ASHP water heaters

[Ashful]

I guess it's been a few years since my hunt for a good tankless ASHP water heater was stalled by lack of good options. Anything new on the market?

I've got a Amtrol boilermate tank tied off my oil-fired boiler, which has all the storage and continuous regen capability I need. In fact, it's a great setup, with one big problem: heating all water via the boiler makes my basement too warm in summer. My primary electronics lab is adjacent to the boiler room, as is the kids rec room, and they both get too warm in summer.

I'm looking for a solution to pre-heat the water from 50F to 120F before it goes into the boilermate tank. I have no interest in actually trying to run a household off ASHPWH alone, too many stories here of luke-warm water, limited regen capability, the thing having to go into resistive mode to keep up. Not worth it, when I have the boiler with effectively unlimited capacity. The boiler will probably still be used to heat the water to final temperature, at least in winter, we may play with running cooler final temperature in summer.

Our hot water usage is very high, and the system is presently plumbed all 3/4" copper, yet I still get cold shocked in the shower if too many additional appliances are turned on at the same time (we have four showers, two dishwashers, a perpetually-running clothes washer, etc.). It's not a matter of heater capacity, but line/flow-rate capacity, so I have no interest in anything with less than 3/4" in/out.

Options?

Yes, I did look at a Rheem tank unit, but between the low ceiling height in my boiler room, and just the sheer floor space they consume, I don't see it as a very attractive option.

 

[EbS-P]

Not to my knowledge. There was a unit called the geyser. It was meant to retrofit for a standard tanked resistive unit.

The flow rate would be really high so the capacity would need to really really high. That really goes against the highest efficiency at low output for heatpumps.

 

[Ashful]

Not to my knowledge. There was a unit called the geyser. It was meant to retrofit for a standard tanked resistive unit.

The flow rate would be really high so the capacity would need to really really high. That really goes against the highest efficiency at low output for heatpumps.

Yeah, same I found years ago. Unfortunately, setting up a loop to allow recirculation on a lower-flow unit plays against using the same tank for low-temperature HP and higher-temperature boiler.

 

[EatenByLimestone]

Finding out why you go through so much hot water would be the key to lowering it.

Say you find out it's the kids taking 30 minute showers.. Pre rinsing helps with the dish washer. I'd chase the kids around the yard with either the garden hose or a super soaker. This might be less effective with the wife.

 

[EbS-P]

Yeah, same I found years ago. Unfortunately, setting up a loop to allow recirculation on a lower-flow unit plays against using the same tank for low-temperature HP and higher-temperature boiler.

I thought About swapping to a DC element in my tank and going solar (without an inverter). You really need a tank though.

Electric tankless and solar. That’s my only solution.

 

[Ashful]

Finding out why you go through so much hot water would be the key to lowering it.

Oh, I know exactly why we use so much. But fighting that isn't worth the interruption to domestic tranquility. We're on a well, and really only using ~1 gallon of oil per day for DHW, so the latent heat in the basement is really the only penalty I'm suffering here.

I thought About swapping to a DC element in my tank and going solar (without an inverter). You really need a tank though.

Electric tankless and solar. That’s my only solution.

I have a tank! Sorry if it wasn't clear, but that's what an Amtrol Boilermate is, a tank with a built-in water/water heat exchanger. There's a loop off the boiler with a dedicated circulator motor, which heats the tank. The trouble is, that loop runs WAY too hot to put it thru any heat pump that I know of.

Solar isn't an option. Ugly roof panels, and our southern exposure is shaded by trees, which I have no interest in changing. Also, this isn't about cost, although I always love shaving cost, it's really about air-conditioning my basement!

Other than the lost floor space and potential ceiling height issues, it appears the best solution is a classic tank-mounted ASHP upstream of the Boilermate tank, with bypass valving that allows me to completely bypass either unit for service or failure management. In winter mode, have the ASHP feed the Boilermate, so we can get acceptable hot water temperature and volume. In summer mode, just shut down and bypass the boiler rig altogether.

While there's a big open space in the middle of the boiler room (18' x 18'), nearly every bit of useable perimeter space is already filled with other utility equipment. Since HPWH's tend to vibrate hard plumbing, the recommended hookup is PEX or other soft connections. That does make putting this in front of another piece of equipment, and just keeping it mobile for easy disconnect/relocation a bit more feasible. So, maybe it's the way I should be looking to go.

 

[EbS-P]

Oh, I know exactly why we use so much. But fighting that isn't worth the interruption to domestic tranquility. We're on a well, and really only using ~1 gallon of oil per day for DHW, so the latent heat in the basement is really the only penalty I'm suffering here.


I have a tank! Sorry if it wasn't clear, but that's what an Amtrol Boilermate is, a tank with a built-in water/water heat exchanger. There's a loop off the boiler with a dedicated circulator motor, which heats the tank. The trouble is, that loop runs WAY too hot to put it thru any heat pump that I know of.

