R290 (propane) and R744 (CO2) heating/cooling in the United States?
I’ve been holding out for an air-to-water heat pump that can handle heating in cold climates, cooling in the summer, has low global warming potential, and the ability in heating mode to produce water that is actually hot, so that it could be used for domestic hot water or perhaps even to replace a boiler on old fashioned radiators.
My understanding is that R290 (propane) and R744 (CO2) refrigerants can both do all of these things, and LG has a model (and perhaps other companies?) available in Europe, but not in the United States, due to regulatory restrictions (propane is flammable and CO2 requires high pressure).
Does anyone know if any product like this exists in the US? Or when products like this will be allowed in the US?
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SANCO is selling a CO2 based system in the US. However, it seems that every person who comes here inquiring about it eventually decides it won't work for them. The specs are demanding.
I’ve talked to the people at SANCO2. Their water heater gets hot enough, for sure, but wouldn’t work in a residential heating context, apparently because the return water temperature is too high (it needs a bigger temperature differential to work properly, from what they told me). Plus it isn’t set up to provide cooling.
There are significant limitations, but they most certainly CAN work for space heating as well, as detailed here https://www.smallplanetsupply.com/sanc02
The Combi-System : DHW plus Space Conditioning
With a capacity to deliver 15,000 btu/hr, a SANCO2 heat pump hot water heater can be designed into a system that delivers all of the domestic hot water (DHW) as well as heated water for space conditioning. This is accomplished with one circuit feeding a DHW mixing valve to reduce the temps to 120°F, and another supplying a standard heat exchanger supplying hot water radiators or radiant slabs.
For homes with a design temp of 12°F or higher, and a heat load of 8kbtu/hr or less, this can be the entire DHW and space conditioning system. Additional on demand hot water heater systems can be added into a design for homes with larger heat loads or used back up systems to provide added capacity for extreme weather events or large homes where all but the coldest days can be supplied by the default Sanden system. It's important to note that this COMBI technology is still in the development phase. As features are improved and more projects report success, the 8kbtu heat load can be increased, and lower design temps added, based on capacity improvements and project results.
I read that information a couple of years ago, and wrote directly to SANCO2 and the response was basically: don't do it. It won't be efficient. Here are some direct quotes:
"Heat transfer is not as efficient into water that is already warm. If you are using that electricity to heat water from 120 to 145F, for example, the COP of the whole system takes a beating.
Considering that when the SANCO2 unit is simply providing Hot Water to recover the Tank it is drawing 45/50/55F Cold Water to the Gas Cooler Heat Exchanger and heating it
The method of the Tank design is to ensure that the SANCO2 unit will heat a good volume of the Cold Water in standard operation as the Cold Water volume at the bottom of the Tank will be around 35 to 50 Gallons (83 or 119 Gallon Tank)
Then as the Tank becomes more refilled with 145F Hot Water the Cold Water at the bottom of the Tank becomes warmer and warmer as it drawn to the GS4 for heating
The period that this level of performance will take place is around 30 minutes and the Cold Water will raise in temperature up to 126.5F and the SANCO2 unit will cycle off
As the Cold Inlet Water temperature rises both the unit capacity and the COP reduce significantly
This is what is leading to the capacity reduction for the Hydronic loop
We would consider that the Taco X Block is drawing 145F Hot Water from the Tank, it will give up Heat to the Hydronic loop and return to the Tank at 100 to 120F depending on the heat load of the home
Even if we were to consider the ambient of 14F then with the SANCO2 unit drawing in 110F Cold Water as we are just doing Hydronic Heating not DHW then the capacity of the system is 2.5kw or 8,500 Btu/h
However to make this Hot Water the COP of the SANCO2 system is now only 1.2 which means that the SANCO2 unit is drawing 2kw of power
The Heating load of the home will be high with the heating system having to operate for more hours in the day that it would need to be if the ambient temperature is 27F, 47F etc etc
Given that now we may be looking at say 8 hours of Heating load this would be 16kw of power per SANCO2 unit which is a completely inefficient method of heating the home
The Colder the ambient is outside the home more the capacity will drop as the SANCO2 unit when operating below 5F will now start to reduce the capacity so at -11F the unit capacity will be 20% lower so 2kw with a COP of 1 just about the same as an electric fire for heating the home
This is the detailed reason that will not allow the use of a SANCO2 system for providing Combi heating and DHW to a home with an ambient that can be less than 27F
Capacity, efficiency are significantly affected
This reduction in capacity and efficiency does occur in the DHW production but the time period that the unit is required to operate in is extremely low so while more power is required it is not going to be for a longer period of time as the SANCO2 unit will still produce Hot Water even if it is a little less than the standard production value
I hope that this detailed explanation of the SANCO2 operation is clear and shows why we only allow Combi systems in the "warmer" areas of the US
Thanks Paul, that's a great rundown of the significant limitations I was referring to.
