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Old 07-24-15, 01:53 PM   #1
stevehull
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Default water cooled precoil before evaporator coil?

It has been beastly hot here in central Oklahoma. To be accurate, not so hot (mid 90s F; ~36 C), but very humid. I literally don't recall dew points in the upper 70sF (25C) here in Oklahoma.

Am looking at my open loop, one ton unit that I put together and the condensate is just pouring out. It is in the 2400 sq ft (~240 M2) shop made of SIPS and it is doing a great job. Keeps the inside temp about 20 degrees F below the outside and lowers humidity dew point to the mid 50's F.

One ton per 2400 sq feet . . . . SIPS are simply wonderful.

Noticed the cold water line going into the unit. My cold water input is about 64F. What if I plumbed in a very crude coil BEFORE the cold evaporator coil. The air would be precooled by first passing through the water cooled coil. Then the far colder evaporator coil would remove even more moisture.

This water, having gone through the "precooler" would then go into the cold water input line maybe just a few degrees warmer, but insignificantly so. Remember, this is an open loop or "pump and dump" set up.

I know that with colder water (40-45F) you could chill the coil sufficiently to condense latent water. Before I make a mess and cut up yet another defunct 12KBTU air conditioner (to get out a coil that I can use as a water precooler) - is this worth it?

I am wondering if the difference in the entering air temp (78F) and the input water temp (65F) is a large enough delta T (~13 degrees F; 8 degrees C) to sufficiently cool the input air. Assume about 500 cfm.

I could drag out my coil heat transfer tables, but I value the group's input.

Steve

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Old 07-24-15, 03:34 PM   #2
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It will work. Randen tried doing this in his workshop and it did a good job of making cool, damp air. The supply air temperature will fall to the point where the water starts to condense. The heat pump coil will then lay waste to the air stream, both latent and sensible. The performance indicator is the EFFECTIVENESS of your pre-cooler. Any extra effectiveness of your water-side heat exchangers is good for the air side. Yes, raising your entering water temp to the condenser will shift your balance point slightly, but not enough to matter. You are basically relieving the compressor and evaporator of whatever heat load the tempering exchanger transfers.
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Old 07-24-15, 07:58 PM   #3
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Jeff,

Thanks! I am going to try an experiment. Guys, look to critique it.

Remember, this is an open loop GT heat pump and the goal is to get more condensate volume output. The result of this should be a lower output air temperature with the same relative humidity. I don't think I will get any condensation on the precooler coils as the dewpoint of the entering air (~ 60F) is less than the inlet water temp (~ 65F)

Measurements.
Air inlet temps, before and after water "precooler"
Water temps before and after precooler (inlet and outlet)
Output air temp
Output air relative humidity
Condensate rate

I am going to first put in a precooler that is just supplied by cold water and will not run it into the GT heat pump after it exits precooler (just dump it). This is the best test as all the GT heat pump delta t dynamics is exactly the same.

Goal. Determine if output air is decreased in temperature and if condensate volume/time is significantly increased by precooling input air with water coil.

Measure same parameters as above to show goal.

My hypothesis is that using the precooler exit water (slightly warmer) into the GT heat pump will not significantly degrade performance compared to the stand alone (no precooled water).

Second hypothesis: Using the precooler will significantly increase condensate volume, and will lower exit air temp with little change in output air relative humidity.

The nice thing about the shop is that the entering air temp will be essentially the same for the tests. The inlet water temp is known and I can easily measure condensate volume/time and output air parameters (temp and rel humidity).

Secondly, use output from precooler to go into heat pump thereby increasing water temp slightly

Same measurements as before.

Thoughts?



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Old 07-25-15, 12:50 PM   #4
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Awesome idea and awesome set up for a good test. I've done similar projects in the past. The main problem for me was always surface area of the water coil. When you are not dropping the tempuature by 30+ degrees F then there air goes through not really dropping the temp as much. I would maybe suggest a car radiator, they spread the water out much flatter and allow much more volume of flow. Maybe even 2 pancaked back to back. I have had luck picking up some leaking radiators at car shops and fixing them with alumibond.
I wish you lived closer, I have some that I'm not using anymore.
Good luck I look forward to some great data!
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Old 07-25-15, 01:29 PM   #5
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Stevehull
Yes a pre exchanger will work well but I don't believe with such a short delta T will produce the desired effect.

A local geo-installer had told me of a unit he pre exchanged for an indoor pool the help dehumidify but the ground water was in the 40-50 Deg. F range.

A car radiator is a poor excuse. Use a more substantial piece of equipment.
20x19 Water to Air Heat Exchanger Hot Water Coil Outdoor Wood Furnace | eBay

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Old 07-25-15, 01:42 PM   #6
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I'm wanting to put a heat exchanger in the shop to help cool it. Water directly from the well through the coil inside. Not sure what size or how much heat it will take out. Haven't found any good info on the net yet. Just supplemental cooling in there. Water temp is 70* or less not sure right now though. Air temp in the shop when ac off is 110* ish or more when summer hits. The pump and pipes of the well sweat pretty good when it's 100* . Humidity is in the mid 40s when it's 100*
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Old 07-25-15, 03:50 PM   #7
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Elcam84,

Check out the Coolerado. A unit based on its design will do wonders for your shop with a cool water source and a little electricity. A straight air exchanger will not remove enough water from the air, the shop would end up 80 degF and muggy. To remove the extra water from the air, a lower temperature is needed to draw it out.
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Old 07-25-15, 04:13 PM   #8
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I like this idea, its a good use of something we just let go down the drain. Quite humid here too. Might be good to measure actual water output first. Here an a/c can put out 5 gallons of water a day. 40lbs water in 24 hrs would be about 1.66 pounds an hour, raising water temp 10 degrees would only be 16.6 btu per hour. I've been toying with using the condensate water as a liquid line sub cooler either at the compressor discharge or condensing unit discharge to achieve maximum sub cooling. Perhaps instead of a radiator an automotive heater core would give you the exchange area you'll need.
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Old 07-25-15, 04:31 PM   #9
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Quote:
Originally Posted by jeff5may View Post
Elcam84,

Check out the Coolerado. A unit based on its design will do wonders for your shop with a cool water source and a little electricity. A straight air exchanger will not remove enough water from the air, the shop would end up 80 degF and muggy. To remove the extra water from the air, a lower temperature is needed to draw it out.
Will check it out. Since the well pump is next to the shop I'd like to use that cold water to do something before it ends up on the yard. I'd be extremely surprised if it got the temp in the shop to 80*,,maybe on a cool day in the spring or fall. Just want to be able to pull out some heat so the ac van have a little break and shorten the cool down time in the shop. It's a nice sealed insulated 20x40 metal building but 2 tons of ac takes a long time to cool it when the building and contents are over 100* including the slab...
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Old 07-25-15, 04:55 PM   #10
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Looking at the coolerado.... Interesting and I don't doubt it works but it will only work in a few locations IE Colorado where it's dry as its a glorified swamp cooler. Just multi stage and indirect.

Problem is here when it's 100* like it is now the humidity is over 40% and for any evaporative system to work at this temp the humidity needs to be 10 or less.

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