Thermal storage and water to water heat pump - Page 4

Fordguy64 · 07-07-17, 07:51 AM

http://www.ashraebistate.org/sites/d...ge_systems.pdf

So what would be more efficient ? Direct exchange for the refrigerant right into the water tanks? Or brazed plate heat exchangers with pumps?

jeff5may · 07-07-17, 08:40 AM

The ice tank idea is good for a water chiller setup. You would have refrigerant lines running through the tank to freeze the water and a glycol loop running an air cooling rig indoors. With a residential scale system, the biggest concern is insulating the ice tank. The main purpose of the ice tank is to level the cooling load and minimize the compressor capacity required. If the ice tank is not super insulated, heat leaks in and wreaks havoc on your efficiency.

This is a different approach than most ground source units employ. Rather than trying to freeze the cold side, most ground source systems attempt to keep the suction pressure high to lower the compression ratio. The higher the compression ratio, the more work (electrical power) required to move the same mass of refrigerant. So the two strategies are at odds with each other.

The main deciding factor in choosing which method to implement is the peak power required to satisfy the load. Either way, something is going to be massive. Either you have a massive underground loop or a well and a larger compressor that can supply the peak load, or you have a smaller compressor and a massive insulated cold store.

Fordguy64 · 07-07-17, 09:25 AM

Ok that makes sense. So with the ice tank idea the compressor will work harder do to running a lower pressure on the cold side to get below freezing. Makes sense.

My latest idea. Is to run a smaller compressor say 6-8kbtu unit off of my solar during the day. To freeze/cool the tank down as much as possible. Then have a larger unit of maybe 12kbtu or so to help out in high demand.

We have noticed that the house is very well insulated and does not have a lot of heat gain in the hottest part of the day. We have spent a few nights offer the 4th of July weekend setting the thermostat down to 73 at night. Then when we got up we set it to 84 because we spent most of the day outside. By the time we would go to bed the house would be at 80 or so. The outside temp was in the upper 80s and low 90s all weekend with very high humidity. Night time lows were about 70 and still very humid.

I have a whole house kW meter I'm going to hook up to the ac unit and try to get some average readings in the next week or so. Just trying to get a better idea of what the houses actual cooling need is

jeff5may · 07-08-17, 12:50 AM

Your idea should work out fine for the purpose you intend. If you feed the condenser side ground source water, that would improve efficiency by lowering the discharge pressure. Once you commission the rig, you will get a better idea of the factors at play. Lowering the Delta T just a few degrees can improve your energy savings a substantial amount. Plus, you can dig further into freezing territory without shutting down the heat transfer.

With a custom made system, you get to do all of the testing and measuring, so the sky is the limit as to the potential for savings. It just depends on how much you want to spend up front on the design.

Fordguy64 · 07-11-17, 05:58 AM

Alright I think I like where this is headed. im not afraid to spend money on this project. Obviously the cheaper the better.

So I had talked about trying to use one pump per side of the system (hi and low side) but I'm not totally sure that will be possible. Seems like I would have to size the heat exchangers pretty well based on x flow rate. That might be difficult but we will see.

jeff5may · 07-12-17, 08:31 AM

I found a good blog article about a system just like you are considering:

https://elkement.blog/2016/01/07/how...ystem-that-is/

Totally custom and self-built by a couple of engineering professional hackers. These 2 have gone down the road that many people avoid and a few have explored briefly. I have no doubt about the theory and synergy of the type of system that they have commissioned and the small amount of energy required to run it. However, reading about time tested operation in reality is quite another matter. This type of information is usually kept under lock and key by those who would seek to exploit it. Happy reading!

Fordguy64 · 07-13-17, 08:26 PM

That is an amazing blog.. I think I might have to read a few times lol

Fordguy64 · 07-13-17, 09:02 PM

http://www.spf.ch/fileadmin/user_upl...inalReport.pdf

Found this on one of his posts

where2 · 07-13-17, 09:09 PM

Quote:

Originally Posted by Fordguy64

That is an amazing blog.. I think I might have to read a few times lol

Study the photos carefully while you read the captions. It's really quite fascinating. I was just explaining what happens in various months to my wife sitting across the room without benefit of her viewing the photos. By having to explain what was happening in each month verbally, I got a better understanding where the heat comes from. My wife grew up at 45.8°N, where heating is quite necessary. We both understand the concept of geothermal, but had never seen it coupled to solar thermal and air source combined.

Fordguy64 · 07-14-17, 12:04 PM

So something I find interesting is the ice storage tank sizes.. Most of them are under 300 gallons. My cistern is up around 10000 gallons. Does that hurt or help me? It also appears that the solar gives major gains and I don't have enough room for solar to keep the same ration as they do for gallons to sqft lol

07-12-17, 08:31 AM	#36
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,431 Thanks: 431 Thanked 619 Times in 517 Posts	I found a good blog article about a system just like you are considering: https://elkement.blog/2016/01/07/how...ystem-that-is/ Totally custom and self-built by a couple of engineering professional hackers. These 2 have gone down the road that many people avoid and a few have explored briefly. I have no doubt about the theory and synergy of the type of system that they have commissioned and the small amount of energy required to run it. However, reading about time tested operation in reality is quite another matter. This type of information is usually kept under lock and key by those who would seek to exploit it. Happy reading! Last edited by jeff5may; 07-14-17 at 12:30 PM..

