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busman
13-12-2004, 10:18 AM
Well, I'm a newbe to the forum, and wanted to get a little bit of insight on some design considerations.

This is a "basement" project, so no customers involved (just dear wife). I have built my own heat pump for my house, from a converted 10 ton Trane a/c unit. Now I want to build a heat pump water heater. By the math on paper, it's far, far more efficent than any means to heat water (resistance heating, or other fuels). So here's my question:

I'm building an outdoor unit, out of old 3 ton a/c unit. I found it out back of someone's store. Turns out tech condemned it for a bad run capacitor. So, I want to use this 'freebe' as my h/p.

In my designing, I'm wondering about defrost. I don't think that I really need a reversing valve, but just a silnoid valve to dump hot gas in the evap. I was going to coil copper tubing in the tank for the condensor, and leave plenty of extra to act partially as a receiver, but to give added capacity of refrigerant during defrost. When the h/g valve opens in defrost, hot gas will come off of the discharge line into the side connector of the distributor. When the hot gas is depleting during defrost, the liquid remaining in the condensor coil will begin to flash off and provide warm vapor to assist until defrost is complete.

Any thoughts, or design considerations I'm missing here before imbarking on this project? Thanks!

frank
13-12-2004, 09:54 PM
Now I want to build a heat pump water heater.

This is a good idea but the temps you will get for the water won't be very high, based on the condensing temperatures of the refrigerant.


I don't think that I really need a reversing valve, but just a silnoid valve to dump hot gas in the evap.

Again, a good idea, but you must ensure that you do not push liquid back to the compressor. The best way to do this is to control defrost by a pressure switch and ensure that you have a suction accumulator in the system.


I was going to coil copper tubing in the tank for the condensor, and leave plenty of extra to act partially as a receiver, but to give added capacity of refrigerant during defrost.

Any extra coil in the tank will not act as a receiver but an extended condenser due to the heat exchange possibilities. The receiver must be after the condenser. The receiver does not give added capacity to the defrost cycle.


When the hot gas is depleting during defrost,

During hot gas defrost the hot gas is supplied by the compressor. If the compressor keeps running then the hot gas is not reduced. Any temperature hot gas above the evaporator temperature will cause defrost to occur.

busman
14-12-2004, 05:08 AM
Okay, so there are a few details I have left out of the master plane on my first post.

1. Yes, suction accumulator will be employed.
2. Temperature of the water will not be as critical. I was primarily using this system to boost water temperature and decrease the rise in temp that my electric resistance water heater will be responsible for.
3. I was going to use a "de-superheating" coil at the inlet of the condensor, where the pre-heated water of the tank will pick up more heat before departing the system. (counterflow setup)
4. In hot gas defrost, (which I'm still learning about) there seems to be a need for a heat source, which appears to be the high side gas, and the heat within the compressor motor itself. Upon lengthy defrost periods, my feeble mind thinks that there maybe a point where heat will not be available to complete defrost. My theory on this operation is similar to that of Manitowoc's Cool vapor defrost. It uses cool vapor off of the receiever to complete harvest. Since the condensor coil will be imersed in a heat source (heated water), it could be used to assist in defrost, by providing warm vapor back off of the condensor.

My other heat pump (regular reverse cycle system) can actually shutdown on a low pressure switch during a significant ice build up on the outdoor coil. I have two heat pump systems in my house currently, both of which battle raging winds coming off a farmer's field in my backyard. Both tend to struggle during those times to defrost. I'm wanting to eliminate extended defrost times with this system if possible, due to it's unique situation.

frank
14-12-2004, 10:11 PM
The simplist solution would be to rewire defrost to energise (or de-energise) the reversing valve while keeping the compressor running, and inhibit the indoor fan during de-frost. No chance of a lack of de-frost then as the system would just be acting as a normal cooling only unit with the outdoor coil acting as a normal heat rejecting condenser.

busman
15-12-2004, 01:43 AM
Well, there's no reversing valve in this new water heater heat pump I building right now. It's an old a/c unit. That's why I wanted to see if I could use a simple silnoid valve for defrost, rather than a reversing valve.

peterweston
15-12-2004, 11:24 AM
can you load the evap with something else? maybe recover it. Or use the ground(a constant temp?). Would an off cycle be good enough for a defrost? how much water are you using?

busman
15-12-2004, 12:39 PM
Well, I could use a different heat source for the evap, but that would take too much time. I said in the first part of this thread, that this was a "basement" project, meaning, "yes I'm doing this at home, in amongst my other honey-do projects." I can't really dedicate that much time and energy to this project to dig up the back yard for a ground loop, as nice as that might be right now. I only have a shallow well pump, which would not handle enough water flow for water source heat pump.

