At the farm, heat pump works fine. My question is how can a heat pump, using the compressor, be more efficient than the heat strips included in the system. The heat pump compressor runs for a long time, but the heat strips will warm it up in a few minutes. I know a little about electricity, but very little about heat/refrigeration. Can you explain this so I might not be so ignorant??
- Thread starter Pappy
- Start date
A heat pump moves heat from one location to another. Even if the original location is colder, the pump can still get heat out of it and move that heat to someplace else.
Like your refrigerator, it is not really making cold inside of it. It is taking the heat inside the refrigerator and moving it out to your room.
And the air conditioner is adding heat to the outside world, making your house colder.
A heat pump takes heat out of the air outside, or the ground in a colder climate, and moves the heat into your house.
It does not take much electricity to do that.
paul
Like your refrigerator, it is not really making cold inside of it. It is taking the heat inside the refrigerator and moving it out to your room.
And the air conditioner is adding heat to the outside world, making your house colder.
A heat pump takes heat out of the air outside, or the ground in a colder climate, and moves the heat into your house.
It does not take much electricity to do that.
paul
MarkB_MI
Well-known Member
- Location
- Motown USA
The thing to understand is that whatever energy you put into the heat pump comes out the hot side, PLUS whatever heat it's able to pump out of the air on the cold side. So it will NEVER be less efficient than resistance heat, and will normally be significantly better.
For example, let's say you run your 1500 watt resistance heater for one hour. That's 1.5 kilowatt-hours x 3413 Btu/kw-hr = 5120 Btu.
Now let's say you ran your heat pump long enough to use that same 1.5 kw-hr, and at the particular inside and outside temperature the heat pump has a Coefficient of Performance of 3. You'll get three times as much energy out as energy in. So that 1.5 kw-hr gained you 3 x 5120 = 15,360 Btu.
For example, let's say you run your 1500 watt resistance heater for one hour. That's 1.5 kilowatt-hours x 3413 Btu/kw-hr = 5120 Btu.
Now let's say you ran your heat pump long enough to use that same 1.5 kw-hr, and at the particular inside and outside temperature the heat pump has a Coefficient of Performance of 3. You'll get three times as much energy out as energy in. So that 1.5 kw-hr gained you 3 x 5120 = 15,360 Btu.
RamblinMan
Member
"So it will NEVER be less efficient than resistance heat, and will normally be significantly better."
With moving parts you will always have wear. With fossil fuel or electricity there are no moving parts. You can talk efficiency all day long, but in the end the repairs will be the true measure.
With moving parts you will always have wear. With fossil fuel or electricity there are no moving parts. You can talk efficiency all day long, but in the end the repairs will be the true measure.
MarkB_MI
Well-known Member
- Location
- Motown USA
I did not say the total cost of ownership is cheaper for a heat pump than for resistance heat. Obviously that depends entirely on the application. Let's say you live in southern California and you rarely need either heat or air conditioning; resistance heat will do fine and if you can live without air conditioning it's probably cheaper to go with resistance heat versus a heat pump. But let's move to the east coast, say North Carolina: Air conditioning is pretty much mandatory, and the incremental cost of a heat pump over an air conditioner is negligible. You'll save a ton of money heating with a heat pump over resistance heat, yet the cost of depreciation and repairs is about the same as if you'd installed only air conditioning.
I don't know why you bring up fossil fuels. The question was the relative efficiency of heat pumps versus resistance heat.
I don't know why you bring up fossil fuels. The question was the relative efficiency of heat pumps versus resistance heat.
Bus Driver
Well-known Member
"the coefficient of performance of a heat pump---" Good information. I had not seen those ratios posted anywhere before now. Last night at 17 deg, my heat pump was doing most of the heating with the auxiliary light coming on occasionally. That might have been for the defrost cycle.
RamblinMan
Member
No central AC. A high efficency window unit in both ends of the house. My utility bill (including $30 for water and sewer) ran $150 for a 1,800 sq. ft. house, single level in the coldest month last year which was January. This is with baseboard electric heat in every room. I only went over $100 twice in twelve months. My house is well insulated with good windows.
1/13 $120
2/13 $100
3/13 $90
4/13 $75
5/15 $60
6/13 $59
7/13 $65
8/13 $70
9/13 $55
10/13 $60
11/13 $75
12/13 $90
I'm on a low rate because my house in all electric.
