The Homemade Heat Pump Manifesto

[Ko_deZ]

@randen

You might know this already, but I will explain anyway in case someone reads this post. The reason for your high humidity is the temperature you get from your ground loop. I will try to explain.

Take a look at this: File:Relative Humidity.png - Wikipedia, the free encyclopedia

When you have 36C outside at 50% humidity, when you cool that down to 21C, you are at >100. This gives condensation, which is what you see. I expect most of this to happen where the cold water enters the heat exchanger, as at 17 dew point is even lower. Now, you say that the exit air has 21C. When you dehumidify air, you must get the temperature down to below the dew point, which you do. At that point the RH is nessesarily 100%. If you the go up from 17C to 21C, the RH will still be very high, and you don't even go down to 17C over the entire heat exchanger, so it will actually be even worse.

So, what options are there. Well, you could dehumidify the air by cooling it even further with a small AC. That is a good idea, but it sounds to me like you should also consider another improvement as well. You said that there where a lot of condensed water, constantly. This can only be explained by moisture being added to your indoor air constantly, either from outside, in which case your building is not very air-tight (you might even have a window open for fresh air), or from inside. If you burn hydrogen gas, propane or something, that increases the amount of water in the air. If the first is your real problem, you can improve it by making your building more air-tight. You get special age resilient tape that can be used to improve air tightness. You want it as air-tight as you can. Well, that would give crap indoor air quality you might say. Yes, that is true, but then you must install a regenerating balanced ventilation system. What this does is to regenerate heat/cold from the exiting air, and reapplying it to the incoming air, and in doing so, naturally also dehumidifies the incoming air during summer, and humidifies it during winter. The reasons for this will take some time to explain, but I can confirm that it works both in theory and in practice as I have such a system in my house. Most systems uses a regenerating wheel in the ventilation unit. As a bonus, you will not pull in air that is the outside temperature, but it will be pre-heated/cooled by the regenerator. Some of these are up to 90% efficient, some even more. Mine should do about 93% when running at the lowest speed. That means that the fresh air coming in, when I have 20C inside and there is -20C outside, would be heated to ~17C. That leaves very little energy needed to get it up to the indoor 20C I want. It also means that the outgoing air will be at about -17C, and already dehumidified, so I will not get a huge lump of ice forming around the ventilation exit pipe.

Another option would be to make the extra "dehumidifier" pump pull air from the inside and send it outside. That would give you an indoor low pressure so that you know cold air always exist trough the dehumidifier, and thus makes use of the cold air instead of using the warmer outside air to give the extra cooling. This will pull in a lot of humidity as well, but will give the dehumidifier a higher COP.

-Ko_deZ-

[AC_Hacker]

* * *
I'm sure that I am not alone in expressing how very sorry we are
about the terrible tragedy that has happened in your country.
* * *

Originally Posted by Ko_deZ

I got in touch with a metallurgy professor, which seemingly had a great time talking about other things than his mundane everyday customer questions...the high hydrogen content of the Thermolene will make the weld brittle, or at least more brittle.

I am not a metallurgy professor, or even anything close, but I did do some web searches on the MAPP (AKA: Thermolene) gas issue and found this in Wilipedia

The MAPP/oxygen flame is not entirely appropriate for welding steel, due to the high concentration of hydrogen in the flame - higher than acetylene, but lower than any of the other petroleum fuel gases. The hydrogen infuses into the molten steel and renders the welds brittle. For small-scale welding with MAPP this is not too serious a problem as the hydrogen escapes readily, and MAPP/oxygen can in practice be used for welding small steel parts.

So it looks to me that the brittleness issue is a problem when welding steel. In our work we are brazing copper and maybe brass. I know that MAPP gas is widely used for HVAC in the US, apparently without brittleness being a problem.

...and I also found this:

MAPP gas although great for soldering, heating and brazing, it is not suitable for welding due to the high concentration of hydrogen in the flame which renders the weds brittle, this is because the hydrogen infuses into the molten steel.

