Want to use my existing central A/C to chill water tanks

[rider77]

I was thinking a minimum of 1,000 gallons stored in insulated tanks at a temperature of 30-40 degrees

[Gernby]

I was thinking a minimum of 1,000 gallons stored in insulated tanks at a temperature of 30-40 degrees

Well, it wouldn't need to be that much to provide benefit. The "low hanging fruit" would be to capture enough cold water to cool the house during on-peak electric pricing (for me that is 3PM-8PM). If the chilled water wasn't quite enough to cool through the whole peak pricing period, then it could reduce the amount of cooling needed by the AC.

If I'm only able to chill the water down to the temperature my unit is already achieving (50°F), and I want to keep my house at or below 74°F, then 200 gallons of water would theoretically hold 40,000 BTU's worth of cooling potential (200 * 8.33 * 24). I would not need to insulate the containers, since they will be located inside the air conditioned space. The heat transfer between the water containers and surrounding air won't really be a loss.

[rider77]

But the water would be steadily increasing in temperature, even if you could cool it to 50*

[Gernby]

But the water would be steadily increasing in temperature, even if you could cool it to 50*

That's the goal! The water temperature will rise as it cools my house.

[rider77]

But as the temperature rises cooling capacity will be greatly reduced.
I honestly think your going to murder your unit attempting this. You need a chiller.

[Gernby]

Well, this project started about a year ago, and has been extremely beneficial so far. My highest electric bills in 2014 and 2015 were in August, one of them being over $400 for more than 4000 KWH of usage. However, my bill for August 2016 was $200 with slightly more than 2000 KWH. The trend continued ever since. I did this by using the contents of my house as a thermal capacitor, in order to optimize the cycles of my AC units.

Prior to last year, my thermostats were set to maintain 73°F all the time. During most of the year, they would each run ~20 times per day for 5-7 minutes. However, by changing my cooling strategy so that I cool the house much colder over the night and morning hours (down to 68°F), then STOP cooling at 3PM, the house is able to stay cool enough until 8PM without the AC's coming on at all. It will usually stay below 74°F by the time electric cost drops at 8PM.

I think many people would say that doing this would increase stress on the AC units, but I don't think it has. Instead of running 20 times for 5-10 minutes, they run around 10 times for 10-15 minutes. I would think that probably reduces wear on the units.

My goal with the water containers is to improve the process a bit further, by chilling water instead of over-cooling my house. Unless I make a mistake, the total load on the system should be reduced by some amount.

[ga-hvac-tech]

This would work with proper gearing

IMO not really...

We are talking a peaky high reving engine... in an application requiring strong low RPM torque....

IMO a dumpy needs this:

https://www.youtube.com/watch?v=yR9I1x2Ix-0

That engine, is actually a 2 cycle design... only runs up to around 1800 RPM's...
But she really sounds great doing it!

[beenthere]

Damn... why wouldn't the documentation specify some numbers regarding the safe operating temp ranges. If a person was designing a very well insulated building that needed to be 50 degrees inside, how would they determine that a particular unit couldn't safely achieve that temperature?

If an area/building needed to be cooled to 50°F. Then a refrigeration unit would be used instead of an A/C.

[beenthere]

Well, it wouldn't need to be that much to provide benefit. The "low hanging fruit" would be to capture enough cold water to cool the house during on-peak electric pricing (for me that is 3PM-8PM). If the chilled water wasn't quite enough to cool through the whole peak pricing period, then it could reduce the amount of cooling needed by the AC.

If I'm only able to chill the water down to the temperature my unit is already achieving (50°F), and I want to keep my house at or below 74°F, then 200 gallons of water would theoretically hold 40,000 BTU's worth of cooling potential (200 * 8.33 * 24). I would not need to insulate the containers, since they will be located inside the air conditioned space. The heat transfer between the water containers and surrounding air won't really be a loss.

200 gallons of water cooled to 50°F, would only give you around 16,600 BTUs of usable cooling. Once the water reaches 60°F, you won't be dehumidifying the air anymore, and the house would be very uncomfortable. 74 at a 60 degree dewpoint is an RH 61%.

[beenthere]

My goal with the water containers is to improve the process a bit further, by chilling water instead of over-cooling my house. Unless I make a mistake, the total load on the system should be reduced by some amount.

