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Affordable air-to-water heat pump

First, just want to say thank you to Dan for starting HH and to all the members here for your frequent insight and dedication to the craft. I stumbled upon the site a few months ago and have already learned so much!

There are a handful of mid-size air-to-water heat pumps out now (SpacePak and Chiltrix have been discussed here, and I've also looked into Arctic and Nordic) but it seems they are still a bit of a niche item compared to minisplits, with a premium price to go along. Most are also monobloc designs, thus requiring either an extra heat exchanger or glycol in the entire loop.

The Gree FLEXX / Mr. Cool Universal (apparently also sold as GE Connect Series and the Innovair Flex) has an outdoor unit meant to pair with either their own or a third party air handler, offered in a 2-or-3 ton or 4-or-5 ton version (just two hardware versions, with dip-switch selectable capacities). It uses standard 24V thermostat wiring for control. According to Mr. Cool, the outdoor unit "monitors line temperatures and pressures and ambient temperatures to govern the compressor operation." and "The condenser has an electronic control board which monitors several different temperature sensors and adjusts the variable speed compressor to handle the load it is under." This is an R410A unit.

Could this unit work in a hydronic system? Other than a heat exchanger, electronic expansion valve, circulator pump or zone valve, and some controls, what else would be required in the 'indoor unit'? Is this available as a packaged unit or would it need to be site-built?

Luke

Luke Stodola

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,817
    edited April 2021
    I don't quite understand what you want to end up with. Are you looking to heat water to run thru radiators? Are you looking to make potable hot water?

    The DHW heat pumps are already on the market. check them out here. https://www.energy.gov/energysaver/heat-pump-water-heaters

    if you are looking at heating radiators or radiant floor heating with a heat pump, then you may want to look at this company with the same ideas.
    https://www.imsheatpumps.co.uk/blog/can-i-use-radiators-with-a-heat-pump/#:~:text=Answer: Yes, you can use,calculate whether to replace them.

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • lkstdl
    lkstdl Member Posts: 41
    edited April 2021
    Thanks for the reply Ed. This would be for space heating & cooling, using a combination of convectors, fan coils, and radiant floors/walls. Part of me is just curious from a "how things work" / "why don't we see this more" perspective, but I'll provide the backstory for my particular application in case its helpful.

    I am redeveloping an old industrial complex in Rochester, NY into mixed use spaces: roughly 80 units, between 200 and 7500 sq. ft. each, 100K sq ft total, used as workshops, storage, art studios, offices, and live/work units. We have already renovated and rented out about 40 of the spaces over the past few years. This year we will be doing the remainder, and continuing to upgrade the existing spaces.

    I am trying to figure out the best way to heat & cool the spaces going forward. I've learned a lot from Siggy's book, Caleffi's Idronics journal and 'Coffee' talks, and this forum, but I'm still pretty new to hydronics.

    There is currently a mix of older natural gas unit heaters, condensing gas furnaces, electric space heaters, and either no A/C or window/portable A/C units.

    Some tenants will keep their space at 72F all the time, some are fine with it at 50F, some just want it above freezing. This 'setpoint' changes (even in the same space) over time depending on tenant turnover & even just growth of their business. Its hard to do precise load calculations when the setpoint is so variable. We are also continuing to do improvements to the building envelope (adding insulation, new windows, etc.) that will further change the heating/cooling load over time.

    One option would be to have minisplits in each unit, but sizing them to cover cold weather peak demand would make them oversized the rest of the time. From what I've seen, typical minisplits have a 5:1 (or less) turndown ratio, resulting in short-cycling.

    A central hydronic system is appealing. The load diversity of the entire building would smooth out the heating/cooling demand. 10 of the 5-ton heat pumps would cover the expected cooling load and much of the heating load. A half dozen 199K natural gas mod-cons would provide additional heat (with a 50:1 turndown) and could be automatically switched on whenever conditions warranted. There's a lot of redundancy, allowing for equipment maintenance without leaving tenants in the cold. Maintenance is easier with everything in one place rather than spread all over. Additional convectors or fan coils could be easily added. If the tenant makeup changed over time resulting in increased total loads, more heat pumps could be added as needed. If it decreased, we'd just have even more redundancy.

    This all hinges though on finding a cost-effective air-to-water heat pump. The ones I have seen are roughly 4 or 5 times more expensive versus a mini split (on $/ton), so once the cost of distribution piping, circulator pump(s), and the terminal units for each space are added in this solution would be significantly more expensive than minisplits.

    Is there something intrinsic about air-to-water that makes it so expensive? Or is this still a bit of a boutique market compared to minisplits?

    Luke

    Luke Stodola
  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    It's partly that it's a boutique market. It's also, however, partly due to the minor detail that hydronic systems run at significantly higher temperatures than domestic hot water -- and the greater the temperature differential between the heat source, the more compressor power is needed, and you may have to go to different (more expensive) refrigerants.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    lkstdl
  • lkstdl
    lkstdl Member Posts: 41
    That's true for many traditional baseboard or radiator systems, but my understanding is that a typical modern hydronic system is designed to require a maximum of 120F water, and much of the year will be using even cooler water. On the other hand, due to Legionella concerns our DHW needs to be heated to 140F.