Originally Posted by Ko_deZ

With propane in the system, a sudden big leak in an enclosed area could be less than desired.

You are quite right to be concerned about the safety of a significant amount of propane escaping into an enclosed area. In the UK, they keep propane charged refrigeration equipment in seperate sheds or enclosures, well removed from dwelling spaces.

I have noticed other countries that use propane, employ sensors in conjunction with venting fans (non-arcing relays, switches and motors, of course.).

I would not recommend acting in violation of your local laws that concern such issues.

There may also be implications regarding insurance, too.

-AC_Hacker

[kbonk]

Found these if any one is looking for matched flat plate heat exchangers, might be too small but thought I would share. I would think they could be flushed out for use.
Stainless Steel Brazed Plate Heat Exchanger 8x3x1.5 In | eBay

[AC_Hacker]

Originally Posted by kbonk

Found these if any one is looking for matched flat plate heat exchangers, might be too small but thought I would share. I would think they could be flushed out for use.

Yeah, pretty good price. These could be used in series and/or in parallel to get more heat transfer surface area, too.

I have had good luck brazing to stainless, but it then again it was a type of stainless that was meant to be brazed to.

I used a pair of HXs similar to these on my prototype unit that had a very small compressor, but the overall efficiency and performance was very good. It would make a very efficient GSHP heater for a well-insulated medium sized room.

My HXs were 8 x 3 x 1.75 (20 plates). So these might be (wild guess) 16 plates. I would estimate their transfer capacity (wild guess) to be in the neighborhood of 4000 BTU/hr.

The compressor I was using drew about 400 watts, so you might have a hard time finding an AC compressor that small. My compressor was from a 25 pint per day dehumidifier... that's a really small compressor.

But I have had a lot of fun building the unit, and I have learned more than I could possibly have imagined.

You might want to buy one or two and do some test brazing to see if it will braze ok. When you braze stainless to copper, you need to clean everything up really well, and use the appropriate flux. I used Silfos flux and MAPP gas and 5% Silfos rod worked good. Practice out at the end of the tubes.

Best of Luck...

-AC_Hacker

[Ko_deZ]

Thank you AC.

For my part I know noone directly affected, but several of my friends where really close to the blast, but naturally, in such a small country like ours (city of Oslo is 600k people, entire country < 5million), everyone is affected. A big chunk of downtown Oslo is wrecked, but of course the real tragedy is that we have a serial killer here with a shady world record number of separate killings, mainly kids. What a waste.

[Ko_deZ]

After extensive searching, and finally through some people I know, I have found a Chinese company that makes heat exchangers. Compared to dudadiesel, these guys can deliver a b3-32a 20 plate to a little more than a third of the prize. I have ordered five since this was favourable with regards to the shipping (21 kilo approx). Also I got to choose the quality of the steel and the connectors. My train of thoughts cant stop me from thinking that the longest possible exchanger is the most efficient. Will be interesting to see how these work out. Dudadiesel claims 5-15kW on these, which is way more than I will use them for. I should receive these units in a couple of weeks, and if they turn out to be excellent, I will post information here, together with homepage and contact info. From the ordering process, these guys seem to know what they are doing. They will even have their engineers help select which heat exchanger to use, liquid to liquid or gas, gas to gas, or evaporator/condensers. Very cool, but you really must have full control of your system, because all the different pieces of information ended up as a whole lot. I am really looking forward to getting started for real now. Too much work to be done outside the house right now though.

