Electric Heater vs Heat Pump: Efficiency for Heating Water to High Temperatures

[ATT55]

I want to heat 10kg of water from 20C to 80C-90C with the lowest power consumption.
One option I consider is to use an electric heater and the other option is to use a heat pump.

Are heat pumps common for such an application?

The calculated power consumption of the electric heater is 0.7 kW*hr.
What will the power consumption the heat pump, if the COP is 2?
Is it 0.7/2=0.35 kW*hr?

 

[russ_watters]

I want to heat 10kg of water from 20C to 80C-90C with the lowest power consumption.
One option I consider is to use an electric heater and the other option is to use a heat pump.

Are heat pumps common for such an application?

The calculated power consumption of the electric heater is 0.7 kW*hr.
What will the power consumption the heat pump, if the COP is 2?
Is it 0.7/2=0.35 kW*hr?

Your calculation is correct, but....your application as described is not common so it's tough to say if heat pumps are common for it or not. Air to water heat pumps are becoming more common for domestic water heating and distributed hot water space heating. But 80-90C is above the typical limits of such products. 80-90C is in the range for typical hot water space heating, but such systems can be designed for lower.

 

[Rive]

What will the power consumption the heat pump, if the COP is 2?

With the output temperature not constant, constant COP just does not feels realistic.
This thing will be nothing simple.

 

[russ_watters]

With the output temperature not constant, constant COP just does not feels realistic.
This thing will be nothing simple.

I interpreted the values as a hypothetical average efficiency and range of acceptable output temperatures.

 

[Baluncore]

Welcome to PF.

Are heat pumps common for such an application?

Not common.
Solar preheating is more likely, but it could be done with a heat pump.

Please tell us what climate do you have? Or identify a nearby city.
If it is raining and just above freezing, a heat pump will be a poor investment. One limitation on a heat pump for heating water is when the heat exchanger freezes. Then, a heating element outside in the heat exchanger is used to melt that ice.

I want to heat 10kg of water from 20C to 80C-90C with the lowest power consumption.

How often will you do that ?
Use radiant solar preheating if possible.
Alternatively, use solar PV, to power the water heater.

 

[ATT55]

How often will you do that ?
Use radiant solar preheating if possible.
Alternatively, use solar PV, to power the water heater.

I do it constantly, I think solar preheating/PV will be too complicated for my application.

 

[ATT55]

i saw this article: High temperature heat pumps and it seems that are few models who can do it, all with COP of ~3-4. Is it an exotic equipment?

For example:
Friotherm Unitop 22/22
Dürr Thermeco2 HHR1000
Kobelco SGH 120/165

 

[russ_watters]

I do it constantly, I think solar preheating/PV will be too complicated for my application.

That doesn't match your original post. How often, exactly? Is that 10kg per minute? Hour? Day? And is this for heating or bathing (80C is too hot for bathing...). Or an industrial process?

I wouldn't necessarily say it's exotic, just not common at least in the US. I have seen more in Europe but have no actual experience there.

 

[Flyboy]

Hmmm. I know that heat pump water heaters are starting to roll out in the US at production rates, but as others have mentioned, they’re lower temperature systems. 80-90*C is awfully hot water.

What’s the use case for this water? Because that may have a very important impact on the efficiency of the system.

If we’re talking about strictly using vapor cycle heat pumps, might be worth looking at a two-stage system? And if in a colder climate, the aforementioned icing problem can be offset by a geothermal loop anywhere there’s a reasonably shallow frost line.