The Homemade Heat Pump Manifesto

[charlesfl]

Questions on R290.
Should the low side temperature be kept above the freezing point of water?
How does this effect the efficiency of the system?
I noticed randen and AC Hacker had very different low side pressures (temperatures).

thanks, charlesfl

[AC_Hacker]

Originally Posted by charlesfl

Questions on R290.
Should the low side temperature be kept above the freezing point of water?

No, the loop water will not go to freezing temperatures as long as it is moving, AND the water temp in the loop is above, maybe 36 degrees (I shut mine off early, I didn't want to freeze my HX solid).

Originally Posted by charlesfl

How does this effect the efficiency of the system?

It makes it very efficient!

Originally Posted by charlesfl

I noticed randen and AC Hacker had very different low side pressures (temperatures).

When I reflected on it, my test pressures started out too high, and like I said, I had a long slow leak. I monitored the performance during the leak, which went on for a couple of months. And my best working pressures were also in the range reported by randen.

BTW, thanks for the propane resources.

-AC_Hacker

[Geo NR Gee]

Originally Posted by AC_Hacker

Well, you didn't mention the price...


You said your brother is in the HVAC trade, maybe he can loan you a pump and/or a micron gauge.

If I were you and had a bit of time, I would haunt ebay for a modern working micron gauge. The modern ones are pretty small and electronic, there were some older ones that were the size of a school lunch box and looked like they were Heath Kits... don't go there.


-AC_Hacker

Thanks AC, my brother dropped off the vac pump and the older micron gauge that looks like something my dad would have used back in the 1960's or my old lunch box.....

I think I will take your advice and scan ebay.

[AC_Hacker]

Originally Posted by Geo NR Gee

I think I will take your advice and scan ebay.

Well, you ought to at least try the beast out. You might be able to find a manual for that model on the net. If it seems to work, you're that much further ahead.

Your pump, with fresh oil and just the micron gauge should be able to pull at least 300 to 400 microns...

You can probably get by with that...

You should try it.

-AC_Hacker

[randen]

I thought I would post the statis of the little 2Ton shop GSHP. Now that the night-time temps are dropping well below freezing -5 deg C(23F) the GSHP is running continually. The shop inside temps during the day are around 17 deg C (62F) and the office in-floor heat is 24 deg C (75F)for now comfortable. The ground loop temp has not changed still about 13 deg C but we did oversize the ground loop. I have been thinking about adding more insulation to the attic. It is now R20 fiberglass batt. After Christmas holidays and the dust settles I will start on the 3.5T HP. One other improvement thats in the works is to make some solar hot water panels for the south wall. I have them installed on my home with remarkable results. I know that the solar hot water will bring the shop up to a balmy temp but here in Ontario Canada we may not see the sun for a couple weeks and the low temps and wind will be there. So a good back-up is required.

The 2 T is doing well now but when we start to see -22 deg C I think it will have its pants full.
Even though the GSHP is running full out the prize at the end of the day is the cost for heating works out to $4.35/ day when heating with furnace oil was almost $30.00/day

[AC_Hacker]

Originally Posted by randen

Even though the GSHP is running full out the prize at the end of the day is the cost for heating works out to $4.35/ day when heating with furnace oil was almost $30.00/day

Thanks for this report...

Your results are very encouraging.

A little more insulation, a little solar... sounds like you are almost there.

-AC_Hacker

[launboy]

Randen, when you were stating your temps for HX's, did you say that the outgoing refrigerant and the outgoing radiant water temps were within two degrees of each other, or did I read that wrong? If that's correct, then your radiant water is entering at 72*F, leaving at 82*F and your refrigerant is entering at 179*F and leaving at 85*F(is that correct?). That water temp seems low compared to AC Hacker's or anyone else's hot water side temps. Does this suggest something not efficient with the HX(does not appear to be likely) or does it simply mean that your floor able to transfer out every bit of heat this HP is putting into it with a floor to air Delta T as small as 4*F, or 13*F(66*F or 75*F to 62*F)? Have you tried shutting off the flow to the air handler and seeing how well it's able to heat just the radiant floor in the office space, or vice versa and run just the air handler? That might tell you more about your heating and sizing needs.

I myself am severely pained that I can't work on my heat pump project. I'm currently away at college so I don't have the space or tools and an air conditioner to tinker with. My project is an air source to water heat pump which I plan to use as the main heat source for my hot tub. I know a 1375w(approx 4800 BTU) heating element is enough to maintain the temp if it runs constantly, but that literally doubled our power bill last winter the one month it was running. The A/c should put out a little more then that, or hopefully at least that many BTU's, but using half the power. I don't have much time to hack, but I've already got a window A/C lined up(early Christmas present to myself) to use when I go home for winter break.

