Dual compressor heat pump

[NeilBlanchard]

Hi,

I have it from two sources that Hallowell is out of business -- a friend of mine who owns one of their Acadia systems, and from someone I know who lives in Hallowell ME. They are "victims of the economy". Which is sad, since their heatpumps were so efficient.

By the way, if you are ever in Hallowell ME (just south of Augusta, the capitol) you have to have lunch or dinner at The Liberal Cup, and try one of their brews, as well. Excellent food and beer.

[Xringer]

It's been a while too..

City official confirms Bangor heat pump firm out of business — Maine Business — Bangor Daily News

NH man has fix for failed heat pumps made by defunct Bangor manufacturer — Maine Business — Bangor Daily News

[Paul_L]

Hi Piwoslaw,

Most heat pump manufacturers are really just assemblers. They don't have extensive engineering departments. In the US they depend on the engineering departments of the compressor manufacturers, Copeland and Tecumseh. Attempts to use multiple compressors with a common condenser, expansion valve and evaporator are usually very tricky.

The evaporator, condenser and Freon charge will be sized according to the displacement of both compressors running simultaneously.the condenser will be mostly filled with Freon gas which will be releasing its heat of vaporization. A small amount of Freon liquid will be in the bottom of the condenser. The expansion valve will be sized to allow sufficient Freon liquid to flow to the low-pressure side. The evaporator will mostly be filled with Freon liquid absorbing its heat of vaporization. A small amount of Freon gas will be in the top of the evaporator.

when you switch off one of the compressors a lower body among Freon wolfs, the expansion valve throttles back, releasing less Freon liquid into the evaporator, more Freon liquid accumulates in the bottom of the condenser, and less Freon liquid accumulates in the bottom of the evaporator. The condenser releases heat by condensing the gas, not by cooling the liquid. The increased liquid in the evaporator results in less heat being released. Similarly, the evaporator absorbs heat by vaporizing the liquid, not by heating the already vaporized gas. The increased liquid in the condenser results in less heat being absorbed.

I think that you're probably better off with one compressor. The chief reason for using multiple compressors would be to limit starting current if your electric service is not capable of delivering the high in Russia current. The two compressors would start sequentially a few seconds apart.

( how are things in Warsaw. My grandmother came from Bialystok, my grandfather from Kraków.)

Paul_L
(Pavel)

[Mikesolar]

There are many situations when multiple comps are used with no problems. The problem with Hallowell is that they used a Bristol comp and made changes to it that Bristol did not condone. It was a troublesome system from day one and they left a number of people in the lurch with warranty issues.

That said, there are many ways to get great low temp performance without two comps. Large evaporators, liquid or vapour injection and VSD are just some of them. The biggest single improvement to an ASHP is to use the lowest output temp possible which means floor heating and not forced air. The system (house insulation and floor tubing) needs to be designed for 30C max temps and with this the COP will be acceptable.

[AC_Hacker]

Originally Posted by Mikesolar

...The biggest single improvement to an ASHP is to use the lowest output temp possible which means floor heating and not forced air. The system (house insulation and floor tubing) needs to be designed for 30C max temps and with this the COP will be acceptable...

So, when you say 30C (86F) max temp, you are talking about 30C being the temperature of the water going into the hydronic floor, right?

I agree that this would be a highly desirable temperature as regards your ASHP efficiency.

I wonder if you could go into some detail regarding what your understanding is of the house insulation and tubing requirements to make this happen.

Also when you say that the COP would then be acceptable, what in your opinion would be an acceptable COP in this case.

Thanks,

-AC

[Mikesolar]

Yes, 30C being the highest temp going into a floor. There is a move to SCOP over COP because we should be looking at annual bills for the real indicators.

With the use of an outdoor reset mixing valve on the floor heating, we can often keep the temp to 24 -28C at milder temps which, with the right HP, could give a COP or 4 or better.

My friends in europe are putting tubing at 100mm(4") in many cases which until a few years ago I would only do in a sunroom. Now I do it most places. Tubing is a cheap one time cost.

[AC_Hacker]

Mikesolar,

This low temperature floor heating information is really great in many respects. Since it is wandering a bit off topic for a Dual compressor heat pump thread, but is especially relevant information for the DIY Hydronic Floor Heating thread, perhaps you could copy your response to THIS LOCATION.

