The Homemade Heat Pump Manifesto

[Drake]

AC, You say your incoming water temp is 40 degrees? Should not water from ground loop be in mid 50's? And you has said how cap tube should be right one for compressor, have you saved matching tube with each salvaged comp or can proper one gotten from other source? In your Beta design the ground loop water has a "holding tank"? In theory this tank could get it "heat" from solar source as well potentially?

I too am most interested in water to water for heating. What I have found from hydro install info is 7/8 pex is recommended for best under joist heating and needs higher temp than "in floor" so if you can do even your durarock install you should be better off. Was also told efficiency of 3/8 and 1/2 pex(just need closer 3/8, maybe more loops) is same if you are really limited on wieght/thickness. And as your mystery puddle shows I have learned hydro cooling is limited by condensation problems(why A/C's have drip pans I am told). On topic of your whole hydronic system if you haven't discovered it already explore "open systems" it is exactly the install for my needs. Even incorporates some cooling possibilities.

[AC_Hacker]

Originally Posted by philb

A newby question just popped into my mind. If you are producing cool on one side of the unit and heat on the other side, could you use both? That is, pump the hot into your hot water tank with the heat exchanger before further cooling it in the ground? So, as long as you are using electricity to power the unit you might as well get all the benefit you can.

BTW, I barely understand what the HVAC stands for.
This thread has improved my definition of the word drastically!

Hello philb,

Yes, you sure could use both hot side (for heating) and the cold side (for refrigerating).

Two birds with one stone. I don't understand why more people aren't doing it?

-AC_Hacker

[AC_Hacker]

Originally Posted by Drake

Is your heat pump design reversible to "cool" radiant floor in summer?

Where I live, the days you need AC in a year are very few.

Originally Posted by electrostunt

Cooling a room with running cold water in a radiant floor is not very efficient. You get a really cold floor in a hot room... (heat rises... )

Technically, hot air rises, heat radiates in all directions. I hate to be picky, but by thinking that "heat rises", it is possible to overlook some important ideas and solutions.

Originally Posted by electrostunt

You can use a fan convector as the common choice.

Yes, I'm considering that one.

Originally Posted by electrostunt

There is also some test being done by putting the floor pipes and heat spreaders in the ceiling and running cold water in it. This should not be used for heating, as that would be inefficient.

I have read that the Germans are employing the ceiling-cooling approach in office buildings, and it is working very well. The trick is to monitor temperature and humidity so as to avoid condensation on the ceiling.

-AC_Hacker

[AC_Hacker]

Originally Posted by Drake

AC, You say your incoming water temp is 40 degrees? Should not water from ground loop be in mid 50's?

Yes, it started off at 51F, and as I have been extracting heat energy from the loop field, the temperature has been dropping. It dropped fast at first, but has leveled off somewhat to near 40F as time goes on. I can't tell how much farther it will drop. I'm also about to build Heat Pump #2 which will produce (extract) almost twice as much heat as the prototype unit. I will be very interested to see what kind of temperature drop curves that will produce. My plan is to run it intermittantly. I have an Arduino controller that will do the intermittant cycling, the next firmware will incorporate temperature sensing and duty-cycle modulation into the intermittant operation.

Originally Posted by Drake

And you has said how cap tube should be right one for compressor, have you saved matching tube with each salvaged comp or can proper one gotten from other source?

Yes, I have been very careful to save the cap tube with the compressor that it came with. That is really the key to making the homemade heat pump go together easily. There is free software available (DanCap) for sizing cap tube, and charts that do the same thing, but re-using the cap tube saves dollars and hours.

Originally Posted by Drake

In your Beta design the ground loop water has a "holding tank"? In theory this tank could get it "heat" from solar source as well potentially?

Drake, you must be reading my mind (or else my blog... sometimes even I can't tell the difference).

I now see a need for two kinds of heat storage... one kind for smaller amounts of energy, where the energy stored will be of short duration, like an hour or two. In hydronic heating this is usually referred to as a 'buffer tank'. I would guess that the efficiency of energy deposit and energy withdrawal (to use banking terms) should be as high as possible.

The other kind would be more of a mass-energy storage, like grabbing as much solar energy as possible (making hay while the sun shines) and calling upon it later, for future use. Here I dont' think the efficiency would need to play such a crucial role as capacity.

But back to solar gain, I have several flat plate solar collectors in the back yard for that very purpose. I'm thinking now that the mass-energy holding tank should be pretty big to hold a useful amount of heat from the sun... Alternately, I'm considering running solar heated water through the ground loop itself for heat storage.

