Air to water heat pump system design
Hello again!
I’m anticipating movement for the arrival of more efficient air to water heat pumps here in the USA. Perhaps that is too optimistic but technology, especially utilizing refrigerants like R32 and R290 are expanding to more manufacturers almost daily.
Nonetheless, I want to be prepared for that eventuality.
Currently, I am not efficient when it comes to making water hot. For domestic hot water I have a 40 gallon electric hot water heater. For a 560 sq ft extension I have an insulated concrete floor (2 loops, 1 zone) heated by a 28 gallon electric hot water tank. The main part of my home is heated by a two zone, air to air heat pump. Needless to say, my energy costs are electric with a good portion of it making hot water.
Looking to the near future (hopefully) I want to do away with the two electric water heaters and install an air to water heat pump for DHW and for the 560sq ft radiant floor. I want to keep the radiant floor a closed loop so I imagine a mixing valve would be needed.
Is it possible to keep the radiant floor closed looped and provide adequate DHW at a higher temp? How many storage tanks would be involved?
I’ve done everything thus far in this house including the air to air heat pump, radiant floor and incorporating it to its heat source. This leap forward kinda scares me particularly sizing issues.
Any wisdom is greatly appreciated.
Comments
-
With AWHP, you can connect it directly to your floor heat loops. Most units can read a room temp and control the ouput based on that so no need for zone valves or existing thermostat.
You can also leave in the exisitng tank and use it as a buffer so AWHP feeds buffer tank, zone valve/pump takes heat from the buffer tank to the floor heat.
The DHW would have to be an indirect connected with a 3 way valve to the AWHP.
You can look at the setup here of what you roughly need:
The issue is the BOM cost of this is too high, so ROI is never. Unfortunately cheaper to get some extra PV to offset the cost of the resistance heat.
0 -
Domestic hot water is a poor fit for air-to-water heat pumps designed for space heating. Yeah, they'll do it, but compared to a heat pump water heater inside the house you don't save anything on operating costs, nor on installation costs, nor on space required, and you end up with a system that is more complicated and less reliable.
With all that said, during heating season heat pump water heaters take heat from within the house, so their efficiency is entirely dependent upon the efficiency of the house heating system. If that's a heat pump the combined efficiency is pretty good. If heating is coming from resistance electric, the combined efficiency is worse than if you just had a resistance water heater.
0 -
The simplest, cheapest way to do air-to-water under-floor heat is to get a unit with outdoor reset (I think they all have it now) and plumb it direct to the under-floor loops. No thermostats, no zone valves, no buffer tanks, no circulators other than the one in the heat pump. Get the curve of the outdoor reset dialed in and there you have it.
It won't hold temperature as consistent as a system with thermostatic control, but it will do a pretty good job. If there's a minisplit in the same building that will take out some of the fluctuation.
0 -
it depends on the brand and model you buy. Several brands ship with a buffer tank, viessmann has a dhw tank option also.
Caleffi has a line of wall hung buffers that we sell in other market. European systems tend to go with wall hung components
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Kaos,
Thanks for your insight. I like using 28 gal electric hot water heater as a buffer between the HP and the radiant floor manifold. I’m sure there would be no need for the elements to be electrified. I suppose a 3 way valve could add return side water to moderate the temperature to the floor. Would I be able to keep the radiant floor side a closed loop?
Also, I live in NY State and the codes are quite stringent. You mentioned an indirect tank for DHW. That would mean the DHW tank coil would be heated from the HP output which has antifreeze. Is there a code issue having the two in a tank with only the one coil or does the DHW have to be in separate coil within the same tank?0 -
those NEW refrigerants have nothing to do efficiency!
0 -
forget codes. Again they have nothing to do with efficiency. Concentrate on cost of operation and longevity.
0 -
DCContrarian,
I understand the concern about AHWHP being a bad fit for DHW. Unfortunately, the waiting game in North America for the release of better fitted units may force my hand to existing alternatives. There are however impressive AHWHP’s elsewhere that change the dynamics. For instance, Carrier just released a R290 AHWHP with a very high water temperature, at very low outside temperatures with solid COP’s.
I really don’t think it’s worth the cost and effort to change what I have unless I what I install can handle the two sources of heat I need, hot DHW and less hot radiant floor heat.0 -
Pecmsg,
If I look at my existing situation, using electricity via elements to heat water I believe my COP is 1 to 1. If I want to improve that equation what do you suggest? Supposedly, AHWHP COP’s can achieve 4 to 1 which I believe would significantly reduce my operating costs. That COP comes from the use of R290 as a refrigerant. How else am I to think of this?
