating and cooling systems present significant opportunities to exploit exergy
Exergy
In thermodynamics, the exergy of a system is the maximum useful work possible during a process that brings the system into equilibrium with a heat reservoir. When the surroundings are the reservoir, exergy is the potential of a system to cause a change as it achieves equilibrium with its...
.
Efficiency considerations for flooring surface materials
System efficiency is also affected by the floor covering serving as the radiational boundary layerBoundary layer
In physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of a bounding surface where effects of viscosity of the fluid are considered in detail. In the Earth's atmosphere, the planetary boundary layer is the air layer near the ground affected by diurnal...
between the floor mass and occupants and other contents of the conditioned space. For example, carpeting has a greater resistance
Thermal conductivity
In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....
or lower conductance
Conductivity
Conductivity may refer to:*Electrical conductivity, a measure of a material's ability to conduct an electric current*Conductivity , also the specific conductance, is a measurement of the electrical conductance per unit distance in an electrolytic or aqueous solution*Ionic conductivity, a measure of...
than tile. Thus carpeted floors need to operate at higher internal temperatures than tile which can create lower efficiencies for boilers and heat pumps. However, when the floor covering is known at the time the system is installed then the internal floor temperature required for a given covering can be achieved through proper tube spacing without sacrificing plant efficiency (though the higher internal floor temperatures may result in increased heat loss from the non-room surfaces of the floor).
The emissivity
Emissivity
The emissivity of a material is the relative ability of its surface to emit energy by radiation. It is the ratio of energy radiated by a particular material to energy radiated by a black body at the same temperature...
, reflectivity
Reflectivity
In optics and photometry, reflectivity is the fraction of incident radiation reflected by a surface. In general it must be treated as a directional property that is a function of the reflected direction, the incident direction, and the incident wavelength...
and absorptivity of a floor surface are critical determinants of its heat exchange with the occupants and room. Unpolished flooring surface materials and treatments have very high emissivity’s (0.85 to 0.95) and therefore make good heat radiators
Radiator (heating)
Radiators and convectors are heat exchangers designed to transfer thermal energy from one medium to another for the purpose of space heating. The heating radiator was invented by Franz San Galli, a Prussian-born Russian businessman living in St. Petersburg, between 1855–1857.- Radiation vs...
.
With underfloor heating and cooling ("reversible floors") flooring surfaces with high absorbance and emissivity
Emissivity
The emissivity of a material is the relative ability of its surface to emit energy by radiation. It is the ratio of energy radiated by a particular material to energy radiated by a black body at the same temperature...
and low reflectivity
Reflectivity
In optics and photometry, reflectivity is the fraction of incident radiation reflected by a surface. In general it must be treated as a directional property that is a function of the reflected direction, the incident direction, and the incident wavelength...
are most desirable.
Global examples of large modern buildings using radiant heating and cooling
- Manitoba Hydro Place, Canada
- California Academy of Science, United States
- Copenhagen Opera House, Denmark
- Post TowerPost TowerPost Tower is the headquarters of the logistic company Deutsche Post DHL with the two brands postal services for Germany Deutsche Post and the worldwide logistic company DHL. The Post Tower is a 162.5-metre, 41-storey office building in Bonn, Germany...
, Germany - Ewha Womans UniversityEwha Womans UniversityEwha Womans University is a private women's university in central Seoul, South Korea. It is one of the city's largest institutions of higher learning and currently the world's largest female educational institute. It is one of the best-known universities in South Korea, and often considered to...
, Korea - NREL Research Support Facility, United States
- Suvarnabhumi AirportSuvarnabhumi AirportSuvarnabhumi Airport , also known as Bangkok International Airport, is an international airport serving Bangkok, Thailand. It was officially opened for limited domestic flight service on 15 September 2006, and opened for most domestic and all international commercial flights on 28 September...
, Bangkok - la Defense Office, Netherlands
- Pearl River TowerPearl River TowerThe Pearl River Tower is a clean technology skyscraper under construction at the junction of Jinsui Road/Zhujiang Avenue West, Tianhe District, Guangzhou, China. The tower's architecture and engineering were performed by Skidmore, Owings, and Merrill with Adrian D. Smith and Gordon Gill as...
, China - 41 Cooper Square41 Cooper SquareThe Cooper Union's 41 Cooper Square, designed by architect Thom Mayne of Morphosis, is the newest addition to The Cooper Union for the Advancement of Science and Art campus. The building, originally known as the New Academic Building, stands on the site where the School of Art Hewitt Building was...