    What are the typical evaporator and condensor temperatures for an air-handler-based R410A system? Wouldn't they only need to be 10F or so beyond the desired water temperature?
    Luke Stodola
  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    lkstdl said:

    That's true for many traditional baseboard or radiator systems, but my understanding is that a typical modern hydronic system is designed to require a maximum of 120F water, and much of the year will be using even cooler water. On the other hand, due to Legionella concerns our DHW needs to be heated to 140F.

    What are the typical evaporator and condensor temperatures for an air-handler-based R410A system? Wouldn't they only need to be 10F or so beyond the desired water temperature?

    Your understanding is correct -- for a brand new system designed to operate at very low (condensing) temperatures. Most new installs aren't, except for radiant floor designs It is much more common to use around 140 or sometimes even higher as the return temperature.

    Not that systems other than radiant floor can't be designed and installed to run on 120 or less, they can. But they are going to cost more -- like a lot more. Roughly double for the radiation and piping. This can be a real tough sell, except among the elite with money. If your planning to retrofit something, raise that again -- as you will have demolition and removal of the old system.

    Reality is such a bore.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    lkstdl
  • hot_rod
    hot_rod Member Posts: 22,114
    I'm just starting a shop at my place, 24 X 36 with inslab tube. I hope to heat and cool here in arid Utah, maybe a 2 ton size A2WHP.

    What brands have you considering? I believe there are around 8- 10 brands in the smaller residential sizes, under 5 ton.

    Looks like Mitsubishi is getting ready to release on also. If you stay in that 120° and below range, you should not need a cold climate version, which tend to be more $$ and complex.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    lkstdl
  • lkstdl
    lkstdl Member Posts: 41
    edited April 2021
    Jamie, although this is an existing building, there are only random remnants of an HVAC 'system', so I would be putting in all new radiation & piping, and designing the system for milder water temperatures. The heat pumps are needed for summertime cooling. Personally I'm happy with an open window but some people like A/C. So if I gotta buy a chiller anyway, might as well make it a heat pump & use it for heating when it makes sense, switching over to the natural gas mod-cons as the temperature drops.

    Bob, the models I've looked into are:
    Chilltrix CX-34
    Nordic ATW-75
    SpacePak LAHP48, SIS060, and SCM-060
    Arctic 060ZA
    RBI RHP0275
    Aermec PACV
    Samsung DVM

    These are generally priced at between $0.12 to $0.26 per Btu/hr capacity. This seemed high to me considering a standard outdoor unit like the Mr. Cool Universal (i.e. one that is meant to be paired with an air handler) is closer to $0.05. Is there really that much cost & complexity in the indoor unit?


    With some more googling I did find some companies offering split systems using standard off-the-shelf outdoor units:
    Thermatlantic DX2W-3
    Electro Industries NorAire
    Has anybody had experience with them? Both seem like fairly small companies.

    I'm wondering if I could just use a single, larger EEV & brazed plate heat exchanger (like the Alfa Laval ACH232DQ-138H-F?) for multiple outdoor units. It could be cheaper than a dozen smaller heat exchangers but it would mean a single point of failure (a refrigerant leak, fouled heat exchanger, etc. would affect multiple units).

    Luke Stodola
  • kaygeemaine
    kaygeemaine Member Posts: 3
    Ran a Spacepak LAHP2 AWHP at our midcoast Maine home for 5 years. Lovely quiet hydronic heat until the compressor quit. Our installer retired. Trouble getting a tech on site and not sure we can even get a replacement compressor. Chopping wood til we figure this out. Maybe the newer inverter model has more promise…but this was a heck of an investment for a mere 5 years of service.
  • pecmsg
    pecmsg Member Posts: 4,839

    Ran a Spacepak LAHP2 AWHP at our midcoast Maine home for 5 years. Lovely quiet hydronic heat until the compressor quit. Our installer retired. Trouble getting a tech on site and not sure we can even get a replacement compressor. Chopping wood til we figure this out. Maybe the newer inverter model has more promise…but this was a heck of an investment for a mere 5 years of service.

    Compressors don't die there murdered. What failed, LRA, Burned or shorted wiring, mechanical? Before replacing or shortly thereafter find out WHY it failed so quickly!
  • WMno57
    WMno57 Member Posts: 1,256
    @kaygeemaine Call Spacepak, (413) 564 - 5530
    Spacepak's warranty page
    https://www.spacepak.com/warranty-policy
    Spacepak's Certified Installer page
    https://www.spacepak.com/certified-installers
    Is there someone on HeatingHelp from Spacepak or Mestek who can help their customer?
    I DIY.
  • tim smith
    tim smith Member Posts: 2,752
    Why not go Geothermal water to water. Upfront cost will be more but long term maintenance repair will be less. Also tax credit. Much more proven. Sounds like a large enough site to accommodate it.