The Homemade Heat Pump Manifesto

[Vlad]

I do not think that you should use refrigerant inside your floor because:
1. Potential health hazard. Modern refrigerants become more and more toxic.
2. Huge temperature difference at the different floor areas
3 low temperature will lead to low discharge pressure and low efficiency.
4. Low discharge pressure will lower system capacity
5. Many components in your system work efficiently only together.
6 You can have problems with oil and refrigerant flood.
This list can be much longer.

AC_Hacker I saw your explanation how to choose compressor in one of the posts. You said that AC compressors are more robust this is why you should use them for heat pump. Actually the best compressors are refrigeration compressors, but you can not use them in heat pump application because of their compression ratio. They are built to pump low density low temperature refrigerant vapor.

You have to be a refrigeration mechanic at least to see all aspects. Refrigeration system is a SYSTEM you can not change something without affecting rest of it.

[Vlad]

To size compressor for your system you have to have ALL your parameters ready.Things like suction temperature/pressure, discharge temperature/pressure, load, refrigerant, lines run, lines diameter and many other. You can not change them on the go. The same compressor will have different capacity if you change temperature range. You can not use watt meter to determine compressor (system) capacity.

[AC_Hacker]

Originally Posted by Vlad

AC_Hacker I saw your explanation how to choose compressor in one of the posts. You said that AC compressors are more robust this is why you should use them for heat pump. Actually the best compressors are refrigeration compressors, but you can not use them in heat pump application because of their compression ratio. They are built to pump low density low temperature refrigerant vapor.

This is good to know. Now I can reccomend A/C and de-hymidifier compressors for the right reason.

Originally Posted by Vlad

1. Potential health hazard. Modern refrigerants become more and more toxic.

Isn't this a good argument for not having any refrigeration equipment inside a house?

• Refrigerators?
  
• Air Conditioners?
  
• De-Humidifiers?
  
• Heat Pumps?

Originally Posted by Vlad

3 low temperature will lead to low discharge pressure and low efficiency.

Can't this be corrected by design and experimentation?

Originally Posted by Vlad

4. Low discharge pressure will lower system capacity

Can't this be corrected by design and experimentation?

Originally Posted by Vlad

5. Many components in your system work efficiently only together.

Can't this be corrected by design and experimentation?

Originally Posted by Vlad

6 You can have problems with oil and refrigerant flood.

I would assume that this could happen in the field. What causes it? How do you fix this?

Originally Posted by Vlad

This list can be much longer.

I'm sure the list could be much, much longer...

Originally Posted by Vlad

You have to be a refrigeration mechanic at least to see all aspects.

I built a small heat pump from a de-humidifier that was essentially thrown away because it was of no further value.

I also used heat exchangers that I bought, at the time with no idea what their capacity might be.

And I brazed it all up without really even knowing how to braze anything.

Want to know why I did this? it's because I found out that children were doing this before I even tried. That's right... children led the way, because they wanted to play video games faster, and they knew that if they chilled their CPUs they could run their video games faster than they were supposed to be able to.

And you know what? It worked. In fact I'm getting a COP of about 4 by running water through the ground loop field I was not suppose to be able to build.

And I dug holes for the loop field with a 1/4 horse motor drill (and a shop vacuum). Any well-digger knows 1/4 horse motor is not enough to dig a hole.

But I did it anyway.

And it worked.

So Vlad, I have great respect for your experience and training. I am very impressed by the drilling rig you built.

If you know something that can help us in our efforts to build refrigeration equipment out of junk, please tell us. I'm ready to learn, and I'm sure the people who have contributed to the 74,000 hits on this thread, are also ready to learn (that's why there are 74,000 hits on this thread).

But don't try to tell us that this stuff is too complicated for non-experts to do. I have already proved that idea wrong, and so have the many hundreds (maybe even thousands) of children who have made CPU chillers for their video games.

We, who have become part of this thread, by reading and by sharing our questions and ideas, are ready to build, ready to test and re-build, ready to learn...

Because we know that if it can be done by children, it can be done.

The secret is out.

Best Regards & Happy New Year!

-AC_Hacker

[AC_Hacker]

Originally Posted by North_Pole_Guy

...am getting a pretty steady 320watts X 2 X 3.412 gives me 2,183.68 BTU's/hr.

This looks pretty good to me. On with the show...

Originally Posted by North_Pole_Guy

I think I would like to at least try to recover the refrigerant with a setup like what you showed. I have a friend that does heat and vent work for a living if I get into a bind I imagine that I could get him to help.

Sounds good. If you learn anything new, you gotta share...

