The Homemade Heat Pump Manifesto

[Geo NR Gee]

Originally Posted by AC_Hacker

The nitrogen idea sounds pretty good, if it is really nitrogen.


-AC_Hacker

FYI, its nitrogen, both at Costco and Discount Tire they have nitrogen generators. Discount Tire has a policy that they cannot fill portable air tanks. However, they can fill spare tires.

Costco was kind enough to fill the portable air tank for me. I will report back and let you know if clean and flake free brazing was successful.

[eco_fred]

the problem with brazing is that when you dont use nitrogen you have air in that pipe so you will have flakes the proces is called oxidation.
Nitrogen is an inert gas and will not burn so have a little flow in the pipe (nitrogen)and start brazing
the circuit has to be open to do this otherwise your building pressure....
check youtube :

or even better moisture the enemy of the cooling circuit...

[eco_fred]

Always install a NEW filter dryer in the liquid line to minimize problems....
Normaly every time you open the circuit you install a new filter dryer to "catch" your flakes or even better moisture the enemy of the cooling circuit...

[AC_Hacker]

Originally Posted by launboy

AC, you haven't posted an update on your personal system in a while, how are things coming with it?

Adam,

Thanks for your inquiry...

My badly broken arm (April 5) has really set me back. I’m just getting to the point where I can move things around, like a compressor...

I had a new heat pump on the bench awaiting final assembly when I broke the arm, it’s still right where I left it.

Originally Posted by launboy

Any performance updates or things you've learned?

I have learned a lot from this project. Some of it is very specific to my lifestyle and expectations, the size and thermal characteristics of my house, the particular weather characteristics where I live, etc. Some of the things I have learned are more general and might be applied anywhere.

Last winter, I ran my little 400 watt unit 24/7 for a couple of months, without a thermostat... just wide open the whole time. I just wanted to see what would happen. I used the ground loop as my heat source, and I ran the heat output loop into a car radiator that had a box fan sitting behind it running on medium speed. I dumped all the output air into my small un-insulated basement. Most of the time the heat pump kept the basement pleasantly warm and some of the time it became too warm for comfort. When there was more ground heat available, there was higher air temp in the basement. I learned a huge amount form the experiment:

• The homemade heat pump project actually works. Compared to the rest of the project, making a functioning heat pump is easy and cheap.
• The ground loop produced less heat than I calculated and should be bigger and deeper. My assumptions that many shallower boreholes would equal a few deep boreholes did not pan out as I expected. I am getting heat, useful heat, but I don’t have the large margin of extra capacity I expected.
• Even with the shortfall from my small ground loop, if I retained the heat produced in the house with really excellent insulation, it will fulfill my expectations.
• Even with the shortfall from my small ground loop, if I augmented the loop heat with solar and/or ASHP, it will fulfill my expectations. Especially if I rely on solar and ASHP when the sun is shining, and/or higher air temperatures are available, and use the ground loop energy when the thermometer really takes a dive.
• The ground loop was one loop, about 730 feet long, with all 16 boreholes in that one loop. Using this arrangement, the friction was too high and the power required to produce the flow rate was also too high, especially as a percentage of the compressor power. Pump power was over 50% of compressor power, much too high (the number of butt welds I use, almost 100, didn't help a bit). I already, with the help of my son, dug up a small part of the loop field and now it is two loops running in parallel. This should reduce my required pump power to 25% of the previous power. My new heat pump will be larger, also so the % of power going to circulate water should be manageable.
• I tried to get away with using water pipe threads for the refrigerant HX loop... no love. I had a very slow but relentless leak of oil and refrigerant. Everything should be brazed, or if absolutely required, flare fitting used only where absolutely required.

While the test was running, I kept a log of basement air temp. I learned that a difference of a few tenths in loop temperature meant a difference in whole degrees in air temperature output.

