Solar Assisted Heat Pump Water Heaters

[Solarguy3500]

Has anyone else heard about these yet? A partner company (New England Solar Hot Water) to the PV installation company I work for has the distributorship for the Northeast U.S.

Solar Hot Water Heater | New England Solar Hot Water

A heat pump water heater is best described as ‘A Fridge in Reverse’. A household refrigerator uses an exposed panel to keep its contents cold. A heat pump water heater utilizes the same principle to achieve the opposite effect- circulating refrigerant liquid through a panel and absorbing rather...

www.neshw.com

They look interesting. My understanding is they have been installed primarily in the UK and are just starting to become available here.

They have an evaporator panel that gets mounted on the exterior of the house which eliminates the fan and condensate drain/pump that would be in the basement on a regular HPWH. The exterior panel doesn't need direct sun exposure so it can be mounted on a wall that doesn't face south. They are also eligible for the 26% tax credit.

 

[andym]

Obviously it wouldn't put out much heat at 10° outdoor temp. What is the seasonal COP?

 

[begreen]

Why is this called a solar heat pump? It does not appear to be solar dependent except for the sun warming the earth. The design is intriguing. Looks like a basic HWHP with the evaporator outside. I like that it eliminates the need for a condensate drain, but the large panel outdoors is not very attractive. More important is who makes the components and what is the service network and warranty?

This statement is confusing. Did they get the numbers wrong?
"The heating cycle initiates when refrigerant liquid starting at 8*F is pumped into the panel. This remarkably low temperature allows the panel to transfer ambient energy to the refrigerant, at any hour of the day- even in freezing conditions. As the refrigerant liquid passes through the panel, the ambient energy raises the temperature of the liquid. Once the liquid is heated to 5*F it vaporizes and becomes a gas."

Lots of questions, so I emailed them for some more detailed explanations.

 

[andym]

One of the big draws for me on a traditional HPWH is the dehumidifying effect it has. It would probably allow me to eliminate the dehumidifier that runs all summer in my basement. This 'solar' unit would not do that.

 

[begreen]

Yes, that is a benefit for many. We have a pit basement with no drain and surrounded by a sealed crawlspace. It is bone dry so no need dehumidification.

 

[peakbagger]

It the same concept the elusvie outdoor air source heat pump. COP varies with outdoor temp so not great for very cold climates where it stays below zero. Good thing is if the basement is not heated it does not cool it down further. Down side is no free dehumification as the coil is outdoors.

 

[Solarguy3500]

Yes, definitely some pros and cons, depending on your motivation for getting a HPWH.

As mentioned, a drawback for someone who is interested in the dehumidification aspect of a heat pump unit is that these don't provide that benefit. On the flip side, if you have a dry basement and don't want the unit to make the basement colder, these would work well for you.

I think the big solar panel makes it eligible for the tax credit, even though it doesn't require direct sunlight.

@begreen I think that reference to 8° was a typo on the website and was supposed to be -8°. They just left off the - symbol. I will email John from NESHW and tell him about it.

 

[peakbagger]

My bet is positive 8 F. The COPs really drop like a rock below 20 deg F

 

[begreen]

I think the big solar panel makes it eligible for the tax credit, even though it doesn't require direct sunlight.

That does not look like a solar panel, it looks more like a finned, evaporator coil. Kind of ugly at that. Would look better with a cover.

 

[ABMax24]

I can see where they would work in the UK, where winter temps are moderate enough for an air source heat pump water heater to remain viable, and summer temps moderate enough to not necessarily want that heat pulled from the living space.

My climate doesn't work like that, winter is too cold for this to be viable, and in the summer I would like the heat pulled from the house to limit AC use. So really only for a short period in spring and fall would I consider this viable.

IMO it would be a better use to have 2 evaporator coils, one in the house for the summer, and one buried outside below frost for winter, with a logic board to select the best option at any given time in spring and fall.

 

[begreen]

I can see where they would work in the UK, where winter temps are moderate enough for an air source heat pump water heater to remain viable, and summer temps moderate enough to not necessarily want that heat pulled from the living space.

My climate doesn't work like that, winter is too cold for this to be viable, and in the summer I would like the heat pulled from the house to limit AC use. So really only for a short period in spring and fall would I consider this viable.

IMO it would be a better use to have 2 evaporator coils, one in the house for the summer, and one buried outside below frost for winter, with a logic board to select the best option at any given time in spring and fall.

I think they would work fine in the Pac NW too, but I want a reliable large service, warranty and parts network behind an infrastructure purchase like this.

