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Old 01-11-20, 04:24 PM   #1
vlada33
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Default Homemade 2 ton HP, air to water now, DX in future

Hi people,

I'm sorry if my English isn't perfect...

Just to say few words about my project that it's in progress for some time now. First of all I find some scrap AC 21000btu cooling and 23500btu heating. Indoor unit was damaged and price was low for that reason, and because it can be used like it was made I dexide to take outdoor unit and make HP from it. Reason why HP need to be air to water or direct expansion to water is that houses in Europe usually are made from bricks and concrete and walls are not empty so tunnels for heating and cooling are not possible to made when house is already made. In my case house is almost been finished, and I lose option to make a floor heating (that will be best option in my case) so in this setup I will try panel radiators and fancoil radiators.

Outdoor unit using R407c, in this moment i'm think that it's little low with refrigerant, indoor exchanger freon to water is swep b25th and it's possible that is undersized for power that HP produce.

I have many pictures and i will post it soon, but first to say few more words about problems I have with it, maybe someone is HVAC technician and can help...

Problem that I have is low temperature water, freon temperature is ok, it will be few degrees higher when I add refrigerant to normal level but even than I will be low for 5-8 degree Celsius(that is somewhere about 10-15F I think) , and difrence between temperature of freon and water is to big, about 10 degrees Celsius

Solutions that i'm think about

1.Changing exchanger for bigger one, maybe will bigger excanger give few degrees extra...

2 Maybe just to somehow get more heat from freon, and that is going in few ways,

is it ok to put more R134a to mixture of R407c (R134a on same pressure has much bigger temperature than clean R407c) so can I expect that I get lets say 5 degrees more with that mixture?

Maybe to change refrigerant and use R22 (bad for environment but better heating) maybe this is last option I don't like to destroy nature?

Or maybe to change refrigerant to R290, also better temperature but its flammable and I'm not sure how will compressor will react?

I hope that post will not tired you with reading, and I'm apology for very very long post...

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Old 01-12-20, 08:05 AM   #2
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Here are some photos taken in time when HP was not complete
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Last edited by vlada33; 01-12-20 at 08:12 AM.. Reason: Pictures missing
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Old 01-16-20, 01:24 PM   #3
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More data please. We can see the big picture here, but details are lacking. Main question: what's the outdoor unit? Obviously rated for 2 ton, but what refrigerant is original and how does it control? Bang bang, on off constant speed? Cap tube or expansion valve? Static data to define envelope.

Next realm of data is operating parameters. Obviously you have run the rig, and are looking for something to improve.
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Old 01-16-20, 05:20 PM   #4
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I forgot to mention all details, some of them are somewhere in text...

Unit using R407c refrigerant, it's mix of R32, R125 and R134a, in Europe that refrigerant is substitute for R22 (I'm not sure does R407c is in use in USA) and it has almost same characteristics like R22. This unit is fabric made for R407c, also metring device is fabric capillary tube that I will change for TXV when I will be sure that this unit have enough power to heat my home or I will change whole unit with stronger one.
In this moment it's controlled by already existed controls of inside unit, sensor for coil temperature is put on copper tube after exchanger (water line) and room sensor is put in main room, that part of this unit work without any problem.
Yes, I run the rig and it runs in this moment also, but I'm not satisfied with water temperature, I need few more degrees...

My low pressure is also low 3 bar's, high pressure is about 22-23 bar's, temperature of refrigerant (high side) is about 52 to 58c (Celsius), water output 42c water inlet about 37c,temperature of refrigerant low side is minus 4c ( - 4c).

Like I said before i need a few more degrees of water output, this temperature for me is not enough to heat up my home,probably it will be enough for radiant floor but my house was already have finished floors and there is no way to change that because it's made from concrete...

Now I want to try to change something to get few more degrees on water output
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Old 01-16-20, 11:48 PM   #5
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Ok, from some quick napkin scribbling, the refrigerant charge and outdoor side looks to be in the standard operating range. The bottleneck here seems to be the brazed plate heat exchanger and or too much heat sink and or too high water flow rate through the brazed plate heat exchanger.

The devil is in the details. I haven't seen any information about the indoor heating setup, so that part of the story is still a blank. Staring into the void, I would say measure the water flow rate through the brazed hx and calculate your heat flow. Slow the water flow down to see if the parameters change. If you find a happy place, you're golden. If not, the numbers will point you in the right direction.

Last edited by jeff5may; 01-17-20 at 04:09 PM..
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Old 01-17-20, 05:26 AM   #6
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Indoor unit is b25th10 swep (only 10 plates and capacity is 0,44 l (litres) and probably that is the biggest problem. Even when I put water pump to slowest speed (3 speed grunfos pump) it look that water still pass through exchanger to fast.,when i stop pump for 3-4 seconds and turn it on again water is hotter (i can't measure temperature because of short time) and it look like that water need to spend more time in exchanger,because of this I already looking to find some bigger exchanger probably 30 plates.

Also I was thinking about the way to get few more degress on refrigerant side.
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Old 01-18-20, 05:10 PM   #7
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Ok so the refrigerant temperature and pressure will follow the heat exchanger temperatures. Obviously you don't have enough indoor heat exchanger or heat store or both. Adding more charge to try to get over the top never ends well. Something goes pop or trips on overload. Don't let out the magic smoke, it happens inside the plumbing. Unless it pops.
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Old 01-18-20, 05:31 PM   #8
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Then I suppose I will not try to add more refrigerant before I find bigger exchanger.

Real problem in this moment is that January is cold and we have many foggy days, so outdoor unit is almost always freezing,so capacity is very low. Because of that I need some extra power, and that is reason why I planning direct expansion like final solution for HP.

Thanks on advices...

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