I'm also very intrigued by Phase Change Materials (AKA: PCM) like parrafin and eutectic salts. In case you are unfamiliar with the idea, when these materials transition from solid to liquid and back again, a very large amount of heat is transferred into and then out of the material. PCM are not as inexpensive as water or sand or rocks for heat storage, but they have much less volume and mass for the amount of heat stored. Since my house is pretty small, they have an appeal.

But, another appeal of PCM is that when the heat is being stored, unlike water, there's very little temperature rise in the PCM, so the 'delta-T' stays pretty much the same and the heat storage continues at a high rate. This can have an efficiency-increasing effect on heat storage.

PCMs have been widely recognized for quite a while, and have held the promise of being the Holy Grail of heat storage, but for some reason they have not really found their place in the sun (appropriate pun).

So, I have 50 pounds of driveway salt that will either work for me, or will make it clearer why PCMs are not being used.

Originally Posted by Drake

I too am most interested in water to water for heating. What I have found from hydro install info is 7/8 pex is recommended for best under joist heating and needs higher temp than "in floor" so if you can do even your durarock install you should be better off. Was also told efficiency of 3/8 and 1/2 pex(just need closer 3/8, maybe more loops) is same if you are really limited on wieght/thickness.

Yeah, I think I have heard similar regarding the diameters. I wish I could find something that was more specific regarding diameter and spacing and heat output.

If you knew what the heat load was and the square footage, then you could start thinking about the BTU's required per square foot. I have an idea what I want my feed temperature to be (80 to 90 degrees F) and I know I want to do a "sandwich" floor due to weight issues. So now I am at point of determining diameter and spacing, and I don't have a good way to proceed...

Originally Posted by Drake

And as your mystery puddle shows I have learned hydro cooling is limited by condensation problems(why A/C's have drip pans I am told). On topic of your whole hydronic system if you haven't discovered it already explore "open systems" it is exactly the install for my needs. Even incorporates some cooling possibilities.

By "open systems", are you referring to mixing heating water with potable water?

If that is what you mean, I'm afraid I don't see the cooling tie-in...please explain.

-AC_Hacker

[Drake]

Economical long term heat storage seems to be the "holy grail" of eco-heating. Seems to be some real possibilities out there I just can't spend $10 to save a dime. So far the only data supportable earth storage I've come across is being tested in Isabella Eco house in N MN(wish I could LINK). 16 INCH insuld taconite/sand bed. That doesn't mean other methods aren't working.

Do you think your temp drop could be because your ground loop might be undersized or that your connecting run appears to be somewhat shallower than the 5-6' deep installations I've seen(losing some heat to colder surface)? Don't know what should actually be stable at. Your field design is nice that it is expandable. If I can get the cost in hand enough go heat pump to drive my hdro system I would like to. In my construction plan I will be trenching(80-100') for septic and foundation drainage out thru hillside to mound septic field. For me this would be the ideal opportunity the lay ground loop in same earth work. Even if I don't use it's only a few hundred feet of tube.

[AC_Hacker]

Originally Posted by Drake

Economical long term heat storage seems to be the "holy grail" of eco-heating.

Did you see this post on heat storage systems?

Originally Posted by Drake

Do you think your temp drop could be because your ground loop might be undersized or that your connecting run appears to be somewhat shallower than the 5-6' deep installations I've seen(losing some heat to colder surface)? Don't know what should actually be stable at.

All loop fields have some kind of temperature drop curve. When you extract heat there will be some kind of temperature drop over time. The curves are shaped like this:

The bigger and deeper the loop field, the slower the temp drop. Soil characteristics play a part in it too. When you stop extracting heat, there is also a recovery curve.

So, for my project, I need to see if the temp drop curve is slow enough to allow me to get through winter where I live.

If I increase insulation in my house, will that lower the heat load enough so I won't need to extract so much heat?

Will I need to drill more holes for a larger field?

I don't know these things yet.

And here in my area, there are periods during the winter when the air temp actually goes higher than the ground temp, so it would make better sense to use ASHP then, and rely on GSHP for when the temps take a nose-dive, which they do for some period each winter.

Originally Posted by Drake

Your field design is nice that it is expandable.

Yes,I have expansion as an option because I really don't know how the movie is gonna end yet.

Originally Posted by Drake

If I can get the cost in hand enough go heat pump to drive my hdro system I would like to. In my construction plan I will be trenching(80-100') for septic and foundation drainage out thru hillside to mound septic field. For me this would be the ideal opportunity the lay ground loop in same earth work. Even if I don't use it's only a few hundred feet of tube.