I’m located on the central coast of California, so it's one of very few climates where it might actually make sense. Very mild winter temps that still need some heat, mostly in the morning, with cool enough summers that AC is unnecessary.
What I’m still unsure of is how this compares to a Spacepak or Chiltrix system where they don’t note such significant drawbacks when providing domestic heat. I’ve been hoping to have a client fund this investigation for their own project, so far I haven't had any takers…
Thanks for the detailed explanation, I've heard variations of the same story from others but yours is the most in-depth.
I just wonder how SANCO stays in business. It seems like almost everyone who is interested in their product goes down the road a ways with them and then ultimately gets talked out of it.
@DCcontrarian I'd venture a guess that the majority of their business is commercial and multifamily. The outdoor units are oversized for all but the most absurd domestic use, but are seemingly quite competitive where multiple units are needed, particularly the prepackaged water drop systems https://www.waterdropsystems.com/
The other problem with the SANCO2 system is that it is designed to work on an inflow of water from the supply to the house. It isn't designed to recirculate a closed loop of water. It's set up for just one purpose, which is domestic hot water. I wish they would tackle hydronic heating, but they haven't attempted to enter that space yet.
@escape road It sounds like you're looking for a highly versatile and eco-friendly heat pump solution, which is definitely an exciting area of development.
I’ve had several online conversations with the person in charge of https://www.2040energy.com/ which would do everything I need on the heating side — but no cooling — except that it is an experimental project with no commercial product any time soon. If I’m honest, I’d prefer an option from a larger company with a longer track record, but I do wish him well in what he’s creating. For the heating side of things it sounds kind of perfect, at least in theory, if he’s able to turn it into a product someday.
I'd be curious to see some numbers on the energy consumption of equipment using either of these two "refrigerants" here. In my work, I deal with very large chillers, and we usually have a choice of two refrigerants we can use: R123, or R134A. R123 is a low pressure refrigerant, and it's getting phased out, but it's more energy efficient: basically you can get more tons of cooling per kwh with it compared to R134A. You end up trading energy efficiency for ozone friendliness.
The difficulty is if you want to be green overall, you need to balance energy efficiency with ozone friendliness. We usually call this "GWP" (Global Warming Potential, which has to do with CO2 production and is primarily concerned with energy efficiency) vs "ODP" (Ozone Depletion Potential, which pretty much already describes itself). If you go down a bit with ODP by switching refrigerants, but you go up substantially (as is sometimes the case) with GWP due to reduced efficiency, I think you end up net negative, and you'd have been better off using the "old" refrigerant.
I'm not sure how things compare with the propane and CO2 systems, but I haven't seen much in terns of energy efficiency comparisons for those. I know at work, I still like R123 because it's more efficient, and our primary concern is typically energy efficiency of the system. I'd use something newer if it was better for ODP but had similar (or better) GWP though.
Bill
The SANCO2 system has a COP between 2 and 5, depending on the ambient temperature, which seems like a pretty good efficiency rating for any refrigerant, and their system can produce temperatures up to 150 degrees F. Their system isn't designed for heating/cooling of the house; only for domestic hot water, but if that efficiency range could be achieved in a product designed for heating/cooling, that seems acceptable.
