Air to water heat pump
blackfeet
| Posted in Mechanicals on
Hi there. Does anyone have experience with this company and their AWHP for radiant floor heat. The prices seem much better than Spacepak, Chitrix and so forth. https://hydrosolar.ca/collections/hydro-solar-air-to-water-heat-pump
I really want radiant heat in a new house I am building. Will DIY it. No natural gas in the area. But these AWHP are pricey!
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If you insulate very well you really do not need much heat capacity even in a cold climate. Spend the money on a high performance building envelope, not expensive heating systems. A heating target of 1 Btu per square foot per heating degree day will get you there.
Doug
Thank you. We will be insulating well. The climate zone is 4 marine. New Washington state energy code requires me to accumulate at least 8 “energy saving credits”. Because of this, we will be doing at least 5kw of solar (you get 1/2 credit for every 600 watts up to a max of 4.5 credits). Ore current c3 calculator is calculating heat required of 34,000 btu on coldest design day which is 25 degrees. We have a lot of windows but primarily .23 u factor. R60 ceiling, r23 walls, conditioned crawl. The most efficient way to heat this is with mini splits. But we love the idea of in floor heat. I certainly appreciate any thoughts!
Sounds like you are on top of the efficiency program, do you have hydro electricity there and what is the kWh cost these days. Followed what I remember as the Model Conservation Standards in the 1980's with Bonneville Power. A heat pump does sound very reasonable for your climate. The in-floor heat debate has been gone over here quite a bit, hot floors equal a hot house especially with a quality thermal envelope. Radiant floor heat without mass would likely be able to run a bit warmer, offsetting the heat loss? I dearly love the radiant baseboard heat in our farmhouse, 170F water feels good with the extended cold we have currently.
Doug
17BTU per sqft is way too high even with a lot of glass in your milder climate. I would re-check the math before looking at equipment.
Pretty much all AWHP units in north America are re-baged Asian brands. You can see which one that is and see what the internet says.
The Hydrosolar units need an external pump. If you want a speed controlled one, their pump is not cheap and there aren't many 240V options in NA.
"A heating target of 1 Btu per square foot per heating degree day will get you there."
Do you mean per thousand HDD?
Example, 2000 sf x 35 hdd = 70,000 Btu for the day. Annual heating load would be home sf x seasonal hdd for total heating fuel usage.
35 HDD would be one day at 30F.
A moderate climate might be 4000 HDD for the year, a severe climate 9000.
I get the idea of including HDD in a rule of thumb, I'm just trying to decipher what you mean.
BTW, 35 BTU/SF would not be impressive.
2000 square feet x 7500 heating degree days = 15,000,000 Btu's or 150 therms. MSP cost of gas currently is .66 per therm (not including all of the other charges)or $100.50 annual heating. My best effort was around .9 Btu per sf per hdd, Passive House best I could figure is around .6 Btu/sf/hdd. Coincidently a superinsulated house would come in right at the ACH50 for the Btu/sf/hdd. So 1 ACH50 would be 1 Btu/sf/hdd. Cold climate superinsulation as defined by annual hdd divided by 180 for wall R-value and 120 for ceilings.
OK, I see where's you're going. What had me confused is that usually heating loads are expressed in BTU/hr or BTU/hr/sf.
So 70,000 BTU/day= 2900 BTU/hr. That's pretty aggressive for a 2,000 SF house at 35F.
Just back of the envelope, let's say the house is 2 stories, each 25x40. That's 1000 SF of floor, 1000 SF of roof, 2600 SF of wall, total 4600 SF of insulated area. That's an average of R55 for the whole assembly.
I think a realistic goal might be 3-4 times that, or 1/3-1/4 for the R-value.
DC,
Using my formula, Btu/sf/hdd, what are you proposing as a benchmark? I like 1, did this 40 years ago in a 9,300 hdd climate.
Doug
You do understand with the good thermal envelope you described the building will not need much heat if most of the floor is heated when the air in the house is 75° the floors will be 85° so you will not get the toasty warm floor so often found in the leak uninsulated homes of the past.
One option is to install a cheap DIY MR COOL brand A to A HP collect your government brownie point and remove and resell it after the inspection. Install the extra solar to power an electric boiler and get the heated floors you want.
When you are an early adopter of a tech like AWHP it will be expensive and risky in that company you select may fold and you are left with no support or parts. Any minor part failure could become a system replacement.
Walta
Hi Walta. You are spot on regarding my concern! I am not an early adopter for the reasons you state. Too much risk. But I wanted to at least look into it.
I love radiant heat, grew up with it in a 60's ranch.
Radiant can absolutely give you warm floors if you design from the get go.
In a 90's or older house, you struggle to get enough tube in the floor to heat the space without overheating the floor.
In a modern house, you just reduce the amount of tube in the floor to to raise the water temp so that you can feel the heat.
But....
Why are floors cold?
Floors are cold because old houses with old windows pool cold air on the floor
Eliminate the crap windows and the air leaks, no river of cold air pooling on the floor
I ran tube in my entire downstairs of my remodel of my 1970 contemporary.
Replaced the majority of the glass with ~U.16 and spray foamed almost all the wall cavities
We never hooked up the tube
The floors are not cold.
So, I agree with Walta in this regard.
A/W heat pump, right now, today, not worth the trouble.