I was just kinda boucing this defrost idea off ya, because I hadn't come across anything like it before, and wondered if it would work or not. I was looking to use my "spare parts" layin around to build this little "tank-enstine" project, and see what will happen.

Lc_shi
10-01-2005, 08:17 AM
For your air heat pump, the defrost is the main concern. how about the lowest temp ? my house used split heat pump (with variable frequence compressor) heat capacity dropped much. the defrsting method is reversible cycle(four-way valve change).
It need careful adjusting the defrost time to keep the system effient.

sharma
11-03-2005, 10:47 AM
i have just commissioned my new heat pump water heater i have designed. Now to save power consumption ur system atleast need to discharge 60 degrees C water out constant. As far as your unit is concern, you have to find some technical data on your compressor, say for a domestic water heating roughly about 800/900w compressor will do the job. if you can provide me with the model and the brand of the compressor and the refrigerant type, i will be able to work out the evaporating temperature where you will not to worry about defrost at all.

now keep in your mind, just winding condensor coil around a tank will heat up your water but you not saving power cause you dont know your COP. and say if you wanna heat your water up to 40-60 degrees C, just think what will happen to your discharge pressure and temperature, the head pressure will rise like hell and this will kill your compressor.

hope this will help.

Peter_1
12-03-2005, 12:03 AM
...i will be able to work out the evaporating temperature where you will not to worry about defrost at all.


Uhhh..... evpaorting above 0C perhaps?

Temprite
12-03-2005, 12:50 PM
Well, I'm a newbe to the forum, and wanted to get a little bit of insight on some design considerations.

This is a "basement" project, so no customers involved (just dear wife). I have built my own heat pump for my house, from a converted 10 ton Trane a/c unit. Now I want to build a heat pump water heater. By the math on paper, it's far, far more efficent than any means to heat water (resistance heating, or other fuels). So here's my question:

I'm building an outdoor unit, out of old 3 ton a/c unit. I found it out back of someone's store. Turns out tech condemned it for a bad run capacitor. So, I want to use this 'freebe' as my h/p.

In my designing, I'm wondering about defrost. I don't think that I really need a reversing valve, but just a silnoid valve to dump hot gas in the evap. I was going to coil copper tubing in the tank for the condensor, and leave plenty of extra to act partially as a receiver, but to give added capacity of refrigerant during defrost. When the h/g valve opens in defrost, hot gas will come off of the discharge line into the side connector of the distributor. When the hot gas is depleting during defrost, the liquid remaining in the condensor coil will begin to flash off and provide warm vapor to assist until defrost is complete.

Any thoughts, or design considerations I'm missing here before imbarking on this project? Thanks!

Maybe you need to find an existing brand of hot water system that employs refrigeration and pinch their ideas

Reeferjon
13-03-2005, 09:51 AM
Regarding your lack of heat capacity for defrost.
What we do in Transport is pressurize the reciever tank forcing liquid out the TXV, this increases the pressure and so heat capacity. You will also need to incorperate a check valve in the condenser outlet to prevent migration.

AYIBIBIO
30-01-2008, 06:09 PM
Well, I'm a newbe to the forum, and wanted to get a little bit of insight on some design considerations.

This is a "basement" project, so no customers involved (just dear wife). I have built my own heat pump for my house, from a converted 10 ton Trane a/c unit. Now I want to build a heat pump water heater. By the math on paper, it's far, far more efficent than any means to heat water (resistance heating, or other fuels). So here's my question:

I'm building an outdoor unit, out of old 3 ton a/c unit. I found it out back of someone's store. Turns out tech condemned it for a bad run capacitor. So, I want to use this 'freebe' as my h/p.

In my designing, I'm wondering about defrost. I don't think that I really need a reversing valve, but just a silnoid valve to dump hot gas in the evap. I was going to coil copper tubing in the tank for the condensor, and leave plenty of extra to act partially as a receiver, but to give added capacity of refrigerant during defrost. When the h/g valve opens in defrost, hot gas will come off of the discharge line into the side connector of the distributor. When the hot gas is depleting during defrost, the liquid remaining in the condensor coil will begin to flash off and provide warm vapor to assist until defrost is complete.

