How faster control cuts heating costs

The best intentions of controls can easily be thwarted by people, especially if those controls are slow to react. Steven Henry of Chalmor explains how controls that are faster to react deliver greater comfort and save energy.

It is all very well for us to discuss the theoretical energy efficiency of buildings, but we must also be realistic. The performance of the HVAC system is often compromised by building occupants taking matters into their own hands when they become uncomfortable due to changes in weather conditions. Occupants opening windows to combat winter solar gain or plugging-in electric heaters to make a chilly office more comfortable can destroy even the most carefully designed energy-efficiency strategy.

Fig. 1: The temperature peaks and troughs that are characteristic of traditional TRVs lead to building occupants adopting their own local heating or cooling solutions — actions which the more stable temperature achieved with eTRVs heads off.

The full extent of these occupant interventions is becoming clearer through analyses of energy usage data. A recent pilot trial in which smart radiator valves were fitted to radiators in a central-government office building, for example, provided surprising results.

Chalmor eTRV+ electronic thermostatic radiator valves including PAIR (passive active infra-red) were installed in offices, meeting rooms and customer-facing areas. Corridors were set to 18°C, offices to 21°C, with a one-hour boost facility to 23°C.

The PAIRs provide occupancy-based control in offices and meeting rooms, with a setback to 16°C when not in use, rising to 21°C when occupied. After tracking energy usage over a 12-month period, an 8% reduction in gas use was identified (broadly in line with expectations), but electricity consumption had also fallen, by an unanticipated 12%. Analysis revealed that this was because staff were no longer using portable electric heaters to enhance individual local comfort, as peaks and troughs in room temperature had been evened out by the eTRVs. With electricity costing up to four times as much as gas, financial savings exceeded expectations by 18%.

The speed with which the HVAC system is capable of responding to temperature spikes and drops is the crucial factor. If the weather is unseasonably chilly, the occupant often plugs in the space heater long before the BMS can ramp up temperature in the room. Similarly, on sunny winter days, someone opens a window before the BMS (or a traditional TRV) has a chance to reduce the radiator temperature.

When a window is opened, the BMS (sensing the drop in temperature) may actually ramp heating up instead of down, and, where air conditioning is installed, you can become locked in a vicious circle with the heating and cooling devices fighting to restore comfort conditions.

Research carried out by Chalmor with London South Bank University indicates that smart radiator valves provide a solution to these problems. The Chalmor eTRVs used in the research were shown to sense and react to local temperature changes more rapidly than traditional TRVs — achieving greater consistency of temperature, and evening out the peaks and troughs that trigger building occupants to adopt their own local heating or cooling solutions (Fig. 1 on the previous page). A manual boost button on the valve provides room occupants with the opportunity to trigger one hour of heating if the room should feel chilly, providing a more efficient alternative to portable electric heaters (which, once switched on, are frequently forgotten about and left on unnecessarily).

Fig. 2: Chalmor’s eTRV Chalmor’s eTRV has a fast response that evens out fluctuations in room temperature. It can also turn off heating if a window is opened.

In addition, our latest model, the eTRV+, incorporates an open-window feature. When someone opens a window, the sudden drop in room temperature is detected by the smart radiator valve. The valve reduces the radiator temperature, preventing heat being supplied to the room unnecessarily and wasting energy.

In conclusion, the capabilities of smart radiator valves are only just beginning to be recognised and optimised. Research demonstrates, however, that they have a major role to play in tackling these often hidden, but significant, causes of energy wastage — enabling the HVAC system to achieve its energy-saving potential.

Steven Henry is managing director of Chalmor.

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