Heat pump - Revision history

Jmdonev: 1 revision imported

2018-05-18T22:53:09Z

1 revision imported

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Jmdonev at 21:27, 11 May 2018

2018-05-11T21:27:45Z

← Older revision		Revision as of 21:27, 11 May 2018
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	[[category:371 topics]]		[[category:371 topics]]
	[[Category:Done ~~2015~~-04-01]]		[[Category:Done 2018-05-18]]
	[[File:Heat_Pump.jpg\|thumb\|400px\|Figure 1: A residential heat pump's outdoor components.<ref>Wikimedia Commons [Online], Available: http://upload.wikimedia.org/wikipedia/commons/4/4c/Heat_Pump.jpg</ref>]]		[[File:Heat_Pump.jpg\|thumb\|400px\|Figure 1: A residential heat pump's outdoor components.<ref>Wikimedia Commons [Online], Available: http://upload.wikimedia.org/wikipedia/commons/4/4c/Heat_Pump.jpg</ref>]]

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	The performance of a heat pump is expressed by the ratio of heat output to the work needed to be input. Essentially, this value is how much cooling or heating is being done for a person's dollar (electricity isn't free after all). This ratio is known as the coefficient of performance (K), represented by the equation:<ref name=hin/>		The performance of a heat pump is expressed by the ratio of heat output to the work needed to be input. Essentially, this value is how much cooling or heating is being done for a person's dollar (electricity isn't free after all). This ratio is known as the coefficient of performance (K), represented by the equation:<ref name=hin/>

	<center><m>K=\frac{heat}{electricity}</m></center>		<center><math>K=\frac{heat}{electricity}</math></center>

	So for heating, this coefficient is:		So for heating, this coefficient is:

	<center><m>K=\frac{Q_H}{W_{in}}</m></center>		<center><math>K=\frac{Q_H}{W_{in}}</math></center>

	and for cooling it is:		and for cooling it is:

	<center><m>K=\frac{Q_C}{W_{in}}</m></center>		<center><math>K=\frac{Q_C}{W_{in}}</math></center>

	where:		where:

	* <m>Q_H</m> is the heat input to a room to warm it		* <math>Q_H</math> is the heat input to a room to warm it
	* <m>Q_C</m> is the heat expelled from a room in order to cool it		* <math>Q_C</math> is the heat expelled from a room in order to cool it
	* <m>~~W_i_n~~</m> is the work input as electricity		* <math>W_{in}</math> is the work input as electricity

	The higher the value for this coefficient is, the better a heat pump is transferring heat because it requires less work to do a certain amount of heat transfer. ~~There~~ is a [[coefficient of performance#Maximum Coefficient of Performance\|limit]] ~~however,~~ set by the laws of [[entropy]] and the second law of thermodynamics.		The higher the value for this coefficient is, the better a heat pump is transferring heat because it requires less work to do a certain amount of heat transfer. However, there is a [[coefficient of performance#Maximum Coefficient of Performance\|limit]] set by the laws of [[entropy]] and the second law of thermodynamics.

	==Air conditioning==		==Air conditioning==
	:''[[air conditioner\|main article]]''		:''[[air conditioner\|main article]]''

	Air conditioning (A/C) is a system that performs on the same basic principles as heat pumps, although they do require some different components.<ref name=ac>Consumer Energy Center, ''Central Heating Ventilation and Air-Conditioning (HVAC) Systems'' [Online], Available: http://www.consumerenergycenter.org/residential/heating_cooling/heating_cooling.html</ref> Air conditioners are not as versatile as heat pumps, because they only perform the function of cooling. However they are of more practical use in many cases, since certain places on Earth do not require heating. They function by performing ~~essentially~~ the same cooling cycle as heat pumps.		Air conditioning (A/C) is a system that performs on the same basic principles as heat pumps, although they do require some different components.<ref name=ac>Consumer Energy Center, ''Central Heating Ventilation and Air-Conditioning (HVAC) Systems'' [Online], Available: http://www.consumerenergycenter.org/residential/heating_cooling/heating_cooling.html</ref> Air conditioners are not as versatile as heat pumps, because they only perform the function of cooling. However they are of more practical use in many cases, since certain places on Earth do not require heating. They function by essentially performing the same cooling cycle as heat pumps.

