Chilled beam
Encyclopedia
A chilled beam is a type of convection
HVAC
system designed to heat or cool large buildings. Pipes of water are passed through a "beam" (a heat exchanger
) suspended a short distance from the ceiling of a room. As the beam chills the air around it, the air becomes denser and falls to the floor. It is replaced by warmer air moving up from below, causing a constant flow of convection and cooling the room. Heating works in much the same fashion, similar to a steam radiator
. There are two types of chilled beams. Some passive types rely solely on convection whilst there is a "Radiant"/convective passive type which cools through a combination of radiant exchange (35%) and convection (65%) which can provide higher thermal comfort
levels , while the active type (also called an "induction diffuser") uses ducts to push ("induce") air toward the unit (increasing its heating and cooling capacity).
The chilled beam is distinguishable from the chilled ceiling. The chilled ceiling uses water flowing through pipes like a chilled beam does; however, the pipes in a chilled ceiling lie behind metal ceiling plates, and the heated and cooled plates are the cause of convection and not the pipe unit itself. Chilled beams are about 85 percent more effective at convection than chilled ceilings.
of 37 joules
per kelvin
(JK-1), water has a heat capacity of 20,050 JK-1. A metal pipe of water just 1 inches (2.5 cm) in diameter can carry as much energy as an 18 by metal duct of air. This means that chilled beam HVAC systems require much less energy to provide the same heating and cooling effect as a traditional air HVAC system.
Chilled beam cooling systems require water to be treated by heating and cooling systems. Generally, water in a passive chilled beam system is cooled to about 16 to 19 °C (60.8 to 66.2 F). In active chilled beam heating systems, water temperature is usually 40 to 50 °C (104 to 122 F). (Chilled beam heating systems usually cannot rely solely on convection, however, and often require a fan-driven primary air circulation system to force the warmer air to the ground where most people sit and work.) There are effectiveness and cost differences between the two systems. Passive chilled beam systems can supply about 5.6 to 6.5 watt
s per foot (60 to 70 watts per metre) of cooling capacity
. Active chilled beam systems are about twice as effective. In both cases, convection is so efficient that the ratio of incoming air to heated/cooled air can be as high as 6:1. However, studies of the energy cost-savings of active versus passive chilled beam systems remained inconclusive as of 2007, and appear to be highly dependent on the specific building.
The active chilled beam system employs fins
to help heat and cool. Active chilled beam systems are effective to the point where outdoor air can be mixed with the indoor air without any traditional air conditioning (such as heating, cooling, humidifying, or dehumidifying), thus enabling a building to meet its "minimum outdoor air" air quality requirement.
at Chapel Hill lowered its HVAC costs by 20 percent with an active chilled beam system. This is a typical energy cost savings. Chilled beam systems also have some advantages in that they are almost noiseless, require little maintenance, and are highly efficient. Traditional fan-driven HVAC systems create somewhat higher air velocities, which some people find uncomfortable. Chilled beam HVAC systems also require less ceiling space than forced-air HVAC systems, which can lead to lower building heights and higher ceilings. Since they do not require high forced air flows, chilled beam systems also require reduced air distribution duct networks (which also helps to lower cost).
Chilled beam systems are not a panacea. Additional ductwork may be needed to meet minimum outdoor air requirements. Both types of chilled beam systems are less effective at heating than cooling, and supplementary heating systems are often needed. Chilled beam systems cannot be used alone in buildings where the ceilings are higher than 2.7 metres (8.9 ft), because the air will not properly circulate. A forced-air circulation system must be employed in such cases. If the water temperature is too low or humidity is high, condensation on the beam can occur—leading to a problem known as "internal rain." (In some cases, drier outside air can be mixed with the wetter inside air to reduced interior humidity levels while maintaining system performance.) Chilled beam systems are not recommended for areas with high humidity (such as theaters, gymnasiums, or cafeterias). Because they are less effective at cooling, passive chilled beam systems are generally ill-suited for semi-tropical and tropical climates. Hospitals generally cannot use chilled beam systems because of restrictions on using recirculated air. Chilled beam systems are also known to cause noticeable air circulation which can make some people uncomfortable. (Passive air deflection devices can help disrupt these air patterns, alleviating the problem.) Some designers have found that enlarging the ducts around active chilled beam systems to increase air circulation causes echoes in working areas and amplifies the sound of water moving through the pipes to noticeable levels.
of the air in the building. The systems generally need little cleaning (vacuuming of dirt and dust from the fins every five years).
