Dual compressor heat pump

[Piwoslaw]

Anyone know where I can find info on heat pumps with more than one compressor? There are models with 2 compressors which come on independently depending on load. I wonder how they are plumbed together: just plain parallel, or with some complicated valves?

Googling shows that often "dual heat pump" mean either a split (both heating and cooling) or a heat pump assisted by an electric/gas heater.

[NeilBlanchard]

These are the best commercially available dual stage heat pumps I know of:

Hallowell International - Heating and Cooling Systems

[Xringer]

At that Hallowell site is this paper. http://www.gotohallowell.com/images/...te_PaperLR.pdf

It has diagrams showing the dual pump setup..


I'm glad that I can get away with just one compressor in my Sanyo..
It's never Maine Cold down here in Massachusetts.

[NeilBlanchard]

But, their efficiency is almost as good as a groundwater geothermal heatpump, so it would be great to have this down here in "warm" Massachusetts! Especially, if you were powering it with renewable electricity...

[Xringer]

If the Sanyo keeps working, I foresee using very little oil during the coming years.

With NStar charging about 20 cents per kWh, my single compressor Sanyo seems
to be burning up about 1/4 to 1/3 the money needed for oil heat alone.

It's April, but still cool around here. So we are still heating the house.
http://ecorenovator.org/forum/projec....html#post5090
And, we are using less than 4 kWh per day..

So, even if NStar is someday forced by Cap-n-Tax to increase our rate to $0.40/kWh
we will still be saving money using the Sanyo mini-split.
(And, I'll bet that oil prices will not have dropped)..

Maybe by then, my wife will become more accepting of PV on our roof..

This week, we saw a local install by these guys..
Where We Work - Massachusestts and New England - SunBug Solar

It sure looked sweet to these old eyes..
I have a feeling that even a small array on my small roof would pay
for heating & cooling this small house..


IMHO, the inverter type mini-split ASHP is nearly the equal of GSHP
when used in the Boston area. But, it's the installer cost that makes
the old GSHP take a lot longer before break-even.

[Piwoslaw]

I found a picture of a heat pump with dual compressors.

You can clearly see that the compressors are simply plumbed in parallel, with no valves. This is not a cascade of two heat pumps, this is one HP with two compressors, everything else is common.

From what I've read, the controller turns on only one compressor at a time (in an alternating fashion). Some controllers keep an account of how much on-time each of the compressors has had and turns on the one which was used less often. When one compressor takes too long to do its job, then the second one kicks in.

So building one of these can't be much harder than a normal HP: two identical compressors plus everything else sized for a compressor twice as big. Making the controller would be a little harder, but still doable.

[charlesfl]

mcquay dot com application guide ag 31-11
refrigerant piping design guide
application guide technical bulletins

[charlesfl]

I tried to put website in but wasn't allowed.
Hope this helps. charlesfl
There are more application guides available if needed

[AC_Hacker]

Originally Posted by Piwoslaw

You can clearly see that the compressors are simply plumbed in parallel, with no valves.

From what I've read, the controller turns on only one compressor at a time (in an alternating fashion). Some controllers keep an account of how much on-time each of the compressors has had and turns on the one which was used less often. When one compressor takes too long to do its job, then the second one kicks in.

I'm really not an HVAC technician, but I think that they work differently...

Here is a quote I found on this page:

...two compressors of these Trane Heat Pumps help with the efficiency rating because when there is a mild day, the smaller compressor of the two will work while the large compressor will work on the days that it may be extremely hot.

...and on this page:

Two compressors are better than one. That's the message from HydroDelta, the latest manufacturer to announce a dual-compressor, ground-source heat pump. Most of the time the smaller of the two compressors can meet the house's heating or cooling load. Running the smaller unit closer to its capacity uses less energy. When the smaller compressor can't keep up, the larger one takes over.

And there is another efficiency booster. The evaporator and condenser coils are sized to match the larger compressor, so they are oversized for the smaller one. The dual compressors help HydroDelta's Meg-Tek heat pump reach very high efficiency with COPs up to 4.1 and EERs as high as 20.7.

So, I think that it would be needed to use a simple check valve on the compressor output line of each compressor.

It also seems to me that with an arrangement like this would work pretty well:

• Compressor #1 = 400 watts
• Compressor #2 = 650 watts
• Compressors #1 + #2 = 1050 watts

An arrangement like this could give you three speeds with only two compressors.

-AC_Hacker

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[kbonk]

Looks like Hallowell is out of business? anyone confirm? How do they cascade compressors?