Harvest hot water heatpump system

[begreen]

I just saw this mentioned by a homeowner on Reddit. It appears to be California only. Does anyone know much about this system?

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[woodgeek]

Meh. It uses a HW thermal battery to store BTUs pumped during the day (cheap kWh) for use at night (expensive kWh). The same battery is your HW tank.

Seems sensible enough, and CA appropriate.

If you heat the HW too much, you get COP losses, so the swing is likely small. The Air handler has a hydronic coil, so low service water temsp are not much of a problem. Say you swing from 100*F to 140°F, and the tank is 100 gallons. 800 lbs* 40°F = 32,000 BTUs.

My house needs about 10x that much overnight in winter, and I don't have TOU pricing. So useless for me.

For a well insulated CA house with TOU and cheap (solar) daytime rates... sure. But if you're only using 32 kBTUs at night, you are using <2 MMBTU per month, and your energy bill for a conventional system is pretty cheap already.

Meh.

 

[DBoon]

I do something similar to this idea using an oversized 180 gallon geothermal heat pump water storage tank, but agreed that it can't supply continuous heat for more than a few hours. Mine could store about 3-4 hours of heat on a "normal" winter day. But pushing the water temps higher to increase capacity reduces the COP a lot on the geothermal heat pump. Since I have the water supply coupled to radiant floor heating, I can scavenge really low temperature heat and reduce the tank temperature to 70 degrees or so before I recharge it again to 110 or so, giving me about 58 kBTUs (and ridiculously great COPs on the heat pump the first half of the recharge). Since I run the wood stove most of the colder winter days, this provides enough heat to augment where the wood stove heat doesn't circulate really well. Again, this is more of a dork experiment than any kind of cost-saving move.

Summary - what Woodgeek said, basically.

I'm somewhat experimenting in anticipating a future of TOU rates in which the local utility doesn't want my daytime solar and I want to charge vehicles or store heated water with cheap daytime solar PV in winter to mitigate nighttime expenses. For me, realistically, this is 15 years away.

 

[Whitenuckler]

When I had my last mini split work down this spring I mentioned to the tech that I had heard of a heat pump that heated
water. The reason I asked is I still have all of the water rads in place from the previous Oil Boiler. He said yes, there is a
system available but it is very expensive. He said 20,000CAD? I didn't look up the details, so not sure about a storage tank.

 

[EbS-P]

Federal efficiency incentives are as good as dead after this year. I don’t see this taking off.

 

[woodgeek]

When I had my last mini split work down this spring I mentioned to the tech that I had heard of a heat pump that heated
water. The reason I asked is I still have all of the water rads in place from the previous Oil Boiler. He said yes, there is a
system available but it is very expensive. He said 20,000CAD? I didn't look up the details, so not sure about a storage tank.

The issue here is the 'lift' needed. Most radiators assume water at 160-180°F, and making a heat pump pump to that output temp really kills the COP. My air to air heat pump pushed heated air into my space at 85-90°F in the winter, for comparison. Circulating 100°F water in your radiators is not going to do the job.

 

[Whitenuckler]

The issue here is the 'lift' needed. Most radiators assume water at 160-180°F, and making a heat pump pump to that output temp really kills the COP. My air to air heat pump pushed heated air into my space at 85-90°F in the winter, for comparison. Circulating 100°F water in your radiators is not going to do the

I'd be better off just getting another 40 gallon electric hot water tank if I wanted to get them working again. I think one or two more
minisplits would be good instead. I like the cooling.

 

[EbS-P]

I'd be better off just getting another 40 gallon electric hot water tank if I wanted to get them working again. I think one or two more
minisplits would be good instead. I like the cooling.

Once you add solar it’s just heat pump or freeze Well not really it’s heatpump or Wood stoves. I try to keep the resistive strips off.

 

[Whitenuckler]

Once you add solar it’s just heat pump or freeze Well not really it’s heatpump or Wood stoves. I try to keep the resistive strips off.

I'm not sure if I'll ever get solar panels here. I don't want to get a contract and have someone else own them. I don't have the money available to invest in them. I am always thinking of being able to go without utility though. I have a couple of generators and the pellet stove for heat. I would really miss the cooling though if I lost power in the summer heat wave. Luckily, I set up an unused spot in the basement as my beer zone and an air bed. Seems to only get about 21C so far down there. I have convect heaters in all bedrooms plus others. If the weather is really cold, and the heat pumps crash, I will still have good heat. I plan on running the pellet stove all winter

 

[DBoon]

Most radiators assume water at 160-180°F, and making a heat pump pump to that output temp really kills the COP.

If your house has old cast-iron radiators, these are usually ridiculously oversized (by a factor of 3) for the heat load of the house. If your house was originally built in the late 1800s or early 1900s, and the building envelope has since been updated, then you could possibly get by with 120 degree F water through cast iron radiators on the coldest days of the year, and that is within reasonable COP range (COP = 2 to 2.5) of a geothermal heat pump. COP would be better during the 80-85% of the winter you would run water temperatures of 100 degrees F or less.

If you have the small, thin baseboard fin-based radiators, then you need the very high water temperatures Woodgeek referenced.

 

[Whitenuckler]

If your house has old cast-iron radiators, these are usually ridiculously oversized (by a factor of 3) for the heat load of the house. If your house was originally built in the late 1800s or early 1900s, and the building envelope has since been updated, then you could possibly get by with 120 degree F water through cast iron radiators on the coldest days of the year, and that is within reasonable COP range (COP = 2 to 2.5) of a geothermal heat pump. COP would be better during the 80-85% of the winter you would run water temperatures of 100 degrees F or less.