As of 2007, chilled beam HVAC systems were used more widely in Australia and Europe than in the United States. In Australia, the system was first used in 30 The Bond, Sydney which was the first building in Australia to achieve the rating of 5 stars ABGR . Chilled beam HVAC systems have been used at London Heathrow Terminal 5 and Constitution Center
(the largest private office building in Washington, D.C.). The system has also received prominent use at Harvard Business School
, Wellesley College, and the American headquarters of the pharmaceutical company AstraZeneca
.
The multiservice chilled beam is a relatively new form of the chilled beam. Developed in 1996, it incorporates computer and electrical wiring, lighting, motion-detection sensors, and sprinklers into the chilled beam unit. The multiservice chilled beam was first installed at the Barclaycard
building in Northampton
, England
, but has since been used at the headquarters of Lloyd's Register
(London
), Airbus UK
(Bristol
), and the Greater London Authority
; Riverside House (London); Empress State Building
(London); 55 Baker Street (London) and 101 New Cavendish Street (London).
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....
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...
system designed to heat or cool large buildings. Pipes of water are passed through a "beam" (a heat exchanger
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...
) suspended a short distance from the ceiling of a room. As the beam chills the air around it, the air becomes denser and falls to the floor. It is replaced by warmer air moving up from below, causing a constant flow of convection and cooling the room. Heating works in much the same fashion, similar to a steam radiator
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...
. There are two types of chilled beams. Some passive types rely solely on convection whilst there is a "Radiant"/convective passive type which cools through a combination of radiant exchange (35%) and convection (65%) which can provide higher thermal comfort
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...
levels , while the active type (also called an "induction diffuser") uses ducts to push ("induce") air toward the unit (increasing its heating and cooling capacity).
The chilled beam is distinguishable from the chilled ceiling. The chilled ceiling uses water flowing through pipes like a chilled beam does; however, the pipes in a chilled ceiling lie behind metal ceiling plates, and the heated and cooled plates are the cause of convection and not the pipe unit itself. Chilled beams are about 85 percent more effective at convection than chilled ceilings.
Physics of the chilled beam
Water can carry significantly more energy than air. Although 1 cubic foot (0.028316847 m³) of air has a capacity to hold heatHeat 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...
of 37 joules
Joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
per kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
(JK-1), water has a heat capacity of 20,050 JK-1. A metal pipe of water just 1 inches (2.5 cm) in diameter can carry as much energy as an 18 by metal duct of air. This means that chilled beam HVAC systems require much less energy to provide the same heating and cooling effect as a traditional air HVAC system.
Chilled beam cooling systems require water to be treated by heating and cooling systems. Generally, water in a passive chilled beam system is cooled to about 16 to 19 °C (60.8 to 66.2 F). In active chilled beam heating systems, water temperature is usually 40 to 50 °C (104 to 122 F). (Chilled beam heating systems usually cannot rely solely on convection, however, and often require a fan-driven primary air circulation system to force the warmer air to the ground where most people sit and work.) There are effectiveness and cost differences between the two systems. Passive chilled beam systems can supply about 5.6 to 6.5 watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
s per foot (60 to 70 watts per metre) of cooling capacity
Cooling capacity
Cooling capacity is the measure of a cooling system's ability to remove heat. Common units include tons, and tonnes, which describe the amount of water at a given temperature that can be frozen in a given amount of time...