, United States - Hearst Tower (New York City)Hearst Tower (New York City)The Brilliant Hearst Tower is located at 300 West 57th Street, 959 8th Avenue, near Columbus Circle in Midtown Manhattan, New York City, New York...
, United States - Akron Art MuseumAkron Art MuseumThe Akron Art Museum is an art museum in Akron, Ohio, USA.The museum first opened its doors on February 1, 1922, as the Akron Art Institute. It was located in two borrowed rooms in the basement of the public library...
, United States - BMW WeltBMW WeltBMW Welt , is a multi-functional customer experience and exhibition facility of the BMW AG, located in Munich, Germany...
, Germany - David Brower Center, United States
See also
- American Society of Heating, Refrigerating and Air-Conditioning EngineersAmerican Society of Heating, Refrigerating and Air-Conditioning EngineersThe American Society of Heating, Refrigerating and Air Conditioning Engineers is an international technical society for all individuals and organizations interested in heating, ventilation, air-conditioning, and refrigeration...
- Electric heatingElectric heatingElectric heating is any process in which electrical energy is converted to heat. Common applications include space heating, cooking, water heating and industrial processes. An electric heater is an electrical appliance that converts electrical energy into heat...
- HydronicsHydronicsHydronics is the use of water as the heat-transfer medium in heating and cooling systems.Some of the oldest and most common examples are steam and hot-water radiators. Historically, in large-scale commercial buildings such as high-rise and campus facilities, a hydronic system may include both a...
- Gloria (heating system)Gloria (heating system)Gloria was a central heating system used in Castile beginning in the Middle Ages. It was a direct descendant of the Roman hypocaust, and due to its slow rate of combustion, it allowed people to use smaller fuels such as hay instead of wood.-Description:The Gloria consisted of a firebox, generally...
- HeaterHeaterA heater is an object that emits heat or causes another body to achieve a higher temperature. In a household or domestic setting, heaters are usually appliances whose purpose is to generate heating...
(types of heaters) - HypocaustHypocaustA hypocaust was an ancient Roman system of underfloor heating, used to heat houses with hot air. The word derives from the Ancient Greek hypo meaning "under" and caust-, meaning "burnt"...
- Kang bed-stoveKang bed-stoveThe Kang is a traditional long sleeping platform made of bricks or other forms of fired clay and more recently of concrete in some locations. Its interior cavity, leading to a flue, channels the exhaust from a wood or coal stove...
- PsychrometricsPsychrometricsPsychrometrics or psychrometry or Hygrometry are terms used to describe the field of engineering concerned with the determination of physical and thermodynamic properties of gas-vapor mixtures...
- OndolOndolAn ondol, also called gudeul, in Korean traditional architecture, is underfloor heating which uses direct heat transfer from wood smoke to the underside of a thick masonry floor...
- Renewable heatRenewable heatRenewable heat is an application of renewable energy and it refers to the renewable generation of heat, rather than electrical power ....
- Underfloor air distributionRoom air distributionCharacterizing how air is introduced to, flows through, and is removed from spaces is called room air distribution. HVAC airflow in spaces generally can be classified by two different types: mixing and displacement.-Mixing systems:...
External links
Relevant Industry Organizations, Institutes and Associations (based on contributions to scientific research, standards development and professional education for engineers, architects, interior designers and trades)- American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
- ASHRAE Technical Committee TC 6.5, Radiant and Convective Space Heating and Cooling (ASHRAE T.C. 6.5)
- ASHRAE Technical Committee TC 6.1, Hydronic & Steam Heating Equipment & Systems (ASHRAE T.C. 6.1)
- American Institute of Architects (AIA)
- American Society of Interior Designers (ASID)
- Canada Mortgage and Housing Corporation (CMHC)
- Canadian Institute of Plumbing & Heating (CIPH)
- Dutch Building Services Knowledge Centre (ISSO)
- Dwellings Energy Assessment Procedure - Ireland (DEAP)
- Federation of European Heating and Air-Conditioning Associations (REHVA)
- Hydronics Industry Alliance (HIA)
- Heating, Refrigeration and Air Conditioning Institute of Canada (HRAI)
- International Energy Agency, Energy Conservation in Buildings and Community Systems (IEA/ECBCS)
- International Organization for Standardization, TC 205/WG 8, Radiant heating and cooling systems (ISO TC205/WG8)
- National Research Council Canada / NRC Institute for Research in Construction, Hydronic Radiant Floor Heating (NRC/IRC)
- Radiant Panel Association (RPA)
- Thermal Environmental Comfort Association (TECA)
- German Association of Surface Heating and Cooling (BVF)
- British Underfloor Heating Manufacturers Association (UHMA)