BEAMA

6 January 2010

The number of homes that require both time and temperature control may be greater than you think. A 2006 report by Nationwide showed that the average floor area of a four-bedroom detached house was 157m2, while the average for a five-bedroom detached property was over 200m2. Older houses can also be surprisingly large, with the average of all detached homes built before WWII being over 150m2.

Zoning with separate temperature control

If a dwelling is operated as a single temperature zone, then a central room thermostat will turn the heating on and off depending on whether the temperature it senses is below or above the thermostat’s set point. This thermostat will be in the main living area, usually the living room or hallway. Controlling the heat going in to the whole house from one point is fine in theory, but assumes that the level of heating in every room is satisfactory when the living area attains the desired temperature. Separate temperature zones provide a more sophisticated approach where different parts of the house can be at different temperatures. Lower temperatures can be maintained in unoccupied parts of the house and the system can take full advantage of solar gains, which can have quite a pronounced difference between rooms with south facing or north facing windows, even in mid-winter.

Zoning with separate time control

Behavioural factors are the main reasons why zones with separate time control offer advantages. Heat can be focussed on only the parts of the house that are occupied. For instance, the living room and kitchen could be one zone, with the heating kept on during the day if only one person is home. The rest of the house is then a separate zone that comes on in the evening when the entire family comes home. Separate zones offer convenience and improved comfort, while reducing unnecessary energy use – after all, how many of us would accept all their lighting controlled by a single switch?

Zoning in practice

While zones are required by the Building Regulations, the installer must decide how to arrange the zones to offer the best advantages in terms of energy saving and usability for the customer.

This can only be done by looking at the characteristics of the house and talking to the occupants about how they use it. Then the installer can try to identify zones offering the best comfort and flexibility - while using minimum energy. The aim is to avoid overheating areas, either because they need less heat to keep warm, or because the set point could be lower. Installers shouldn’t forget that the number of zones specified in the Building Regulations is the minimum and there may be real benefits in recommending additional zones to customers.

The choice of equipment to install in achieving separate zones should be decided on the basis of how these zones will work. There are various options that can be used alone or combined to achieve an appropriate result:

• The use of a separate programmer and room thermostat in each zone is the obvious solution; particularly if a zone within a building is physically separate, such as with a ‘granny flat’ or home office where separate controls are desirable.
• Multi-channel programmers can allow time control of individual rooms or multiple zones to be set from a single point. This is more flexible than having multiple programmers if all the zone settings will be made by one person.
• Thermostatic radiator valves (TRVs) can automatically vary a radiator’s heat output depending on the room temperature (e.g. quickly responding to sudden solar gain), and provides temperature control of individual rooms. You can also get TRVs fitted with special heads, which include on-off control linked to the programmer (either wired or wireless).

Zoning is a statutory requirement that saves energy and reduces harmful gas emissions. It also provides opportunities for installers to add to their earnings.