The Homemade Heat Pump Manifesto

[jeff5may]

Pegasus,

Your pressures displayed in the photos look pretty darn good for a system retrofitted with propane. Have you measured your heat transfer? From your description, it looks like your evaporator us doing well. But what about the condenser? Your high side pressure looks good for a domestic water heater or air-cooled condenser. Depending on the conditions in the condenser, you may or may not stand much to gain.

Remember that r22 and r290 are pretty much polar opposites except for their similar pt curves. Where r22 does not fare well with superheat, with r290 a little extra is not a bad thing. Where r22 and oil do not mix well, r290 and oil mix like co2 and water. Running the superheat too low could fill your evaporator with frothy foamy blend that doesn't transfer heat well at all. If the evaporator cannot digest it all, you're in for a nasty surprise. Don't ask me how I know, proofs are overrated and such.

[Pegasus]

Originally Posted by jeff5may

Pegasus,

Have you measured your heat transfer?

No, I haven't measured the heat transfer yet, I plan to install a heat metering device in the next set-up. I am guessing though, I am not utilising all of the evaporator for two reasons :

a) On the first run with R-22, I was getting water chilled down to 19 deg C and on the other end, the discharge temperature was in the range of 70 deg C.

b) Now with R-290 I am getting 20 deg C (with less heat load!) and a discharge temp ~50 deg C. This indicates that there is less heat pumped than with R-22.

I have added more propane (~ 800 gr in total) because I thought that the liquid might be pooling in to the condenser since it is sitting lower (into the barrel). I now have a subcool of about 18 deg C without lowering the chilled water temp but with rising the compressor Amps by ~ 0.5 A

I followed the trouble shooter and since the pressures seem OK it points to "liquid restriction" witch in my case would be either the filter or the TXV orifice.

When I changed from R-22 to R-290 I didn't change the filter, could it be blocked?
Is the R-407 filter suitable for R-290?

Attached are a few more doc's.

[Pegasus]

Originally Posted by jeff5may

Pegasus,
Remember that r22 and r290 are pretty much polar opposites except for their similar pt curves. Where r22 does not fare well with superheat, with r290 a little extra is not a bad thing. Where r22 and oil do not mix well, r290 and oil mix like co2 and water. Running the superheat too low could fill your evaporator with frothy foamy blend that doesn't transfer heat well at all. If the evaporator cannot digest it all, you're in for a nasty surprise. Don't ask me how I know, proofs are overrated and such.

To be honest, when I released some propane from the low side it came out with some foamy oil !!! (it settled within a few seconds). If that' s the case then the solution would de a bigger evaporator?

P.S. I am really tempted to ask how do you know !!!

[jeff5may]

I was running trials on a window a/c hacked into a window heat pump. I was adjusting the txv so it would run with less superheat so that my evaporator would run closer to its maximum effectiveness. I turned the adjustment nut a little too far, and the unit let me know. I can't say exactly what happened, because I didn't have a sight glass installed in the suction line leading into the compressor. I was scolded by fellow ecorenovators for not having a sight glass installed, but I could tell what had happened without one.

[mejunkhound]

'how do you know'

re: pipe slope and oil

43 years ago built first diy HP from 1968 Chrysler AC which was a 2 cylinder recip compressor. Drove it with a 5HP 184T frame motor (real 5 HP).
Worked great or a few months.

Learned about suction line slope and non-compressible oil slugs when a connecting rod got driven thru the cylinder head!

[SeagoSteve]

AC Hacker et al,

I am really enjoying this thread, (on page 20 and still reading) but I wanted to jump up here and pose a question, (if the answer has been covered, please feel free to tell me to keep reading)

My question is, would it be possible, and is there any gain in performance to be had, by adding a coaxial heat exchanger to the outdoor coil of a conventional air to air heat pump, along with a ground loop.

