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Benefits of Temperature Setback in Residential Applications
ARTICLE POSTED BY: RICK VOLK, PE, LEED AP
Most homes are controlled through a wall mounted thermostat. This device allows the resident to control the heating / cooling equipment so that it maintains a desired space temperature. A common dial type thermostat that is installed in many homes controls the equipment to maintain a single temperature. For example if the thermostat is set at 75 degrees in the summer, the device will activate the cooling system when the temperature rises above this setpoint. When the temperature drops below the set-point, the cooling equipment will cycle off. The same premise would apply for the winter operation where the device would cycle the heating equipment on when the home temperature drops below set-point and off when it rises above it.
A temperature setback is a simple strategy to help save utility cost by reducing how often your heating or cooling system operates. This is achieved by allowing the temperature in a home to drift to a lower (heating mode) or higher (cooling mode) temperature. Adjusting your thermostat can reduce how often your furnace or air conditioning unit runs resulting in lower utility cost.
Of course most people want to feel comfortable when they are in their homes – so allowing the temperature to drift when residents are active in their home typically is unfavorable. The best approach to implementing a setback strategy is to allow the temperature to drift when no one is home. Some households have set schedules where they are gone a portion of the day. Applying a setback during these vacant periods would eliminate concerns of discomfort while reducing utility usage. Another popular approach to implementing setback that can apply to most households is to allow the temperature to drift when the occupants are asleep. This concept is called night-setback and allows the temperature drift to occur without too much notice from the occupants.
The amount of energy saved is dependent on how far you set back your thermostat and for how long. The more you let your home temperature drift and the longer you let this drift occur – the more utility savings can be expected. To help quantify this savings, a general rule of thumb can be used to approximate the savings. According to the US Department of Energy, it is estimated that 1% energy savings can be achieved for every 1 degree setback for an 8 hour period. One day of setting back will not achieve any significant results. To see the suggested savings presented by the USDOE, the setback needs to occur on a daily basis. The same results can be approximated for setting forward (letting the home get warm in the summer). So if you can allow the home to drift down 5 degrees at night during the winter for 8 hours – there is potential of 5% savings on your utility bills. Of course every house is different so the potential savings will vary from home to home.
Another tool to help approximate your annual energy savings can be found on the Energy Star website. The link allows you to enter more specific operation and utility values to provide a more accurate savings as opposed to the rule of thumb values indicated.
http://www.energystar.gov/index.cfm?c=thermostats.progThermostat
Before one starts cranking the thermostat back in an attempt to reduce their next utility bill, there are a few items to consider. The first is discomfort. Setting the temperature down too far especially with small children or elderly individuals in the home can make them uncomfortable and more prone to sickness. In addition, the house temperature may take a long time to reach the setback temperature. Until the house reaches this new set-point, the heating / cooling unit will typically remain off – potentially leaving areas of the house unventilated and stuffy. Another concern is humidity. Letting your house drift down in temperature at night during winter months can increase the relative humidity. This increase in relative humidity has potential to cause issues with condensation on exterior surfaces (windows, walls, etc.). If condensation occurs during night setback, you should consider raising the temperature to help eliminate. In summer months, minimizing how often your air conditioning unit operates can lead to a lack of dehumidification. Homes can become too humid which can present all sorts of unwanted moisture issues. Humidity in the summer and winter should be carefully monitored when applying setback. A final consideration is when to switch your setback feature back to normal temperature. Ideally, the heating and cooling system should recover prior to when the residents wake up or get home. The amount of time to achieve this can vary dramatically. Some adjustment may be necessary to fine tune the switch back to normal mode to optimize comfort.
Most new thermostats are programmable and include an internal clock that allows this setback feature to be easily incorporated. If you do not have a programmable thermostat, a lot of diligence is needed to adjust the thermostat everyday to achieve this benefit. In addition, with a manual thermostat you do not have the benefit of having the cooling / heating system recover automatically before everyone awakes or gets home. From a convenience standpoint – it might be a good investment to buy a programmable thermostat. A new programmable thermostat can cost around $40-$50 and are not overly difficult to install by most home owners. Setting up a programmable thermostat is not always simple. The instruction manual is a necessity to get things set up appropriately. But if you can manage to get through the often confusing setup – a programmable thermostat can offer some real savings when applying a setback strategy.
Although this example refers specifically to residential applications, setback strategies can also be applied to commercial buildings. The heating / cooling systems are typically more advanced in commercial applications but energy savings can still be expected at a slightly different scale if a setback strategy is applied appropriately.