The LG290 Therma V Monobloc uses propane (GWP = 3), and reaches 167 degrees F, but is not available in North America. I'd buy this one if I could. It seems pretty much perfect, but I'm in North America. https://www.lg.com/global/business/hvac/residential-solutions/air-to-water-heat-pumps/therma-v-r290-monobloc
There are users on Reddit who have imported units from China that run on R290. However, it is technically not legal to do so. I personally imported a Macan A2W heat pump from China, but it is R410a or R32, I don't remember. I have not run the unit yet however, still working on getting things hooked up.
I have used the SanCo system for DHW and radiant floor in a few well insulated airtight (near passive) houses here in the relatively mild PNW. They seem to be doing just fine. A well insulated house does not need a really warm floor to heat it so the return temp into the heat exchanger/tank is not as high, around 70-75 degrees. So if the owner uses a bit of DHW the tank is not really too stratified. Was wondering though if anyone has done this and taken the additional step of running the return radiant floor fluid through a fancoil that preheats the incoming air of an HRV/ERV. Seems like a win/win...increasing the incoming air temp to the HRV/ERV while further cooling the return water before going back to the taco heat exchanger and tank? Perhaps the rate of circulation for the floor is too fast for the fancoil to really release enough heat to justify the cost?
John, any tips for designing the combi system to get such low return water temps? Thanks,
Adam
Adam - Sorry but not following. I a very well insulated house, high-performance windows, low air leakage, and moderate climate, it really does not take much to heat a house with radiant floor, so the floor temp can be set much lower, otherwise the house would be too warn. With the addition of single mini-split for a bit of cooling and a bit of heat for the extremes then the system works pretty well.
You mentioned the return water temp of 70-75 degrees. My understanding is that in order for the water to leave the tank at ~150 degrees and return at 75, the distribution system must by designed to pull all that heat out in a way that doesn’t overheat a high-performance house. So I was just wondering if there are best practices for designing the distribution system to maximize that temp delta (for ex, slab thickness, piping layout, etc). I’m currently trying to absorb Siegenthalers book, but as a layperson it’s slow going. I need a “for dummies” version!
Perhaps I should clarify, I am an architect, not a engineer. I have this system at my house, and have done it in a few homes, so by no means am i an expert. As far as I know there was nothing special about the layout - although I as think about it, I don't have many loops so perhaps each loop is at max length. I don't think there is a way to get the water temp any lower than a few the slab temp with out auxiliary device, such as maybe a fan coil unit or radiator. I know a client/builder of mine added a few small radiators to provide a bit of supplemental heat to a bedroom. He said he gets very little heat out of them, but does get some. Seems to me one could use this method to get the return temp down a bit more, but again not an engineer.
Heat output is always going to be temperature delta times flow rate. So if the flow is low enough, you can have a high delta without a high heat output.
At the same time, the heat output of an emitter is always going to be proportional to the average water temperature in it. The challenge with low return temperatures is not limiting the heat output when load is low, it's being able to get enough heat out of the emitters when the heating load is high. If your source is 150F and your return is 70F, there's no way to get your average higher than 110F. If your emitters can't meet the heating load at 110F average then you have a problem.
You can get the average anywhere between 110F and 70F by slowing the flow.
Send the hot water to the area you want to be hot first. A heated tower rack and some small panel rads are good first load. From there it should go the your main floor area you want extra cozy (bath tile, kitchen floor), this should be a small percentage of the overall floor area.
Finally loop through the rest of the slab especially near the outside walls so RWT is pretty much room temp.
You would ideally use a 0..10V circulator driven by a 0..10V thermostat for controls. Idea is the circ is running pretty much all the time.
The earlier idea of a pre-heater for an ERV to drop the RWT even further is also great option. Problem is this needs a glycol loop so unless the whole Sanco2 is running on glycol, not sure if it is worth the cost or complexity.