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buffalobillpatrick 01-08-18 01:10 PM

1/2 ton heat pump questions
Before backfilling around rear of my new house & retaining wall, I put down a 450’ loop of blue 1” pex.

I’m thinking about how I can use this loop to help heat or cool house.

The soil (ha) is really about 90% small decomposed granite gravel with about 10% clay.
It stays damp year round from Summer rain & Winter snow.

I think? it could support a 1/2 ton heat pump.

The emitter/collector could be the upstairs underfloor pex loops?

The climate has low RH, so reaching dew point is not likely??

AC_Hacker 01-08-18 02:38 PM


Originally Posted by buffalobillpatrick (Post 58155)

I think? it could support a 1/2 ton heat pump.

The emitter/collector could be the upstairs underfloor pex loops?

The climate has low RH, so reaching dew point is not likely??

Hi Bill, nice to hear from you again.

You should call around to some of your local GSHP installers and ask exactly the question you have posted. The situation varies greatly from area to area. Here in Portland, it takes a 220 fooot deep borehole to yield a Ton (12,000 BTU). Or an 80 foot trench dug 6' deep with slinkies totaling maybe 250 feet, to get a Ton.

It has very much to do with your rate of heat extraction and injection. It also has a lot to do with the 'duty

It will be very interesting for you to put a data logger on your incoming water temp, and graph it over time, say a month or two.

I predict that you will see a series of down-curves, each followed immediately by a recovery curve. And that in the long term, you will have a declining ground temp.

I'd love to see the graph.

In short, my hunch is that 1/2 T is too large. I'd go for 1/3 or 1/4 Ton. But use what you have and let us know. I am very interested!!

As to your Dew-Point question, it won't matter to the buried loop.



Ron342 01-09-18 09:39 AM

I think its going to depend a big bunch of things but largely on how deep its buried and over what area and how well compacted?
So many variables that AC is likely right - try it by running about 1/2 gpm or so from your well into a slinky of pex or poly laying in your yard to cool it to about 35f (probably nite is best) then run it thru your buried loop for at least 8 hrs while recording the temps in and out of the buried loop. Purge the air first.
I think geo systems run at about 1 gpm per ton with 8 to 10 degree difference so if it supports that without freezing you should be good at least if your demand isn't continuous.
Be careful tho not to use antifreeze and freeze the ground deep down against your house wall. You have a good length of relatively large diameter pipe - if its compacted and fairly deep, i'd bet you're good for 1/2 ton!
Good luck!

buffalobillpatrick 01-09-18 12:35 PM

Upon further study:

I think that I could use the buried outside loop to cool the downstairs slab (1440ft2) using the Pex loops designed for heating (7” OC)

Cooling needed about 4 weeks a year.

Climate is dry so this might work, I would need to avoid condensation.

It would be easy to tie into the radiant slab loops with a flat plate heat exchanger & pump the buried loop controlled by a greatroom thermostat and a dew point controller.

I haven’t found any heat pumps under 1/2 ton?

jeff5may 01-09-18 11:47 PM

Here's a handful of 1/10 ton come compressors:
Look up aspena

Ron342 01-10-18 07:27 AM

There is a common stand alone wall console type of water supply heat pump (think hospital rooms and halls and hotels) that use mid temp boiler water of 50 to 80f in winter and chiller water in summer with the heat pump boosting that. They come in different capacities from 1/2 ton to about 1 1/2t and are easy to reconfigure to ground water use and are available cheap from remodel jobs etc. And also available as ground coupled units but much harder to find.
I have a 3/4 ton McQuay in a large living room that is a big help in this weather.

buffalobillpatrick 03-03-18 02:58 PM

I think this would be good Wet slab prevention?

Honeywell HSS-DPS Early Warning Dew Point Switch

It’s a contact the surface type vs the air only type

solemamark 03-26-18 02:11 AM

1/2 ton heat pump questions

Here are answers to frequently asked questions about air conditioning.


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