Wednesday, June 8, 2011

Programmable Thermostats

Programmable thermostats save energy by permitting occupants to set temperatures according to whether the house is occupied. These thermostats can automatically store and repeat settings daily with allowance for manual override. By eliminating manual setback, which is easy to forget, they allow the setting of more comfortable temperatures in the morning before occupants wake. Temperature setback can be adjusted for both heating and cooling seasons.
Programmable thermostats can be set to adjust the temperature setting according to a user's schedule. These thermostats typically have a digital interface that allows more precise temperature control and a wider range of options or features.
Programmable thermostats typically offer a number of programming options:
  • Daily programming that allows one schedule to be used each day.
  • Weekday/Weekend (5/2) programming that allows adjustment of timing for setbacks with different settings for weekdays and weekends, and with 5/1/1 programming that permits separate schedules for Saturday and Sunday.
  • Full seven-day programming that permits a different setback schedule for each day of the week.
Other special features depend on manufacturer and model and may include the following:
  • Vacation Override, which allows temporary override of the programmed settings.
  • Keyboard Lock, which prevents unauthorized changes to the preprogrammed settings.
  • Low Battery Indicator indicates whether the battery used to hold the programmed schedule is low.
  • An Energy Monitor that can keep track of how many hours the HVAC system has run for any selected time period.
  • An Auto Season Changeover that automatically provides heat or cooling at the onset of the heating and cooling season.
  • A Filter Change Indicator that goes on after a pre-set time period to remind when it is time to clean or replace the filter.
Different types of heating/cooling systems may require different types of programmable thermostats. For example, heat pumps require programmable thermostats that minimize the use of less efficient auxiliary electric resistance heating. Only a few companies manufacture line-voltage setback thermostats that directly control 120 volt or 240 volt line-voltage circuits connected to electric baseboard electric heaters. When purchasing a programmable thermostat, it is necessary to insure the thermostat is compatible with the HVAC system.

Affordability While some thermostats can appraoch $300, the money saved can offset the initial cost of the thermostat over a year or two's time.
Energy Efficiency By allowing the homeowner to program a schedule, these thermostats turn off the HVAC systems when they are not needed. This reduces the energy consumption of the home by not conditioning the house when it is not needed.
Environmental Performance In addition to saving energy, ventilation can be programmed into the thermostat's setings to provide fresh air to the house at important times.

Programmable thermostats are readily available from various HVAC contractors/suppliers and home centers. The EPA maintains a list of ENERGY STAR® labeled programmable thermostats.
In order to receive the ENERGY STAR® label, thermostats must have at least two programs (one for weekdays and one for weekends), four temperature settings (two "normal" settings and two set-back settings for each day), a hold feature that allows users to temporarily override settings, and the ability to maintain room temperature with 2°F of desired temperature.

The cost of programmable thermostats varies from $30 to as much as $250 or more, depending on the desired features. Models designed for heat pumps are more expensive due to the need for two stage heating.

Not Applicable

Utility companies or government agencies in some areas may provide incentives or rebates for installing programmable thermostats.

The technology "Programmable Thermostats" has been evaluated by PATH. The hyperlink for the field evaluation is listed below:

The installation of most programmable thermostats is relatively safe and simple because they are connected to low-voltage wiring, but may become complicated if such wiring does not already exist. Only qualified electricians or HVAC contractors should install line-voltage programmable thermostats for electric baseboard heaters because the wiring carries higher voltages.

Programmable thermostats typically come with a 1 year limted warranty. However, Honeywell offers 5 year warranties for thermostats that must be installed by a professional.

Energy savings depend upon the extent of daily variation in local temperatures and the setback settings. Department of Energy (DOE) estimates, however, that cost savings of approximately 10 percent per year are possible for heating and cooling by setting temperatures back to ten to 15 percent of the comfort level eight hours each day. Electronic-programmable thermostats are far more accurate than older, manually programmed thermostats, and provide better control and comfort. For example, manually set thermostats might allow temperature variations of up to five degrees, while newer electronic thermostats are generally accurate to within a one degree.
Limitations on use vary according to HVAC system type. For example, turning the heating temperature back in heat pumps will often cause the auxiliary electric resistance heating to turn on, defeating any potential energy gains. The digital interface for some electronic thermostats can be somewhat complicated to program, although manufacturers are making programming easier.

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