Rheem proterra 2024 as a air to water heat pump
35 year old infloor hydronic system powered by Polaris water heater works great. Polaris already way past expected lifespan, trying to spec air to water heat pump system to power 1st floor only (2nd floor mini splits and passive solar) when the Polaris dies.
Historic gas use in the coldest month of the year (massacusetts) 12,000 btu/hr. Polaris way oversized, has short cycled for 35 years. Recently took the domestic water loop off the polaris and replace domestic water with 50 gal Rheem 5000watt heat pump water heater, in anticipation of Polaris’ immanent demise. Have excess kwh off solar array and would like to use them instead of buy gas, but probably have to buy some kwh .
Air to water heat pumps crazy expensive and companies seem to be not ready for prime time in the USA. One plumber suggested ditch the thought of the dedicated air to water heat pumps. Instead use the Rheem heat pump water heater I already have running domestic water (approx 2kwh/day energy saver mode) to run the floors. Use the Rheem to heat a flat plate exchanger, to isolate potable water, heating a superstore off the flat plate exchanger for the infloor loop.
Question: Rheem COP# not easy to find for “energy saver mode” or the “high demand mode” which I think cold outside temps would require. With electricity at 32 cents/KWH, at COP3 I spend minor amounts on kwh over what my array provides. If the “high demand” COP is 1, it could be expensive. Any info on what Rheems COP#’s are in various modes?
Does this scenario seem like it might be successful?
Also with the “Energy saver mode” any idea what the bth/hr might be. “High demand mode” btu/hr?
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Two issues there. The heat pump on the unit is good for about 4000BTU and you can't take heat from the house to heat the house. If you duct it outside, it will only work down to about 50F outdoor, so not feasible in most places and definitely won't work in MA.
The one you could use though is a Sanco2 unit. These can do about 8k in combi heat mode. Still won't fully cover your heat loss but get close. The rest you can meet with a bit of supplemental resistance heat.
Air to water is not that expensive. The big issue is lack of installer knowledge. If you don't mind a bit of a DIY project it can be done on the cheap. The nice part about monoblock units is there is no gas piping, so you don't need a license to install one.
I have had no luck getting calls and requests for bids returned from Arctic, Apollo, Enertec, which leads me to believe these are flaky outfits whose service promises can not be trusted. I would love to DIY it and have friends who want to help figure this out, but I'm having trouble sourcing the "box" itself and the design/controls. Any suggestions on where to find the units appreciated
I had similar issues. If you are going to DIY it, you could order directly from Macon. They supply Arctic anyway. Mine showed up from China recently. Takes time for delivery, so you have to plan for that.
what does one do about parts and service for these if parts are in China or in a rebranded US or Canadian outfit that doesn't actually offer any timely service?
There aren't many options for for parts and service. Macon is pretty easy to get ahold of, and shipping from China really isn't that long for small items. Anything big enough to come by boat takes a while. But finding someone to service it would be tough, and you'd be paying them to figure out a unit they've never worked on.
Don’t not let that plumber near your home again. That will not work.
I have to agree. Although he's probably very good at things like fitting pipes and clearing drains, you just don't want him designing your heating system.
A heat pump water heater takes heat from inside the house. It can't also provide heat to the house, that would be asking it to be a perpetual motion machine. You need a heat pump that is pulling heat from outdoors.
lol.. I have an 80 gallon Rheem Proterra. It takes about 4 hours to heat up to 120f from empty. It wouldn’t have the ability to provide the volume of hot water for the hydronics- by a long shot. Get a monoblock and DYI it into your existing setup. It is not complicated. Oh, and you can’t beat gas with ASHP @ 32 cents per kWh. There are calculators- do the math. It will not be feasible. Gas and ASHP off the top of my head will break even at about COP 3.5 for the ASHP at 32 cents per kWh given the current cost of therm of gas. And you are not running at COP 3.5 in Jan and Feb in New England
recommendations on the monoblock?
rheem is in the basement which despite insulation in the infloor heated joist spaces, still loses heat to the basement. So the basement at 64f, would be cooled somewhat and currently wasted heat could be reclaimed. Don't care about the relative temp of the basement, its not living space.
I spoke to the Snco2 folks about this kind of hot water heat pump scenario with their unit. They said no don't do it. Reason: Hot water heat pumps are most efficient raising cold water to about 100f, then become more and more inefficient as temp approaches target. He said I'd only get 8000btu out of a 15ooobtu sanco2 unit and it would be painfully slow. That is simply raising the temp of the floor return from 95-ish to 11of.