Any thoughts, or design considerations I'm missing here before imbarking on this project? Thanks!

HI THERE, I,M DANNY. I WAS VERY HAPPY WHEN I REARD YOUR TOPIC ON THE HEATPUMP YOU,V BUILT. NOW I,M ALSO TRYING TO BUILD ONE FOR MY HOME. I AM THINKING OF A GOETHERMAL TYPE OF HEATPUMP WATER HEATER,, WITH A GROUND COIL. I KNOW THERE IS GREAT DEAL OF WORK TO INSTALL THE GROUD COIL,, BUT YOU WILL HAVE A VERY EFFICIENT WATER HEATER AND YOU WILL NOT HAVE ANY DEFROST TO DO. PLEASE REMEMBER ON COLD AND HUMID DAYS YOU MAY NOT HAVE ENOUGH HOTWATER,, AS YOU WILL HAVE TO DEFROST FREQUENTLY BECAUSE OF THE AMOUNT OF HUMIDITY AND THE LOW TEMPERATURE OF EVAPORATION. IF YOU HAVE ENOUGH LAND,, I WILL ADVICE YOU GO GEOTHERMAL,, AND YOU WILL BE OK. TAKE CARE . I WILL LIKE TO HEAR FROM YOU. DANNY

nike123
30-01-2008, 06:15 PM
HI THERE, I,M DANNY. I WAS VERY HAPPY WHEN I REARD YOUR TOPIC ON THE HEATPUMP YOU,V BUILT. NOW I,M ALSO TRYING TO BUILD ONE FOR MY HOME. I AM THINKING OF A GOETHERMAL TYPE OF HEATPUMP WATER HEATER,, WITH A GROUND COIL. I KNOW THERE IS GREAT DEAL OF WORK TO INSTALL THE GROUD COIL,, BUT YOU WILL HAVE A VERY EFFICIENT WATER HEATER AND YOU WILL NOT HAVE ANY DEFROST TO DO. PLEASE REMEMBER ON COLD AND HUMID DAYS YOU MAY NOT HAVE ENOUGH HOTWATER,, AS YOU WILL HAVE TO DEFROST FREQUENTLY BECAUSE OF THE AMOUNT OF HUMIDITY AND THE LOW TEMPERATURE OF EVAPORATION. IF YOU HAVE ENOUGH LAND,, I WILL ADVICE YOU GO GEOTHERMAL,, AND YOU WILL BE OK. TAKE CARE . I WILL LIKE TO HEAR FROM YOU. DANNY


Check the dates of that posts!;)

AYIBIBIO
01-02-2008, 01:56 PM
Check the dates of that posts!;)


HI MR. NIKE123 THANK YOU FOR YOUR PEPLY,, ANYWAY, WE ARE NOT HERE TO SHOW PEOPLE THAT WE KNOW BETTER THAN THEM. THIS SITE IS TO EXCHANGE INFORMATION AND HELP OTHERS. THANK YOU AGAIN AND KEEP ALL TO YOURSELF. I CHOOSES HOW TO WRITE AND THAT IS IT. TAKE CARE,,

DANNY

The MG Pony
01-02-2008, 03:41 PM
would be nice to see after all these years wether or not he got it up and running?

AYIBIBIO
02-02-2008, 12:20 PM
would be nice to see after all these years wether or not he got it up and running?


Hi, I don't really understand, are you talking to me or the original poster of the thread???????
Hope to hear from you later.

DANNY.

The MG Pony
04-02-2008, 10:13 PM
Talking about the origional post, would be neat to see the end of it if he finnished or not.

Tesla
05-02-2008, 08:11 AM
Busman
I've spent a lot of my time on the same project. Would you consider using the waste grey water as a heat source, in my mind hot water going out is money down the drain. A tube in tube heat exchanger would be more efficient but requires tight control. Use of comp cooling with water jacket too.

The MG Pony
05-02-2008, 04:10 PM
Tesla Take a look at the date ;) I'd wager you shouldn't expect an answer while at her!

Josip
05-02-2008, 05:04 PM
Hi, all :)


.......Take a look at the date ;) I'd wager you shouldn't expect an answer ......!

...unfortunately we have so many posts like this one....question and then....silence....original poster never come back....

and we do not know....did we help / made bad or...whatever.....:confused:

Best regards, Josip :)