Naked Science Forum
Non Life Sciences => Technology => Topic started by: Johann Mahne on 17/09/2011 09:47:42
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What makes a heat pump more efficient than an element heater?
Assuming it also has an air temperature sensor and a fan.
Let's also assume that the element heater has an electronic controller to elminate switching losses.
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Heat pumps work on a completely different principle to an element heater.
Heat pumps simply concentrate a low level thermal source - that is none of the energy demanded by the heat-pump system is actually used to raise the temperature directly.
So a large heat reservoir (such as the ground near your house; for all intents, an inexhaustible reservoir) can be concentrated by the heat-pump to a much smaller, but warmer 'hot' reservoir (ie. The space in your house).
For another example a fridge is a heat pump but the 'product' is a cooler than ambient inside to the fridge rather than a warmer than ambient interior of a house, etc. As such, home heat pumps can be reversed to cool in summer.
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Peppercorn is (at least this time) quite correct.
Heat pumps take advantage of an energy source (electricity) that can easily do "work" on a gas by driving a pump to compress it so that it gives up a lot of heat as it becomes a liquid. The liquid can then absorb a large amount of heat from its surroundings as it expands back into a gas.
This method only works if you have an energy source that is capable of doing work, otherwise you would be able to concentrate heat to do work without doing any work [:D]
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What makes a heat pump more efficient than an element heater?
Assuming it also has an air temperature sensor and a fan.
Let's also assume that the element heater has an electronic controller to elminate switching losses.
An electric heating element is one of the few things wihich is effectively 100% efficient - that is, it converts all the incoming electrical energy into heat.
A heat pump can literally pump (move and 'concentrate') heat energy from a nearby reservior (be it air or ground) ... and might pump perhaps four times as much heat-energy as it used electrical energy to do the pumping (which you also get back as heat too). You might therefore get '500%' efficiency or somesuch in terms of useful heat out compared to electrical energy in. Exactly how much more energy it pumps depends on the technology and the temperature difference - the bigger the temperature difference the harder the pump has to work and the less efficient it becomes. As you pump the heat out of the reservior, the reservior becomes colder - if you have a ground-source pump with too small pipework you might freeze the garden...
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There is amazing non commercial student web page: www.ecohome.org.pl that convert existing ecologically heated and cooled house into open lab where one can see live! refreshed every 3 min all temperatures, air ventilation, energy consumption and costs at that building. Now I can see how Heat Pump, HVAC works and how efficient is in fact!!
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Ahhh but there are different COP's from different heat pumps?