 

[Solarguy3500]

I heard back from John at NESHW. He said that the text on their website is from the manufacturer and they are going to be getting new text from the manufacturer soon. He did send me this which he said is from the engineer at the manufacturer in response to questions like the one I asked about the reference to 8°:

"Not a simple answer I'm afraid as the temperature of the refrigerant is proportional the ambient air temperature externally, so it does not always initiate at the same temperature. And although it is capable of dropping the pressure of the refrigerant down to -8F, the system normally operates at circa 15F to 20F assuming ambient air temperature is above this. As ambient air temperature drops, this will drop proportionally."

 

[EbS-P]

I heard back from John at NESHW. He said that the text on their website is from the manufacturer and they are going to be getting new text from the manufacturer soon. He did send me this which he said is from the engineer at the manufacturer in response to questions like the one I asked about the reference to 8°:

"Not a simple answer I'm afraid as the temperature of the refrigerant is proportional the ambient air temperature externally, so it does not always initiate at the same temperature. And although it is capable of dropping the pressure of the refrigerant down to -8F, the system normally operates at circa 15F to 20F assuming ambient air temperature is above this. As ambient air temperature drops, this will drop proportionally."

The real draw here is not “collecting” the heat from the conditioned living space. For smaller houses/ spaces the heat extracted from the living space in cooler times in cooler climates would most certainly need to be replenished. The air source HPWHs can be ducted outside but you still need makeup air and this system solves. That issue. Im just going out on a limb here and guessing a COP of less that 2 at outdoor temps less than 17 and falling fast as temp drops.
Install will be more complicated. Think mini split install. System would have to have a defrost mode?

To me the answer is a whole house refrigerant heating/cooling system. Where all your heating and cooling appliances use the same interconnected refrigerant system. Hot water, clothes dryer, refrigerator. Space heating and cooling ect. It’s complicated and probably locks you into a single brand for every major appliance. Running my clothes dryer in the summer with the ac on irks me

evan

 

[ABMax24]

I think they would work fine in the Pac NW too, but I want a reliable large service, warranty and parts network behind an infrastructure purchase like this.

They may work well in your area.

The other issue I see with this are the refrigerants used, many having extremely high GWPs, 1300 and 2088 for R134a and R410a respectively. In an ideal world these are always recovered, in the real world that's not always the case due to system leaks or improper removal and disposal. I'm not sure what this specific system uses, but from an environmental perspective I think the GWP of possible refrigerant leaks needs to be calculated as part of the global warming reduction ability of these products. Obviously it stands to reason that self contained HPHW's would have less refrigerant, and be less likely to leak refrigerant due to less field connected joints and less possibility for damage to the system.

My central AC unit contains 5lbs of R410a, which is equivalent to about 10,000lbs of CO2, so if my AC system leaks out its refrigerant it effectively undoes the equivalent CO2 reduction of 2.5 years of generation from my solar panels. (assuming an average of 790 g/kwh of CO2 for grid generated electricity)

Personally I'm a believer in hydrocarbon based refrigerants with little to no GWP. We have a small deep freezer with cyclopentane refrigerant that works very well, propane or even CO2 would be other options. The only downside being the flammability hazard in the event of a leak.

 

[begreen]

Ammonia is being suggested as a replacement. It works reasonably well for gas absorption refrigerators.

 

[peakbagger]

CO2 is a refrigerant is reportedly being used in commercial refrigeration systems. Far less toxic then ammonia. The big issue reportedly with CO2 is higher pressure with more potential for leaks plus it can displace air in closed spaces (as most refrigerants do

To me the answer is a whole house refrigerant heating/cooling system. Where all your heating and cooling appliances use the same interconnected refrigerant system. Hot water, clothes dryer, refrigerator. Space heating and cooling ect. It’s complicated and probably locks you into a single brand for every major appliance. Running my clothes dryer in the summer with the ac on irks me What you are talking about is a 3 pipe Variable Refrigerant Flow (VRF) system. The system decides what the overall heating and cooling demand and picks the predominant one. If heating is predominant, than any demands that require cooling will save the waste heat and recycle it to heating demands. The process can reverse if the overall demand flips. It also can pull heating or cooling out of the outdoor air but COPs factor in so 20 deg F is the normal low point where the economics do not pencil out. Since there is phase change involved the refrigerant pipes are a lot smaller. It makes sense for commerical but as you said it currently locks someone into the same manufactures system. IMHO spend the money on a Pasisvhaus or Pretty Good House and use super efficient appliances is money better spent. Throw in some PV on the roof to make up the difference.

 

[Rob711]

A whole house system sounds like a great idea. I think about that as my HPHWH is running next to my deep freezer.
Logistics would be tricky. Refrigerant lines everywhere and when the main compressor or a line leaks everything is down.
Years ago I saw a this old house where the houses central air compressor also heated the swimming pool. You can already see the problem if it stops working though. Pool guy will tell you to call ac guy. You would need a real good service persons with actual factory training.