-Ko_deZ-

[AC_Hacker]

Originally Posted by Ko_deZ

After extensive searching, and finally through some people I know, I have found a Chinese company that makes heat exchangers. Compared to dudadiesel, these guys can deliver a b3-32a 20 plate to a little more than a third of the prize. I have ordered five since this was favourable with regards to the shipping (21 kilo approx). Also I got to choose the quality of the steel and the connectors. My train of thoughts cant stop me from thinking that the longest possible exchanger is the most efficient. Will be interesting to see how these work out. Dudadiesel claims 5-15kW on these, which is way more than I will use them for. I should receive these units in a couple of weeks, and if they turn out to be excellent, I will post information here, together with homepage and contact info. From the ordering process, these guys seem to know what they are doing. They will even have their engineers help select which heat exchanger to use, liquid to liquid or gas, gas to gas, or evaporator/condensers. Very cool, but you really must have full control of your system, because all the different pieces of information ended up as a whole lot. I am really looking forward to getting started for real now. Too much work to be done outside the house right now though.

-Ko_deZ-

This is very good news regarding the heat exchangers. The high price of large capacity brazed plate HXs has been a obstacle to progress.

This single breakthrough could start a tsunami of homemade heat pumps...

I have my fingers crossed that the HXs turn out to be good quality.

-AC_Hacker

[randen]

Ko_deZ

The explanation for the humidity of the (ground loop only)air conditioning is true to result. This arrangement was only the prelude to a GSHP system I intend to assemble and to provide some relief from the summer heat in the shop. The shop itself is insulated well and fairly air tight. The shop originally had a 2T air to air conditioner that on very hot humid days would not keep up expecially with the machines running. I would expect the 3.5T GSHP would do very nicly.

Looking very forward to the hack The compressor is removed and the electrics are in a box. I have the circulation pumps, one is on the loop and the other is waiting in another box. Currently I'm machining a 4 way valve. This will exchange the flow of water/glycol from one HX to the other HX. Cooling/Heating. The copper tube is just placed in for a visual upon assembly it will be silver soldered into place.

Randen

[Ko_deZ]

@randen

Good to hear that theory fits with the actual world =)
I would _strongly_ suggest one small thing. If you do not intend to have lower temperature indoors than the temperature in the loop, keep using that heat exchanger. Tunnel the air then on to the heat pump heat exchanger. Then you will precool the air at least slightly (unless indoor temperature is lower than the ground loop of course). Every little bit of cooling that is done directly is pretty much free energy. Also, put your fan before all heat exchangers, so the heat from that motor also is cooled for "free".

About your 4way valve. Very interested in your solution there. I have not been able to find a good provider for such a valve. Hopefully it does not transfer too much heat between the circuits.

[pachai]

Has anyone had success with converting an air conditioner to a heat pump without breaking the circuit?

I have an air conditioner that would make a great donor, as it is free and has a bad blower fan. (although, if I open it, I might find the one loose wire :-)

The work on my house is getting close to completion, and so my multiaqua hydronic air handlers will be installed soon.

As far as the 4-way valve is concerned, my friend mentioned an idea which I am thinking about.

What if you had 2 buffer tanks, one cold and one hot, and the repurposed air conditioner always moves air from the first to the second. Then, as my friend said it, you just switch which heat exchanger is immersed in which storage tank.

I am very much leaning in the direction of used 55-gallon plastic drums. I had googled them, and found they were cheap enough, but shipping would be expen$ive. Then I learned that a friend of a friend sells cleaning supplies...including liquid soap....that comes in these drums.
He puts them out for recycling, and the City takes them to use as garbage cans. And, his truck makes deliveries around town, so he doesn't mind dropping them off in my driveway.

I need 2 for my rainwater collection system, and a few for my Hot water Storage, Chilled Water Storage, and Off-season Water-glycol storage.

If implemented as I imagined, at the end of the winter, I move the ground pump discharge over to the off-season barrel, and run the pump dry. Then Seal the barrel. Move ground loop in and out over to the hot tank; move the radiant discharge to the cold tank and run the pump until the hot tank is empty, then move the intake to cold and refill the hot with water.



BTW, one question that comes to mind....will the compressor work properly if it is not in the original upright orientation ? (I fear I know the answer :-)


BTW2 - What are people using for pumps? Unfortunately, I think I need a pump with about 25' of head, which is more than an inexpensive Grundfoss that I saw.