. Active chilled beam systems are about twice as effective. In both cases, convection is so efficient that the ratio of incoming air to heated/cooled air can be as high as 6:1. However, studies of the energy cost-savings of active versus passive chilled beam systems remained inconclusive as of 2007, and appear to be highly dependent on the specific building.
The active chilled beam system employs fins
Fin (extended surface)
In the study of heat transfer, a fin is a surface that extends from an object to increase the rate of heat transfer to or from the environment by increasing convection. The amount of conduction, convection, or radiation of an object determines the amount of heat it transfers...
to help heat and cool. Active chilled beam systems are effective to the point where outdoor air can be mixed with the indoor air without any traditional air conditioning (such as heating, cooling, humidifying, or dehumidifying), thus enabling a building to meet its "minimum outdoor air" air quality requirement.
Advantages and disadvantages
The primary advantage of the chilled beam system is its lower operating cost. For example, because the temperature of cooled water is higher than the temperature of cooled air but delivers the same cooling ability, the costs of the system are lower. Because cooling and heating of air are no longer linked to the delivery of air, buildings also save money by being able to run fewer air circulation fans and at lower speeds. One estimate places the amount of air handled at 25 to 50 percent less using chilled beam systems. By being able to target the delivery of clean outdoor air where it is needed (rather than injecting it into the entire system and heating or cooling it), there is a reduced need to treat large amounts of outdoor air (also saving money). In one case, the Genomic Science Building at the University of North CarolinaUniversity of North Carolina
Chartered in 1789, the University of North Carolina was one of the first public universities in the United States and the only one to graduate students in the eighteenth century...
at Chapel Hill lowered its HVAC costs by 20 percent with an active chilled beam system. This is a typical energy cost savings. Chilled beam systems also have some advantages in that they are almost noiseless, require little maintenance, and are highly efficient. Traditional fan-driven HVAC systems create somewhat higher air velocities, which some people find uncomfortable. Chilled beam HVAC systems also require less ceiling space than forced-air HVAC systems, which can lead to lower building heights and higher ceilings. Since they do not require high forced air flows, chilled beam systems also require reduced air distribution duct networks (which also helps to lower cost).
Chilled beam systems are not a panacea. Additional ductwork may be needed to meet minimum outdoor air requirements. Both types of chilled beam systems are less effective at heating than cooling, and supplementary heating systems are often needed. Chilled beam systems cannot be used alone in buildings where the ceilings are higher than 2.7 metres (8.9 ft), because the air will not properly circulate. A forced-air circulation system must be employed in such cases. If the water temperature is too low or humidity is high, condensation on the beam can occur—leading to a problem known as "internal rain." (In some cases, drier outside air can be mixed with the wetter inside air to reduced interior humidity levels while maintaining system performance.) Chilled beam systems are not recommended for areas with high humidity (such as theaters, gymnasiums, or cafeterias). Because they are less effective at cooling, passive chilled beam systems are generally ill-suited for semi-tropical and tropical climates. Hospitals generally cannot use chilled beam systems because of restrictions on using recirculated air. Chilled beam systems are also known to cause noticeable air circulation which can make some people uncomfortable. (Passive air deflection devices can help disrupt these air patterns, alleviating the problem.) Some designers have found that enlarging the ducts around active chilled beam systems to increase air circulation causes echoes in working areas and amplifies the sound of water moving through the pipes to noticeable levels.
