BSEE_July09_p27:Layout 1 17/6/09 10:56 Page 27
FA N C O I L S
The changing face of fan coils
By Barry Trewhitt, fan coil manager for Trox
T
he demand for energy using an infinitely variable
saving fan coils has speed motor is to use this
increased significantly facility instead of leaving the fan
due to Part L 2006 of running at a constant speed,
the Building irrespective of load, etc. Since
Regulations setting a target of the power consumption of the
28% reduction in carbon EC motors follows a cube
emissions from the base in Part relationship to fan speed and air
L 2002. We all know that it volume a small reduction in
doesn’t stop there; industry speed gives a big reduction in
representatives are confirming energy consumed as show in
the new 2010 Part L will target a table 1.
further 25% reduction in carbon So varying the fan speed with
emissions with a view to getting a VAV fan coil gives significant
Comparison of conventional fan coils with VAV fan coils on fan energy (kW) at hourly intervals over 12 months
commercial buildings carbon savings in motor power entering the room is not too low specifications ensure that there Example Coil, which includes SFP of 0.8,
neutral by 2019. consumption. A limit of 60% of and thus cause potential air is a minimum heat transfer The total building services 10 ACH of room air, 0% fan
Prior to the focus on rated air volume will generally distribution issues. It may be between the heating and system carbon emissions can turndown and design margin;
promoting the improvement of avoid “dumping” but selections prudent to introduce a cooling coils with a typical limit be evaluated using real fan coil against a VAV Fan Coil, which
energy performance of of diffusers should be checked temperature sensor to monitor of 100 Watts. This limit can be test data with a bespoke includes SFP, fan of 0.25, 10
buildings in the community fan by air distribution engineers. the coil air-off and at the achieved if the fan coil is software package such as TAS ACH room air, 60 % fan
coil development had been specified minimum designed with insulated flaps EDSL. turndown and design margin.
relatively slow, however How VAV Waterside fan temperature, start to increase either side of the coils A simple building model has Savings in total carbon
recently there have been several coils operate the air volume. If the room air controlled by electrical been used to provide basic emissions for a well designed
developments to the fan coil Isothermal mode - this is where temperature continues to actuators. Badly designed space heating and cooling building due to using a VAV FCU
market. demand hourly for a typical compared with CAV FCU could
London weather set (TRY). The be around 15%.
Energy efficient motors model is to Part L2 to
Traditionally AC motors have standards. Summary
been used in fan coils. They The open plan first floor of With fan coil systems the
have operated at a constant the model (30m by 30m) forms manufacturer is now taking
speed. DC motors have been the basis of the analysis. It has more and more responsibility
experimented with, due to them been subdivided into perimeter for both the fan coil unit and the
inherently being more energy and core zones according to the air distribution through the
efficient, but problems persist NCM. ceiling diffusers. It is not
about how to distribute DC Thermostat controls have been unusual for the client to
around the building or the cost set at 18ºC heating and 24ºC underpin the specified
of local transformers, etc. cooling with 2ºC proportional parameters by getting the
For a given size fan coil, the control ranges and a 2ºC dead specialist manufacturer to
difference in power band (as per figure 1). provide guarantees covering
consumption could be up to
Figure 1
A basic set of internal heat aerodynamics, thermodynamics
50%. Electrically commutated the room temperature is at the increase, the controller opens airside fan coils can waste in gains has been used for all and acoustics.
motors have the energy benefits design value (set point) and no the chilled water valve further excess of 500 Watts. zones. It is now possible to design
of DC combined with the ease of heating or cooling is required. and then increases the motor The simulation of the building buildings using fan coils which
being able to be directly In this mode the water control speed. The system approach provides hourly profiles of will exceed the requirements of
connected to the 230 VAC valves, hot and cold, will be Heating mode - as the room Using VAV FCU the importance heating and cooling demand. the building regulations
power circuit. AC motors require closed but the fan will be air temperature decreases a of air distribution must be A comparison of a CAV Fan changes planned for 2010.
a multi-tapped transformer to running typically at 60% signal from the sensor to the emphasised to ensure comfort
adjust the speed/air volume in volume. controller starts to open the hot conditions are met at all times.
increments. One of the key Cooling mode - as the room water control valve. If the room At minimum air volumes
benefits of EC motors is air temperature increases a air temperature continues to adequate air movement is
Benefits of VAV fan coils
infinitely variable motor speed signal from the sensor to the fall, the controller opens the hot maintained and the diffuser
Energy efficient when compared with constant volume units
using a 0 – 10v dc signal. controller starts to open the water valve further and then coanda effect is sustained. At
chilled water control valve. Care increases the motor speed. maximum air volumes, the
Exceed the requirements of the Building Regulations and
VAV fan coil must be taken with the coil air All of this is captured in the diffuser does not overthrow,
reduce carbon emissions
The natural progression, once off temperature such that the air control diagram Figure 1 which create excessive noise or
also shows a 2°C dead band external static resistance. This High motor efficiency leading to lower specific fan power
Air Volume (fan speed) Motor Power
where the fan coil operates in re-enforces the complete
the isothermal mode. system approach.
Efficient speed control, improved room comfort condition
100% 100%
This cuts energy
Airside fan coils consumption and reduces
Lower maintenance costs due to longer bearing and motor
Waterside fan coils as opposed emissions. On top of this, by
life
80% 51.2%
to Airside fan coils have always varying the motor’s speed to
Lower room air velocities and reduction in draughts
enjoyed the lion’s share of suit the heating or cooling
60% 21.6%
sales. Due to the focus being on requirement, the motor running
Reduction in sound levels providing overall greater comfort
energy saving the sale of Airside cost is reduced and energy is
Table 1 fan coils is reducing. Recent saved.
VISIT OUR WEBSITE: www.bsee.co.uk
JULY 2009 BUILDING SERVICES & ENVIRONMENTAL ENGINEER 27
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