0 -
4 to 1 at ideal condations Look at the low temp COP. Low temp 1.5 to 1.1 Still better but not there yet!
0 -
The bad fit is due to fundamental physics, it's not something that more refined products are going to fix.
0 -
You don't say what your priorities are.
If it's simply saving money, heat the space with an air to air heat pump. You may even be able to add a zone to the one you already have.
If the comfort of heated floors is worth the expense to you, but you want to save on operating costs, get an air to water heat pump.
If you do either of the above, you can get a heat pump water heater and replace the existing tank.
-1 -
Where you get 1.5 to 1.1 from? Floor heat needs 100F or so, my AWHP does a COP higher than 2 any time above 10F, some of the r290s would be closer to 3. Very few places spend much of the heating season bellow 10F.
1 -
@DYI2day Temperature of the water with an AWHP costs you COP. You never want to make water hotter than what your emitters needs, so no mixing.
The 3 way valve I mentioned is for selecting between the emitters and your DHW tank. When the AWHP goes into domestic heat mode, it switches over to the 2nd circuit and bumps up the water temp. Once done, it switches back to low temp mode and continues to feed your space heat.
The indirect tank has a coil in for the the connection to the heating water, this separates the space heat water from your domestic hot water. The space heat loop is a closed system.
1 -
Regarding 4 to 1 COP’s. “They’re not there yet?” It may be more accurate to say, “ they’re not here in America yet.”
0 -
The pictured Carrier AWHP is an R290 Snap unit just launched in Europe. The Carrier Snap series here uses R32 which is not as remarkable as the R290.
Yeah, it’s lower operating cost I’m trying to achieve especially with the harsh winter’s in my neck of the woods. Yes, low outside temps lower the COP’s in general. That’s why refrigerants matter, a lot.
Though the technology exists the regulators are dragging their feet, it’s frustrating.0 -
The R290 is not legal here in America. For insurance reasons that can be dangerous as r290 is very flammable. So if a explosion or fire happens no insurance will cover an unapproved product.
I am the walking Deadman
Hydronics Designer
Hydronics is the most comfortable and energy efficient HVAC system.
1 -
R-290 and R-600 ARE legal in refrigeration just restricted to no more then 5 or 6 oz total charge.
1 -
aren’t some of the mini splits sold here already running 290?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
A COP of over 4 is easy to achieve. I graduated from the Heat Geeks Mastery courses. It is three courses and over 100 hours of training. I also have many other certifications in hydronics and radiant heating. I have over 40 years of training. I train, design and consult for installers of ATWHP systems for a living now. Adam Chapman (Founder of Heat Geeks Engineers) says in the video below "The main variable for Heat Pump performance is installer training" I can help you achieve a SCOP of over 4 with proper training. This is not possible with older houses that have existing radiation and need higher temps. I am training Americans on the East Coast right now!!
2010 U.K. national average 2.4 SCOP
2017 U.K. national average 2.6 SCOP
2024 U.K. national average 2.8 SCOP
Heat Geek graduates out of a 107 installers field measured and verified by installed monitoring equipment.
Heat Geek average 4.15 SCOP
Heat Geek Elite 4.55 SCOP
https://openenergymonitor.org/
Heat Geek video on SCOP over 4
https://www.youtube.com/watch?v=RlcvncWvNUQ
I am the walking Deadman
Hydronics Designer
Hydronics is the most comfortable and energy efficient HVAC system.0 -
No. They will never let R290 run inside the house. It is approved in Europe for ATWHP monoblocs only. The limit for R290 is to small to work in a ATWHP here in America. ASHRAE is working on approval.
I am the walking Deadman
Hydronics Designer
Hydronics is the most comfortable and energy efficient HVAC system.1 -
If they can do it with less than 6Oz total charge fine.
0 -
Mini Splits require r290 to be ran into the house and a technician to make the fittings. It will never see approval. Maybe in a refrigerator it might meet approval.
I am the walking Deadman
Hydronics Designer
Hydronics is the most comfortable and energy efficient HVAC system.0 -
I said that about R-290 and 600 and look what happined!
1 -
https://naturalrefrigerants.com/ashrae-committee-chair-expects-2025-or-later-for-approval-of-higher-r290-charge-for-heat-pumps-in-u-s/
I am the walking Deadman
Hydronics Designer
Hydronics is the most comfortable and energy efficient HVAC system.0 -
R290 refrigerant, for those who haven't read the data sheet, is just a very highly refined propane. It is a good refrigerant — it has some very desirable properties from that standpoint. Unhappily, it also happens to be highly flammable as well. In fact, a somewhat cheaper and less refined version is sold as "LP gas" as a fuel. It forms explosive mixtures with air over a remarkably wide range of concentrations.