The system load, will actually be more. You can't cool the home and water during the off peak times for less then you can cool the home only during off peak times.

If your system has so many short cycles. Then it sounds like it was grossly over sized. And that is what caused your high cooling bills.

[jbhenergy]

The system load, will actually be more. You can't cool the home and water during the off peak times for less then you can cool the home only during off peak times.

If your system has so many short cycles. Then it sounds like it was grossly over sized. And that is what caused your high cooling bills.

Im surprised it took 3 pages for someone to state this.

[HVAC_Marc]

IMO not really...

We are talking a peaky high reving engine... in an application requiring strong low RPM torque....

You've never heard of a gasoline operated tractor? High revving, low horsepower, capable of yanking a house off its foundation.

it's all in the gearing. yeah, they get crappy fuel economy, too.

[Gernby]

IMO not really...

We are talking a peaky high reving engine... in an application requiring strong low RPM torque....

IMO a dumpy needs this:

https://www.youtube.com/watch?v=yR9I1x2Ix-0

That engine, is actually a 2 cycle design... only runs up to around 1800 RPM's...
But she really sounds great doing it!

I've never considered the corvette to be peaky or high revving, since the cars I've had over the years are MUCH more peaky and high revving. However, low gearing does wonders to overcome that. My 2002 Honda S2000 had just 145 ft-lbs of torque (peak @ ~6500 RPMs) and 210 hp (peak @ ~8800), but the 4.77:1 final drive made it possible to pull my ~3500 lbs boat out of the lake.

[Gernby]

If an area/building needed to be cooled to 50°F. Then a refrigeration unit would be used instead of an A/C.

Okay. I definitely agree that it's best to use the "right equipment for the job", but even then, where is the cross-over temperature that makes a refrigeration unit better than a residential central A/C unit (in terms of target temperature)? Also, if a residential central A/C unit is already in place, what would be the absolute coldest it could go, even if it isn't "optimal"?

[Gernby]

200 gallons of water cooled to 50°F, would only give you around 16,600 BTUs of usable cooling. Once the water reaches 60°F, you won't be dehumidifying the air anymore, and the house would be very uncomfortable. 74 at a 60 degree dewpoint is an RH 61%.

That's a good point, but I am not sure I would need to worry about humidity after cooling all the water down. It seems that the air inside my home would be ULTRA dry after going through the water cooling process. My home is very air-tight, so it seems that thoroughly dehumidifying the house in the morning should help the humidity down all day, right?

[Gernby]

The system load, will actually be more. You can't cool the home and water during the off peak times for less then you can cool the home only during off peak times.

If your system has so many short cycles. Then it sounds like it was grossly over sized. And that is what caused your high cooling bills.

Please don't take this as argumentative, but I don't think you are looking at this from my perspective. I'm actually not trying to convince anyone here that my project will be successful. I'm just trying to get some answers about the capabilities of the equipment I have.

It does seem that my units might be grossly over-sized, but we do have a very large temperature swing throughout the year. It gets over 100°F, and humid here in the Dallas area. There's only about 2 months when I don't run my A/C, so it winds up running very inefficiently about 6 months of the year.

[Gernby]

The system load, will actually be more. You can't cool the home and water during the off peak times for less then you can cool the home only during off peak times.

If your system has so many short cycles. Then it sounds like it was grossly over sized. And that is what caused your high cooling bills.

Duplicate post...

[rider77]

Your unit would have far less capacity to cool your home while chilling water. Depending on water temperature you could end up adding heat back into the home. So your unit would not necessarily be dehumidifying while chilling water.

[Gernby]

Your unit would have far less capacity to cool your home while chilling water. Depending on water temperature you could end up adding heat back into the home. So your unit would not necessarily be dehumidifying while chilling water.

The cold AC coil will remove moisture from the air, even if the air gets warmed back up by the water-to-air heat exchanger. That's a bonus IMO.

[Juan Madera]

For the money, time and energy involved in what you want to do, you could have a good tech install the right sized A/C system with either a 2 speed or variable speed condensing unit and save a whole lot more on energy than going down this path. That said, the next best bet is to add thermal mass to the envelope. Google water wall, trombe wall etc.