Originally Posted by North_Pole_Guy

So I looked on granger.com last night and see you can buy all kinds of refrigerant (with proper paperwork) but no R12.

Yeah, like I said, this was the worst one for ozone damage... It got nixed right away. Good thing too. The R-134a and R410a are not so bad for ozone, but are very bad for global warming.

In time, the whole refrigeration industry may be forced to use organic refrigerants.

Sounds like you're on the right track. Keep us posted.

Regards & Happy New Year!

-AC_Hacker

[AC_Hacker]

I have been wrestling with the problem of radiant heating design when using a heat pump, and I have just made a significant, but small breakthrough.

The Problem:

Most of the design methods available for radiant floor heating are based on fossil fuels which in the past were very cheap, and could easily produce very high temperatures.

Heat pumps can offer a much higher level of efficiency, but only if the limited temperature range, at which heat pumps work best, is exploited in the design.

The Solution:

Now there is a term for it: Low Temperature Heating

I was searching over material which addressed the design of radiant heating, using heat pumps and I came across a page on ASHRAE Learning Institute Seminar and Course Descriptions. I noticed that the conventional offerings were at the top of the page, but down at the bottom were some very forward-thinking seminars. One which caught my eye was called Low Temperature Radiant Heating & High Temperature Radiant Cooling Systems.

So then I found references that there is information (some free) available:

• The LowEx Guidebook
• Low Temperature Heating
• REHVA Guidebook nr 7
• NO: 7 Low temperature heating and high temperature cooling
• Low Exergy Systems for Heating and Cooling of Buildings
• Low Temperature Hydronic Heating System with Radiators and Geothermal Ground Source Heat Pump
• Hydronic Alternatives
• Swedish Dissertations
• Before You Star t an Energy-Efficient Retrofit

It looks like throughout these books, papers, and products, the one of the main principles is that for low temperature heating to work, large radiant surface areas must be brought into play.

From looking at most of these papers, these ideas are being developed primarily in Denmark & Sweden.

Best Regards,

-AC_Hacker

[Fred_Fredowski]

AC,

The heat pump you made is very impressive, and from the data it looks like its working pretty well.

I did a quick comparison of the pressures you measured against the data Goodman publishes for its GSH14 heat pump. This is a fairly efficient R22 air-to-air heat pump for which reasonable operating data is available online here:
"www<dot>goodmanmfg<dot>com/Portals/0/pdf/SS/SS-GSH14<dot>pdf"

I think the high side pressures compare pretty well. The GSH14 operates at about 190-220 psig with about a 100 degree warm air temp. This seems to match your data of 210 psig for 100 degree water.

There is a bit more difference with the low side pressures. It appears from the data that your unit stabilizes at about 40 psig with a 48 degree loop temp, and for propane this pressure corresponds to an evaporating temperature of about 20 degrees. For the Goodman unit, at a 47 degree outdoor air temp the pressure is about 60 psig, which corresponds to an R22 evaporating temperature close to 35 degrees. It looks like the Goodman heat pump works with about 15 degrees lower lift. This might be worth looking into as it has a big effect on COP.

I have a couple other thoughts:

1. Have you measured the dT in the water going through each heat exchanger? I thought that you mentioned that the sump pump was pumping about 2 gpm through the earth loop, so with a 5000 BTU/hr compressor I would expect about 5 degrees of dT across the low side heat exchanger. Is this what you see?

2. Have you measured superheat (SH) and subcooling? I think that if the SH is high, you might be able to resize the cap tube to reduce the pressure drop. This should increase the low side pressure and increase the COP. If the SH is not high and the water flow is up around 2 gpm then I would look at the low side heat exchanger and see if that is working efficiently. Many new heatpumps use a large outdoor coil/fan which it allows them to operate with lower lift even using air as the coolant. I would think that a water cooled unit like yours could work even better provided that the heat exchanger is efficient enough.

Please keep the posts coming ... I've really enjoyed reading about all your work.

[AC_Hacker]

Just a quick note, I just came across a PDF document called, "Geothermal Heat Pump Design Manual".

It is quite extensive and has loads of information, even including ground temperatures for various locations in the world.

If you have even a casual interest in Ground Source Heat Pumps, you would benefit from becoming familiar with the information herein.

(* Needless to say, it has no information on how to build a heat pump out of junk, nor does it tell a common citizen how they might construct their own loop field.*)

Seldom has so much valuable information cost so little...

Regards,

-AC_Hacker

[AC_Hacker]

Welcome,Fred_Fredowski to the conversation...

I downloaded the Goodman PDF you mentioned. I'm not quite sure which part has the information you are referring to, however.