Installation and adoption
The most common active chilled beam design is in the form of a capital letter "T", upside down and suspended from the ceiling. They are generally 1 to 2 ft (0.3048 to 0.6096 m) wide, and require less than 1 foot (0.3048 m) of overhead space. A typical 2 foot (0.6096 m) wide chilled beam system generally weighs about 15 pounds (6.8 kg) per 1 foot (0.3048 m) length of the beam. Chilled beams are generally installed so that the center of each beam is no more than 3 metres (9.8 ft) from the center of the next beam. Some designers dislike the beams because they do not cover the entire ceiling so ducts, wiring, and other infrastructure can be seen. Some designers have installed one chilled beam system around the building perimeter (where temperature differences can be the greatest) and another in the interior of the building, to better control temperature throughout the structure. Higher system performance may be obtained by increasing the static pressureStatic pressure
In fluid mechanics the term static pressure has several uses:* In the design and operation of aircraft, static pressure is the air pressure in the aircraft’s static pressure system....
of the air in the building. The systems generally need little cleaning (vacuuming of dirt and dust from the fins every five years).
As of 2007, chilled beam HVAC systems were used more widely in Australia and Europe than in the United States. In Australia, the system was first used in 30 The Bond, Sydney which was the first building in Australia to achieve the rating of 5 stars ABGR . Chilled beam HVAC systems have been used at London Heathrow Terminal 5 and Constitution Center
Nassif Building
Constitution Center is an office building located at 400 7th Street SW in Washington, D.C. It is high and has 10 floors. Covering an entire city block, it is the largest privately owned office building in the District of Columbia...
(the largest private office building in Washington, D.C.). The system has also received prominent use at Harvard Business School
Harvard Business School
Harvard Business School is the graduate business school of Harvard University in Boston, Massachusetts, United States and is widely recognized as one of the top business schools in the world. The school offers the world's largest full-time MBA program, doctoral programs, and many executive...
, Wellesley College, and the American headquarters of the pharmaceutical company AstraZeneca
AstraZeneca
AstraZeneca plc is a global pharmaceutical and biologics company headquartered in London, United Kingdom. It is the world's seventh-largest pharmaceutical company measured by revenues and has operations in over 100 countries...
.
The multiservice chilled beam is a relatively new form of the chilled beam. Developed in 1996, it incorporates computer and electrical wiring, lighting, motion-detection sensors, and sprinklers into the chilled beam unit. The multiservice chilled beam was first installed at the Barclaycard
Barclaycard
Barclaycard, part of Barclays Retail and Business Banking, is a global payment business. The Barclaycard was the first credit card introduced in the UK, coming into service in 1966. It enjoyed a monopoly until the introduction of the Access card in 1972....
building in Northampton
Northampton
Northampton is a large market town and local government district in the East Midlands region of England. Situated about north-west of London and around south-east of Birmingham, Northampton lies on the River Nene and is the county town of Northamptonshire. The demonym of Northampton is...
, England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
, but has since been used at the headquarters of Lloyd's Register
Lloyd's Register
The Lloyd's Register Group is a maritime classification society and independent risk management organisation providing risk assessment and mitigation services and management systems certification. Historically, as Lloyd's Register of Shipping, it was a specifically maritime organisation...
(London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...
), Airbus UK
Airbus UK
Airbus UK is a wholly owned subsidiary of Airbus SAS which produces wings for the Airbus aircraft family. When Airbus was incorporated as a joint stock company in 2001 BAE transferred its UK Airbus facilities in return for a 20% share of the new company. These facilities became Airbus UK...
(Bristol
Bristol
Bristol is a city, unitary authority area and ceremonial county in South West England, with an estimated population of 433,100 for the unitary authority in 2009, and a surrounding Larger Urban Zone with an estimated 1,070,000 residents in 2007...
), and the Greater London Authority
City Hall (London)
City Hall is the headquarters of the Greater London Authority which comprises the Mayor of London and London Assembly. It is located in Southwark, on the south bank of the River Thames near Tower Bridge...
; Riverside House (London); Empress State Building
Empress State Building
The Empress State Building is a skyscraper in the London Borough of Hammersmith and Fulham. It was built in 1961 and was tall with 28 floors, designed by Stone, Toms & Partners. It was renovated in 2003 to a design by Wilkinson Eyre Architects. Three floors and were added to its height...
(London); 55 Baker Street (London) and 101 New Cavendish Street (London).