Originally Posted by Mikesolar

There is a move to SCOP over COP because we should be looking at annual bills for the real indicators.

Very interesting... I take it that SCOP is Seasonal Coefficient Of Perfromance? It does make sense that this would be a more useful measure of performance.

Originally Posted by Mikesolar

With the use of an outdoor reset mixing valve on the floor heating, we can often keep the temp to 24 -28C at milder temps which, with the right HP, could give a COP or 4 or better.

I must admit that I have never heard of an outdoor reset mixing valve before. I just googled the term and came up with THIS USEFUL PDF DOCUMENT.

It would be very helpful if youu could go into a little more detail regarding the rationale and function of this type of valve.

Originally Posted by Mikesolar

My friends in europe are putting tubing at 100mm(4") in many cases which until a few years ago I would only do in a sunroom. Now I do it most places. Tubing is a cheap one time cost.

OK, this kind of information has been very hard for me to find but I knew it was being practiced... so I really want to know more...

I certainly see the reason behind why such close spacing is being used, my questions here, regard gaining a full understanding of how it is being done, specifically:

• How to cope with bend radius problems
• What diameter tubing is being used in these installations
• What flow rate is regarded as optimal in these installations
• What are the details if construction for such floors? (poured/not poured?, built up?, the use of high-conductivity materials?, etc)

Lastly, it is very interesting that you are living in Toronto, where your average Heating Degree Days (F) = 7223 (assuming a base temperature of 68 degrees F) or Heating Degree Days (C) = 4010 (assuming a base temperature of 68 degrees C), that folks are successfully using ASHPs.

Many of our readers live in HDD-challenged areas and have a great interest in ASHPs.

Best,

-AC_Hacker

* * *

[randen]

I had thought about building a double compressor GSHP but the complexity seamed to make it a lofty dream. I had two compressors in captivity but again the further I had looked into it it got difficult. If I was to build another GSHP I would use a 3 phase compressor and moderate the speed with a VFD. This would provide a nice soft start and you could slow it for a reduced out-put. Even still a plain single phase GSHP is pretty efficient. It starts with no load and I'm not really convinced if slowing the compressor and reducing the heat out-put when a temperature set point is reached would save a noticable amount of energy.

Randen

[Mikesolar]

Originally Posted by randen

I had thought about building a double compressor GSHP but the complexity seamed to make it a lofty dream. I had two compressors in captivity but again the further I had looked into it it got difficult. If I was to build another GSHP I would use a 3 phase compressor and moderate the speed with a VFD. This would provide a nice soft start and you could slow it for a reduced out-put. Even still a plain single phase GSHP is pretty efficient. It starts with no load and I'm not really convinced if slowing the compressor and reducing the heat out-put when a temperature set point is reached would save a noticable amount of energy.

Randen

There is a real dearth of comps with EVI or liquid injection or VFDs in our market so I was only able to find some sanyo or other Japanese comps but they are also smaller and not so suitable for our heat loads. If you ever looked inside a Mitsi or Daiken, the level of complexity is astounding. I will be putting a VFD on a standard copeland R410A comp. There are some inverter controls available for single phase, IIRC, depending on needed current draw but you have to be very careful with oil return to the comp, slow speeds can be a problem.

[Acuario]

I've just embarked on my latest project.

Having run a heatpump all last winter I did find that on a few occasions (very few though!) the capacity was a little short of what I needed and I needed to run the oil boiler - I probably only used about 20 litres of oil though so not bad really!

Anyway, as a new (second hand) twin compressor LG M19L2H U6 (LM1966H2L) unit happened to come my way I decided to link it into the system so I have some extra capacity.

The unit is rated at 5.5Kw and was designed as a twin split. So, I'll have the ability to run 1, 2 or 3 units as needed.

So far I've just done the gas tubing (photos attached). Next job is to build and program the control board - based on a PIC 16F877A development board I bought off ebay.

The plan is to run control wires to each of the 3 compressors to control the compressor and reversing valve. Also to incorporate my auto defrost control circuit (or at least the program) to defrost the units as necessary.