1/13 $120
2/13 $100
3/13 $90
4/13 $75
5/15 $60
6/13 $59
7/13 $65
8/13 $70
9/13 $55
10/13 $60
11/13 $75
12/13 $90
I'm on a low rate because my house in all electric.
MarkB_MI
Well-known Member
- Location
- Motown USA
Two things can be extrapolated from your data:
1. You don't live in Florida.
2. You don't live in Minnesota.
As far as providing any insight into the relative cost of heat pumps versus resistance heat, you've added nothing to the discussion.
1. You don't live in Florida.
2. You don't live in Minnesota.
As far as providing any insight into the relative cost of heat pumps versus resistance heat, you've added nothing to the discussion.
RamblinMan
Member
I live in Central Illinois as I have previously stated. The owner of a HVAC business that is in the third generation of ownership told me personally that he would never have a heat pump and prefers natural gas but he installs them (no bottom dollar units)because the utility recommends them and gives a rebate.
RamblinMan
Member
That's bs. I live in Central Illiinois. The numbers don't lie. Those are actual electric bills.
john in la
Well-known Member
What your numbers and location really show is you have no way of telling how good a heat pump is.
It is simply not made to work in your area.
A heat pump is made for the south where there are days in December when we run the A/C and we rarely get more than a few hour snap where it is below 32F.
Yes if you live in the fidget north (above I 20) a heat pump may not be your best choice. This is because the backup heating coils are constantly working to compensate for your poor choice of installing a heat pump. But if you lived in the deep south where central A/C is a MUST have and heating is just a small comfort feature you might then realize heat pumps are a choice you may want to consider.
It is simply not made to work in your area.
A heat pump is made for the south where there are days in December when we run the A/C and we rarely get more than a few hour snap where it is below 32F.
Yes if you live in the fidget north (above I 20) a heat pump may not be your best choice. This is because the backup heating coils are constantly working to compensate for your poor choice of installing a heat pump. But if you lived in the deep south where central A/C is a MUST have and heating is just a small comfort feature you might then realize heat pumps are a choice you may want to consider.
M-MAN
Well-known Member
- Location
- Bostic, NC
Coefficient of performance at 3 is under ideal conditions so don't expect to actually see it. One other thing people don't realize is when it gets frigid like it has this week a heat pump is less efficient than the resistance heat strips the emergency heat uses. Any heat pump will check the coil temp every thirty minutes, hour, or hour and a half to see if it needs defrosting. With the frigid temps we've seen this week it will go into defrost and switch to ac every time it checks. The heat pump uses the same amount of power whether it's running in heat mode or ac mode BUT every time it goes into defrost you are also using the heat strips to counter the ac. That's when it's using more power than plain old resistance heat.
MarkB_MI
Well-known Member
- Location
- Motown USA
What did I say that was BS? I said you don't live in either Florida or Minnesota; correct on both points. And just because you get your electricity essentially for free doesn't mean resistance heat is cost effective for most folks.
Texasmark1
Well-known Member
Excluding any residual electricity to run supplemental heating elements that a specific unit may contain, the heat pump acts in reverse to an air conditioner. It relies on absorbing the heat in ambient air to generate it's output. The less of the above, the less the performance, without considering efficiency. So the colder the weather the worse the conversion when you need the best of conversion.
Other thing is that if you have a dual use window AC you are at the mercy of the cooling/heating fins which are the limiting factor in the system due to corrosion and congestion from external debris.
No way would I waste my money on such a contraption.
Mark
Other thing is that if you have a dual use window AC you are at the mercy of the cooling/heating fins which are the limiting factor in the system due to corrosion and congestion from external debris.
No way would I waste my money on such a contraption.
Mark
Anonymous-0
Well-known Member
I work on straight cool and heat pumps and I prefer the straight cool over heat pumps any day. the cost of repair and the ease of diagnosing a straight cool is way better. Plus, when you use straight cool the compressor is not running every day out of the year to wear out the compressor. Straight cool does not have defrost boards to diagnose, no reversing valve or reversing valve coils. Too me a heat pump is a waste of money. Now let me also add that a straight cool thermostat has only 4 wires, the ones I work on have 8 wires.
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