A minor detail, perhaps.
There is another aspect to this discussion, however, and I must apologise to @Erin Holohan Haskell in advance here, and ask her to either edit this or take it down, if she feels it's out of line. That aspect is economic, and can be seen both in the resistance in much of the US and Canada to the idea of air to water or air heat pumps, but perhaps even more dramatically in Europe, where regulators and government have more power to attempt to force change. The plain fact is that a substantial minority — if not indeed a majority — of the population simply can't afford to make the necessary upgrades in their housing to make use of heat pumps even remotely feasible, nor can they afford to purchase a heat pump system if they could. The money simply isn't there. As has been seen in Europe (particularly the UK), if people are forced to stop using their old fossil (or wood) fueled heating systems, they will simply be cold.
If I consider my own parish and the region in which it is located, I estimate that no more than one in four of the houses and other housing units in the area could be heated adequately with a heat pump only without major upgrades to the house or unit (and that may be optimistic) and I am quite certain that no more than a fifth of the population could afford to do the upgrades and install a heat pump — even with the government subsidies.
Mind you, I am not opposed to heat pumps. There is one in an apartment where I live and it takes the edge off the cold for the lady who lives there (Cedric does most of the work, though). In their place, for those who can afford them, they are a very good way to provide heat (and cooling!) and comfort. For those who can't, they are in the same class as filet mignon, vacations in Spain, BMWs and Lexus cars, and so on. Either nice to look at or a source of anxiety and fury, depending on the situation.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
2 -
There is huge growth world wide in ATWHP sales. In 2022 the growth was 22% and sales 4.95 million. In the U.K the vast majority of HPs are ATWHP by a huge margin. Here in the North East I have a lot more LEEDS than I can handle. Its a booming and growing business.
I am the walking Deadman
Hydronics Designer
Hydronics is the most comfortable and energy efficient HVAC system.1 -
Agreed. It is. Shame that more people can neither afford nor make use of them, Ed Milliband notwithstanding.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
I like my heat pump. The problem is there are not enough tech out there that can fix simple A/C’s much lessheat pumps, inverter technology, speed drives on and on. We’re not even going to discuss the infrastructure that’s needed to go with all electric!
1 -
John Ruhnke,
I read that article concerning ATWHP refrigerant approvals. The key words are “2025 or later…”
I’m not one who has disregard for the environment. I once defended the EPA at a party discussion. A gentleman came over and gave me an earful. He was a high tech boiler engineer who has dealt with ridiculous regulations he aptly described as “just what the manufacturer’s money wanted.”
I’m afraid that is precisely the issue with moving the ball forward for R290 monoblock approval here in the United States0 -
"R290 refrigerant, for those who haven't read the data sheet, is just a very highly refined propane. It is a good refrigerant — it has some very desirable properties from that standpoint. Unhappily, it also happens to be highly flammable as well. In fact, a somewhat cheaper and less refined version is sold as "LP gas" as a fuel. It forms explosive mixtures with air over a remarkably wide range of concentrations."
That's true, but in a monobloc configuration no refrigerant every enters the house.
1 -
"I estimate that no more than one in four of the houses and other housing units in the area could be heated adequately with a heat pump only without major upgrades to the house or unit."
Care to share the basis for that estimate? I see people throwing in minisplits all over the place.
0 -
Come and walk around my parish with me and talk with people. Real people. Look at real houses. Real houses. I forget the exact median family income in town, but it's somewhere around $70,000, and in almost every family both parents (or adults, in childless families) are working. Most families own their own homes (very few rentals). A good many are "housing poor" when property taxes and maintenance are factored in, never mind a mortgage.
And you want these people to scrap a perfectly good, if older, heating system which works and install some fancy new gadget which won't heat them adequately in January, and pay half their income for it? You want them to tear apart their home to install insulation everywhere and pay another half?
Those numbers and dreams may work in the wealthy suburbs east of here. Not here. Not in the two bigger "cities" west of us.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England1
Categories
- All Categories
- 86.5K THE MAIN WALL
- 3.1K A-C, Heat Pumps & Refrigeration
- 53 Biomass
- 423 Carbon Monoxide Awareness
- 96 Chimneys & Flues
- 2K Domestic Hot Water
- 5.5K Gas Heating
- 101 Geothermal
- 156 Indoor-Air Quality
- 3.5K Oil Heating
- 64 Pipe Deterioration
- 928 Plumbing
- 6.1K Radiant Heating
- 384 Solar
- 15.1K Strictly Steam
- 3.3K Thermostats and Controls
- 54 Water Quality
- 41 Industry Classes
- 48 Job Opportunities
- 17 Recall Announcements