The thermostat is the remote-control device for all the space-conditioning equipment. It’s a convenient means to monitor the space temperature and to control the equipment to use less energy while maintaining a comfortable environment. It’s also a potential source of error in the system, and therefore of inefficiency and wasted energy.
The first thing to notice about each unit thermostat is its location. It should be located on an inside wall since exterior walls are usually not at the average room temperature. Another common practice is o situate thermostats near a return-air grille to provide a constant flow of air across the sensor for a consistent sampling of air from the room. Sometimes the thermostat location may have changed from the original design location because of remodeling, so it is important to periodically optimize thermostat locations in their given environment.
The thermostat should not be located in direct sunlight. This causes higher than ambient temperature readings. Locations near artificial heat sources are also to be avoided, such as copy machines, computer consoles, refrigerator compressor coils, or an office worker with a space heater under the desk. It is decisive that the flow of air around the thermostat must be clear and unrestricted. Putting the unit behind a door, curtains, or filing cabinet isolates it from the space served and skews its operation. A thermostat in such a location will not be able to properly modulate the space temperature.
Thermostats should be calibrated regularly so they can maintain the designated setpoint. Mechanical devices may become dirty. The working parts may become seized with rust. A portion of the mercury may have seeped out. The sensing elements of electronic devices can become fouled or corroded, diminishing their sensitivity. The control wires back to the unit may have become frayed or pinched, so the full design voltage does not relay the correct signal back to the HVAC unit. Pneumatic controls systems have similar problems: pinched tubing, leaking connections, and low pressure delivered by the compressor.
These kinds of circumstances may not cause the unit to malfunction completely, or even cause obvious problems for the occupants. By delaying reaction time and permitting large swings in temperature, though, errant controls may introduce an unnecessary level of discomfort in a space. This can affect productivity and morale while causing a higher energy use than is necessary.
Once the equipment is operating as designed, it’s time to be sure the thermostat does its job. Posting signs to advise tenants of the ideal setting is one way. A more assertive way is to install locking covers to prevent unauthorized tampering (or relocate the thermostat to the return-air duct where it will be completely inaccessible). Of course, if the thermostat location is improper or the unit is not calibrated right, a locked cover will only frustrate the tenants. Best to put the horse before the cart in this case and be sure to give occupants no reason to adjust the thermostat.
The final course of action, in the pursuit of energy savings, is to simply adjust the setpoint higher in the summer and lower in the winter. Ceiling fans help, too. They move the air in the summer, and this sensation of movement across the skin gives the effect of a temperature 5 to 10° cooler, so that the thermostat can be setback accordingly. The ceiling fan direction can be reversed in the winter, to force warm air at the ceiling down to the occupied zone where it can do some useful work instead of languishing in the top of the room.
Relaxing dress codes is another possibility, for relief in the hottest weather. In the winter wearing sweaters or wool clothing makes it possible to turn down the thermostat a few degrees.
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Excerpt from Energy Conservation Projects.