I also learned that rain brought heat with it. Every time it rained, there would be a delayed rise in basement temperature. I realized that in the same way that the refrigerant gives up its heat in the heat pump, the rain is doing exactly the same thing in nature. That insight is still ringing in my brain.

I also no longer see the loop field as just a heat source, but also as heat storage. I plan to put up at least one hot water panel to use be used during the summer for storing heat in the ground.

So the loop field shortfall has motivated me to keep improving my insulation. A lot of the heat pump action is now kitchen insulation action. But in reality, it's all the same project.

Originally Posted by launboy

Did you have time to do anything with the portable ac/hp you got?

I tested the dead-starting-capacitor theory by substituting another capacitor from another similar-sized unit. The test cap was the wrong size and I didn't hook up all the wires, just the motor starting wires... no love.

Then I hooked up all the wires and the beast sprang to life! Apparently some of the other wires were sense wires for the little Chinese computer brain module thingie.

So I have a working 1 Ton ASHP unit! And I was able to preserve my virtue. I looked closely at the heat exchangers in the unit, and they're pretty small for a 1-Ton unit. I guess sacrifices were made for portability. For a limited-use shop warmer, it's not a bad deal, but for-full time service I think it will be disappointing.

I also have my radar on full-power for a small 2 or 3 Ton split air conditioner condenser unit for free or cheap. Quite a few of them are being retired, and I could graft the 1 Ton compressor onto a 2 or 3 Ton condenser coil. That should make a pretty good ASHP to use in combination with my GSHP. I would also need to graft a lower-powered fan, too.

I did find a perfect 1 Ton LG mini-split air conditioner, but it's in AZ and the seller is uber-flakey about returning phone calls or email... not a confidence builder at all.

And, on a somewhat unrelated note, here are a couple of refrigerant to water HXs I picked up for $25 each, a couple of days ago.

I'm starting to meet other HVAC hackers here in the area where I live. It would be a great idea to organize a local group who would be into swapping knowledge and parts. We'll see where that goes. The folks I have met so far are very enthusiastic about hacking HVAC stuff.

This one HVAC hacking guy I talked to even tried to do a hydronic floor. He did a staple-up with one foot tube spacings, and tried to drive it with a heat pump. It just didn't pull the grade. If he had read the EcoRenovator thread on DIY hydronic floors, he would have done much better... he would NOT have done staple-up, he would have done some kind of top-of-floor sandwich, and he would have used MUCH closer spacing than 12", and he would have been warm & happy...

ALSO, Xringer has been messing about with a PLC controller board, that looks to be exactly the ticket for controlling the heat pump(s). This has had me stuck for quite some time, but now I'm quite confidant that it will do the job. I bought one, and some sensors, and it's working right out of the box. I have yet to start getting the PLC logic to respond to set points, etc. But it's all there, and reasonably priced, too. There's nothing it will do that an Arduino will not do. There were some Arduino guys on the blog from time to time, but they faded like the morning dew. This PLC board is easier to get going but is more limited in it's capability. But it will do what I want, more than I want. I do wish it had included a data-logging capability... But for $35, I shouldn't complain.

Originally Posted by launboy

Inquisitive minds would like to know...

Well, now they know.

-AC_Hacker

[Geo NR Gee]

Originally Posted by AC_Hacker

And, on a somewhat unrelated note, here are a couple of refrigerant to water HXs I picked up for $25 each, a couple of days ago.

-AC_Hacker

Jealous, I am. How big are those?

[AC_Hacker]

Originally Posted by Geo NR Gee

Jealous, I am. How big are those?

Physically, they're about 10" in diameter, and make about three turns. But as far as capacity, the guy I got them from said they were "...maybe 9,000 BTU, maybe a Ton...". I'm a little dubious about that. I tried briefly too look up the make & model number on the 'net, but the company seems to be out of business. I'll probably need to find another maker of tube-in-tube HXs to get a fix on the capacity of similar units.

My intuition says they're probably about half of what he claimed, but even at that, I can find a use. I could maybe even run them in parallel.

Good price.

