High efficiency heat pumps

Servicewiz_3

how do high efficiency heat pumps operate at such low temperatures , without the use of supplemental
Heat?

Steamhead

They don't operate that well.

Hot_water_fan

They use EVI, enhanced vapor injection. Page 16 of this Idronics talks about it. https://www.caleffi.com/sites/default/files/media/external-file/Idronics_27_NA_Air-to-water%20heat%20pump%20systems.pdf

The two I have work great at low temperatures, which means I don’t notice anything different from the way they work the other 99% of the time. But I’ve only seen single digits with them. 

hot_rod

Inverter drive motors and vapor injection are a few of the latest improvements in heat pumps

you need to include an operating condition to get an answer. Both the source and sink temperature 

The temperature you are running it at and the temperature of the air or ground that you are transferring to or from 

This is the case with air to air, air to water or water to water heat pumps 

Efficiency defined as any time it is running over 1 COP?

Thus issue is mostly on air to water, but explains the concepts well

https://www.caleffi.com/sites/default/files/media/external-file/Idronics_27_NA_Air-to-water%20heat%20pump%20systems.pdf

Jamie Hall

Servicewiz_3 said:

how do high efficiency heat pumps operate at such low temperatures , without the use of supplemental
Heat?

The useable temperature range of a heat pump (any heat pump type device) is determined by three things: the choice of refrigerant, the ability of the compressor to create and maintain pressure differences, and the maximum and minimum pressures which can be achieved in the system.

The choice of refrigerant relative to the desired temperature range of operation is critical. Almost all substances have a range of temperatures and pressures in which they can transition from a liquid phase to a gaseous phase, in the process absorbing heat from the environment, and similarly back -- releasing heat to the environment. In virtually all of those substances, the transition temperature is lower at low pressures, and higher at high pressures. So -- you study the available refrigerants, compare them with your desired temperature range, figure out if your compressor and system can handle those pressures (or design one which can), and off you go.

pecmsg

Wait until they use the same designs that cascade systems use in -40* freezers. 

Jamie Hall

pecmsg said:

Wait until they use the same designs that cascade systems use in -40* freezers. 

Cascade systems are very promising. And necessary -- there are very few refrigerants which are usable for much more than a 70 degree Celsius range.

Hot_water_fan

@Jamie Hall Nordic has one for liquid to liquid heating

https://www.nordicghp.com/product/residential-heat-pumps/geothermal-heat-pumps/high-temperature-heat-pumps/wc-series/

they have another that is R134A that can be paired with any other source that’s warmish, so an air to water heat pump or other. 

I’d have to imagine that the refrigerant to refrigerant cascade option will always more more efficient adding another heat exchanger into the mix, but allows some flexibility.

Jamie Hall

That

Hot_water_fan said:

@Jamie Hall Nordic has one for liquid to liquid heating

https://www.nordicghp.com/product/residential-heat-pumps/geothermal-heat-pumps/high-temperature-heat-pumps/wc-series/

they have another that is R134A that can be paired with any other source that’s warmish, so an air to water heat pump or other. 

I’d have to imagine that the refrigerant to refrigerant cascade option will always more more efficient adding another heat exchanger into the mix, but allows some flexibility.

That Nordic is a nice unit. It does deliver 70 C water -- which is right about at the practical limit for a single stage water to water (which that is) heat pump, as I noted above.

Hot_water_fan

Yup. With the minimum required water temps it’s hard to call it a single stage except for unique waste heat applications, but it could be great paired with a wood gasification boiler