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Heat pump efficiency

Anonymous Sat 13 Nov 11:31:00 2021 No.13848195 View Reply Original Report

Quoted By: >>13848206 >>13848231 >>13848263 >>13849133 >>13849177 >>13849230 >>13850321

How am I to understand heat pump efficiency?
people keep telling me that they can create more energy than what you put in them. They say if you put in 1000W of electricity you can get 5000W of heat.
Is that a misinterpretation or is it true, and what are the physics of it?
can anything really have an efficiency over 1?

Anonymous

Anonymous Sat 13 Nov 2021 11:35:20 No.13848206 Report

Quoted By: >>13848223

>>13848195
The heat you get is drawn from the air outside the apartment, plus the waste heat of the motor. Its pumping heat, not just wasting electricity in a resistor to cause heat. It uses 1 watt to pump 4 watts of heat that was already in the air outside.
Do you believe by any chance that water pumps make water?

Anonymous

Anonymous Sat 13 Nov 2021 11:42:47 No.13848223 Report

Quoted By: >>13848537

>>13848206
so will it be be more effective if I put the heat pump in the sun or reflect sun on it with mirrors?

Anonymous

Anonymous Sat 13 Nov 2021 11:44:57 No.13848231 Report

Quoted By: >>13848247

>>13848195
>what are the physics of it
it's just like a fridge, it cools the world and pushes the collected heat into your apartment
The amount of heat you get inside costs you 1/5 as much in electricity as compared to an electric heater

Anonymous

Anonymous Sat 13 Nov 2021 11:51:41 No.13848247 Report

Quoted By: >>13848254

>>13848231
>The amount of heat you get inside costs you 1/5 as much in electricity as compared to an electric heater
an electric resistance heater is 100% efficient.
so if what you're saying is true, then it would mean a heat pump really does have an efficiency of over 1. that's pretty remarkable.

Anonymous

Anonymous Sat 13 Nov 2021 11:54:04 No.13848254 Report

Quoted By: >>13848297

>>13848247
Wait, how is an electric heater 100% efficient?

Anonymous

Anonymous Sat 13 Nov 2021 11:57:02 No.13848263 Report

Quoted By: >>13848314

>>13848195
What I can't understand is how they get heat from the cold winter air outside. Like if inside your house is 15 degrees, and outside is -1, how do they get heat from the colder air to warm your house up to say 21 degrees?

Anonymous

Anonymous Sat 13 Nov 2021 12:04:34 No.13848297 Report

Quoted By:

>>13848254
P Input = P Output
ok, maybe not 100% but very very very close.
most is converted into useful energy, in this instance heat; some of it converts into light; some into kinetic energy; but that amount is insignificant in a somewhat efficient resistance heater.

Anonymous

Anonymous Sat 13 Nov 2021 12:08:54 No.13848314 Report

Quoted By:

>>13848263
>What I can't understand is how they get heat from the cold winter air outside.
It's because there is plenty of heat even in frozen water; if it's above absolute 0 then there is energy in it that can be extracted and concentrated in the compression-decompression refrigeration cycle.

Anonymous

Anonymous Sat 13 Nov 2021 13:18:32 No.13848522 Report

Quoted By: >>13848547 >>13849140

How is the efficiency of a heat pump calculated?
can it really be true that if I put 100W in that I can get 500W out?

Anonymous

Anonymous Sat 13 Nov 2021 13:24:39 No.13848537 Report

Quoted By: >>13848574

>>13848223
Heat pumps are more efficient when the temperature differences are smaller. I define efficiency here as the heat moved vs the energy used by the motor.
If you wanted to make your house 5 degrees hotter than the external environment the pump would be more efficient than if you tried to make it 30 degrees hotter. Same with cold, its just reverse direction.

Anonymous

Anonymous Sat 13 Nov 2021 13:28:30 No.13848547 Report

Quoted By:

>>13848522
Yes, because it pumps heat from the air outside. It heats your house by cooling the air outside, or the opposite it cools your house by heating the air outside. This requires some minimum amount of work set by Carnot's law, which can be much smaller than the heat moved.
Imagine it as a heat engine in reverse, an engine turns some small % of heat into work, so it moves 5000 watts of heat and gives you 1000 watts of work, but in reverse you put in 1000 watts of work and it gives you 5000 watts of heat.

Anonymous

Anonymous Sat 13 Nov 2021 13:41:16 No.13848574 Report

Quoted By: >>13848703

>>13848537
>If you wanted to make your house 5 degrees hotter than the external environment the pump would be more efficient than if you tried to make it 30 degrees hotter.
do you know know how to calculate that ratio or what the concept is called?
I'm also wondering if Delta T is the determining factor; and if the specific temperature at which it runs (meaning the ambient temperature outside) has a lot to say about how efficient it runs if you just want to raise the temperature 5 degrees.

Anonymous

Anonymous Sat 13 Nov 2021 14:40:59 No.13848703 Report

Quoted By: >>13849128

>>13848574
Yes its Efficiency=1-Delta T/(Hot Temperature) but thats for heat engines. A heat pump is the same but in reverse, so the percentages are reversed too.
For instance a Delta T that gives you a 10% efficient motor, would allow you to move 10 times more heat than what the motor uses, in a heat pump. With a delta that gives you 1% efficiency in a motor, you can move 100 times more heat than the energy used by the motor, in a heat pump.
These are the hard physical limits, actual performance wont be as good.

