HEATING AND AIR CONDITIONING SYSTEM
This guide has been drawn up to help occupiers understand the operation of the HVAC (heating, ventilation and air conditioning) system in Exchange Tower. The non-technical explanations should help occupiers understand why certain problems may be experienced within their offices.
The conclusion and recommendation of this guide is that any alterations made within the offices, e.g., partitioning, should have consideration given to the heating and air conditioning system within the building. The building is designed in such a way that it can accommodate various office layouts and uses. However, any alterations proposed by occupiers should be notified to Building Management, so that they can help ensure that all issues are considered, in particular any work to the air conditioning system.
Cooling is provided on each floor by way of air being blown down through the slot diffusers in the ceiling. The air that is being blown into the area will be at varying volumes and at varying temperatures, hence varying the cooling load to any area. The system is therefore known as a Variable Air Volume system or VAV for short.
Heating is in part provided to the offices by means of perimeter radiators. These radiators in particular offset heat loss at the perimeter glazing and also counter-act any down draughts next to the glass. The remainder of the heating gain to the offices is provided by equipment (photocopiers, PCs etc), lighting and people.
Fresh air is filtered and ducted from roof level to one of two plant rooms on each floor of the building (known as East and West). This fresh air is heated at roof level to 11-15ºC if the external air temperature is too low, or the air is cooled by the chillers.
Office Air Supply
On each floor level in each plant room, the air is filtered and cooled and then ducted through to what is known as VAV boxes within the ceiling of the offices. These boxes are either a “master” or “slave”, the difference being that the master unit dictates the air volume from its own unit but also from the slave units. From the VAV boxes, the air is diffused though the linear slots in the ceiling. The air circulates within the office from the ceiling downwards.
The master unit location is vital to the comfort of staff in the offices in that, it is that unit that will control the volume of air delivered to the slave units. In a simplistic situation, if the master is in an open plan cool area, and the slave box is within a small cellular office used for say meetings, then it is likely that the slave unit will not give adequate cool air to that small office area. This is because the master unit dictates the amount of cooling air supplied and if it thinks the temperature is adequate in the open plan area, it will not supply adequate cool air to the cellular office, even though that cellular office is too hot.
Air is extracted from the offices mainly through the ceiling grilles but also partially through the lights. The temperature of this extracted air is recorded, so that the master VAV box can determine whether more cool air is required to that area.
1. “The room is too cold”.
The original offices were designed to an open-plan format. Partitioning can be used successfully but the fit-out contractor must consider the air conditioning layout when placing partitions etc. The supply air temperature to the floor may be set too low; the control to the VAV master can be adjusted (by moving the “flag” on the ceiling to red to warm or to blue to cool). All alterations to the controls take time to ‘kick in’ and over compensating one day may have an adverse effect the following day.
2. “The room is too draughty”
A partition may stop air transfer across the ceiling and so air will be directed downwards causing a draught. Careful location of partitioning and desks is vital.
People may also complain that the pressure of the air may be creating noise. Reducing the noise means reducing the pressure, which reduces the amount of cooling air, which may lead to a warmer office.
3. “The room is too stuffy”
Again, adequate air circulation is required within the offices and if partitions are placed without consideration to the airflow, then it is likely that some areas will not benefit from either air supply or air extract. This creates a “stuffy” atmosphere. This complaint often corresponds to a complaint of being too hot.
a. Adjusting controls (including the “flags”) or the volumes of the supply air. Temperature of the air supplied to the whole floor can also be adjusted.
b. Moving master/slave VAV units.
c. Reconfigure partitioning taking into account the air conditioning system. Go to a more open plan layout or introduce more extract grilles etc.
d. Introducing new VAV boxes to problem areas or provide a dedicated system to computer suites, meeting rooms etc.
e. Use of blinds to reduce solar gain (when/if the sun shines).