[* I assume by hydro, you are refering to radiant floor, right? If that is the case, bear in mind that heat pumps work happier (and more efficiently) when they don't need to produce very high temperatures. That's where the PEX spacing comes into play. By reducing the PEX spacing, you can reduce the feed temperature, and increase heat pump efficiency. *]

I think that you may have a good idea here. It just might be a great way to recover heat from domestic water use.

But read up on how much tube to put into a trench... I have a feeling that you may need more tubing that you might think.

Regards,

-AC_Hacker

[Vern2]

AC Hack,

If periods of time the ground source is depleted, can the ground source be used for summer cooling. Then during summer cooling the ground source can be replenished for the winter heating.

I would think, but have no idea... If the ground source is depleted at a fast rate that might mean the ground loops are working very well (removing heat). Then you might jump to the conclusion that replenishing the ground source might be very successful as well.

Just my observance (understanding so far).

Lets use a double edge sword here.

[Drake]

Yes, I think it may become part of my hydronic heating system. I am sold on low temp radiant as the distribution method for my new addition project. It fits into passive solar so well and because I am building new designing for thermal mass floor is easier. So for me how to best heat water is next. Being a very high R structure heat demand should be low under 5,000 Btu/hr at highest. Easily supplied with just a high efficiency H20 heater of any type. Most economical for my location(rural elec COOP) would be offpeak hot water storage which I can have but not for space heat(long UL story). Heat pump is ideal efficiency method but $25-40K made my DIY blood boil. AC's work on DIY W/W GSHP is my dream. Pulling away the curtains from the Wizard of GSHP will benefit us all, clearing fact from fog.

I see a water buffer in place of your beta 55 drum as a heart a circulatory system that can gather "heat" from many sources(even recovered) think what your HP could do with even low grade solar hot water. It would really help with cycling(like pressure tank does) and I think make oversizing a ground loop not problematic(better to big than too small)(there may be as yet unknown enviro cost to +/- too much heat from ground - thermal pollution). Loop sizing is something that all dealer/installers I've talked to say must be "professionally" balanced.

For me "space" for any equip needs to be considered as much as $ cost, it is at a premium in small home design.

[Drake]

In the photo of your Beta HP it looks like you have barrels on both sides. If so is the one on "hot" radiant there because you are not completed on that side(floor not installed) or do you see need for a tank as well. I have completed design of my radiant system, having two levels, a basement short term floor storage bed and main floor "heat" run and combined they only contain 15-16 gls of fluid. Wondering if this can be run directly thru HX or if small tank would not help buffer as well. Could "hot" HX(proper type) be worked directly into a recycled tank? For the less mechanically adventurous such as my self wish they made a water source HP domestic H2O heater.

[AC_Hacker]

Originally Posted by Vern2

If periods of time the ground source is depleted, can the ground source be used for summer cooling. Then during summer cooling the ground source can be replenished for the winter heating.

This is absolutely the case. The only gotcha is that if there is water flowing through the loop field it will carry away heat stored during the summer... on the other hand, it will also carry away any cold stored during the winter.

Originally Posted by Vern2

I would think, but have no idea... If the ground source is depleted at a fast rate that might mean the ground loops are working very well (removing heat). Then you might jump to the conclusion that replenishing the ground source might be very successful as well.

My knowledge is incomplete, but I have seen that heat in the ground moves very, very slowly.

To help me understand it, I imagine it to be like cold molassas flowing in from surrounding sand. When you first start extracting the stuff, it comes out pretty easily. But then the 'make-up heat' (molassas) flows in from slightly more distant sand (tales longer), and so on and so forth.

If your heat pump's extraction rate is matched by the long term heat-flow rate of the heat soil (molassas sand) then you should see a temperature decline which finally levels off and your heat extraction is matched by the migration of heat to the boreholes, for the duration of the winter.

If the decline rate is fast it means that the heat pump is removing heat faster than it can "ooze in". So then you need either more loopfield, or less heat extraction (possibly conservation through auxillary fuel or better insulation, or perhaps wiser use of the heat produced).

So the proceedure is

Dig a test hole, or test trench, and test it to see what it's steady-state heat production rate is per foot.

Next you need to find out what the heat load is for your house or shop or water heater or whatever.

Then you divide the heat load by the heat produced per foot, and you will know what the minimum amount of borehole is required to do the trick. More than that is gravy.

-AC_Hacker