Anonymous

Anonymous Sat 13 Nov 2021 17:26:42 No.13849128 Report

Quoted By: >>13849218 >>13849226

>>13848703
ok, thanks.
What I understand is that the process is more efficient at a lower Delta T.
If we take a practical example and say I have a closed system of 2 equally big rooms.
Room A that needs to be heated 5 degrees, and Room B where the heat is taken from.
both Room A and B are 20 degrees to start with.
for increasing the temperature to 25 degrees in Room A I would have a Delta T of 5, so 5/298K= 1.68% efficiency for a Carnot engine.
I would then reverse it to 100/1.68= 59.52 times more energy output per energy input.
so if I understand it correctly I would have made the air in Room B decrease exactly 5 degrees as well.
Would you consider that as a correct interpretation?

Anonymous

Anonymous Sat 13 Nov 2021 17:28:46 No.13849133 Report

Quoted By: >>13849208

>>13848195
no, they can MOVE more heat than is input. Stop calling it efficiency. This is called coefficient of performance and it can indeed be greater than unity.

Anonymous

Anonymous Sat 13 Nov 2021 17:33:05 No.13849140 Report

Quoted By: >>13849208

>>13848522
>How is the efficiency of a heat pump calculated?
CoP of a heat pump is heat transfered/power supplied; this value can be greater than 1 irl, even up to ~2-3.
Heat engine and refrigeration cycle EFFICIENCY is never ever greater than 1.

Anonymous

Anonymous Sat 13 Nov 2021 17:46:26 No.13849177 Report

Quoted By:

>>13848195
Take your 1000 watt home electric/oil heater, it will produce a heat up the room in certain time period.

Now take a 300 watt heat pump, it will produce similar if not faster level of heat in the room.

Heat pump is like AC except it allows bi-directional heat exchange system. This is why you can cheat in certain conditions where you just reverse the AC and it will work just fine. You need to also hack the AC as well by replacing the temp sensor inside.

Anonymous

Anonymous Sat 13 Nov 2021 18:00:51 No.13849208 Report

Quoted By:

>>13849133
>>13849140
thanks for clarifying. I was wondering why I couldn't find any information about heat pump efficiency.

Anonymous

Anonymous Sat 13 Nov 2021 18:03:18 No.13849218 Report

Quoted By: >>13849223

>>13849128
The definitions of efficiency are reversed for a heat pump and a motor. A small delta T gives you low efficiency in a motor but high efficiency in a heat pump.

Anonymous

Anonymous Sat 13 Nov 2021 18:05:12 No.13849223 Report

Quoted By: >>13849232

>>13849218
>efficiency
stop calling it that REEEEEEEE

Anonymous

Anonymous Sat 13 Nov 2021 18:05:58 No.13849226 Report

Quoted By: >>13849255

>>13849128
Yes if the rooms are the same size, yes. But you know the delta changes as the temperature drops in one room so by the end the delta is 10 degrees. Basically you can calculate that but the real life motor has to work harder than the ideal.

Anonymous

Anonymous Sat 13 Nov 2021 18:07:37 No.13849230 Report

Quoted By:

>>13848195
It's basically heat engine running in reverse. Get the model of stirling and understand how it works. It is trully reversible, you can supply power to pump heat.

Anonymous

Anonymous Sat 13 Nov 2021 18:08:07 No.13849232 Report

Quoted By: >>13849253

>>13849223
I dont like it but i dont want to derail the thread with pedantism. Im actually ideologically opposed to the word efficiency and frown whenever i hear it. Most misused word ever.

Anonymous

Anonymous Sat 13 Nov 2021 18:15:15 No.13849253 Report

Quoted By:

>>13849232
it isn't pedantic, though. CoP and efficiency have totally different definitions.
>Im actually ideologically opposed to the word efficiency and frown whenever i hear it
autistic and cringe

Anonymous

Anonymous Sat 13 Nov 2021 18:16:22 No.13849255 Report

Quoted By:

>>13849226
so by the end the delta is 10 degrees
yes, my bad.

Anonymous

Anonymous Sat 13 Nov 2021 18:26:31 No.13849285 Report

Quoted By:

The outside air has heat in it, even its cold weather. Thus you dont have to make the whole heat. Think that with pure electric heater you start from 0 kelvin.

Anonymous

Anonymous Sun 14 Nov 2021 00:07:29 No.13850321 Report

Quoted By: >>13850340

>>13848195
>Heat pump efficiency
DA TOTAL HEAT MINUS DA HEAT REJECTED DIVIDED BY THE TOTAL HEAT.

Anonymous

Anonymous Sun 14 Nov 2021 00:12:41 No.13850340 Report

Quoted By: >>13850349

>>13850321
wait a minute...I think I made a mistake

Anonymous

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Anonymous Sun 14 Nov 2021 00:16:28 No.13850349 Report

Quoted By:

>>13850340

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