Heat pump water heater question

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jetsam

Minister of Fire
Dec 12, 2015
5,323
Long Island, NY
youtu.be
I just went solar, and I want to get rid of my oil-fired water heater (used every day) and my oil-fired boiler (connected to 3 zones of hydronic baseboards, not used unless we go on vacation).

My first thought was to swap the water heater for a heat pump water heater (like the popular Rheem hybrid), leave the oil boiler there for emergency/vacation use, and maybe get some heat pump minisplits in to help heat and cool the upstairs.

However, while researching heat pump water heaters, I tripped over the LG Multi V. This is a commercial product that does domestic hot water, baseboard hot water, it feeds split system heads, and even uses heat scavenged from air conditioning to heat the hot water. On the down side, the smallest unit is 14kw, so they're not exactly targeting the home market here.

This got me thinking: It would be really nice to have the hydronic baseboards running off of an electric heat pump.

So on to the question: Is anyone familiar with a residential-sized heat pump that can do DHW and hot water for hydronic heating? How about one that also does cooling via minisplit-style heads?
 

woodgeek

Minister of Fire
Jan 27, 2008
4,455
SE PA
Conventional wisdom is that HPs lose efficiency (COP) when heating water hot enough for normal US hydronic radiators.

If you have a low-temp radiation system, then is could work. That is why its drawn with in-floor heating.
 
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SpaceBus

Minister of Fire
Nov 18, 2018
6,449
Downeast Maine
American solar technic offers a water to air unit that can do what you ask.

After looking at the website to get you a link I can't find it...

@tom in maine knows more and can probably furnish a link.
 

jetsam

Minister of Fire
Dec 12, 2015
5,323
Long Island, NY
youtu.be
I just tried to do some googling to see how old hydronic baseboard systems perform with ~120° input water, and the results tend to be (often angry) opinions rather than data.

BUT... I also found this easy idea. Wanna know if it'll work? Just run your old system at 120° and see if it can heat the house!

All of the 160°+ heat pump boilers I've seen so far require a geothermal loop.
 
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jetsam

Minister of Fire
Dec 12, 2015
5,323
Long Island, NY
youtu.be
I found some great info on running old hydronic baseboards on 120° water here. (The bottom line is that you should add lots of radiator; trying to avoid that.)

So if a air-to-water heat pump that can put out 160° doesn't exist, I could still use the existing baseboards to do some amount of heating for the house with an air-to-water heat pump.
 

lml999

Minister of Fire
Oct 25, 2013
562
Cape Cod, Massachusetts
I just went solar, and I want to get rid of my oil-fired water heater (used every day) and my oil-fired boiler (connected to 3 zones of hydronic baseboards, not used unless we go on vacation).

If you're only running the oil-fired boiler a couple of weeks per year, you're better off (financially) by just continuing to use it. You're talking about $100 or so in oil per week, during the winter, more or less.

On the other hand, if you spend three months away in the winter, you will have a quicker payback...
 

Highbeam

Minister of Fire
Dec 28, 2006
19,539
Mt. Rainier Foothills, WA
This got me thinking: It would be really nice to have the hydronic baseboards running off of an electric heat pump.

Well yeah, we've been waiting for this basic technology for many years. Other countries have it. It's usually an all in one heat pump (monobloc) that is connected to the home with water lines instead of a split system with refrigerant lines.

No mainstream manufacturer sells these in the US yet. Crossing my fingers that the technology arrives soon. Tom's unit has the right specs but is what I would call a "grey" market appliance with few to no reviews.

Your need for super hot supply water is probably the reason that we don't see these things all over yet. For those of us that just want to heat domestic water or low temperature hydronic systems like a radiant slab it would be perfect!
 

peakbagger

Minister of Fire
Jul 11, 2008
6,825
Northern NH
Search around for John Siegenthalers articles in PME, he is a big advocate of air to water but he pushes you need to have low temperature radiant emitters. Most homes with fin tubed baseboard were sized for high temp supply water so there is not enough baseboard to heat the house at low temps. If you have the wall space you may be able to triple the length and get away with it. John is big advocate of low temp emitters. He actually prefers inwall radiant and ceiling over in floor.

Vermont is giving incentives for air to water equipment. The downside is there are very few companies you have heard of selling this equipment in the US so the volume is low.
 

