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Controls


Controls Repair and Install

What is a Thermostat?

It is a temperature-sensitive switch that controls a space conditioning unit or system, such as a furnace, air conditioner, or both. When the indoor temperature drops below or rises above the thermostat setting, the switch moves to the on position, and your furnace or air conditioner runs to warm or cool the house air to the setting you selected for your family's comfort. A thermostat, in its simplest form, must be manually adjusted to change the indoor air temperature.

General Thermostat Operation

You can easily save energy in the winter by setting the thermostat to 68 degrees F (20 degrees C) when you're at home and awake, and lowering it when you're asleep or away. This strategy is effective and inexpensive if you are willing to adjust the thermostat by hand and wake up in a chilly house. In the summer, you can follow the same strategy with central air conditioning, too, by keeping your house warmer than normal when you are away, and lowering the thermostat setting to 78 degrees F (26 degrees C) only when you are at home and need cooling.

A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. This misconception has been dispelled by years of research and numerous studies. The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature. You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed. So, the longer your house remains at the lower temperature, the more energy you save.

Another misconception is that the higher you raise a thermostat, the more heat the furnace will put out, or that the house will warm up faster if the thermostat is raised higher. Furnaces put out the same amount of heat no matter how high the thermostat is set - the variable is how long it must stay on to reach the set temperature. In the winter, significant savings can be obtained by manually or automatically reducing your thermostat's temperature setting for as little as four hours per day. These savings can be attributed to a building's heat loss in the winter, which depends greatly on the difference between the inside and outside temperatures. For example, if you set the temperature back on your thermostat for an entire night, your energy savings will be substantial. By turning your thermostat back 10 to 15 degrees F for eight hours, you can save about 5 to 15 percent a year on your heating bill - a savings of as much as 1 percent for each degree if the setback period is eight hours long. The percentage of savings from setback is greater for buildings in milder climates than for those in more severe climates.

In the summer you can achieve similar savings by keeping the indoor temperature a bit higher when you're away than you do when you're at home. But there is a certain amount of inconvenience that results from manually controlling the temperature on your thermostat. This includes waking up in a cooler than normal house in the winter and possibly forgetting to adjust the thermostat (during any season) when you leave the house or go to bed.

Thermostats with Automatic Temperature Adjustment

To maximize your energy savings without sacrificing comfort, you can install an automatic setback or programmable thermostat. They adjust the temperature setting for you. While you might forget to turn down the heat before you leave for work in the morning, a programmable thermostat won't! By maintaining the highest or lowest required temperatures for four or five hours a day instead of 24 hours, a programmable thermostat can pay for itself in energy saved within four years. Programmable thermostats have features with which you may be unfamiliar. The newest generation of residential thermostat technologies is based on microprocessors and thermistor sensors. Most of these programmable thermostats perform one or more of the following energy control functions: They store and repeat multiple daily settings, which you can manually override without affecting the rest of the daily or weekly program. They store six or more temperature settings a day. They adjust heating or air conditioning turn-on times as the outside temperature changes. Most programmable thermostats have liquid crystal temperature displays. Some have back-up battery packs that eliminate the need to reprogram the time or clock in case of a power failure. New programmable thermostats can be programmed to accommodate life style and control heating and cooling systems as needed.

Types of Automatic and Programmable Thermostats

Honeywell Residential Thermostats http://yourhome.honeywell.com

Electromechanical (EM) thermostats, usually the easiest devices to operate, typically have manual controls such as movable tabs to set a rotary timer and sliding levers for night and day temperature settings. These thermostats work with most conventional heating and cooling systems, except heat pumps. EM controls have limited flexibility and can store only the same settings for each day, although at least one manufacturer has a model with separate settings for each day of the week. EM thermostats are best suited for people with regular schedules.

