Fan coil unit - AbsoluteAstronomy.com

A fan coil unit is a simple device consisting of a heating or cooling coil and fan

Fan (mechanical)

A mechanical fan is a machine used to create flow within a fluid, typically a gas such as air.A fan consists of a rotating arrangement of vanes or blades which act on the air. Usually, it is contained within some form of housing or case. This may direct the airflow or increase safety by preventing...

. It is part of an 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 found in residential, commercial, and industrial buildings. Typically a fan coil unit is not connected to ductwork

Duct (HVAC)

Ducts are used in heating, ventilation, and air conditioning to deliver and remove air. These needed airflows include, for example, supply air, return air, and exhaust air. Ducts also deliver, most commonly as part of the supply air, ventilation air...

, and is used to control the temperature in the space where it is installed, or serve multiple spaces. It is controlled either by a manual on/off switch or by thermostat.

Due to their simplicity, fan coil units are more economical to install than ducted or central heating systems with air handling units. However, they can be noisy because the fan is within the same space. Unit configurations are numerous including horizontal (ceiling mounted) or vertical (floor mounted).

Design and operation

It should be first appreciated that 'Fan Coil Unit' is a generic term that is applied to a range of products. Also, the term 'Fan Coil Unit' will mean different things to users, specifiers and installers in different countries and regions, particularly in relation to product size and output capability.

A fan coil unit may be concealed or exposed within the room or area that it serves.

An exposed fan coil unit may be wall mounted, freestanding or ceiling mounted, and will typically include an appropriate enclosure to protect and conceal the fan coil unit itself, with return air grille

Grille

A grille or grill is an opening of several slits side by side in a wall or metal sheet or other barrier, usually to let air or water enter and/or leave but keep larger objects including people and animals in or out.-Spelling:In the United States, "grille" is used to differentiate the automotive...

and supply air diffuser

Diffuser (thermodynamics)

A diffuser is the mechanical device that is designed to control the characteristics of a fluid at the entrance to a thermodynamic open system. Diffusers are used to slow the fluid's velocity and to enhance its mixing into the surrounding fluid...

set into that enclosure to distribute the air.

A concealed fan coil unit will typically be installed within an accessible ceiling void or services zone. The return air grille and supply air diffuser, typically set flush into the ceiling, will be ducted to and from the fan coil unit and thus allows a great degree of flexibility for locating the grilles to suit the ceiling layout and/or the partition layout within a space. It is quite common for the return air not to be ducted and to use the ceiling void as a return air plenum.

The coil receives hot or cold water from a central plant, and removes heat from or adds heat to the air through heat transfer

Heat transfer

Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...

. Traditionally fan coil units can contain their own internal thermostat

Thermostat

A thermostat is the component of a control system which regulates the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature. The thermostat does this by switching heating or cooling devices on or off, or regulating the flow of a heat transfer...

, or can be wired to operate with a remote thermostat. However, and as is common in most modern buildings with a Building Energy Management System

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...

(BEMS), the control of the fan coil unit will be by a local digital controller or outstation (along with associated room temperature sensor and control valve actuators) linked to the BEMS via a communication network, and therefore adjustable and controllable from a central point, such as a supervisors head end computer.

Fan coil units circulate hot or cold water through a coil in order to condition a space. The unit gets its hot or cold water from a central plant, or mechanical room

Mechanical room

A mechanical room or a boiler room is a room or space in a building dedicated to the mechanical equipment and its associated electrical equipment. Unless a building is served by a centralized heating plant, the size of the mechanical room is usually proportional to the size of the building...

containing equipment for removing heat from the central building's closed-loop. The equipment used can consist of machines used to remove heat such as a 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:...

or a cooling tower

Cooling tower

Cooling towers are heat removal devices used to transfer process waste heat to the atmosphere. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or in the case of closed circuit dry cooling towers rely...

and equipment for adding heat to the building's water such as a boiler

Boiler

A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.-Materials:...

or a commercial water heater.

Fan coil units are divided into two types: Two-pipe fan coil units or four-pipe fan coil units. Two-pipe fan coil units have one (1) supply and one (1) return pipe. The supply pipe supplies either cold or hot water to the unit depending on the time of year. Four-pipe fan coil units have two (2) supply pipes and two (2) return pipes. This allows either hot or cold water to enter the unit at any given time. Since it is often necessary to heat and cool different areas of a building at the same time, due to differences in internal heat loss or heat gains, the four-pipe fan coil unit is most commonly used.

Fan coil units may be connected to piping networks using various topology designs, such as "direct return", "reverse return", or "series decoupled". See ASHRAE Handbook "2008 Systems & Equipment", Chapter 12.

Depending upon the selected chilled water temperatures and the relative humidity of the space, it is likely that the cooling coil will dehumidify the entering air stream, and as a by product of this process, it will at times produce a condensate which will need to be carried to drain. The fan coil unit will contain a purpose designed drip tray with drain connection for this purpose. The simplest means to drain the condensate from multiple fan coil units will be by a network of pipework laid to falls to a suitable point. Alternatively a condensate pump may be employed where space for such gravity pipework is limited.

