Does a "heat pump" not spew HFCs like an "air conditioner"?

[swampwiz]

https://slate.com/technology/2022/0...hin-heat-pump-solar-panels-electric-cars.html

In this era of heat waves, air conditioning can be a lifesaver. The problem is that popular A/C tech—primarily used within the U.S.—emits hydrofluorocarbons, which are even more effective than carbon dioxide at trapping hot gases in the atmosphere and heating the overall planet. To help solve this problem, President Joe Biden signed an executive order last month to spur the production of heat pumps, which use electricity to shift hot air in and outside of a given indoor space as needed (and without spewing HFCs), through the Defense Production Act.

First, this text makes no sense as it seems to say that the problem with A/C can be solved by "shift[ing] hot air in". But then it also seems to say that a "heat pump" - which I have always thought had the *popular* definition of basically being an air conditioner with the controlled & ambient sides reversed (technically both are heat pumps - i.e., does a cycle that is counter-clockwise in T-s space) - somehow doesn't spew HFCs like an "air conditioner" does.

EDIT: OK, the author had dropped the term "geothermal", as this device is referred to as a "geothermal heat pump":
https://en.wikipedia.org/wiki/Ground_source_heat_pump

There needs to be some better terminology in HVAC as this is not a "heat pump", but rather a "ground source heat conduction device".

 

[Joliet John]

The whole thing is ridiculously uninformed. The statement reads as if the writer knows nothing factual regarding heating and cooling except for firmly believing in the magic of the thermostat.
For air conditioning we use a sealed system that doesn't "spew" anything, they leak if you neglect them to the point that they break. We absorb heat from the inside air circulating in the home, transfer it to refrigerant circulating in the sealed system, and reject the absorbed heat outside. A heat pump is identical, but capable of being reversed.

 

[bob012345]

I was under the impression that residential geothermal systems used the stable underground temperature to both heat and cool but was disappointed to find out they are basically the same as air source heat pumps but just are a bit more efficient using the ground as the heat exchange media instead of the air (as I understand it). They still rely on compressors. Seems like a big expense over an air source system for a little increase in efficiency. Maybe in some areas the air is too cold in winter but in Texas I can't see the advantage of a ground source heat pump over air source.

 

[hutchphd]

"I can't see how" is not valid engineering.
They do use stable underground temperatures. There are efficiencies to having cold (warm) thermal sink (source) for cooling (heating) using a thermal pump. The question is whether they are big enough gains to warrant the added environmental expense of below ground heat exchangers when amortized over system lifetime. You run the numbers and choose wisely.
This sort of is like rocket science
!

 

[bob012345]

The question is whether they are big enough gains to warrant the added environmental expense of below ground heat exchangers when amortized over system lifetime. You run the numbers and choose wisely.
This sort of is like rocket science
!

I answered that question for myself after a 2 hour presentation I recently went through and was rather disappointed. I could buy three air source systems for one geothermal system. I did not think that was worth the extra efficiency. You might have a different answer but there are other complicating factors than just the technical details too.

 

[russ_watters]

I was under the impression that residential geothermal systems used the stable underground temperature to both heat and cool but was disappointed to find out they are basically the same as air source heat pumps but just are a bit more efficient using the ground as the heat exchange media instead of the air (as I understand it). They still rely on compressors. Seems like a big expense over an air source system for a little increase in efficiency.

But is it really a small increase in efficiency? I thought it was a big increase.

I answered that question for myself after a 2 hour presentation I recently went through and was rather disappointed. I could buy three air source systems for one geothermal system. I did not think that was worth the extra efficiency.

What, exactly, did you find?

Efficiency is a function of temperature difference. In AC mode instead of running 90F air across the coil you use 60F water. In heating it's 60F water instead of 20F air.

Air source heat pumps also have minimum operating temperatures and some won't even run below 20-30F. And even if they do, it's at lower capacity. So they need supplemental heat.

Edit: according to this ASHARE study, ground source is twice as efficient:
https://blog.geocomfort.com/case-study-geothermal-vs-air-to-air-heat-pumps

 

[bob012345]

What, exactly, did you find?

3x expensive. For this vendor giving the presentation you have to schedule the digging it ~9 months in advance. Wells need to be spaced apart ~20 ft and in small lots you might have to put wells under driveways and other places incurring extra costs. If you have some land, it's all easier. I would send you the presentation of our meeting but it's not up on the web yet.

Edit: according to this ASHARE study, ground source is twice as efficient:
https://blog.geocomfort.com/case-study-geothermal-vs-air-to-air-heat-pumps

Yes, I underestimated the efficiency difference but the cost difference was ~50 dollars a month in energy costs which is not that much considering it would take 50 years of savings to break even with the up front system cost if paid for in cash assuming the air-air system was ~15k vs. the ground system ~45k.

I think the first line of defense for reducing energy usage and cost is upgrading the efficiency of the house itself in terms of insulation, windows and other such things and whatever system one has make sure it is in proper working order. A modern more efficient conventional AC unit with an efficient sealed house and a good digital thermostat at reasonable settings will save a lot of energy.

 

[berkeman]

Due to the inaccurate and inflammatory thread title, this thread is closed.