Due to break only being a month long, and me not having the gauges vac pump or any other equipment(or the budget, poor college kid here) to hook up a real heat exchanger, I'm going to keep the circuit intact. My plan is to bend the tubes(very carefully) and simply lower the condenser coil into the tub in front of a jet for circulation. I know it's not the most efficient but it will work for my temporary trials. Past tests have shown that the small coil used on the evap side of window a/c's can make frosting a problem due to how low the coil temps can get when it's cold outside. My plan to help combat this is to use a more powerful fan like this( FlowPro High Velocity Floor Fan — 18in., 4550 CFM, 1/8 HP, Model# 10180 | Floor Fans | Northern Tool + Equipment ) which I already own, to force much more air through the coil and hopefully keep the coil temp from dropping as low thus slowing the forming of frost, which should also increase heat output a little.

I've even thought about the defrost issue which I'm sure will arise and my plan is simple. Turn off the unit and fan, and place a propane Mr. Buddy heater directly in front of the evap coil to quickly melt the ice. This can also be left there with the unit running to significantly increase heat output if I need the BTU boost to keep up with the heat loss while we use the hot tub.

If the hot air coming off the tub wasn't so humid reusing it would make for a very efficient system, but I'm afraid the speed it would cause frost to form would make it not worth doing.

Any huge holes in my plan I need to address?

By the way, this thread has done a lot in the way of inspiring me to plan projects for my home in the future. I'm already dreaming of and have drawn up plans for a very efficient(somewhat complicated system) using a fresh air economizer(if temp and humidity are optimal) and a Heatpump, maybe a (hacked inverter minisplit running water-water?) with multiple sources, ground, air, and solar water inputs which it senses and automatically picks the best that I have dreams of designing and building one day. Reading more of this thread made me remember I also want to include the three buffer tank system for DHW, in floor radiant, and cold water preheat or snow melt. Of course, taking one last tip I learned here, I will insulate and seal my house as much as possible so my demand loads shouldn't be to big to begin with.

Thanks,
Adam

[AC_Hacker]

Originally Posted by launboy

My plan is to bend the tubes(very carefully) and simply lower the condenser coil into the tub in front of a jet for circulation.

launboy,

I know you have the best of intentions, and I wish you well in your careful bending... but if you end up with R-22 spraying all over the place, please consider that the big HX on the back of the unit would be better than the small HX that is buried inside, for the evaporator HX (the one that gets cold). Copper tube coils with no fins would would be dandy as the HX in the hot tub.

You might even surprise yourself that you just might already know people with most of the tools you need, that they would lend to you. You might want to attempt to line up those tools in advance of your bending effort, just in case, so that you can complete your project over the vacation.

Best of luck with the project! Aquario has done something very similar here on EcoRenovator. You might use the search button to see what he's done... He started heating a swimming pool, and is now heating his house!

Regarding defrosting, just turning the unit off from time to time will allow the hot refrigerant to melt the ice.

May the force be with you.

-AC_Hacker

[launboy]

I wish I had the resources some of the people on this board/thread do. It seems everyone knows someone in the HVAC/R trade, but scouring my brain I don't believe I do, unfortunately. So I just hope I don't break the seal, at least not for my vacation experiment.

I fully agree with you that for heating I'd be better off with a larger Evaporator and the condenser being the smaller one. If I ever do end up modifying this, I would use the condenser(bigger) coil as my evap, but I am wondering if it'd be of any advantage to me to use two of them either run in series or parallel? I think series would be better if I did this, and the coil is free, from a window unit with a leak, but would there be any advantage to it in my application? This would effectively double my evap size.

I also agree that a copper coil without the aluminum fins would be perfect for the hot tub side due to the corrosion issue. Could I just cut the fins off the tubing? It would be an annoying process I'd imagine, but since I already have the coils, it's copper I wouldn't have to buy.

Just thought about the controls aspect, I have a dehumidifier control that senses when ice forms on the coil and shuts the unit off so it can melt, maybe this could act as a sort of defrost board so I could let it run when I'm not out there to check on it. If that doesn't work I can always fall back on the old put it on a timer that shuts it off for 5-10 minutes every half hour or however long it seems to take on average. As far as temp controls go, having the Spa Pack makes that easy. It has a temp sensor, thermostat, and contacts for the heating element already installed. I'm just going to disconnect the terminals from the heating element and reconnect them to an outlet. It's designed to handle the element so it should have no problem with an A/c drawing half that. I'm so impatient to get back home and try this out!

I saw that Aquario did and went to his website to see further details. His results seemed very promising and are even more inspiration to do my own experiments. This summer I fully intend on becoming a full fledged hacker and learning to braze and charge my home made heat pumps.

Adam

[launboy]

Forgot to add, I know about the R-22 spraying all over, that's what happened with my last window unit. Granted it was the second time I was trying to bend the coil out and unbend a U after already unbending and rebending it once. The odd thing was that it didn't come out at that high of pressure or even get cold when it leaked out. It was like compressed air was escaping. So now I have an empty window unit sitting in my shed. Too bad I don't have the equipment to fix it.

Has anyone ever tried the purging method of charging? where you just feed the refer in at one point and go until its pushed the air out of the system, then charged? I know this is bad practice and probably asking for trouble, but some of those chinese minisplits tell you to charge them this way and they run fine, for a while anyway. This wouldn't be my primary machine, just a, well it's already broke so why not, experiment

Adam