-AC_Hacker

[AC_Hacker]

Originally Posted by Geo NR Gee

-AC_Hacker,
I thought I would try the new R290/22A in my little Frigidare Dehumidifier. I recovered the R22 into the recovery tank via the MicroVac Refrigerant recovery unit. I used a scale to see how much came out and it was 4.4oz. which is short of the 5.58 on the label.

I took temperature readings at the compressor high side and low side.
HS with R22, 100
LS with R22, 40

amps 6 at compressor
amps 4.7 at control board area

HS with R290, 180
LS with R290, 81

The amps went up to 7 at the compressor and 5.9 at the control board area.

The compressor was getting hot, so I shut it off.

I put in only 2.33 ounces. Do you know what I did wrong?

Thanks,
Geo NR Gee

It would be much easier to diagnose if you could tell me HS & LS pressures, after the unit has been running about ten minutes.

Did you set it up so that you could read HS and LS pressure? I guess you installed at least one Schrader valve on the LS for charging with propane

Most of the equipment I see does not have Schrader valves installed on the HS and LS, instead they have only one tube (LS), bent over and brazed, with no valve, OR they have two tubes (LS & HS) bent over and brazed, with no valves.

The first thing I do is to install Schrader valves, HS & LS. Then I can put my manifold gauge set on and go by pressure readings instead of temp readings.

The compressor will generate some amount of heat when it is running. It should be warm to the touch, but too hot to hold on to for more than 5 or ten seconds.

The compressor also has an over-temperature switch located on the top, under the black plastic cap, close to the place where the power wires connect to the compressor. If it gets too hot, it will switch itself off, and then when it cools it will go back on again. If it cycles off & on due to over heating, it really is too hot.

However, there is also a frost detector on the HX and it will shut the compressor off too, when there is too much frost build up... but then that is how the de-humidifier takes the water out of the air, so that is normal.

So it might be just a bit tricky knowing if the cycling is due to over-heating or if it is normal operation...

Tell me HS & LS pressures after 10 minute running.

-AC_Hacker

[hydronics]

ahhh ****.. that's so cool that you tested the conductance of your soil... I got some temporary data loggers that you can borrow if you need to do some more analysis...

I would have probably used an ice bath though in order to better simulate the conditions; that is, cold HX fluid... warm earth..

It would have also been interesting to test how quickly the earth temperature recovers during and after a 'long' run-time... and tested that against the theoretical recover times.. I believe the 'lumped capacitance' method is used... I recommend "The Fundamentals of Heat and Mass Transfer" by Incropera/Dewitt.. and I got a copy if you want to borrow it... the formulas are actually pretty easy to do...

Originally Posted by AC_Hacker

So here's my test data & analysis...

Time Temp
____________
0.00<tab>54
0.133<tab>57
0.167<tab>57
0.50<tab>60
1.733<tab>70
4.00<tab>79
6.25<tab>83
7.50<tab>85
8.433<tab>86.5
14.833<tab>92
15.25<tab>92
15.517<tab>92.5
19.883<tab>96
21.00<tab>96
22.083<tab>97
24.03<tab>100
25.82<tab>100
27.65<tab>99
31.67<tab>99
40.317<tab>99
44.23<tab>101
49.60<tab>102
63.65<tab>102
68.93<tab>103
89.55<tab>106
102<tab>107
113<tab>107
123<tab>108
143<tab>109

(I had to use the "<tab>" thingies, because the real tab didn't appear correctly in this blog)

Since I don't have an automatic data logger (yet) I logged all the data by hand. The time intervals were irregular but I think that it doesn't matter so much.

The first thing I did was to put the data into a curve analysis program. The program I found is a really great shareware program called CurveExpert for Windows available here:

I've used this program for lots of things. There are even tutorial pages available, if you need.

At any rate, it was very useful to get well done graphs as the test progressed. The program does automatic curve fits and it was interesting to see that the program selected various curves before finally settling on an MMF type curve.

