The Homemade Heat Pump Manifesto

[AC_Hacker]

Hi, sparkchaser,

Originally Posted by sparkchaser

...Has anyone successfully used an air-source heat pump converted themselves to ground-source?...

(In a way, that's what I have done, but my donors are in truth de-humidifiers, which is more or less air to air.)

There have been some folks on this blog who have put such an idea forward, but I don't know of anybody who has attempted it.

As you probably know, there are

• single-speed ASHP compressors
• dual compressors
• variable-spreed compressors

The single-speed compressor would be the easiest to do, and would pretty much consist of replacing the evaporator coil with an equal capacity liquid-to-refrigerant heat exchanger, and in place of the fan, you would need a properly-sized circulation pump... not so hard to do. As you might have seen, I tend to be pretty fond of brazed plate heat exchangers, but if you have a line on cheap copper tubing, you might be able to make a tube-in-tube that would do it. I have not yet located information that would help me size a tube-in-tube refrigerant-to-water exchanger.

You can find new and used heat exchangers on ebay at reasonable prices. Most give specs for water-to-water, which is not the same as refrigerant-to-water.

A super cool hack would be to convert an inverter technology mini-split to ground source. There are significant technical hurdles with regard to the inverter technology & ECM fans (ECM pumps?), but the efficiency would be stellar.

Is this the kind of info you are looking for?

-AC_Hacker

P.S.: How far up river are you?

[sparkchaser]

Hi AChacker,
I live in White Salmon WA. Looking to install a new heat pump very soon. Air source, but for starters I want to make an economizer for a diy hybrid air/ground hp of sorts. More later when I'm on a real computer...Mark

[AC_Hacker]

Originally Posted by sparkchaser

...I want to make an economizer for a diy hybrid air/ground hp of sorts...

Sounds like a very worthy project.

-AC

[go4haudio]

here is an interesting pdf www(dot)box.net/shared/koeb9dm9ps starting on page 49 there is a section on compost as a heat source. I have seen some info that compost has a bacteria that thrives from 150 to 180 degrees F. Using a one wire temp sensor like A/C hacker and his arduino one could easily set up a circuit that used that heat to supplement the GSHP. That could easily and cheaply raise the COP for the heat pump in the winter. I know from experience that stables often have piles of compost that are cleaned from the horse stalls. If you ask they will often give it away. It gets hot! There may be some situations where a ground loop might be difficult or impractical to install but a compost bin and a heat pump might work, especially if you primarily need heating. The design could be as simple as an earthen mound to a contraption using a recycled drum from an old commercial clothes dryer to turn the compost and increase the efficiency of the heat inducing bacteria. But it would not be practical with a heat pump. Thank you A/C Hacker.

[go4haudio]

I meant it would not be practical "without" a heat pump. Because you would need a mountainous compost pile to maintain useful constant heat without affecting the biological balance of the compost.

[go4haudio]

Actually the pdf I mentioned above has 2 pages per view so you need to check it out starting at page 26.

[AC_Hacker]

Originally Posted by go4haudio

...I have seen some info that compost has a bacteria that thrives from 150 to 180 degrees F. Using a one wire temp sensor like A/C hacker and his arduino one could easily set up a circuit that used that heat to supplement the GSHP. That could easily and cheaply raise the COP for the heat pump in the winter...

If the temperature of the source is raised, then yes, the COP of the heat pump would also be raised.

The "...easily and cheaply..." part needs to be looked at more closely. You need to analyze the energy (mechanical and human) involved in acquiring and disposing of the compostable material to know if this method actually has merit (net positive energy gain). If the compostable material was made into a slurry, and if the bacterial process would proceed in the presence of that much water, it could make handling much easier, as a big pump could do much of the work for you.

If the compost pile or tank was large enough to maintain the 150F to 180F temperatures while home-heating energy was being extracted, then no heat pump would be required, just a circ pump.

But if you look at all the benefits, compost to increase crop yield, methane gas to use for cooking and even transportation, heat for winter comfort and DHW, this would be dandy if you are rural and already involved in raising livestock & farming.

Thinking does not always result in doing. This is after all, primarily a DIY site, and not a brain-storming site. If you are motivated enough to actually implement this idea, I invite you to start another thread and share your photos and experiences with us.

I wish you the best on your project.

Regards,

-AC_Hacker

[go4haudio]

Yes A/C Hacker I should start another thread. There are many concepts involved beyond the scope of the heat pump which is the topic of this thread. I will call it "Compost an alternative Heat source." I prefer to focus on a ecorenevator's backyard scale (where an efficient heatpump can be practical) even though the advantages of a farm scale are obvious. Based on your response it seems you are unfamiliar with this heat source and perhaps even somewhat incredulous. Many others will feel the same. After all fossil fuels have been cheap for generations. I surmise the credibility of compost as a heat source rises in direct relation to the cost of fuel. It can be cheap and easy with a little resourcefulness and a weekend warrior approach. I am somewhat taken back by your use of the term "brainstorming." This is a proven technology and it is not novel. "Planning" is required to make this energy source useful on a suburban scale. One method of extracting this heat could be a "home made heatpump." Because the COP of a heatpump working with compost of 150 to 180 degrees is higher than a heatpump extracting heat from a 50 degree ground loop a much smaller pump could extract the equivalent heat from a compost "furnace" than a geothermal ground loop. And since the composter is more compact it may be possible to use a DX (direct exchange) coil within the compost itself or coupled to a homemade passive heat exchanger within the compost. This would eliminate a water pump thereby increasing efficiency even further when compared to a ground source heatpump. An efficient compost system reduces the mass of the compost. In my garden I had a compost pile. It was delivered to me for free by a friend with an estate. It consisted of leaves, grass, small twigs, and other yard waste from a spring clean up. The pile was originally about 4feet tall, 15 feet long, and 6-8 feet wide. It composted naturally in three years down to a 6-8 inch mound. Had I used more effective means I have no doubt I could have composted it within one season instead of six seasons. I intend to spread it out into some sandy soil to allow grass to grow better. Honestly I need another 20 piles like that to fill in bare spots in my yard alone. If I had an excess I am sure a Craigslist free listing would take care of that in a few weekends. I feel I have addressed your misgivings. Compost as a heat source is valuable because unrest in the middle east, competition from China, and a lack of a renewable energy infrastructure will likely keep energy costs rising. I hope you will check out my new thread. And I hope comments or questions about home made heatpumps operating efficiently in specific temperature ranges as proposed will be welcome in this forum. For instance would water vapor (steam) make sense as a refrigerant fluid? It is cheaper and maybe safer than propane. But I do not know what would happen to a compressor. Would it rust? My question is this: How would I determine the working temperatures of a water vapor based heat pump?

