I am very frustrated buy the HVAC choices available here in the USA, particularly heat pumps..  Other than a few mini splits, US forced air heat pumps drop to a COP of 1, or less if the outdoor temperature is much below freezing.  Further the few heat pump water heaters available all heat water by cooling the indoors.  I'm thinking of developing my own "adapter" unit.  What I have planned could be installed on nearly any home that currently has an air source heat pump and electric water heater.  It would use the existing  indoor and outdoor coils and fans and "tie into" the hot and cold water lines.  It would  become a heat pump water heater that would become the primary heat source for domestic hot water by cooling the indoors with cooling performance about 10 % greater than what was there , in summer or cooling the outdoors when AC is not needed.  In winter heating capacity at mild temperature would be increased by 15% or so and would hold at that new level to about   zero f where the COP=2+.  COP would drop to 1 at about -13f.  Assuming the modified system was a "4 ton"  system, the heating capacity would be 40,000 BTU/h.  The new " equipment" would be located indoors, occupy about 2 sq ft of floor space, operate rather quietly @ 40 Db or less and add about 3000 BTU/h of heat under full load.  It would "modulate" it's output and energy use down to 10% of max before " shutting down".  The "adapter block" would contain an EVI compressor driven by a variable frequency drive (inverter), a reversing valve and several electronic expansion valves along with a "control package".  The "control package" would also control the existing "blower" and outdoor fan.  Installation would require "decommissioning" the present system, "bypassing" the expansion valves, compressor and reversing valve, plumbing into the refrigerant lines and water lines, wiring fans, power and several temperature sensors, vacuuming the lines and starting the new system & adjusting refrigerant quantity.  I'll estimate the "adapter block" could be built and sold for about $3000 and installation would take about a man day.  Should I go for it?  How about crowd funding?



     

I personally share your frustration, but I don’t personally favor heat pumps in general because they require compressors, motors and refrigerant...which in addition to being environmentally unfriendly from a manufacturing and life-cycle perspective also lead to higher maintenance, shorter life and often unfavorable ROI even when you do happen to achieve the higher COP. I think a better long term goal would be low electric utility rates accomplished by large scale implementation of renewable energy technology that would result in simple electric boilers being the only heat source solution allowed in the future. Unfortunately, that vision upsets the billionaires who are currently heavily invested in fossil fuels and all their associated companies and political puppets. It will most certainly require a crowd and perhaps even a revolution to change things for the better.

Consider picking some specific low temp mini or multi split (eg, Fujitsu AOU12RLS3) and build a refrigerant to water "head" for it. Shouldn't cost so much. Also review what Chiltrix has done.

Jorr,
I have considered it! My opinion is it's much more work and development expense and adds an outdoor unit. Simply replacing the indoor portion with a water heater looses the "free" hot water in summer and still costs more than my approach.. I'll look up Chiltrix.
  Well I looked up Chiltrix They sure don't make much of a claim for cold weather performance so I doubt that they use an EVI compressor (they cost more, require some added parts and need a bit  "different" design).  Without vapor injection some heat out at -14f is possible but the COP and amount of heat out are dramatically lowered.  They still have a cooling dominated design with the compressor outdoors.

I don't know, it sounds like an awful lot of work to build something that would easily interface with a wide variety of different installed heat-pump systems as this cat has been skinned quite a few different ways over the years. It sounds like it would be far easier, like Jonr suggests, to design a system around existing efficient components.

Then you need to consider your market. Anyone with a newer system probably isn't going to want to have it decommissioned to install your augmented core. Someone with an older system probably isn't interested in putting a substantial amount of money into the core, when all the components are reaching the limits of their projected service life.

Is it a good idea? Sounds like it could be. But your potential market is probably looking for new(shiny) and efficient, and that is where the mini's are rolling. What you need to put together is something that has the positive attributes of a mini with water heating and the selective heat source rolled into the package...

Have you built one yet?

Chiltrix claims a COP of 2.97 at -14F. 5.31 at 32F. I agree that it doesn't lend itself to retaining waste heat (from summer AC) for DHW. But one can just buy a Geospring ($1K) to get that.

The Chiltrix name is being thrown around a lot. Does anyone have one or knows of any installed?

ChrisJ

Green Building Advisor reported a user experience:

Jeffrey Eastman of Athens, Tennessee, is a GBA reader who installed a Chiltrix heat pump. The installed cost of his heating and cooling system was $16,000. He is very satisfied with the system’s performance.

“We had to do some backpedaling to make it work,” Eastman told me. “There really is no skill set for a hydronic system here in the South. The skill set is not as widely available as up north. We’ve learned that you need commercial levels of pipe insulation for the pipes from the outdoor unit that go to the air handlers. That’s been a little frustrating. I was getting insufficient heat. The pipes are outside. When I put my hand on the pipes, I could feel heat loss. I had to put another layer of insulation over it. For longer pipe runs, like one of our runs that goes upstairs, we found out that we needed an auxiliary pump, to make sure that we have full flow up to the second floor.”

In light of the design and installation glitches that Eastman encountered, he has some advice for homeowners interested in a Chiltrix system: “You have to have a mechanical engineer.”

Read more: http://www.greenbuildingadvisor.com/articles/dept/musings/air-water-heat-pumps#ixzz43CMNNApi

Liebler, I want to see if I am understanding your proposed system correctly: It's an indoor compressor with a bunch of valves that can send the hot refrigerant to the indoor fan coil, the hot water tank, or the outdoor fan coil, and can send the cold refrigerant to the indoor fan coil or the outdoor fan coil. Do I have that right?

What I like about the Chiltrix system in comparison is that it has more water piping and less refrigerant piping. That means it's less likely to release refrigerant to the atmosphere.

And you can store water in a storage tank and you don't have to worry about things like oil/refrigerant separation at low flow rates.

chrs,
You have the general idea. However, I plan on the DHW heat ex changer and a pump for it being in the "box" with the compressor etc. Also in the box will be a "reversing valve" so either hot or cold refrigerant will go to the outdoor coil and the indoor coil. The box will have 2 pipe connections to the water system. 2 tube connections to the outdoor coil and 2 tube connections to the indoor coil. There will also be wires from the indoor box for the fans and temperature sensors in the outdoor coil and indoor coil

One challenge is that controlling the speed of single-phase induction motor fans can't be done easily and efficiently. So getting the full benefit of modulation would be hard, if you plan to interface with existing fans. All in all, as much as I like your idea, I think Chiltrix is more likely to succeed in more situations.

Take a look at Nordic Heat pumps I like their air to water design,
http://www.nordicghp.com/product/nordic-products/air-source-heat-pumps/air-to-water/