From CurveFit, it's even possible to get the equation of the curve that is the best fit and to project the curve forward in time. I was interesting to predict what the temperature would be at a particular time and to check the results as they came in.

But this wasn't really getting me what I needed, which was a quantified characteristic of the earth formation in my yard. This is where the document mentioned in the previous post: TCTestingSum.pdf, came to the rescue.

I tried to follow the proceedure but wasn't able to get the same results as the author had. Either I was making a mistake, or I was using a version of Excel that was older and didn't have the exact feature he was using. But I devised a work-around and got reasonable results.

Here was my proceedure:

1) Start Excel
2) Open the data from a tab-delimited text file. This just means that the data is written in a test file and you hit the 'tab' key after the Time data, but before the Temp data. If the tab could print like this: <tab>, your data would look like this:

...
0.00<tab>54
0.133<tab>57
0.167<tab>57
...

Anyway this is a standard text format that Excel understands.

...of course you could just enter the data straight away into Excel and I could save myself some time & typing.

If you graph the data I have included, it would look like this:

See picture

Looks similar to the graph from CurveExpert.

At this point, the author of TCTestingSum.pdf was able to do a right-click on the graph curve that Excel made. Then he was able to choose "Add Trendline" and then a Logarythmic trendline, and the result, as illustrated, was a linear graph. I was not able to get these results, certainly not the graph as illustrated. So my modification to the process was to return to the spreadsheet, 'Insert' a column between the Time data and the Temp data. Then I wrote a simple formula (=ln(A1)) that took the natural log of the data in the time cell. I copied this formula down to the rest of the data cells. Then I made another graph of these data columns, "ln(Time)" and "Temp". At this point, I got a graph that resembled the illustrated results.


I then did the right-click and 'add trendline' this time I chose "Linear", since the natural log function had essentially linearized the graph. This did give me a formula with slope. Then I was able to use the rest of the proceedure as described. This all gave me a "k" value of 0.569464441. I was in turn able to use this value to calculate the total length of borehole, which would yield 12,000 BTU/hr. This calculated borehole length came to 214.23 feet. Which is reasonable, as I hear from local installers that they estimate that 12,000 BTU/hr (AKA: one Ton) borehole length to be in the range of 175 to 225 feet.

I have attached my spreadsheet for your consideration.

Some improvements:
* Get a real data logger
* Use the actual type and configuration of Polyethylene pipe I plan to use in the actual installation.
* Use a borehole that is closer to the actual location of the installation (the test borehole was within three feet of my basement, so error is to be expected)
* use the type of grout I plan to use. I'm currently planning to use "mix-111", more information available here:


I welcome your comments.

Best Regards,

-AC_Hacker

P.S.: For those who want to know more about the topic of borehole testing, I have located what might be the definitive paper on the subject:



>>>>>>>>>>>>>>>>>>>>>

[launboy]

AC, thanks for the update, very informative!

Sorry to hear about your arm, but glad to hear it sounds like its well on it's way to being healed. Side note, I never realized just how heavy a compressor was, even a small one from a window unit! That's a significant portion of the weight of one of those units.

Sounds like the test of your GSHP has been pretty successful, especially when one considers it was backyard engineered and on the budget it was done. I commend you on that! If your loop doesn't have the extra predicted capacity, will you be able to run a bigger compressor without issues? Or is it still showing signs it's large enough to handle that. What size is your current system, tonnage-wise? I know you're using a fairly small compressor.

Did making the ground loop two parallel runs have any impact on its feed and return temps?

I think your plan to use solar or ASHP heat when it's more efficient and relying on the ground loop more as backup or additional capacity is the ideal way to set up a system like this, a lot less taxing on the ground loop for sure.

Your note on ground loop temp difference in tenths of a degree resulting in full degree swings in basement temperature is very interesting to me. What sort of temp difference did you notice in heat loop temp when the ground loop temp changes occured?

