Teknogas offers a complete central heating design service to provide clients with the correct design solution for their needs.

The service can include:
- House layout drawing with radiator placements, boiler location and system controls
- Heat loss calculations

A central heating system should be able to match the heat loss from the dwelling at the design conditions, with an allowance for intermittent operation and hot water usage.

The principal design considerations are:-

• The required internal temperatures of each room.
• the design outside temperature (Usually -1C but -3 or -5 in exposed locations)
• The Ventilation rate of the room(s).

The calculations will include provisions to ensure that the heating up time of the entire system is not excessive. Possibly including a factor to allow for a sheltered or exposed site.

Fabric heat losses and Ventilation heat losses.

Fabric heat losses are losses directly through the walls, windows,doors, floors and Ceiling of the room. For ease of calculation, it is assumed that these losses are at a uniform rate through each surface. The heat loss rates are obtained by multiplying the area of each individual surface by the design temperature difference and the heat transfer co-efficient Called the 'U' Value.

Thus:- Design heat loss = Surface area * Temperature difference * 'U' Value.

U values have been calculated for most construction types and are given in the table below.

Ventilation heat losses are caused by the air flowing through a dwelling. Ventilation rates can be quite surprising, and are usually quoted in air changes per hour. Defined as the volume of the air flowing through the room in one hour divided by the actual volume of the room itself.

This air clearly needs to be heated by the central heating system. and the heat required is calculated by multiplying the volume of the room by the air change rate ,the temperature difference between outside and inside and by the the specific heat capacity of air is 0.33 watts per cubic meter per degree celcius">heat capacity of air.

The air change rate is a design consideration which is extremely variable and can be minimised by draft proofing of the home. However, minimum ventilation rates are recommended, to prevent such things as condensation, stuffiness and smells, these design air changes are also given in table 2 In a room which has an open flue (Coal or gas fire) it is common to allow 5 air changes per hour as the operation of the flue entrains excessive air into the room. So opening up a fireplace to put a fire in can often be counter productive.

Allowance for heating up
Additional heating capacity is needed both in the radiators and in the boiler,to allow for the demands of intermittent heating and minimise the heating up period. This allowance is usually made as an addition to the calculated room heat loss. A figure of 10% gives acceptable results and is is normally used. Only in exceptional circumstances, such as where the customer requires a shorter heat up period than usual, should a larger addition be considered. up to 30% may be appropriate in such cases.

Allowance for hot water
Where the boiler supplies both the hot water and central heating simultaneously, an additional 2Kw is usually required in calculating the boiler output.

Allowance for exposure
Where a dwelling is situated at a very exposed site, allowance should be made for possibly higher heat losses than those calculated using standard u values, which assume average exposure. This could take the form of an arbitrary addition to the calculated heat losses (possibly 10%) but should be based on local conditions and experience.

Call us to design your central heating needs. 0121 246 1550