Digital thermostats are identified by their LED or LCD digital readout and data entry pads or buttons. They offer the widest range of features and flexibility, and digital thermostats can be used with most heating and cooling systems. They provide precise temperature control and permit custom scheduling. Programming some models can be fairly complicated; make sure you are comfortable with the functions and operation of the thermostat you choose. Remember-- you won't save energy if you don't set the controls or you set them incorrectly.

Hybrid systems combine the technology of digital controls with manual slides and knobs to simplify use and maintain flexibility. Hybrid models are available for most systems including heat pumps.

Choosing a Programmable Thermostat

Because programmable thermostats are a relatively new technology, you should learn as much as you can before selecting a unit. When shopping for a thermostat, bring information with you about your current unit, including the brand and model number. Also, ask these questions before buying a thermostat:

Most automatic and programmable thermostats completely replace existing units. These are preferred by many homeowners. However, some devices can be placed over existing thermostats and are mechanically controlled to permit automatic setbacks. These units are usually powered by batteries which eliminates the need for electrical wiring. They tend to be easy to program and because they run on batteries the clocks do not lose time during power outages.

Before you buy a programmable thermostat chart your weekly habits including wake up and departure times, return home times, bedtimes and the temperatures that are comfortable during those times. This will help you decide what type of thermostat will best serve your needs.

Nighttime Heating: Using a programmable thermostat you can automatically turn down your heat temperature at night or when you are not at home.

Nighttime Cooling: In the summer, you can save money by automatically turning your air-conditioning temperrature up at night.

Other Considerations

The location of your thermostat can affect its performance and efficiency. Read the manufacturer's installation instructions to prevent "ghost readings" or unnecessary furnace or air conditioner cycling. Place thermostats away from direct sunlight, drafts, doorways, skylights and windows. Also make sure your thermostat is conveniently located for programming.

Some modern heating and cooling systems require special controls. Heat pumps are the most common and usually require special setback thermostats. These thermostats typically use special algorithms to minimize the use of backup electric resistance heat systems.

Electric resistance systems such as electric baseboard heating also require thermostats capable of directly controlling 120 volt or 240 volt line-voltage circuits. Only a few companies manufacture line voltage setback thermostats.

A Note for Heat Pump Owners

When a heat pump is in its' heating mode, setting back a conventional heat pump thermostat can cause the unit to operate inefficiently, thereby canceling out any savings achieved by lowering the temperature setting. Maintaining a moderate setting is the most cost-effective practice. Recently, however, some companies have begun selling specially designed setback thermostats for heat pumps which make setting back the thermostat cost effective. In its cooling mode the heat pump operates like an air conditioner; therefore, manually turning up the thermostat will save you money.

Zoning

Zoned heating and cooling systems allow you to control the temperature of each room individually

Using a series of motorized dampers and thermostats that work independently, zoning can eliminate hot or cold rooms found in almost every home while cutting energy by up to 25 percent.

Simple laws of physics illustrate why it is virtually impossible to keep an entire house at a consistent temperature without zoning. Warm air rises while cold air sinks, 2nd floor rooms can be six to ten degrees warmer and basements six to ten degrees cooler than ground level rooms. A single thermostat keeps the temperature balanced in the room where it is located, but can't tell if the temperature has changed in other rooms of the house. Zoning helps maintain a consistent temperature throughout the house by providing different levels of air distribution to different areas of the home.

Zone controlled systems divide a home into areas with common heating and cooling needs during specific parts of the day. Air flow is controlled in each area by a separate thermostat. Instead of sending the same amount of heated or cooled air into all rooms every time the furnace or air conditioner is turned on, the system sends conditioned air only to the zones that need it. The temperature can be kept at an ideal comfort level when the family is up and about, then changed to an energy-saving temperature overnight or when the family is away.

Most homes can be zoned according to room occupancy, but unique exposure factors may require a different zoning strategy. A room with large amounts of glass facing south or west will have more heat gain than other rooms in the home. A separate zone might be required for that room alone!