Very excited to hear you got the portable unit up and running! Is this the unit you're considering using for the final version of your heatpump? It seems this would be ideal considering it's already got controls and a reversing valve integrated, all you'd have to do is switch it's exchangers no? Even comes in a nice housing that I'm sure would fit both brazed plate exchangers, resulting in a professional looking final product.

That HVAC group you found sounds like a really cool idea, how'd you go about finding these people near you?

This guy has a very interesting blog, he has a(what I believe to be) standard York Heatpump condensing unit hooked up to a coaxial HX for hydronic house heating.
Oikos Blog

Update on my little project,the woman I am buying the window unit from stopped answering calls or texts after agreeing to meet the other day before giving me her address. Today she finally texted back with her address so I'm picking it up tomorrow and the fun can begin.

Currently I'm trying to think of ways to impove the efficiency beside using two blowers. I need to see how much heat my 4'x10' unglazed pool heat collector will pick up on a sunny day. Then I'll decide if it's worth filling with antifreeze solution to set up a system to preheat the incoming evap air for the HP. Also considering using my shed as a greenhouse of sorts as it will get a few degrees above outdoor air temp on a sunny day.

Adam

[AC_Hacker]

So right now it looks like my loop field is small for my entire heat needs, so overall, I am proceeding along three fronts:

• Reducing total heat required by reducing heat loss
• Reducing loop heat demand by augmenting loop heat with other high efficiency (low temperature) sources, solar and ASHP.
• Getting the very best efficiency out of the heat pump(s) by operating with the lowest feed temperature possible.

Originally Posted by launboy

If your loop doesn't have the extra predicted capacity, will you be able to run a bigger compressor without issues?

Good question. My next project will use a larger compressor (7,800 BTU/hr vs. 4,500 BTU/hr) and 30% larger HXs. One thing I now know is that regarding GSHP, the ground loop is where the heat is coming from, so there is a pretty sharp "knee curve". If the compressor is actually matched to the heat capacity of the loop field, a bigger compressor will not buy more heat. In the case of Randen's heat pump, he put in a really large loop field, so a bigger compressor will likely give him more heat... but there is a definite point beyond which, more compressor just gives you a faster decline in loop temperature.

I did the best I knew to determine the thermal performance before I put in the field, but my assumption, regarding several small holes being equal to one big hole was wrong. Truth is, I don't know exactly what the thermal capacity is of my loop. I should test the loop as a whole, using the previous method, and I would be much more sure. I could also move ahead with the new heat pump and see how it goes...

By all rights, testing the entire loop field should be my Plan A.

Plan B might be to try a different heat pump setup and monitor the difference.

So my current thinking is that by splitting the one loop into two loops, and running them in parallel, I can reduce the loop pump power to 25% of its previous level. so instead of 250 watts, it would need to be about 60 watts... much better... So I should have that part of the problem solved.

Also, instead of running a small pump continuously, I will be running a larger pump intermittently, and using a buffer tank as a heat reservoir. So the heat pump will run until the buffer tank reaches its set-point, and I will draw heat from the buffer tank, as required... This tank can also be used as a reserve for some modest solar contribution, and additionally as a store for an ASHP.

Because I am trying to make a system that will have the lowest possible feed temperatures (best heat pump performance and also lowest rate of heat extraction from the loop field), my previous plans have included a high efficiency radiant floor for my final heat exchanger... that looked to be the very best route for me to take. High efficiency floors are not a given... There are lots of configurations of radiant floors, though fairly easily built, are not such good performers. An example would be widely-space staple-up, even with spreader plates is not such a good performer and will require higher feed temperatures.

I have seen top of floor systems that use thick aluminum plate and have grooves for the PEX. These look really good... the downside is very high cost, and the fact that they lock you into 12" spacings.

WarmBoard Thermal Image

I have even seen thermal images of this system (see above) and it is clear that closer spacing would bring great improvement. This system (warmBoard) looks to me to be the best there is. If there was ever a place for some awesome DIY development, this is it.