Solar isn't an option. Ugly roof panels, and our southern exposure is shaded by trees, which I have no interest in changing. Also, this isn't about cost, although I always love shaving cost, it's really about air-conditioning my basement!

Other than the lost floor space and potential ceiling height issues, it appears the best solution is a classic tank-mounted ASHP upstream of the Boilermate tank, with bypass valving that allows me to completely bypass either unit for service or failure management. In winter mode, have the ASHP feed the Boilermate, so we can get acceptable hot water temperature and volume. In summer mode, just shut down and bypass the boiler rig altogether.

While there's a big open space in the middle of the boiler room (18' x 18'), nearly every bit of useable perimeter space is already filled with other utility equipment. Since HPWH's tend to vibrate hard plumbing, the recommended hookup is PEX or other soft connections. That does make putting this in front of another piece of equipment, and just keeping it mobile for easy disconnect/relocation a bit more feasible. So, maybe it's the way I should be looking to go.

Thing is if you are drawing down that quantity of water quickly you really need an 80 gallon unit. Means it takes more space. More cost. Three years now all I have had to do do to mine was the occasional hard reset 1-2 times a year and clean the filter. Probably will have anode replaced and coils cleaned in two years. Given your low electricity cost and high usage it probably makes cents. But $x000 buys a lot of oil. Unit will cost $3k+ and then add install cost. The free dehumidification and cooling (great in the summer) is noticeable in my 1000 sq ft basement.

 

[Ashful]

Thing is if you are drawing down that quantity of water quickly you really need an 80 gallon unit. Means it takes more space. More cost. Three years now all I have had to do do to mine was the occasional hard reset 1-2 times a year and clean the filter. Probably will have anode replaced and coils cleaned in two years. Given your low electricity cost and high usage it probably makes cents. But $x000 buys a lot of oil. Unit will cost $3k+ and then add install cost. The free dehumidification and cooling (great in the summer) is noticeable in my 1000 sq ft basement.

I haven't really put much thought into this math, but a 20 minute shower on a 2 gpm shower head with a 70/30 (winter) mix of hot/cold is going to use 28 gallons of hot water. Two of those back to back... 60 gallons. With our laundry running almost continuously, and a random dishwasher cycle, your number may be a reasonable winter target.

But remember that I'll have the boiler running all winter, and that has its own capacity with infinite regen capability. So running out of hot water is a total non-issue, all that varies is how much pre-heating we're actually getting from the ASHP. Then again, in winter, I don't really mind the waste heat coming off the boiler.

In summer, figure more like 30/70 mix for hot/cold, and thus more like 15 gallons of hot water used in a 20 minute shower. This is why I was thinking we might get away with shutting down the boiler in summer. Maybe the cooler water coming off the ASHP will cause us to shift the hot/cold mix from 30/70 to 50/50, but even that might be okay, with anticipated laundry + dishwasher usage.

Heck, even if I leave the boiler turned on, I'd guess it won't be firing nearly as long after each shower, just doing storage and a little temperature top-up. This could be lowered even further if I lowered the boiler temperature for summer.

Funny aside, I remember now that each of our houses and rental properties growing up had a "summer/winter" switch, that we'd flip around May and October. I'm guessing my father must've had two thermostats on each boiler, and the switch that eventually became my job to flip twice per year must've been toggling between the two thermostats.

 

[begreen]

20 minute shower? That must be a teenage daughter calculation. I'd be twiddling my thumbs to take a 10-minute shower. Let the water go cold to hint that they need to take shorter showers.

 

[ABMax24]

Could run 2 ASHP units if storage volume is an issue, either in series or parallel.

I should calculate our daily energy usage for hot water, we put in central AC 2 years ago, I wonder if an ASHP water heater would put a reasonable dent in our cooling needs?

 

[EbS-P]

Could run 2 ASHP units if storage volume is an issue, either in series or parallel.

I should calculate our daily energy usage for hot water, we put in central AC 2 years ago, I wonder if an ASHP water heater would put a reasonable dent in our cooling needs?

It should be accounted for in a manual J in some fashion. But I don’t know how the manual J accounts for usage. I did the math at one point. It really affects me in the winter. I figure it’s between 1/3-1/2 ton of cooling. Running 4-6 hours a day for us. What is saves me in dehumidification costs for a basement is worth something.

 

[brenndatomu]

The free dehumidification and cooling (great in the summer) is noticeable in my 1000 sq ft basement.

Sane....don't even use the dehumidifier anymore.
In winter the hpwh is using "waste heat" from the Kuuma wood furnace that is 15' away...so I look at it as wood fired hot water
It would be kinda cold down there in winter otherwise