This month, retired air tightness technician Trevor Clark gives his advice on controlling heating and cooling systems to keep your energy bills down.

A control system manages, commands, directs or regulates the behaviour of other devices or systems using control loops.

It can range from a single home heating controller using a timer and thermostat controlling a domestic boiler to large industrial control systems which are used for controlling building environments.

A control system may be as simple as turning a switch on to start something, then off when the conditions have been reached.

On–off control uses a feedback controller that switches abruptly between two states.

A simple bi-metallic domestic thermostat can be described as an on–off controller.

When the temperature in the room goes below the user setting, the heating is switched on. Simple on–off control systems like these are cheap and effective.

In heating or cooling systems the design load is generally the maximum amount of energy that is required at the worst weather conditions for the geographical location for the building location.

For the major part of the heating season, the system may only be called upon to produce the maximum energy when starting up each day or for one or two days a year.

This is because of the weather.

If the weather remained constant, the control of our heating and or cooling system would be easy.

But when have you ever noticed the weather being constant?

In winter, when we need to control our heating system, the weather is always changing, hour by hour or minute by minute.

A basic control system provides a timer and thermostat to turn the heating on and off at set times and turn the heating on and off as close to the set temperature as possible.

A thermostat has to sense the temperature and the action of the on–off switching means there must be a differential between these two extreme positions.

For time controls, set to specific times for the heating to turn on and off, and use with a thermostat to limit the temperature within the dwelling.

For a central house thermostat, it’s generally positioned in the hall and can create problems in other rooms with overheating and is a basic control system.

In terms of radiator and circuit thermostats, as the dwelling heats up different rooms may reach the set point before other rooms, and as such the emitter thermostat will turn the water flow on or off.

This pushes more hot water to the other rooms and eventually all rooms are warmed. Each thermostat independently controls the room temperature.

For input control, where the amount of energy is varied by modulation of the fuel, in a gas boiler the flame size would be seen to increase or decrease as the control system requested more or less energy.

When it comes to speed control, the fluid circulating pumps or fans is controlled according to the energy required. Speed would increase or decrease as the control system requested more or less energy.

Where two or more areas within the dwelling require heating at different times or temperatures in the day is zone control.

This may be by having a number of pumps or by using diverting valves which are motorised to open and close slowly to prevent a sudden pressure spike within the system.

Total control is where a combination of all the above controls are incorporated within the building to ensure energy input is minimised while maintaining comfort conditions internally and keeping the utility costs as low as possible.

Application control is when our phones are capable of being used to control the heating system and there are many options available.

Some applications provide graphs and data from which you can work out the best time to set the heating to come on at for the temperature in the dwelling to be acceptable, and show how long it takes the dwelling to cool after the heating has turned off.

Using this information you can optimise the start/stop timing for your heating. Suffice to say, a control system can be complicated or simple, but to perform efficiently and heating or cooling system needs to be controlled accurately to save on running costs.