Why isn't reversible airconditioning used more for heating in the UK?
I have just installed a unit costing 259 Euro which gives a heat output 3900 W for an electrical input of 1300 W. I calculate that I will save more than the cost of the unit in the first year of use.
OK, it only works down to -5 C external temperature but for a few Euro more you can buy one which will work down to -12 C which will cover most heating requirement and can be supplimented by other heating in really cold weather.
| Why isn't reversible airconditioning used more for heating in the UK? | | I have just installed a unit costing 259 Euro which gives a heat | output 3900 W for an electrical input of 1300 W. I calculate that I | will save more than the cost of the unit in the first year of use.
Well electricity is more expensive than gas, so how much would getting the same amount of heat from gas cost?
Or cheap to run. Gas per kW is approx 1/4 to 1/3 the price of electricty. The figures quoted were best case examples, which is a COP of three. When the outsuide temperature drops that COP 3 will drop to around COP 2. So, for heating, which this country needs more than cooling, they are not cheap, and complex too. A Myson fan heater is about £300 and works off the CH wet system, and will heat a large room and quite quickly too being around 9 kW as opposed to the near 4 kW od this unit, which will tail off when the oiutside get lower - just when you don't want it too.
Also split a/c units make the outside of a house look downright ugly.
It's a heat pump. You know how the back of a fridge gets warm when it's cooling the inside? Well the heat pump takes heat from outside and brings it inside instead. Outside is cooler than inside, which is why you need a pump to make the heat go uphill :-)
Probably because much of it has acess to cheap (ish) gas and expensive electricity (i.e. four times the cost of the gas).
If you are forced to heat with elctricity, then this is a very much cheaper way of doing it. It is also quite handy for spot heating where it would not be simple to extend your existing wet system (conservatories being a good example).
Of course, if you could source a reliable gas fired heat pump, using an IC engine, then it gets much better.
25% of the energy comes out as shaft power, so you can get maybe 110% or so of heating, before adding in the 75% of waste heat, for 185% or so of the heating normally provided by gas.
And this has the side-effect that if you have low temperature sources of heat, such as low temp solar panels, then you can couple these in, to improve the output temperature of the system.
COP=3 is youre best case scenarion. When its freezing outdoors you'll probably find COP=1 or so. Also if its air source, as it probably is, at cold temps you get ice on the absorber, which drops COP even further.
Yes its better than plug in fires, and probably better than E7 storage, but its not as great as it first looks.
Flat plate solar space heating probably gives better returns.
Are you saying that an electric fridge will produce more heat than an electric heater working at the same power? If so then you have discovered a source of free energy which could make fossil fuel, nuclear power etc all redundant!! There must be a catch.
The condensor (rear warm element) gives off more heat than the power consumption of the appliance. The extra heat comes from the inside of the fridge, which is why it gets cold. Ultimately of course, that comes from the outside of the fridge due to the imperfect insulation and opening the door from time to time. This exactly cancels out the extra heat from the condensor, so the fridge's contribution to room heating is exactly its power consumption.
However, if you could somehow put the fridge condensor indoors and the rest of the fridge outdoors, now you are stealing this extra heat from outdoors, and so the net heat output into the room is more than the fridge's power consuption, and the fridge will be cooling down the outdoors very slightly as a result of stealing heat from it. This is exactly how a heat pump heater works -- you use some energy to pump extra energy from the outdoors to the indoors. The outdoors is the source of extra energy -- it's not free because it consumes energy to pump it inside, but the total energy you get inside is the sum of the energy stolen from outside plus the energy used to pump it in.
I've mentioned this before, but one of my favourate questions to put to physics students is: In a perfectly thermally insulated room, if you were to leave a fridge operating with its door open, what happens to the room temperature?
***SPOILER SPACE*** Try to answer the question before scrolling down to the answer...
The 3 different answers show have far the student has understood this area of thermodynamics...
"The room gets cold" -- no understanding at all. "The room temperature stays the same" -- understands that a fridge transfers heat from the inside to the outside, so the fridge won't cool the room. "The room gets hotter" -- understands that it requires energy to transfer heat from a cooler to a warmer location.
If mains gas isn't available, it may be cheaper than oil or LPG. Running on economy 7 will be cheaper if the heat is useful at that time of day, and if you already have the heatpump for use as aircon.
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