	==References==		==References==
	{{reflist}}		{{reflist}}
	[[Category:Uploaded]]		[[Category:Uploaded]]

J.williams: 1 revision imported

2015-08-26T21:31:09Z

1 revision imported

← Older revision	Revision as of 21:31, 26 August 2015
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J.williams at 16:54, 12 August 2015

2015-08-12T16:54:39Z

New page

[[category:371 topics]]
[[Category:Done 2015-04-01]]
[[File:Heat_Pump.jpg|thumb|400px|Figure 1: A residential heat pump's outdoor components.<ref>Wikimedia Commons [Online], Available: http://upload.wikimedia.org/wikipedia/commons/4/4c/Heat_Pump.jpg</ref>]]

<onlyinclude>A '''heat pump''' is a device that pulls the energy out of air for the purpose of either heating or cooling a space. This process is known as space conditioning.</onlyinclude><ref name=hin>R. A. Hinrichs and M. Kleinbach, "Home Energy Conservation and Heat-Transfer Control," in ''Energy: Its Use and the Environment'', 4th ed. Toronto, Ont. Canada: Thomson Brooks/Cole, 2006, ch.5, sec.G, pp.149-153</ref> Heat pumps operate as a [[heat engine]] in reverse, as they do [[work]] from an input of [[electricity]] to push heat from a cold place to a warm place. This would seemingly violate the [[Second law of thermodynamics]], but the key reason it doesn't is because this heat transfer is not ''spontaneous''; it requires an input of energy to do so. For home heating, a heat pump extracts heat from outside air, heats the warm air up even more, and transfers it indoors. For home cooling, a heat pump reverses this process and heat is extracted from the indoor air and expelled to the outside, just like a [[refrigerator]] or [[air conditioner]], thereby making the inside air cooler.<ref name=hin/>

==Operation==

===Heating Cycle===

The heating cycle of a heat pump works by taking heat in from air outside, warming it up further, and using this warm air to heat indoor air. It does so by the following process:<ref name=hin/>

#Liquid refrigerant absorbs heat in the "evaporator" from the outdoor air, turning into a gas.
#The refrigerant is put through a "compressor", which raises the [[pressure]] of the gas, increasing its [[temperature]].
#The hot gas flows through "condenser coils" inside the space to be heated, and since it is at a higher temperature than this space, it transfers heat to the room and condenses back into a liquid.
#The liquid finally flows back through a valve that reduces its pressure in order to cool it down so it can repeat the cycle.

This can be visualized in the picture below.

[[File:Heat pump.png|450px|thumbnail|center|Figure 2: The process and parts involved in a heating cycle.<ref name=adapt>Adapted from ''Energy: Its Use and the Environment'' by R. Hinrichs and M. Kleinbach.</ref>]]

===Cooling Cycle===

The cooling cycle of a heat pump is used to cool a space by removing heat from it and expelling it to another area, usually to the outdoors for air conditioning or to the room for a refrigerator. To do this, the "evaporator" and "condenser coils" switch roles and the flow of refrigerant is reversed:<ref name=hin/>

#The cold refrigerant absorbs heat from the hotter room in the evaporator, so the room will cool down.
#It is then put through the compressor to increase its temperature.
#It passes through the condenser coils, and transfers this heat to the outside air.
#It then expands in order to decrease its pressure and cool down to below the room's temperature to repeat the cycle.

This process can be visualized in Figure 3.

[[File:Cool pump.png|450px|thumbnail|center|Figure 3: A cooling cycle for a heat pump.<ref name=adapt/>]]

==Coefficient of performance==
:''[[coefficient of performance|main article]]''

The performance of a heat pump is expressed by the ratio of heat output to the work needed to be input. Essentially, this value is how much cooling or heating is being done for a person's dollar (electricity isn't free after all). This ratio is known as the coefficient of performance (K), represented by the equation:<ref name=hin/>

<center><m>K=\frac{heat}{electricity}</m></center>

So for heating, this coefficient is:

<center><m>K=\frac{Q_H}{W_{in}}</m></center>

and for cooling it is:

<center><m>K=\frac{Q_C}{W_{in}}</m></center>

where:

* <m>Q_H</m> is the heat input to a room to warm it
* <m>Q_C</m> is the heat expelled from a room in order to cool it
* <m>W_i_n</m> is the work input as electricity

The higher the value for this coefficient is, the better a heat pump is transferring heat because it requires less work to do a certain amount of heat transfer. There is a [[coefficient of performance#Maximum Coefficient of Performance|limit]] however, set by the laws of [[entropy]] and the second law of thermodynamics.

==Air conditioning==
:''[[air conditioner|main article]]''

Air conditioning (A/C) is a system that performs on the same basic principles as heat pumps, although they do require some different components.<ref name=ac>Consumer Energy Center, ''Central Heating Ventilation and Air-Conditioning (HVAC) Systems'' [Online], Available: http://www.consumerenergycenter.org/residential/heating_cooling/heating_cooling.html</ref> Air conditioners are not as versatile as heat pumps, because they only perform the function of cooling. However they are of more practical use in many cases, since certain places on Earth do not require heating. They function by performing essentially the same cooling cycle as heat pumps.

==References==
{{reflist}}
[[Category:Uploaded]]