I have recently become very intrigued by fine wire heat exchangers. If their performance is as good as their sales literature suggests, it would make a huge difference for me. I wouldn't have to massively re-design my floors, I might even be able to get by with lower feed temps, and it could be cheaper.

Originally Posted by launboy

Did making the ground loop two parallel runs have any impact on its feed and return temps?

The ends are coming out into the basement, but I don't have them plumbed together yet, but I see no reason to suggest that there will be any difference.

Originally Posted by launboy

I think your plan to use solar or ASHP heat when it's more efficient and relying on the ground loop more as backup or additional capacity is the ideal way to set up a system like this, a lot less taxing on the ground loop for sure.

Yes, I did see some studies that spoke very favorably about the advantages of leveraging several overlapping modes of heating, specifically GSHP, ASHP & solar. I wish I could claim the idea as my own.

Originally Posted by launboy

Your note on ground loop temp difference in tenths of a degree resulting in full degree swings in basement temperature is very interesting to me. What sort of temp difference did you notice in heat loop temp when the ground loop temp changes occured?

Well, pretty much just as I said before. There was a delay, as some kind of event, usually warmer air, ore rain, but especially warm rain happened. It took maybe 3 days for the heat-pulse to slowly work its way down through my loop field... but a 2 or 3 tenths loop temp difference would mean a 4 to 6 degree temp change... the reason is that I had many tons of earth holding many BTUs of heat and the heat pump would gather and concentrate this energy and bring it in to the basement. If I had been running the heat pump with a thermostat, I probably wouldn't have noticed. In fact, toward the end of the test, I did put in a thermostat set to 60F, and the basement temp went flat, as I thought it would.

Originally Posted by launboy

Very excited to hear you got the portable unit up and running! Is this the unit you're considering using for the final version of your heatpump?

Probably not, because I think the compressor is too big.

Originally Posted by launboy

It seems this would be ideal considering it's already got controls and a reversing valve integrated, all you'd have to do is switch it's exchangers no?

Pretty much, I'd still need to re-route the reversing valve to work with an ASHP... I'll actually need to think this through a bit more... you may be right.

Originally Posted by launboy

Even comes in a nice housing that I'm sure would fit both brazed plate exchangers, resulting in a professional looking final product.

Well, I think I'd be more pleased if I found a 1 Ton Mini-Split Air Conditioner... like I said before, there are quite a few concessions made in this design to favor portability.

Originally Posted by launboy

That HVAC group you found sounds like a really cool idea, how'd you go about finding these people near you?

I'd have to thank my son for that find. The HVAC guy is one of his Bike Polo friends. I think the HVAC guy has other green HVAC hackers that might be interested.

Originally Posted by launboy

This guy has a very interesting blog, he has a(what I believe to be) standard York Heatpump condensing unit hooked up to a coaxial HX for hydronic house heating.
Oikos Blog

I'll check it out...

Originally Posted by launboy

... the window unit... so I'm picking it up tomorrow and the fun can begin.

Indeed, keep us posted, lost of pix.

Originally Posted by launboy

Currently I'm trying to think of ways to impove the efficiency beside using two blowers. I need to see how much heat my 4'x10' unglazed pool heat collector will pick up on a sunny day. Then I'll decide if it's worth filling with antifreeze solution to set up a system to preheat the incoming evap air for the HP. Also considering using my shed as a greenhouse of sorts as it will get a few degrees above outdoor air temp on a sunny day.

I think if you have ASHP you can improve thing by heating the incoming air.

The discussion I read before on this topic pretty much veered off the road. People are getting hung up on the idea of a space full of warm air...

What is needed is extra BTUs coming in, it makes no difference if the space feels cold, if there are extra BTUs, it will be of benefit.

I think a 4' x 8' box with a couple of levels of metal lath painted black, would make an excellent pre-warmer. Top it wil glass or plastic, forget insulating the box, be sure to not restrict the flow of air into the ASHP.