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  1. #40
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    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.

  2. #41
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    Quote Originally Posted by Juan Madera View Post
    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.
    I'm not trying to reduce my own electric bills much further than I already have. I'm just trying to perfect a process (I'm an patent-holding engineer). My electric cost over the last 12 months was 45% lower than the prior 12 months ($2971 down to $1608). I don't really think I could lower my cooling cost all that much more, but I think I could make my house more comfortable while doing it. I prefer being cold than hot, but I'm not always comfortable watching TV in a 68F room. I think it would be much better to cool the interior air down to 73F (instead of 68F), but cool some water down to 50F to achieve the same cost savings.

  3. #42
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    Quote Originally Posted by Gernby View Post
    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"?
    That will vary by the amount of air the indoor unit is actually moving, per ton of cooling. At 350 CFM per ton, the coil may start to freeze when the indoor temp is between 68 and 70. At 450 CFM per ton, might be able to get the temp down to 65.

    A/Cs with a hydro coil added to them usually have low air flow rates after the hydro coil is added.
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  4. #43
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    Quote Originally Posted by Gernby View Post
    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?
    So what RH is your house at when you cool it down to 68? A tight house can actually have a very high humidity.
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  5. #44
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    Quote Originally Posted by Gernby View Post
    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 100F, 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.
    So how long does your A/C run when its 100F or hotter outside.

    Even figuring the water being chilled from 70 to 50. And then using the water until it reaches 70F again. You are only going to get 33,320 BTUs of cooling stored, only having a 200 gallon storage system.

    Due to heat transfer inefficiencies, and circulator heat being added to the water. You will use 3 to 3.1 tons of capacity to store a 2.77 ton capacity, using the water until it reaches 70.
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  6. #45
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    Quote Originally Posted by beenthere View Post
    That will vary by the amount of air the indoor unit is actually moving, per ton of cooling. At 350 CFM per ton, the coil may start to freeze when the indoor temp is between 68 and 70. At 450 CFM per ton, might be able to get the temp down to 65.

    A/Cs with a hydro coil added to them usually have low air flow rates after the hydro coil is added.
    Funny you should mention that. I just discovered a few days ago that BOTH of my furnaces are running at the max blower speed, which the documentation shows is way too high. According to the documentation, it looks like the downstairs unit needed to be between speed 1 and 2 (out of 5), and the upstairs unit needed to be on speed 1 (out of 5). I decided to set both of them to speed 1, and it seems to be running much better. The run times are longer, but power usage is lower. The temperature drop across the evap and blower is about 20F (68F return / 48F supply). Hopefully that isn't too cold...

    I don't know how accurate my RH reading is, but my Ecobee3 stats both show RH dropping down to about 50%. I don't really know what ideal would be, but my aquarium puts quite a bit of water into the air.

  7. #46
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    Quote Originally Posted by Gernby View Post
    Funny you should mention that. I just discovered a few days ago that BOTH of my furnaces are running at the max blower speed, which the documentation shows is way too high. According to the documentation, it looks like the downstairs unit needed to be between speed 1 and 2 (out of 5), and the upstairs unit needed to be on speed 1 (out of 5). I decided to set both of them to speed 1, and it seems to be running much better. The run times are longer, but power usage is lower. The temperature drop across the evap and blower is about 20F (68F return / 48F supply). Hopefully that isn't too cold...

    I don't know how accurate my RH reading is, but my Ecobee3 stats both show RH dropping down to about 50%. I don't really know what ideal would be, but my aquarium puts quite a bit of water into the air.
    While 50%RH is okay. Its not considered a low RH.

    See how the house feels after a day with the blowers on a lower speed.
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  8. #47
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    Quote Originally Posted by beenthere View Post
    So how long does your A/C run when its 100F or hotter outside.

    Even figuring the water being chilled from 70 to 50. And then using the water until it reaches 70F again. You are only going to get 33,320 BTUs of cooling stored, only having a 200 gallon storage system.

    Due to heat transfer inefficiencies, and circulator heat being added to the water. You will use 3 to 3.1 tons of capacity to store a 2.77 ton capacity, using the water until it reaches 70.

    It's a bit hard to say what my run times are when it's 100F outside, since I didn't start capturing run times and temperatures until September of last year. However, when the temperature was in the 90's back then, my run times were longer than 20 minutes while maintaining indoor temp in the low 70's.

    A couple things that I'm hoping will improve efficiency are that I plan to use a variable speed DC water pump, which only uses 20 Watts while flowing more GPM than I need. I also DO NOT plan to use the central AC blower to circulate air while in "water mode". I am going to mount an MBVC1200 modular blower in my garage, with a single return duct going to 2 upstairs rooms (with a Y), and a single supply duct going into the garage hallway. There will be another air-to-water heat exchanger in the supply duct to cool the air using the chilled water.

    I'm not sure how much efficiency I'll gain from it, but it seems likely that I currently lose a ton of cooling efficiency through the ducts in my attic. At the hottest time of day, my attic is VERY hot, and I have hundreds of feet worth of flex duct running up there. However, my garage stays just a few degrees warmer than my house, since it only has 2 exterior walls, which are insulated.

    BTW, I used 200 gallons as a talking point, but I could easily increase my water capacity well beyond that. My plan is to setup a bare-bones POC, just to determine its effectiveness. If the effect is measurable, I'll be able to determine exactly how much water would be required. I think it's likely that water enhancement might just make it so that I only have to over-cool my house 2 degrees, instead of 5 degrees.

  9. #48
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    You would need 1,000 gallons of water. To get you 4 tons of cooling for 4 hours.
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  10. #49
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    Quote Originally Posted by Gernby View Post
    However, the point of this project is to increase efficiency of my HVAC system
    The one thing I can assure you won't happen with a set up like you envision is increased system efficiency!

  11. #50
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    I think the ideal amount of chilled water would be whatever it takes to keep the house comfortable from 3:00 PM to 8:00 PM without supplemental AC usage on all but the ~10 hottest days of the year. If one of my AC units needs to kick on for some amount of time on those hottest days, I would be fine with that.

    On a side note, I'm doing a test with a ~10 year old aquarium chiller that I had out in the garage, and am pretty impressed by the results so far. I am using it to chill 25 gallons of water in my kitchen, and it's making quick work of it. It chilled the temp from 65F to 56F in 60 minutes while consuming 400 watts.

  12. #51
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    Exactly. A dedicated chilling device is far better suited for the task.

    Do the math though...

    1000 gallons of water is 8000 pounds of water, and in a perfectly insulated container, 8000 pounds is going to need 8000 btuh per degree of temp drop... per hour.
    So... 80F water is going to need 400,000btuh or 33 TONS to cool to 30F... in an hour... 15 in 2 hour 7.5 in 4 hours... assuming zero heat gain... 3.25 tons of cooling to drop it in 8 hours... constant 3.5 tons of chill power.

    It is NOT cheap to chill water. However, chilled water is VERY efficient ad absorbing and transferring heat...

    So, a dedicated chilling device is more efficient at getting the heat out of the water as it is absorbed in from water coils.

    Which is why large buildings often use chillers...

    But a small building (under 20,000 sqft) it really isn't practical.
    The TRUE highest cost system is the system not installed properly...

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  13. #52
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    Quote Originally Posted by Gernby View Post
    On a side note, I'm doing a test with a ~10 year old aquarium chiller that I had out in the garage, and am pretty impressed by the results so far. I am using it to chill 25 gallons of water in my kitchen, and it's making quick work of it. It chilled the temp from 65F to 56F in 60 minutes while consuming 400 watts.
    Told you so...

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