[tweeker]

I have a minute now.

I have been hacking A/C units for a while, at first turning them into HP's, and then CHILLERS, and HOT WATER HEATERS in conjunction with my solar equipment.

Using the MINI SPLIT Concept, I started building heat exchangers for the fluids that were heated/cooled by my hacked A/C HP.

My RULE #1: If the A/C unit is working, NEVER BREAK THE UNITS REFRIGERANT SEAL! *Leave the pressurized part of the unit INTACT.
*(A lesson I learned a long time ago, and several times, before I got the hint)

Example: I take a 5000 BTU A/C unit, disassemble it down to the bare bones of the COMPRESSOR, CONDENSOR, & EVAPORATOR, and ONLY the electrical wiring required to run the COMPRESSOR, thats it, NOTHING ELSE. (NO MORE FANS, housings ETC)

Lets just say you have a 5,000 BTU A/C unit with an EER of "10", which means it is making 10 times the cool/heat per watt used, in this case 500 watts to make 5,000 BTU's = a "10" EER. This can only be achieved by HEAT TRANSFER - NOT watts TO PRODUCE HEAT in BTU's.

This is the time consuming part: Build a WATER TIGHT, INSULATED tank/container AROUND the EVAPORATOR & CONDENSOR. This is your FIRST fluid filled (COOL & HOT) HEAT EXCHANGER.

WATER is 24 times more thermally conductive than AIR, Ethylene Glycol (Anti Freeze is 10 times more thermally conductive than AIR. COPPER is 16,040 times more thermally conductive than AIR, and 668 times more thermally conductive than WATER. So I decided to run WATER over/through the CONDENSOR & EVAPORATOR COILS in a small holding tank, and then transfer it to a COPPER HEAT EXCHANGER in a location where it would perform the best at thermally conducting a HEAT TRANSFER from the AIR. (Mini-Split)

Thats what I have to share for now, when I have more time, I will keep going.

Get a KILL-A-WATT for the next nugget experiment, you have to see it to believe it.

Tweeker

[AC_Hacker]

go4haudio,

Originally Posted by go4haudio

Based on your response it seems you are unfamiliar with this heat source and perhaps even somewhat incredulous. Many others will feel the same. After all fossil fuels have been cheap for generations. I surmise the credibility of compost as a heat source rises in direct relation to the cost of fuel. It can be cheap and easy with a little resourcefulness and a weekend warrior approach. I am somewhat taken back by your use of the term "brainstorming."

Starting at the end... I am completely serious when I say that, "I wish you the best on your project." And I want you to know that if there is any information I can share, any idea I have that can help your project succeed, I am completely on board.

As far as being "unfamiliar with this heat source", I spent a good part of my childhood on a farm in Maryland, and I have seen steaming piles of manure in the dead of winter, so I'm not completely unfamiliar with the process. I have also followed with great interest the 'humanure' initiative (I resisted saying 'movement') and I think that recycling is not only smart, but necessary as we are confronted with declining resources. I also am familiar with the fact that compost piles can reach surprisingly high temperatures... high enough in some cases to catch fire, as I learned from my early farm exposure, listening to farmers talk about the danger of hay being stored in a barn, getting wet and spontaneously combusting, resulting in the loss of hay, barn, and livestock.

I also know of related attempts and I have also seen photographs of successful rural experiments in heat extraction from large manure pits, so I know it can work.

When you describe me as being "incredulous", I admit that I don't have a feel for the overall quantity of heat that can be derived from a home scale compost pile, and how far that quantity of heat will go to contribute to home heating. Your project could go a long way toward supplying valuable information.

And, since you live in Florida (heating degree days about 1500), where home heating isn't quite the challenge that it might be in Maine (heating degree days about 9000), you should have an easier time hitting your target.

Regarding water as a refrigerant, it already has a refrigerant designation, R-718. Here are some pages that could be useful to you. If you want to find out the range for water, you will want to study a Pressure Temperature chart (AKA: "PT chart") for water.

If I were going about this, I would limit the technologies I was trying to employ. When I got one system working I'd introduce another technology. For instance a compost pile with a PEX or HDPE loop and a circ pump pumping through a car radiator. Then, when that was working to my satisfaction, I'd introduce a heat pump, maybe along the lines of tweeker's approach, since it is less demanding. When I got that working, I'd tackle R-718, and go for the gold.

But it's not my project, it's your project...

...and I sincerely wish you the best on your project.

Regards,

-AC_Hacker