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Thermostats and Controls
Function and Optimal Operation | Components or Options | Mercury Thermostats | Digital Programmable Thermostats | Automated Zone Control Systems | Zone ValvesQuick Facts
- Thermostats regulate operation of heating and cooling systems to maintain a set temperature in the house
- Mercury or basic digital thermostats can be easily replaced with programmable thermostats for substantial energy savings
- Mechanical flow regulators (including dampers and valves) can be electronically controlled by the thermostat and zoning system to regulate heating and cooling in certain “zones” or regions in a house (if so equipped)
- Programmable thermostats save energy by reducing or stopping operation of heating or cooling while the house is unoccupied or during the night when less cooling or heating is necessary. This is called a “setback.”
- Multi-zoned thermostats for forced air systems maintain comfort and may save energy by not over heating or over cooling certain regions of the home
- Controls for zoned radiant heating can save money and energy by restricting flow of heat only to occupied regions of the home
Function and Optimal Operation
A thermostat is a device for regulating the temperature of a system so that the system’s temperature is maintained near a desired setpoint temperature. The thermostat does this by switching heating or cooling devices on or off or regulating the flow of a heat transfer fluid, such as water in a radiant hydronic system, as needed to maintain the correct temperature. The thermostat should be located away from direct sunlight and the room’s cooling or heating vents or device, yet exposed to general airflow from the room(s) to be regulated.
A multiple zoned system can save energy with properly designed and installed systems by regulating individual spaces, allowing unused rooms to vary in temperature by turning off the heating and cooling. Separating a house into a few different zones depending on their heating and cooling needs can be a way of attaining maximal comfort and energy efficiency, since each zone is only heated or cooled as needed.
Components and Options
Mercury Thermostats | Digital Programmable Thermostats | Automated Zone Dampers | Zone Valves
Mercury Thermostats
The most common forms for mercury thermostats are bi-metallic circular or two-wire. In both systems two metals (mercury and another metal) are bound together (as a concave disc or wound as a spring) and expand and contract at different temperatures, thereby reversing the concavity of the disc or unwinding (or winding) the spring. Though these thermostats can still be found in some older homes, they have been banned for several years due to their toxic mercury content and must be disposed of as chemical waste in appropriate facilities. They tend not to be as precise as digital thermostats and are not programmable, generally leading to overuse of energy for heating and cooling.
Digital Programmable Thermostats
Newer digital thermostats have no moving parts to measure temperature and instead rely on electronic devices to detect temperature. Each has an LCD screen showing the current temperature, and the current setting. Most also have a clock, and time-of-day and even day-of-week settings for the temperature, used for comfort and energy conservation. Some advanced models have touch screens, or the ability to work with home automation or building automation systems.
Most digital thermostats in common residential use in North America and Europe are programmable thermostats, which can provide a 5-10% energy savings by setting back the temperature 10 ° to 15 ° for 8 hours (such operation is not recommended for energy efficiency in high mass radiant heating systems which have much longer reaction times than forced air systems).
Automated Zone Control Systems for Forced Air Heating and Cooling
A zone damper (also known as a VCD or Volume Control Damper) is a specific type of damper used to control the flow of air in an HVAC heating or cooling system. Zone dampers work in conjunction with a zone controller, equipment sensors, and a thermostat in each zone. In order to improve efficiency and occupant comfort, HVAC duct systems are commonly divided up into multiple zones. For example, in a house, the main floor may be served by one heating zone while the upstairs bedrooms are served by another. In this way, the heat can be directed principally to the main floor during the day and principally to the bedrooms at night, allowing the unoccupied areas to remain temporarily unconditioned.
Forced air zoning can lead to improved comfort and efficiency only if the entire system is properly designed and installed.
Zone Valves for Radiant Hydronic Heating with Radiators
In radiant heated homes, the water loop may be as simple as a single pipe that “loops” the flow through every radiator in a zone. In such a system, flow to the individual radiators can not be modulated as all of the water is flowing through every radiator in the zone. Slightly more complicated systems use a “main” pipe that flows uninterrupted around the zone; the individual radiators tap off a small portion of the flow in the main pipe. In these systems, individual radiators can be modulated. Alternatively, a number of loops with several radiators can be installed, the flow in each loop or zone controlled by a zone valve connected to a thermostat. A radiant hydronic system may be broken up into individual heating zones using either multiple circulator pumps or a single pump and electrically operated zone valves.
Zone valves and telestats are also commonly used in radiant floor systems, in which the house may be divided into a few heating zones based on need.