Case study CIBSE award winner
> was raised to E from F. This was solely as a result of
focusing on improvements in the air conditioning
systems. Further capital investments would improve
the energy load further.
So, even in these hard times, we can see there is real
value in assessing the air conditioning and making
low-cost improvements. The value of an energy
performance certificate lies in taking expert advice on
developing the recommendations associated with the
certificate, and then implementing them to achieve
cost, energy and carbon savings in practice. l
Darren Bryant is managing director of Efficient Air.
www.efficientair.co.uk
See this month’s Schools & Education Supplement
for another CIBSE award-winning case study – the City
Academy, Hackney
Figure 3: Detailed inspection findings and recommendations
1. Air-handling unit (AHU) supply demand only, either based on an outside air 6. AHU 4 – This is a fixed speed system
temperatures are not consistent. temperature set point (ambient hold-off) or controlled by a VSD at 43.5Hz. However
Temperature ranges being supplied at the controlled on an internal upper temperature the unit was providing almost 10 air
time of inspection ranged from 15.1C to limit which could be set as high as 26C in changes per hour to a basement plant-
28.4C a temperature differential of 13.3C. any given zone. Predicted savings are based room. It is not considered necessary to
Excessive supply temperatures provided by on the circulating pump being held off for condition plant areas unless these areas are
office AHU’s will not only result in increased just two months of the year. These savings subjected to temperatures in excess of 30C.
heating costs during the winter season but have been calculated on the audited running Therefore consideration should be given to
will also result in the chilled beam circuits frequency of 27.9Hz. permanently isolating the heating battery
having to work harder to overcome higher on this unit and controlling the fan speed
internal temperatures. Specific consideration 3. AHU 2 – Both the pre-heat coil and the to provide a minimum amount of fresh air
should therefore be given to: heating coil control valves appear to be free-cooling (say at 20Hz), when plant-
• Adopting a heating schedule policy letting by on this unit. The BMS was calling room temperatures exceed 30C. This would
to ensure optimum temperatures are for cooling only, however both heating coils reduce both heating loads as well as power
maintained. This should take into were on. This would indicate that there is a consumed by the motor.
consideration the various solar elevations of fault with both control valves. Replacing or
the building; repairing these valves will prevent losses in 7. AHU 6 – It would appear that there is a
• Ensuring a dead band of at least 3C (+/- the system from over-heating and re-cooling. problem with the actuator on the fresh air
1.5C) is factored into BMS strategies to dampers on this unit. The BMS was saying
prevent simultaneous heating and cooling 4. AHU 2 – The control actuator for the that there was no fresh air into this unit
between the Air Handling Units, perimeter fresh air dampers on this unit has been and that it was in full recirculation mode.
heating circuits and the chilled beam units; disconnected. This means that this damper However, on inspection, it was found that
and, is always fully open. This air during winter the fresh air dampers were fully open. This
• More frequent temperature and pressure months will require significant heating to will be causing problems with the control
sensor calibration, for optimum control achieve the desired temperature set point. of the unit, which will then mean that more
efficiency. This will therefore increase heating costs mechanical conditioning will be required to
and reduce the control of heat recovery from condition the space.
2. At present chilled beam circuits are the unit. Replacing the control actuator
operational from 7am to 5.30pm Monday to and regulating the amount of fresh air will 8. AHUs 1, 101 & 104 – There appears to be a
Friday all year round. It is considered however, provide the following estimated savings. problem with the control strategies of these
that during winter months when ambient units. The recirculation dampers were fully
air temperatures are below 15C and solar 5. AHU’s 1, 3, 6, & 104 – The cooling coil closed, suggesting that the units at the time
heat gains are minimal that conditioned air control valve was letting by on these units. of inspection were in full fresh air mode. This
supplied by AHU systems should be adequate The BMS was calling for heating only, air therefore requires significant heating to
to overcome the internal temperature gains however both coils were on. This would achieve the desired condition temperature.
of the building without the need to run the indicate a fault with the cooling valves. By adjusting the control of the dampers, so
chilled beam systems. Consideration should Replacing or repairing the valve/actuators as to use heat recovery from re-circulated air
therefore be given to controlling the ‘on will prevent losses in the systems from over and free cooling from fresh air, the amount
floor’ secondary chilled water pumps on cooling and reheating. of mechanical conditioning can be reduced.
34 CIBSE Journal February 2010 www.cibsejournal.com
CIBSEfeb10 pp30-32,34 eland.indd 34 28/1/10 16:31:50
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