Heating Controls

Control of the heat distribution system

In a typical heating system using water as the heating medium, the normal method of controlling the distribution of heat energy to the heat emitters is by means of a pump. In order to optimise the energy efficiency of the heating system it should be fitted with both time and temperature control so that the pump is activated and heat distributed when and where it is required.

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Time clock/programmer control

The operation of the heating system must match the occupancy pattern of the household. A suitable time clock/programmer will provide electric power to the boiler and pump when there is a requirement for heating. The householder may wish to turn off the heating system during the night when people are sleeping or during the day if the house is unoccupied, which can easily be achieved with suitable settings on the programmer. Time clock control is also important for occasional electric heating, i.e. fan heaters, convectors and oil filled radiators to avoid wasteful use of energy.

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Pump on-off control

Heating water from the boiler will be distributed through pipes to the heat emitters around the house by means of a pump. The normal method of switching on the pump is by means of a room thermostat. The thermostat should be located in a position in the house which will be representative of the comfort conditions in the house. The hall or the living room are the typical locations employed by householders.The householder should set the lowest possible temperature that will provide comfortable conditions in the house, typically 18–20ºC. Turning down the room thermostat by 1ºC can reduce the fuel bill by 10%. For warm air systems a room thermostat should be used to switch on and off the heat generator in response to room conditions. When the heat generator is off, the fan circulating the air would continue to operate in order to utilise the residual heat from the heat generator and may revert to half speed when the heat generator cools.

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Zone control

It is normally advisable to divide the heating system into separate zones. This will allow independent operation of the heating system in different parts of the house. Typical circuits would be the ground floor, the first floor and the domestic hot water storage cylinder. Autonomous operation of the zones will be achieved if individual motorised valves or pumps are fitted to each zone.Timer and thermostatic control will permit individual and economic functioning of the heating system in each part of the house. Each zone will be switched on only at the times required by the household and when there is a demand for heat indicated by the thermostat located in that area. For all heating systems it is recommended that there be a separate hot water circuit to allow for the heating of hot water without needlessly heating the home.This is a requirement of all new buildings in accordance with the Building Regulations published in 1997. Additionally, these regulations suggest that for homes over 100 sq. m the heating system should be split into at least two zones in accordance with typical heat demand differences – namely the bedrooms and living areas, the former of which typically requires lower temperatures.

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Weather compensator

For larger installations consideration may be given to the provision of a weather compensator control to help reduce fuel bills. This type of control system uses a thermostat located outside the house and a 3-port mixing valve positioned close to the boiler. The temperature of the flow water to the space heating circuits is adjusted according to the outside air temperature. A low outside air temperature will direct the control system to supply the highest possible flow water temperature to the heat emitters. When the outside temperature rises, the demand for space heating in the house will be reduced.The control system will cause the 3-port mixing valve to supply a lower temperature water to the space heating circuits and save on heating costs.

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Automatic control

A thermostatic radiator valve (TRV) may be installed instead of the hand wheel valve. The TRV contains a bellows which will close the valve on a rise in air temperature in the room, stopping the flow of heating water to the heat emitter. The TRV has a number of settings, which the householder may use to set the desired air temperature for each room. In locations where a high level of heating is required, the TRV will be set at the top setting.Conversely, if only background heating is desired then the valve will be fixed at its lowest setting.