Speed control of the fan motors within a fan coil unit is effectively used to control the heating and cooling output desired from the unit. Some manufacturers accomplish speed control by adjusting the taps on an AC transformer supplying the power to the fan motor. Typically this would require adjustment at the commissioning stage of the building construction process and is therefore set for life. Other manufacturers provide custom-wound Permanent Split Capacitor (PSC) motors with speed taps in the windings, set to the desired speed levels for the fan coil unit design. A simple speed selector switch (Off-High-Medium-Low) is provided for the local room occupant to control the fan speed. Typically this speed selector switch is integral to the room thermostat, and is set manually or is controlled automatically by the digital rooom thermostat. Building Energy Management Systems can be used for automatic fan speed and temperature control. Fan motors are typically AC Shaded Pole or Permanent Split Capacitor. More recent developments include brushless DC designs with electronic commutation. While these motors do offer significant energy savings, initial cost and return-on-investment should be carefully considered.

DC \ EC Motor Powered Fan Coil Units

These motors are sometimes called DC motors, sometimes called EC motors and occasionally EC/DC motors. DC stands for Direct Current and EC stands for Electronically Commutated.

DC motors

DC motor

A DC motor is an electric motor that runs on direct current electricity.-Brush:The brushed DC electric motor generates torque directly from DC power supplied to the motor by using internal commutation, stationary magnets , and rotating electrical magnets.Like all electric motors or generators,...

allow the speed of the fans within a Fan Coil Unit to be controlled by means of a 0-10 Volt input 'Signal' to the motor/s, the transformers and speed switches associated with AC Fan Coils are not required. Up to a signal voltage of 2.5Volts (which may vary with different fan / motor manufacturers) the fan will be in a stopped condition but as the signal voltage is increased, the fan will seamlessly increase in speed until the maximum is reached at a signal Voltage of 10 Volts. Fan Coils will generally operate between approximately 4 Volts and 7.5 Volts because below 4 Volts the air volumes are ineffective and above 7.5 Volts the Fan Coil is likely to be too noisy for most commercial applications.

The 0-10 Volt signal voltage can be set via a simple potentiometer and left or the 0-10 Volt signal voltage can be delivered to the fan motors by the terminal controller on each of the Fan Coil Units. The former is very simple and cheap but the latter opens up the opportunity to continuously alter the fan speed depending on various external conditions / influences. These conditions / criteria could be the 'real time' demand for either heating or cooling, occupancy levels, window switches, time clocks or any number of other inputs from either the unit itself, the Building Management System or both.

The reason that these DC Fan Coil Units are, despite their apparent relative complexity, becoming more popular is their improved energy efficiency levels compared to their AC motor driven counterparts of only a few years ago. A straight swap, AC to DC, will reduce electrical consumption by 50% but applying Demand and Occupancy dependant fan speed control can take the savings to as much as 80%. In areas of the world where there are legally enforceable energy efficiency requirements for Fan Coils (such as the UK), DC Fan Coil Units are rapidly becoming the only choice.
Examples of EC\DC Fan Coil Units:

Ability EC\DC technical pages http://www.abilityprojects.com/matrixTechnology/upClose.php

Areas of use

Fan coil units are typically used in spaces where economic installations are preferred such as unoccupied storage rooms, corridors, loading docks.

In high-rise buildings, fan coils may be stacked, located one above the other from floor to floor and all interconnected by the same piping loop.

Fan coil units are an excellent delivery mechanism for hydronic chiller boiler systems in large residential and light commercial applications. In these applications the fan coil units are mounted in bathroom ceilings and can be used to provide unlimited comfort zones - with the ability to turn off unused areas of the structure to save energy.

Installation

In high-rise residential construction, typically each fan coil unit requires a rectangular through-penetration in the concrete

Concrete

Concrete 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...

slab on top of which it sits. Usually, there are either 2 or 4 pipes made of ABS, steel or copper that go through the floor. The pipes are usually insulated with refrigeration insulation, such as acrylonitrile butadiene/polyvinyl chloride (AB/PVC) flexible foam (Rubatex or Armaflex brands) on all pipes or at least the cool lines.

Unit Ventilator

A unit ventilator is a fan coil unit that is used mainly in classrooms, hotels, apartments and condominium applications. A unit ventilator can be a wall mounted or ceiling hung cabinet, and is designed to use a fan

Fan (mechanical)

to blow air across a coil, thus conditioning the space which it is serving.

Examples of unit ventilators:

McQuay http://www.mcquay.com/McQuay/ProductInformation/UnitVent/UnitVentilators
Nesbitaire http://www.nesbittaire.com/na_vents_903.html
Trane http://www.trane.com/Commercial/Dna/View.aspx?i=1094
International Environmental http://www.iec-okc.com
Williams [www.wfc-fc.com]

European Market

The Fan Coil market is composed of one quarter of 2-pipe-units and three quarters of 4-pipe-units, and the most sold products are "with casing" (35%), "without casing" (28%), "cassette" (18%) and "ducted" (16%).

The market by country is splitted in 2010 as following: