heat pumps

I have wandered why heat pumps are used. In Summer it is just an AC. In Winter they pump freon (or whatever ozone friendly stuff is used) backwards. Wouldn't using resistive heater be more logical?? The heaters are 100% efficient, have no moving parts... What is the point of running compressor, defrosting coils every once in a while? Am I missing something here??

Reply to
Michael
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Yes, thermodynamics. Heat pumps will "move" 3 or 4 times as much heat as they consume. Which means that for every kWh of electricity you put into the pump you can get out several times that in heat.

Efficiency drops dramatically when the hot-to-cold difference goes up.

robert

Reply to
Robert Latest

"Heat pumps" are a result of the Al Gore School of "Consensus Science"

Only under ideal delta-T conditions do they perform remotely as advertised.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Which an electric heater cannot do. A refrigeration unit takes one unit of electical power, and moves three or four units of thermal energy with it.

Robert is correct.

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Your concern may be more over the "number of moving parts", or the "cost to replace the works when the second law claims this mechanism too". Life is not always simple and easy. If you were the only person on the planet, it would not be an issue. Or if you had a weight critical mission, and cost and matentance were also issues, you'd have to power an electric heater. But powering an electric heater today, only causes more oil or coal to be burned... finite resources.

David A. Smith

Reply to
dlzc

Resistive heaters are thermodynamically very inefficient. A heat pump pushes heat from outdoor ambient temp into the load to be heated, like a house interior space. The amount of power needed depends on the temperature differential times the amount of heat moved. A resistive heater acts like a heat pump working against absolute zero, a huge differential. So a heat pump can move far more heat per watt than a resistive heater.

The common claim that resistive heaters are "100% efficient" is nonsense.

John

Reply to
John Larkin

Not really. They do transform all the power consumed into heat.

Heat pumps are more effective, in that they can shift three or four joules of heat for every joule they consume - more under ideal conditions - but it's harder to characterise their efficiency.

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-- Bill Sloman, Nijmegen

Reply to
bill.sloman

the

Heat pumps were originally developed for refrigeration systems.

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Using them to cool or warm your house is a more recent development - one which doesn't have anything to do with Al Gore.

The thermodynamics involved don't owe anything to fashion, as Jim would know if he'd every done a science degree at respectable institution.

The smaller the temperature differential, the more heat they transfer per unit of energy consumed by the pump, as follows obviously from the thermodynamics, but if Jim can't follow the science, it's fairly clear that he won't be able to understand what the ads are really claiming.

-- Bill Sloman, Nijmegen

Reply to
bill.sloman

Numbers, please? References? Citations?

Thanks, Rich

Reply to
Rich Grise

More like marketing hype - I don't think there's any question that

100% of the input to a resistive heater is converted to heat. ;-)

Cheers! Rich

Reply to
Rich Grise

Typical BS from the Al Gore School of Consensus Science.

REAL heat pumps use a drilled well that is, in essence, at AVERAGE temperature.

So called crap heat pumps exchange with exterior ambient air... losers!

Some energy goes to light, but not much.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Well, what does "efficient" mean? By your definition 100% efficient means that one joule of input from the power grid to the heater produces one joule of heat. Using that definition, a heat pump will have more than 100% efficiency. Under good conditions they make 400%. Saying "resistive heaters have 100% efficiency" really means they are SHIT compared to heat pumps.

Reply to
gearhead

The science that Jim is objecting to happens to be dead right. So Jim doesn't know good science when he sees it, and his objections to the scientific content of Al Gore's "Inconvenient Truth" are based entirely on ignorant conservatism.

He prefers the George W Bush school of consensus non-science - usually abbreviated to nonsense - as would any antiquated old buffer who hasn't read anything new in the past twenty years.

Better than that - the average temperature 50cm below the soil sufrace lags the seasons by six months, exactly 180 degrees out of phase.

Unfortunately, the heat pumps used in both cases are exactly the same

- Jim is distinguishing between different kinds of interface to the ambient for the exhaust side of the heat pump.

Using the outside air as a source or dump for the heat being transferred does increase your fuel bill in tuerns of watts expended for watts moved. but it does give you a much cheaper and more compact exhaust side.

If you want to call far-infra-red radiation "light" ...

-- Bill Sloman, Nijmegen

Reply to
bill.sloman

Depending on the temperature differential, duct insulation, etc., it is possible for a resistance space heater to be more efficient (lower electric costs) than a heat pump.

For many, the use of a heat pump alone for heating is not an option. Auxiliary resistance heaters are necessary in order to maintain a minimum 70 degree indoor temperature in cold weather. The efficiency of these heaters is degraded by heat losses through the ducting, etc.

Chuck

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Reply to
Chuck

Deliberately offensive. Why? Slept through thermo classes?

John

Reply to
John Larkin

The pervasive "heat pumps" found at everyone's home AREN'T. They're cheap ass ways to generate heat from an assembly meant only to cool. Their heating efficiency sucks.

Very few heat pumps really are heat pumps.

On "This Old House" I've seen some true heat pump designs.

The rest ARE INDEED "Typical BS from the Al Gore School of Consensus Science".

If you take that as offensive... GOOD ;-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

I should have mentioned... my personal heat pump is so ludicrous it has a sump heater... ponder that for awhile... that IS offensive ;-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

wear more sweaters and drink more water...... ;-))

Reply to
HapticZ

This doesn't happen for very many people. Not many people live above the permafrost line. For fair comparison, you need to compare houses with equal construction quality etc.

This is only true if you are exchanging with the air and not the soil or are into areas with permafrost. In places with permafrost, the auxiliary heater may be propane.

This is only true if the ducts are outside the building. In very cold places, the heat exchanger and all of the ducts are within the heated space.

Reply to
MooseFET

In southeastern Virginia, pretty much all houses with heatpumps have auxiliary resistance or propane heating. Ducting in an unheated attic or crawl space is the norm. This isn't what you might call a permafrost zone, is it? Where do you live?

Chuck

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Reply to
Chuck

=A0 =A0 ...Jim Thompson

Al Gore invented the internet, not thermodynamics. Oh yeah, you got that Al-Gore-Rhythm. Jimbo, rock on!

Reply to
gearhead

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