Quick wins: The heat is on

9th December 2011


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IEMA

Better control over workplace heating can help save money and reduce emissions

A one-degree reduction in workplace temperatures could save UK organisations a cumulative £35 million a year, according to the Carbon Trust, making a substantial dent in the £450 million that UK businesses and the public sector currently spend each year on heating their buildings.

With analysts at Deutsche Bank forecasting that energy prices could soar over the next four years by as much as 50%, the potential savings from controlling heating more effectively will only increase.

Heating accounts for almost 60% of total energy consumption in the UK, and approximately half of the country’s carbon emissions come from the energy used to produce heat, which is more than from generating electricity. More efficient use of heating can therefore also help the UK to meet emissions-reduction targets.

The Carbon Trust says it is possible to cut heating costs by as much as 30% by taking some simple energy-saving measures. It estimates that with heating accounting for more than 75% of a typical service-sector company’s energy bill, a 15% saving could be achieved by resetting timers and replacing old controls.

Taking control

Set correctly, controls ensure a boiler or heating system operates only when necessary, and at a temperature that provides a comfortable working environment, improving the efficiency of the system.

Heating in most commercial buildings is supplied by one of three systems:

  • Wet systems use mainly water to transfer heat, normally via a boiler, to radiators or convectors.
  • Warm-air systems transfer heated air, normally via air ducts. Controls for warm-air systems are simpler than for wet systems. Many warm-air systems incorporate integrated controls to ensure fan speed matches the firing cycle of the burner, reducing variations in room temperature.
  • Radiant systems (common in factories) use infrared radiation equipment, such as gas-fired heaters or electric-quartz lamps, to heat small areas.

The main types of heating controls are as follows:

  • Timers – switch heating systems on and off, ideally in line with building occupancy. There are several types of time controls. A 24-hour programmable timer switch usually has two dials, with the outer dial showing the minutes, and the inner dial the hour. Electronic or digital versions can also be set for each day of the week. Generally, digital controls provide more control than mechanical programmers. Standard programmable timers tend to apply the same time settings for both space heating and hot water, while a fully programmable timer allows independent settings.
  • Temperature thermostats – control the temperature of a building or room. Wall thermostats switch the boiler (or pump for smaller systems) on and off when the required temperature is reached. Such controls have a typical switching differential between on and off of about 2.5°C. Thermostatic radiator valves (TRVs) are available for wet systems. TRVs control the heat output by regulating the water flow. The Carbon Trust says that correctly fitted and operated TRVs provide a very efficient level of control, allowing individual radiators to be set to suit the environment and requirements of the room, for example if there are heat gains (number of people, solar, lighting and office equipment) or if physical activity takes place there. TRVs are designed with a simple numerical scale and not temperature levels. Tamper-proof TRVs are available so settings cannot be changed. Frost thermostats are also available. These override other controls if there is risk of a building or boiler being damaged in cold weather conditions. The trust warns that people often set thermostats to maximum, believing (wrongly) that a room will heat up faster as a result. In reality, temperature increases at the same standard rate before overshooting and the room becoming too hot. It advises that thermostats are always set at the desired temperature. TRVs in regularly unoccupied rooms should be set at 2–3 to prevent overheating. Thermostats should be tested regularly to ensure they are working correctly.
  • Boiler controls – maintain the temperature of the water at the desired level by controlling the firing of the boiler’s burner. Where more than one boiler is in operation, sequence controls can be installed to ensure a boiler is only switched on when there is sufficient demand. The trust says that turning off boilers that are not required can cut costs by 5%. Boiler-inhibit controls ensure the equipment does not fire when there is no demand for heating, which is something that can occur.

The “right” temperature

It is worth remembering that the Workplace (Health, Safety and Welfare) Regulations 1992 require that minimum temperature levels – between 13°C and 16°C for manual work – are maintained. Many people may prefer a higher temperature than that set by the legislation, however.

The Chartered Institution of Building Services Engineers’ Guide A: Environmental design provides recommendations for suitable winter and summer temperature ranges. For example, it suggests that a comfortable winter temperature in a general office is between 21° and 23°C, depending on the activity being performed, while for a factory where light work is being undertaken it is 16°–19°C.

The Carbon Trust recommends regular monitoring of existing heating controls. Are they displaying the correct time and date? Do the settings match the regular working patterns? Are empty rooms being heated unnecessarily? Have thermostats been altered and not reset?
The trust suggests that in some workplaces it may be possible to shut down the heating system an hour before the end of the working day, reducing costs without affecting comfort levels. It also advises switching off heating systems overnight if buildings are empty, with the heating set to come on and reach the desired temperature at the start of the working day. The optimum time to achieve correct warm-up will vary with the seasons, so will need to be occasionally adjusted.

Keeping heating systems well maintained is also recommended. The Carbon Trust estimates that a poorly maintained heating system can increase costs by as much as 15%. It also suggests boilers that are at least 15 years old or are inefficient should be replaced.

Another issue to consider is the operation of heating and cooling systems. Setting a gap of 4–5°C between the heating and cooling thermostat setting – for example, heating off when the temperature reaches 19°C and cooling off until the temperature exceeds 24°C – should provide a sufficient temperature break to ensure the two systems do not operate simultaneously, consuming unnecessary energy.

Zoning is another option, and involves installing separate controls for different areas, such as where occupancy rates differ or different temperature levels are required. South-facing rooms tend to get heat gain from the sun, for example, and so may need less artificial heating.

New technology

Heating controls are becoming more sophisticated, enabling stricter control over when heating switches on and off. Modern seven-day time switches allow building managers to programme the time setting on heating and ventilation systems to match working patterns over the whole week.

Extension timers and delayed-off controls provide more flexibility than conventional timers, while optimum start controllers and weather-compensation controls automatically control when to switch a system on to achieve the optimum temperature, adjusting to changes in the weather and external air temperature.


Further information

The Carbon Trust’s “Expert in energy” guidance series put the spotlight on heating in November 2011, and included the publication of new guides, a training webinar and online advice. To accompany the new guides – which include a table of recommended temperatures for different types of buildings – and advice, the trust also offered the following “top tips” on reducing energy consumption from heating:

  • Get control – buildings with well-controlled heating systems typically have a 15–30% lower heating fuel usage.
  • Don’t overheat – heating costs rise by about 8% for each 1ºC of overheating.
  • Maintain regularly – energy consumed by heating, ventilation and air-conditioning systems can increase by up to 30% if they are not regularly maintained.
  • Think big-picture – energy is wasted when heating and air conditioning work against each other, so make sure equipment to cool a workplace is not working at the same time as the heating system is on.
  • Train staff – provide staff with guidance on recommended operating temperatures and how to set heating or cooling units correctly.
  • Do not overcomplicate – it is best not to make a system too complicated as there is a danger that controls will interfere with each other.


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