Quote:
Originally Posted by GoinAllTheWay
What's a heat pump?
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A
heat pump is a machine or device that transfers
thermal energy from one location, called the "source," which is at a lower temperature, to another location called the "sink" or "
heat sink", which is at a higher temperature. Thus, heat pumps move thermal energy opposite to the direction that it normally flows. While compressor-driven air conditioners and freezers are technically heat pumps, the class includes many other types of devices, and the term "heat pump" usually implies one of the less-common devices in the class that are not dedicated to refrigeration-only.
During the operation of a heat pump, some of the thermal energy must be transformed to another type of energy before reappearing as thermal energy in the heat sink. The heat pump uses
mechanical work, or some source of
thermodynamic work (such as much higher-temperature heat source dissipating heat to lower temperatures) to accomplish the desired transfer of thermal energy from source to sink.
[1] In the classical thermodynamic sense, a heat pump does not actually move
heat, which by definition cannot flow from cold to hot temperatures. However, since the effect of the device in moving thermal energy is the same as if heat were flowing (albeit in the incorrect direction with regard to temperature difference), the "heat pump" is named by analogy.
A heat pump always moves thermal energy in the opposite direction from temperature, but a heat pump that maintains a thermally conditioned-space can be used to provide either heating or cooling, depending upon whether the environment is cooler or warmer than the conditioned-space. When pumps are used to provide heating, they are used because less input from a commercial-energy source is required than is required for newly-creating thermal energy by transforming heat-free sources of energy (for example, electricity) or low-entropy sources of energy (for example, a gas flame) directly into the required heating. This is because the heat pump utilizes some thermal energy from the environment for part of the delivered-heating, increasing the "efficiency" of the process. In cooler climates, it is common for heat pumps to be designed only to provide heating.
Even when a heat pump is used for heating, it still uses the same basic refrigeration-type cycle to do the job (merely changing operation so that the warm end of the device is inside the conditioned space, heating it). Such heat pumps, which always provide heating of spaces, may be found in climates that never or rarely require cooling.
For the class of "reversible-cycle heat pump" devices designed to work in either thermal direction, the device simply operates in a way that changes which coil is the condenser, and which coil is the evaporator, rather than physically turn the device around. Such a switch in function is normally achieved by a "reversing valve." Reversible-cycle heat pumps are often seen in providing building-space heating in high latitude climates that are much warmer than comfortable in one season, but colder in another season. In heating, ventilation, and air conditioning (
HVAC) applications, the term heat pump normally refers to a
vapor-compression refrigeration device that includes a
reversing valve and optimized
heat exchangers so that the direction of thermal energy flow may be changed without loss of efficiency. Most commonly, when used in heating, heat pumps draw heat from the air or from the ground.
[2]
http://en.wikipedia.org/wiki/Heat_pump
New Furnace.
