Realistic to Avoid Glycol in Monobloc ATWHP?
Hello All… looking to renovate the heating system in my ’50’s Cape in Z5A (CT). Currently we have electric resistance baseboard (yikes!), and I initially planned to install propane tanks and a hydronic system powered by a condensing boiler. Now that the world is coming to an end (tongue in cheek) due to propane and fossil fuels I’m going to resist the urge to do the cheapest option and do the forward-looking option. So. I’m determined to incorporate ATWHP heating into my house, and I have questions for the community. First off, I understand the importance of insulating and air-sealing the house. That’s job one, and I have a comprehensive plan of attack to do so. It will take several years, as I intend to replace the asbestos siding in stages, and I’ll take the opportunity to seriously upgrade the R values and the air/vapor transfer in general. I have a reasonably well sealed house at the moment, and I’ve been aggressive about adding insulation wherever possible. My heat loss calcs show my 2,500 sf home requires approximately 80,000 Btu/h in its current state, though I include my unheated and unfinished basement in that calc. Existing heating in the house is equal to 58,000 Btu/h, and I can attest that it seems fairly equal to the heating load… maybe with liberal application of sweaters in the coldest weeks! Please assume that the current heat load is going to steadily decline in the next few years. After fairly exhaustive research (Among others, I read Siegenthaler through TWICE, fyi!), this civilian (I may or may not be an architect) is convinced hydronic heating using a combination of low temperature emitters is feasible and realistic. I hesitate to use the phrase “money is no object”… ‘cuz I ain’t no millionaire. But I’m the living definition of competent, and I’ll be doing most of the grunt work myself, so I’m not thinking of the exercise in terms of actual payback. My dollars ‘out’ will be almost entirely materials-based, assuming I value my time cheaply. I currently pay over $1,000 monthly for electric in the prime heating months, and while I’m not likely to experience payback on paper in any reasonable amount of time, I’m ready to do this the right way. I’ll burn some savings, and I’ll make a serious dent in my monthly nut. Is it economically sound? Probably not. But I’m doing it. All of that said… background, dontcha know… I have a specific question about bucking the norm. I want to use a Monobloc ATWHP for the efficiency of the heat transfer, but I DON’T WANT TO USE GLYCOL IN THE LOOP. Design temp is 9 degrees in my neck of the woods, and we definitely see that temp for 10 days or so each year. My specific question is, is there an insulated assembly that would allow transfer of water through the basement wall from the outside unit without using Glycol? I understand that warranties may be voided as a result, and that power outages will require backup systems. I’m curious as to whether it’s realistic to build an insulated penetration to house the lines that carry the heated water from the exterior unit to the interior distribution without introducing glycol and without necessitating a heat exchanger. Both of these items eat into the COP of the system, and I’m looking to steal btu’s (and dollars) wherever I possibly can. Can I “superinsulate” the lines running through the foundation wall? Cut a large opening that is densely packed with insulation to prevent the water in the lines from freezing on the coldest days? Use 10″ pipe wrap on the pipes? It’s a little outside the box… and the norm. Curious as to the community thoughts/experience. Long damn post for a single question, but the backstory seems necessary. Love the exchange of info on this site, looking forward to your replies. Even if they suggest I’m crazy to ask the question!
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I know that glycol moves less heat per unit of flow and is more viscous, so you have to put more energy into pumping it and pump greater volumes. But I've never heard the claim that it affects COP. My understanding is that COP is largely determined by temperature delta, which glycol wouldn't affect. And radiator output is determined by temperature, which glycol wouldn't affect if you adjusted the flow rate.
I've repaired a house where the heating system froze up. The radiators were almost a complete loss. It just seems not worth the risk not to use it. With a heat pump the water is circulating outside and you have to worry about spots where the water may not flow and can freeze.
A glycol solution turns to slush before freezing solid. The number given for freeze protection is when slush starts to form. If the system is operating it will never get that cold. What you care about is the burst protection point which is lower.
Thanks for the thoughts. I know all too well about the dangers of burst pipes, lost my mother's house to an ongoing flood that went unnoticed for weeks after she moved to an assisted living facility during heating season. Nightmare scenario, and it's front and center in my mind as I plan my own heating system. The answer for me, absent a convincing argument that there's a workaround to glycol, will be a split system rather than a monobloc system. Just aren't as many options available with that choice of ATWHP, though. I'm planning on hiring an engineering firm to design the system, but I want to go to them with a (mostly) fully baked concept. Can a robust enough insulated assembly protect the exposed lines carrying water? Maybe with the addition of a heat trace wired to a backup battery/generator in the event of power outage? I guess ultimately, it's not just about the lines themselves... it's about the inner guts of the outside unit itself as well. But there will be an auxiliary power source, and the units all have freeze protection / defrost cycles, so as long as the backup power is consistent I don't believe that's an insurmountable concern. Would be interested to hear from anyone who has installed a monobloc without glycol, guessing most likely in a warmer climate zone than mine. Anyone have freeze problems with one?
Take a look at the SANCO2 system. They don't allow the use of glycol in their system, they require heat traced pipe with freeze protection valves. I would think you could do the same setup with an ArcticHeat or similar.
Not to derail your post too much... but which system are you thinking of going with? For milder temps, I wonder if one of the ArcticHeat pool heat pumps would get the job done... They are half the price of the regular heat pump and rated to pretty low temperature. Covers all but the coldest days. You'd obviously have to have a back up, but a cheap electric boiler could be it.
It sounds like your concern with glycol is not the cost but rather loss of efficiency. I would say this is a pretty minor deal considering the massive gains in efficiency you get with adopting this impressive technology. Perhaps you could just consider accepting these minor losses and move on to next challenge (nudge..nudge) ! It is a bit like having an electric car in a snowy climate and not wanting to run snow tires because of the loss of efficiency. If you want to shoot me an email I can help you out with a quick conceptual design as I have installed a lot these units. To follow up on the last message those Sanden units that use CO2 as refrigerant are great. I just wish they had higher BTU output and that they were cold weather ready (I never liked the idea of heat tape as freeze protection on expensive mechanical equipment).
Yeah, I agree. And they will only warranty the heat pump if you use it with a Taco Xblock for radiant. I was more proposing just using their freeze protection valves. I agree, not ideal.
Seems simplest to run glycol, but you could use a split system too. The efficiency loses aren’t worth the risk. Is this system providing cooling?
I'm still not ready to concede that there is an efficiency loss with glycol, other than slightly more electricity to pump the fluid.
I think before running an outdoor unit without glycol I would put a heat exchanger on the system so the indoor and outdoor fluid is separate, and then only run glycol on the outdoor fluid.
"My heat loss calcs show my 2,500 sf home requires approximately 80,000 "
Before you do anything, you have to get this number correct. If your place was indeed 80kBTu heat loss you would not be able to afford to heat it with electric baseboards.
I would run through the calculations here, you can converter kWh to BTU by multiplying by 3412, the rest is the same.
https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler
If you don't already have anything hydronic, air to water makes only sense if you have money to burn and looking for a hobby project. A properly sized and installed hyper heat ducted air source heat pump will be much less and most likely better COP. It also makes cooling easier as you don't need both rads and air coils.