If you have the small, thin baseboard fin-based radiators, then you need the very high water temperatures Woodgeek referenced.

Yes, I have the baseboard type that look like electric. Each room has them except for closet space. The basement was/is finished so I have them all down there too. They had 3 zones I think. After the oil tank was removed they switched to electric hot water, heat pumps, and convect heaters. I still have the boiler and all stuff attached to it. The only part I got rid of so far was the roof mounted water solar heater. I can't easily get rid of all the baseboards. I am hoping maybe someday they will have a heat pump that might be able to use the baseboards.
I just hope they don't leak as I bet they are all full of water.

 

[woodgeek]

Yes, I have the baseboard type that look like electric. Each room has them except for closet space. The basement was/is finished so I have them all down there too. They had 3 zones I think. After the oil tank was removed they switched to electric hot water, heat pumps, and convect heaters. I still have the boiler and all stuff attached to it. The only part I got rid of so far was the roof mounted water solar heater. I can't easily get rid of all the baseboards. I am hoping maybe someday they will have a heat pump that might be able to use the baseboards.
I just hope they don't leak as I bet they are all full of water.

I drained my hydronic loops when I had the oil boiler torn out (13 years ago). I have been pulling the radiators out and replacing with millwork when I paint a room. I've pulled about half of it out at this point.

With the recent run on copper in the US, I might finally take the heavy copper radiator pipe in my garage to the scrap yard...

 

[Whitenuckler]

I drained my hydronic loops when I had the oil boiler torn out (13 years ago). I have been pulling the radiators out and replacing with millwork when I paint a room. I've pulled about half of it out at this point.

With the recent run on copper in the US, I might finally take the heavy copper radiator pipe in my garage to the scrap yard...

I have yet to even take the burner off and give it away. I'd like to get rid of the whole thing to make more space in the room it's in.
I asked someone (a plumber)if I should drain/blow out the piping and he didn't seem to think it was required. What a heating system if somehow I could get it going again. I need to make the decision too at some point to remove them. I am painting all rooms now with them in so it will be easy for me to touch up/repair later as I will know exactly the colors and probably have paint left over.

 

[woodgeek]

I have yet to even take the burner off and give it away. I'd like to get rid of the whole thing to make more space in the room it's in.
I asked someone (a plumber)if I should drain/blow out the piping and he didn't seem to think it was required. What a heating system if somehow I could get it going again. I need to make the decision too at some point to remove them. I am painting all rooms now with them in so it will be easy for me to touch up/repair later as I will know exactly the colors and probably have paint left over.

My boiler was still working when I scrapped it. It had leaked CO just below the alarm threshold, sickening my family (and small kids) for months, and oil was very expensive compared to my new ASHP. The DHW coil and valves were so gunked up the HW alternated bw scalding and cool on a 60 second cycle...

When I pulled out the radiators, I found that the 1960 builder, rather than drilling a small hole for the pipe, had usually just smashed a palm sized hole in the drywall with a hammer. All those giant holes (missed by me and my home energy renovators) added up to a significant source of drafts and heat loss for 60 years. They were also how the army of bugs were entering and exiting my house, and feeding the giant spiders that lived in my (cold) radiators. Good riddance to that noise!

 

[Whitenuckler]

My boiler was still working when I scrapped it. It had leaked CO just below the alarm threshold, sickening my family (and small kids) for months, and oil was very expensive compared to my new ASHP. The DHW coil and valves were so gunked up the HW alternated bw scalding and cool on a 60 second cycle...

When I pulled out the radiators, I found that the 1960 builder, rather than drilling a small hole for the pipe, had usually just smashed a palm sized hole in the drywall with a hammer. All those giant holes (missed by me and my home energy renovators) added up to a significant source of drafts and heat loss for 60 years. They were also how the army of bugs were entering and exiting my house, and feeding the giant spiders that lived in my (cold) radiators. Good riddance to that noise!

Holy cow! I am in a bungalow so all the pipes come through the floor. In the basement I guess they must be in the wall. I hate bugs! I glad you got it figured out but it sounds like a real nightmare to live through. My system seems to cause me no grief. I guess if I lose heat in -20C weather for a couple of days the water will freeze in them. It's copper mostly, but I see they did have some iron pipe to make some of the feed and/or return piping. A lot of copper sitting there ready for someone to take to scrap.

 

[woodgeek]

Holy cow! I am in a bungalow so all the pipes come through the floor. In the basement I guess they must be in the wall. I hate bugs! I glad you got it figured out but it sounds like a real nightmare to live through. My system seems to cause me no grief. I guess if I lose heat in -20C weather for a couple of days the water will freeze in them. It's copper mostly, but I see they did have some iron pipe to make some of the feed and/or return piping. A lot of copper sitting there ready for someone to take to scrap.

I had part of my loop freeze a couple times (since it was cycling rarely with the heat pump), it did not spring a leak. The radiator piping seems to be thicker walled than plumbing pipes.

 

[weee123]

If I were you I would finish ripping them out and scrap em now. I personally loved the hydronic baseboards that my grandfather installed in the house he built when I lived there for a few months. Next to wood heat I would say it’s the most comfortable (no experience with radiant flooring).

It’s always fun to see how the old residential builders did things. I’ve seen walls insulated with newspaper!😂