Seasoned Oak

Minister of Fire
Oct 17, 2008
7,217
Eastern Central PA
Leave your oil is place as a backup. Thats what i did. I also switched to a HPWH. Mini splits sound like a good option for your location. You could always use the oil for those short spurts of very cold weather with overcast skies when your solar would suffer.
 

Brian26

Minister of Fire
Sep 20, 2013
626
Branford, CT
Chiltrix makes a unit that is in widespread use in the US. A google search wilk bring up tons of more information.

Chiltrix heat pump chiller. This is the AHRI-Certified small heat pump unit of the future that is very easy to install and eliminates all lineset length issues. Cooling or heating is transported via simple water/glycol lines. The outdoor unit is completely self-contained. Just add power and connect the water lines. The indoor units are also very simple to install, just add power, connect the water lines, and connect a condensation drain line. The CXI series DC-Inverter fan coil units are the quietest fan coil units on the market. Shown to the right are various indoor unit options, available in various sizes from ~1/4 ton (3,400 BTU) up to 1 ton (12,000 BTU). Larger indoor units can be special ordered. More indoor fan coil unit details are here. Up to 8 indoor units can connect to a single CX34. It also has options to easily connect to ducted/central systems, boilers, and hydronic / radiant heating systems.

 

jetsam

Minister of Fire
Dec 12, 2015
5,323
Long Island, NY
youtu.be

Their CX34 (which appears to be their only heat pump) has a max operating temp of 122. The DHW anti-Legionnare's disease mode, which briefly pushes the DHW higher, requires a special resistive heater to be installed on the DHW tank.

Unless I am looking at the wrong unit?

We're looking for something that puts out (ideally) 180° water on a baseboard loop, and maybe 130°for the DHW output.
 

jetsam

Minister of Fire
Dec 12, 2015
5,323
Long Island, NY
youtu.be
Leave your oil is place as a backup. Thats what i did. I also switched to a HPWH. Mini splits sound like a good option for your location. You could always use the oil for those short spurts of very cold weather with overcast skies when your solar would suffer.

This was the original plan, but I was eager to scrap it when I reasoned that I could use a heat pump to run the baseboards.

Now it seems that this is not practical without at least doubling the surface area of radiator in the house, which I do not think we're going to want to do.

It would actually be perfect for MY needs to hook up 120 degree water to the existing baseboard as backup heat, but since that system would no longer be able to carry the whole house in the winter, it would be pretty rough on resale value. ("This is the wood stove. If you don't like splitting wood, go look at a different house.")
 

jetsam

Minister of Fire
Dec 12, 2015
5,323
Long Island, NY
youtu.be
Search around for John Siegenthalers articles in PME, he is a big advocate of air to water but he pushes you need to have low temperature radiant emitters. Most homes with fin tubed baseboard were sized for high temp supply water so there is not enough baseboard to heat the house at low temps. If you have the wall space you may be able to triple the length and get away with it. John is big advocate of low temp emitters. He actually prefers inwall radiant and ceiling over in floor.

Vermont is giving incentives for air to water equipment. The downside is there are very few companies you have heard of selling this equipment in the US so the volume is low.

Yeah, I see that greatly increasing radiator surface area is an option. If this was new construction or a renovation I'd consider that, but as is, I don't think I will be able to sell it to the wife
 
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Brian26

Minister of Fire
Sep 20, 2013
626
Branford, CT
Did they size your panels to cover your last year average electrical consumption? Almost all utilities will only let you install like up to 110% of your last years average use. If you start adding a huge electric heating load you are most likely going to be paying for the electricity at cost.

What size is your system and did they not size it based on your past year usage?
 

lml999

Minister of Fire
Oct 25, 2013
562
Cape Cod, Massachusetts
Did they size your panels to cover your last year average electrical consumption? Almost all utilities will only let you install like up to 110% of your last years average use.

We were fortunate...we actually signed a contract for a solar installation before we closed on our house. Since we had no prior consumption information, we didn't get much pushback on installing a large system. Currently running 40% annual surplus.

Weird that the utility doesn't want people contributing too much excess... As I understand it, when I put power onto the grid I get credited at a lower rate than when I pull power off the grid...
 
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