07-07-17, 07:51 AM	#31
Fordguy64 Journeyman EcoRenovator Join Date: Oct 2011 Location: Cincinnati ohio Posts: 338 Thanks: 40 Thanked 35 Times in 31 Posts	http://www.ashraebistate.org/sites/d...ge_systems.pdf So what would be more efficient ? Direct exchange for the refrigerant right into the water tanks? Or brazed plate heat exchangers with pumps?

07-07-17, 08:40 AM	#32
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,431 Thanks: 431 Thanked 619 Times in 517 Posts	The ice tank idea is good for a water chiller setup. You would have refrigerant lines running through the tank to freeze the water and a glycol loop running an air cooling rig indoors. With a residential scale system, the biggest concern is insulating the ice tank. The main purpose of the ice tank is to level the cooling load and minimize the compressor capacity required. If the ice tank is not super insulated, heat leaks in and wreaks havoc on your efficiency. This is a different approach than most ground source units employ. Rather than trying to freeze the cold side, most ground source systems attempt to keep the suction pressure high to lower the compression ratio. The higher the compression ratio, the more work (electrical power) required to move the same mass of refrigerant. So the two strategies are at odds with each other. The main deciding factor in choosing which method to implement is the peak power required to satisfy the load. Either way, something is going to be massive. Either you have a massive underground loop or a well and a larger compressor that can supply the peak load, or you have a smaller compressor and a massive insulated cold store.

07-07-17, 09:25 AM	#33
Fordguy64 Journeyman EcoRenovator Join Date: Oct 2011 Location: Cincinnati ohio Posts: 338 Thanks: 40 Thanked 35 Times in 31 Posts	Ok that makes sense. So with the ice tank idea the compressor will work harder do to running a lower pressure on the cold side to get below freezing. Makes sense. My latest idea. Is to run a smaller compressor say 6-8kbtu unit off of my solar during the day. To freeze/cool the tank down as much as possible. Then have a larger unit of maybe 12kbtu or so to help out in high demand. We have noticed that the house is very well insulated and does not have a lot of heat gain in the hottest part of the day. We have spent a few nights offer the 4th of July weekend setting the thermostat down to 73 at night. Then when we got up we set it to 84 because we spent most of the day outside. By the time we would go to bed the house would be at 80 or so. The outside temp was in the upper 80s and low 90s all weekend with very high humidity. Night time lows were about 70 and still very humid. I have a whole house kW meter I'm going to hook up to the ac unit and try to get some average readings in the next week or so. Just trying to get a better idea of what the houses actual cooling need is

07-08-17, 12:50 AM	#34
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,431 Thanks: 431 Thanked 619 Times in 517 Posts	Your idea should work out fine for the purpose you intend. If you feed the condenser side ground source water, that would improve efficiency by lowering the discharge pressure. Once you commission the rig, you will get a better idea of the factors at play. Lowering the Delta T just a few degrees can improve your energy savings a substantial amount. Plus, you can dig further into freezing territory without shutting down the heat transfer. With a custom made system, you get to do all of the testing and measuring, so the sky is the limit as to the potential for savings. It just depends on how much you want to spend up front on the design.

07-11-17, 05:58 AM	#35
Fordguy64 Journeyman EcoRenovator Join Date: Oct 2011 Location: Cincinnati ohio Posts: 338 Thanks: 40 Thanked 35 Times in 31 Posts	Alright I think I like where this is headed. im not afraid to spend money on this project. Obviously the cheaper the better. So I had talked about trying to use one pump per side of the system (hi and low side) but I'm not totally sure that will be possible. Seems like I would have to size the heat exchangers pretty well based on x flow rate. That might be difficult but we will see.

07-13-17, 08:26 PM	#37
Fordguy64 Journeyman EcoRenovator Join Date: Oct 2011 Location: Cincinnati ohio Posts: 338 Thanks: 40 Thanked 35 Times in 31 Posts	That is an amazing blog.. I think I might have to read a few times lol

07-13-17, 09:02 PM	#38
Fordguy64 Journeyman EcoRenovator Join Date: Oct 2011 Location: Cincinnati ohio Posts: 338 Thanks: 40 Thanked 35 Times in 31 Posts	http://www.spf.ch/fileadmin/user_upl...inalReport.pdf Found this on one of his posts

07-14-17, 12:04 PM	#40
Fordguy64 Journeyman EcoRenovator Join Date: Oct 2011 Location: Cincinnati ohio Posts: 338 Thanks: 40 Thanked 35 Times in 31 Posts	So something I find interesting is the ice storage tank sizes.. Most of them are under 300 gallons. My cistern is up around 10000 gallons. Does that hurt or help me? It also appears that the solar gives major gains and I don't have enough room for solar to keep the same ration as they do for gallons to sqft lol