The goal would just be to help supplement the performance when the existing coils during the very hottest days, and maybe allowing the heat pump mode to actually function on a few more of the coldest days of our crazy Texas seasons.

Anyway, thanks again for the thread, I'm digging back in to it!

~Steve

[AC_Hacker]

Originally Posted by SeagoSteve

AC Hacker et al,

I am really enjoying this thread, (on page 20 and still reading) but I wanted to jump up here and pose a question, (if the answer has been covered, please feel free to tell me to keep reading)

My question is, would it be possible, and is there any gain in performance to be had, by adding a coaxial heat exchanger to the outdoor coil of a conventional air to air heat pump, along with a ground loop.

The goal would just be to help supplement the performance when the existing coils during the very hottest days, and maybe allowing the heat pump mode to actually function on a few more of the coldest days of our crazy Texas seasons.

Anyway, thanks again for the thread, I'm digging back in to it!

~Steve

Not a bad question!

What you are proposing would be called a "Hybrid" system. It calls for more information than you have provided to give you a full and complete answer.

The general thinking would go along these lines:

• Ground Source is substantially more efficient than Air Source
• Ground Source is substantially more expensive than Air Source
• Air Source is substantially less efficient than Ground Source
• Air Source is substantially less expensive than Ground Source

When you put all this together, it would be possible to hit an economic 'sweet spot' with a Hybrid system that could be more cost effective, over a given time span than either a pure ASHP or a pure GSHP.

In the long term, GSHP wins out... but the question is the length of that break even point.

You'd have to really know what the heat/cooling load will be, and you'd have to have a realistic knowledge of what the 'per-Ton' cost of of the GSHP installation would be.

It is a very interesting and advanced problem, but it is solvable, and it is being done, particularly in large projects.

Best,

-AC_Hacker

[SeagoSteve]

Thanks for your reply AC,

I'm for sure going to keep noodling this. I'm thinking the savings may be there for a DIY mod, since you already have equity in the existing Air to Air system.

At any rate, excess capacity for for heat transfer provided by adding a ground loop shouldn't have any downside should it? Aside from the possibility of not paying itself back? (If I can stay off the aux heat strips a few days a year there would be some savings)

~Steve

[AC_Hacker]

Originally Posted by SeagoSteve

Thanks for your reply AC,

I'm for sure going to keep noodling this. I'm thinking the savings may be there for a DIY mod, since you already have equity in the existing Air to Air system.

At any rate, excess capacity for for heat transfer provided by adding a ground loop shouldn't have any downside should it? Aside from the possibility of not paying itself back? (If I can stay off the aux heat strips a few days a year there would be some savings)

~Steve

I jut saw where you are located, and that cooling will be the primary application, even though the concerns are pretty much the same, either way.

One of the motivations for doing this whole 'Manifesto' thread is to show that doing your own modifications and installation has a very dramatic effect on payback time, and that very high efficiency can be achieved at very reasonable cost.

The Ground Source segment of such a project is at lot of work and if you hire it out it is very expensive. In fact, the installation of the loopfield is the major part of a project such as you are considering, both in work and in cost.

• Do you have property on which to build a loop field?
• Do you have access to serious earth-digging machinery?

If you are still thinking yes, then there are information sources and procedures you need to become familiar with.


-AC

[superlen]

AC,

Just a quick post to say thanks for getting this thread started. I rolled my own GSHP several years back and had this resource (or more importantly, friendly interested people to bounce ideas off of) been available it would have saved me some steep learning curves. My original loop field sprung a leak after a few years and I tabled that field for a bit... that was back in 2006 I think (a bit turned into to more than a bit). I have made many changes to my house since then & have always had plans to build another better system, but too many projects and not enough cohorts to share the design with have stalled my start.

Now, that I know there is a community that I can share with, I'll be more motivated. At the time I was active there was only hvac-talk (OMG, that bunch will suck the superheat right out of your sails). Anyhow, Thanks.

Len