But sanco2 does not have a resistance element as the Rheem does, so that changes the equation depending on what the COP's of the relevant setting are. My question is remains does anyone know what the Btu/hr rating of the "energy saver" and "high heat modes" are, and what their relative COP's might be.
Please don’t do this. The COP of using a HPWH to space heat is 1. It’s not a good idea and they should not have recommended such a bad idea.
my sense is that you are correct. Is there any specific place to find a schematic and specific unit recommendations of a monoblock system. I hear it talked about, but don't see it in evidence except in the air to air space...not air to water.
Chilltrix, Weismann and Spacepak all sell one. These are mostly rebadged Asian units, so if you want to do a bit of searching you can find them pretty cheap overseas as well.
Most loose about 1/2 their nameplate capacity in deep freeze, so you are probably looking at a 3 ton unit.
Realistically, since you are taking about a basement, the cheapest floor heat option is to install a ducted mini split in the basement. You don't even need to duct it, just have it heat the basement to 80F, works just as well. Bonus, you can also use it for cooling.
Caleffi has a journal called Idronics that explains this perfectly.
Sanco gets its heat from outdoors, it's marketed for both space heating and domestic hot water.
I've never laid my hands on one. But I swear that every person who comes here who considered them was told by the factory it wouldn't work in their application, it makes me wonder what it does work for.
The fine print in the manual is that it can’t space heat except in very limited circumstances
Here is a presentation showing how SANCO2 works for heat & hot water within a "thermal battery" system called Harvest Thermal
https://neea.org/img/documents/Harvest-Thermal-Thermal-Battery-System-for-Heating-and-Hot-Water-Product-Council.pdf
What I get from that presentation is that the Sanco2 is rated for 13kBTU/hr at 85F return water temperature. At 100F, which I would think is about the minimum for generating domestic hot water, it's 10kBTU/hr. It's hard to imagine a lot of use cases where that provides both heat and hot water, which is how they market it.
A 60 gallon domestic hot water tank that is 60F above incoming water temp requires 30k BTU to heat. That's three hours of full output. The "thermal battery" might average that out so you don't have to go three hours without heat when you need hot water, but still your looking at single digits of kBTU/hr available for heating.
Yeah that PowerPoint proves my point.
Systems like that are commonly done in Europe using outdoor reset as the only control. Outdoor reset is a feature where the water temperature depends on the outdoor temperature, the colder it is out the warmer the water. The water circulates constantly, all winter long, and the heat output varies with the outdoor temperature. This won't give you super-stable indoor temperature, if there is a mis-match between the actual heating load and what the heat pump is putting out the room temperature will fluctuate because there's no interior thermostat. But it's super-simple, you just hook up the heat pump to the tubing in the floor, no thermostats, no zone valves, no circulators. There is a circulator internal to the heat pump that is all that is needed. You do want to have an expansion tank and a strainer right before the heat pump.
I think every manufacturer has outdoor reset, it's easy for them to implement because the heat pump is already outside.
If you are currently heating using natural gas or propane, have you ever considered a gas absorption heat pump for space heating & hot water generation?
Apparently they leverage the combustion heat to capture additional energy from the outdoor air & claim a savings range between 30-50%
https://stonemountaintechnologies.com/
Just a thought ...
Chiltrix was prompt answered questions well and came up with schematic and quote. Apollo several days later responded with a quote. Is there any experience on either of these suppliers. Apollo is less money but I frankly got a better feeling from the guy at Chiltrix. Any experience with the reliability of either of these units?
It does seem they are probably assembled at the same Chinese factory, but the Chiltrix guy said their design was their own design and not simply a rebranded generic Chinese unit. At least that's what he said.
I have two Chiltrix heat pumps in my house, they've been through three summers and two winters. So not really enough to get a feel for long-term reliability. It's taken me a while to get the configuration dialed in, I'm still tweaking it, but I have a complicated setup and I'm a tinkerer.
The only maintenance they've required is cleaning the strainer at the start of each season.
what happens when/if you need repair to the monoblock? SInce these seem to be generic machines, can a vanilla HVAC guy deal with it on site?
As with most newer equipment, except for simple parts swaps, you pretty much toss the unit when something major goes wrong.
The nice part about monoblock units is they are factory sealed and filled with refrigerant, so much less chance of anything going wrong on the refrigerant side.
Sucks, but that is the case for a lot of stuff out there.
Yeah, I also have a heat pump water heater. When the compressor failed the manufacturer sent me a whole new unit under warranty, they said there was no way of repairing it.