Mitsubishi starts marketing one, I am all in.
Mini splits are so cheap and work so well they are the best solution
Ducted splits and maybe a little electric floor in the bath would be what I would do today.
Thanks Gus. All good points. The house I built here in Idaho in 2021 has a a conditioned crawl. My heat is mostly solar (house situated to south). For additional heat I use a stand alone NG fireplace. It puts out 28,000 btus. I have electric resistance cove heaters in the guest rooms and floor heat in the two bathrooms. It all works pretty efficiently. The main thing I like is no noise. So I guess that is one big reason that in floor heat is enticing. I do measure the heat in my crawl regularly. It stays at about 57 degrees, even when it is minus outside. The only "heat" down there is a regular electric water heater. An exhust fan pulls a certain amount of air out of the crawl. There is a passive radon system. And the walls of the crawl have r19 batts with the rim joists close cell spray foam. The ACH for the house is 1.18 (pretty darn good for not trying too hard, only upgrade to insulation was a drywall gasket for $700 bucks).
Now I am just rambling....Ha ha.
The only time radiant is totally silent is concrete floors. PEX expands so much that there will be places in a wood floor that make noise.
If you run a good outdoor reset curve with preferably continuous circulation, the pipe temperature doesn't change much. Pretty much silent operation.
Well if outdoor temperature is the only variable in your house, good for you.
I will take a thermostat just the same.
There are so many hundreds[thousands?] of hours where heat is not required in heating season it is hard to imagine running a circulator for no reason, I know people do it. My Buderus is capable of doing it, but I run hot water and no primary secondary, so really cannot. My previous house had P/S but no outdoor reset[and also had hot water] so my experience is related to ~140 degree water on/off.It did not annoy me and it was the installers fault[raises hand] that the U's at the end of runs and a few through wall areas were not properly detailed.
My current house with baseboard and outdoor reset you only really hear the baseboard when the hot water is called for in shoulder seasons and you get 170 degree water running through the baseboard
Radiant can absolutely give you warm floors if you design from the get go... In a modern house, you just reduce the amount of tube in the floor to to raise the water temp so that you can feel the heat.
You have to be very careful with this thinking.
The heat output of a floor is entirely determined by its area and the temperature difference between the surface and the air in the room. There are only two ways to reduce the output of a floor, either make the heated area smaller, or reduce the temperature.
Many, many heated floors are what I call "designed to disappoint." They meet the heating load of the room at a surface temperature that is imperceptibly above room temperature. This is particularly true in houses built to modern standards.
Thanks for those thoughts. To be clear, I am not seeking the toasty warm feeling I get with my bathroom electric infloor heat. I just want to heat the house silently if possible. (I wear shoes in the house anyway so would never feel the floor).
Lower the feet of tube you need to raise the water temperature to get the same output.
In a 1990 house, this will get you underheated, or floors uncomfortably warm
In a state of the artish house one should be able to calculate the feet of tube required at design load at a given water temperature
But the other part of the equation is the floor temperature. Heat in equals heat out, and heat out is governed by the floor temperature.
If the floor is keeping the room at 70F with a surface temperature of 76F, it's achieving its design goal. But the heating of the floor would be imperceptible. Considering how expensive hydronics is, most people would consider that a failure.
floor temperature is regulated by water temperature and feet of tube.
Again, limiting the amount of floor area heated will raise the required floor temperature to achieve the goal. Having that area under the dining room table, the couple feet close to the kitchen counter, in front of the bath vanity and toilet and you achieve your goals
My wood floors do not feel cold at a measured 68 degrees in my 69 degree room
I think perhaps being 8 degrees warmer might be noticeable.
I am Upstate NY, 20-year old 1800 sq ft SIP house that I heat with methane and boiler. We had a Munchkin that was in its death throes and we were leaving the country for a year and did not want to leave the house in jeopardy.
I went round and round on air to water, Manitoba, New Brunswick in the Great North and several US-based products. It was too much of a hop and a jock to determine system, find qualified installers and have assurances that a system would work when I was 4000 miles away.
Wound up replacing the boiler, great even heat, 400 therms a year which even at today's prices is about $600, design temp 4F
Ok....since I am DIYing this, I am starting to think air to air heat pump. A mini split is easy to install. But as to having a quiet peaceful home....should I think about a central ducted system. There are some DIY friendly "kits" out there. I have never run duct work but I am very handy so I think I could do that. Would a central system with floor registers be quieter than the giant loaf of bread on the wall?
I would look at the small ducted units for convenience. Easy to heat 3 or more rooms
Self install for all but the freon
Start looking for an amenable HVAC guy
For the risk in not getting a warrantee, compared to the install cost you could buy 2 of everything
A properly designed and set up ducted modulating heat pump is pretty much silent. Except for very cold days, it will be putting along at low fan speed, you won't even know it is on.
Ducting is not hard. Good tin snips, one of those power shears for your drill, duct crimper and a couple of hand benders (I use a standing seam hemming tool). Not rocket science. If the ducts are inside conditioned space, you also don't need to insulate them which saves a lot of labor, for some reason this fact is missed south of the border.
If you want full diy, you can look at MrCool Universal DIY. Uses quick connect fittings for refrigerant. The semi DIY option is much better as you have much more choice (and better price) for the equipment.