Originally Posted by Fred_Fredowski

I think the high side pressures compare pretty well. The GSH14 operates at about 190-220 psig with about a 100 degree warm air temp. This seems to match your data of 210 psig for 100 degree water.

There is a bit more difference with the low side pressures. It appears from the data that your unit stabilizes at about 40 psig with a 48 degree loop temp, and for propane this pressure corresponds to an evaporating temperature of about 20 degrees. For the Goodman unit, at a 47 degree outdoor air temp the pressure is about 60 psig, which corresponds to an R22 evaporating temperature close to 35 degrees. It looks like the Goodman heat pump works with about 15 degrees lower lift. This might be worth looking into as it has a big effect on COP.

Well, first off I am very interested in improving COP, that's pretty much why I'm involved in this project. I'm interested in any approach that will improve COP.

Now, I do recall reading on one of the 'CPU phase-change chilling blogs' that the charge pressure level for R-290 should be lower than for R-22. It's been a while since I read it, but I seem to recall it was because R-290 has a lower density than R-22. I think the first time I charged the system up, I overcharged it and it never even made frost until I reduced the charge pressure level to be a good bit below that specified for R-22.

Originally Posted by Fred_Fredowski

Have you measured the dT in the water going through each heat exchanger? I thought that you mentioned that the sump pump was pumping about 2 gpm through the earth loop, so with a 5000 BTU/hr compressor I would expect about 5 degrees of dT across the low side heat exchanger. Is this what you see?

I just ran the system for about 40 minutes and I used a non-contact IR thermometer and measured off of the HX water and refrigerant fittings here's what I got (bear in mind that the system was changing all the while I was measuring it):

Low-Side HX

Water In = 56F
Water Out = 52F

Low-Side HX

Refrigerant in = 23F
Refrigerant out = 59F

High-Side HX

Water In = 95F
Water Out = 99F

High-Side HX

Refrigerant in = 123F
Refrigerant out = 93F

(* more comments to come, gotta break for a bit... *)

Regards,

-AC_Hacker

[bigsmile]

Like AC_Hacker, I tend to believe that most of the issues you listed here can be addressed by design and experimentation. For example, for 1, refrigerant is not supposed to leak out anyway. Ground coupled heat pumps also have large amount of refrigerant involved, and the system can be made leakage-proof. For 2, simply reduce the thermal conductivity of the in-floor refrigerant lines, so that the heat won't be mostly released in the first tenth or so of the length. For 3, I think it's not necessarily true that lower discharge pressure means lower efficiency. It depends on the compressor. You can choose the compressor to suit the pressure ratio. For 4, I believe it's quite the opposite, since for the same compressor, lower discharge pressure (lower pressure ratio) means higher flow rate, and thus higher capacity.

Originally Posted by Vlad

I do not think that you should use refrigerant inside your floor because:
1. Potential health hazard. Modern refrigerants become more and more toxic.
2. Huge temperature difference at the different floor areas
3 low temperature will lead to low discharge pressure and low efficiency.
4. Low discharge pressure will lower system capacity
5. Many components in your system work efficiently only together.
6 You can have problems with oil and refrigerant flood.
This list can be much longer.

AC_Hacker I saw your explanation how to choose compressor in one of the posts. You said that AC compressors are more robust this is why you should use them for heat pump. Actually the best compressors are refrigeration compressors, but you can not use them in heat pump application because of their compression ratio. They are built to pump low density low temperature refrigerant vapor.

You have to be a refrigeration mechanic at least to see all aspects. Refrigeration system is a SYSTEM you can not change something without affecting rest of it.

[bigsmile]

I only recently started to read about refrigeration and air conditioning, so I am really not sure about this; but it seems to me that the temperature difference between refrigerant in and out is quite big. More over, why the refrigerant out temperature on the low-side is even higher than the water that heats it? Same question for the high-side. It also looks to me to be too much super-heating and sub-cooling going on, which will increase the lift and thus reduce the efficiency. Perhaps a TXV can help? According to what I read, txv can control super-heating. And am I right in thinking that super-cooling can be controled by amount of refrigerant charged into the system?

Once again, I'm really new in this and not sure about what I said.

Originally Posted by AC_Hacker

Welcome,Fred_Fredowski to the conversation...

Low-Side HX

Water In = 56F
Water Out = 52F

Low-Side HX

Refrigerant in = 23F
Refrigerant out = 59F

High-Side HX

Water In = 95F
Water Out = 99F

High-Side HX

Refrigerant in = 123F
Refrigerant out = 93F

(* more comments to come, gotta break for a bit... *)

Regards,

-AC_Hacker