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Old 07-15-14, 12:37 AM   #1
nokiasixteth
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Default Ways to make The Mini Split More Efficient

Ive been thinking of different ways to make a mini split be more energy efficient for these krispy hot summers weve had . Ive noticed the mini is running more but it is cooling my entire home.

Ways ive thought . Run the sprinkler on the coils outside. Helped by about 400 watts . But decided against that idea . 400 watts or replace coils .

2 I thought about drilling either 1 loop hole for 1 ton 250ft deep and circulating water with some sort of controller so the intake temp would first go through a radiator and cool down before it came across the coils of the mini split.

3rd way . Would be prob more expensive . But i have thought about doing earth tubes and letting the mini suck in the cooled air from the tubes.

4th way i thought about building a room with the well pumping water through a radiator in front of the mini.

Cutting the fittings and all are pretty much out of the question . I dont want to cut my new mini . I want . I guess you could call them (Bolt ons ) Easy to take off if i ever wanted to turn it back to stock.

Any of yall have any ideas on cheap ways to make the mini so it will be a bit more efficient?

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Old 07-15-14, 01:29 AM   #2
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Quote:
Originally Posted by nokiasixteth View Post
Ive been thinking of different ways to make a mini split be more energy efficient for these krispy hot summers weve had . Ive noticed the mini is running more but it is cooling my entire home.

Ways ive thought . Run the sprinkler on the coils outside. Helped by about 400 watts . But decided against that idea . 400 watts or replace coils .

2 I thought about drilling either 1 loop hole for 1 ton 250ft deep and circulating water with some sort of controller so the intake temp would first go through a radiator and cool down before it came across the coils of the mini split.

3rd way . Would be prob more expensive . But i have thought about doing earth tubes and letting the mini suck in the cooled air from the tubes.

4th way i thought about building a room with the well pumping water through a radiator in front of the mini.

Cutting the fittings and all are pretty much out of the question . I dont want to cut my new mini . I want . I guess you could call them (Bolt ons ) Easy to take off if i ever wanted to turn it back to stock.

Any of yall have any ideas on cheap ways to make the mini so it will be a bit more efficient?
There have been some discussions here about option number 2. as I recall, it has been successful.

But I agree with you, I don't think it would be a good idea to hack into your new mini.

But digging a hole, and building your own ground source heat pump air conditioner, now there's a good one.

I don't remember if you ever said how big your mini was, but if you could keep your eye out for a discarded air conditioner of may a one Ton size, and hack in and replace your condenser coil (the hot one) with some kind of heat exchanger (I really like brazed plate heat exchangers), and pump water from your bore hole loop through the new heat exchanger, you might really have something, even more efficient than your mini. A brazed plate heat exchanger wouldn't work very well for well water, you'd have to use a different HX.

-AC
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Old 07-17-14, 02:14 AM   #3
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Default minisplit

I've installed several minsplits. Most minisplits both copper lines are very cold. Usually the liquid line is freezing on it way from the outdoor unit to the evaporator. This would make it difficult to gain anything from a well that would warmer. This also defeats the idea of a heat exchanger between the 2 lines because you would be more likely to gain heat from the suction line before reaching the evaporator. You could aim your drain to drip onto the outdoor coil. The condensate water is usually super cold and over here you might get 3-5 gallons of water a day.
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Old 07-17-14, 06:07 AM   #4
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Whatever you do, remember that the existing fan on the outdoor unit is rated for the design air restrictions so if you do anything to add further restriction, such as another coil or putting extra pressure on either side, you may reduce the performance of the system.
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Old 07-19-14, 04:08 AM   #5
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Most mini splits have been optimized heavily during the design phase, so getting much more than how they ship will take something aggressive. Your main enemy in this case is the outdoor air temperature. When it gets very hot or cold outside, the ground is a much better source. You have to figure out the way to level this temperature shift that works for your site.

As the outdoor temperature moves away from the indoor and ground temperature, direct heat transfer with the groundwater becomes the best power saving option. Running a radiator to temper the outdoor air will not grab as much heat. However, if you use a low power pump to supply it you might save more watts than by using a well pump.
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Old 07-19-14, 12:29 PM   #6
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Most mini splits have been optimized heavily during the design phase, so getting much more than how they ship will take something aggressive. Your main enemy in this case is the outdoor air temperature. When it gets very hot or cold outside, the ground is a much better source. You have to figure out the way to level this temperature shift that works for your site.

As the outdoor temperature moves away from the indoor and ground temperature, direct heat transfer with the groundwater becomes the best power saving option. Running a radiator to temper the outdoor air will not grab as much heat. However, if you use a low power pump to supply it you might save more watts than by using a well pump.
So if i used a radiator it wouldnt lower the temp enough to matter ?
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Old 07-19-14, 08:02 PM   #7
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Since your unit is filled with R410, the high pressure needed to dump heat on a hot day takes a lot more power. Research has proven that above 110 degF condenser coil temperature, R410-based systems are actually less efficient than the older systems running with R22 due to the enormous pressure needed to force condensation. So on those super hot days, cooling the intake air would be highly effective. Likewise, on frigid cold nights, preheating the intake air would be effective also.

The unknown here is this: at what temperature does it take more power to pump water than the heat that water will transfer? The answer: you'll have to build it and run experiments. There will be a balance point during those somewhat hot or cold days where you would be better off letting the unit do all its own work. Or you could spray water on the coils directly and gain more heat transfer. Again, no way for me to tell until you do it.

Something to consider about directly spraying the outdoor unit: a little water goes a long way. You don't have to flood or drown your coils to move lots of heat. An awesome example of this statement is the Coolerado. It uses a thermodynamic cycle called the Maisotsenko Cycle to do the same thing you hope to accomplish with your radiator. Their units consume 2 gallons or less of water per hour per ton of cooling.
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Old 07-22-14, 05:25 AM   #8
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We originally planned mini-splits in the basement, along with high velocity for the first and second floors in our 1895 D.C. row house in an attempt to eliminate bulkheads and preserve some of the tin ceilings. And we are keeping the radiators. Our contractor then suggested that we switch to a mini-split unit system for the top two floors - essentially putting mostly ceiling cassettes or compact cassettes - in each room. Has anyone gone this route? We would like to hear your thoughts, good or bad. Thank you!
I install these types of systems in peoples houses on occasion and just finished one 4 head 36000btu system which worked well through last winter heating while we worked on the radiant floor retrofit. The thing to remember is that the efficiency of multi-head units is not as good as the single head ones. For example, you can get a Fujitsu single head 18000btu unit with a seer rating of 27 but the 3 head unit seer ratings vary from 16 to 21. Still good but not quite as good.

That said, the customers said that they were very comfortable last winter (very cold one too). There was 3 heads on the 2nd fl and 1 larger one on the main fl.
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Old 10-23-14, 12:29 PM   #9
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Somebody is going to make a lot of money when they figure out how to use ground/pool water as a second heat extraction method for the most popular mini-split heat pumps. Improving cooling efficiency alone will get you more "bang for the buck" as min-split heat pumps tend to be installed in climates that do more cooling than heating.
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Old 10-23-14, 12:52 PM   #10
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2 I thought about drilling either 1 loop hole for 1 ton 250ft deep and circulating water with some sort of controller so the intake temp would first go through a radiator and cool down before it came across the coils of the mini split.
Your concept is correct, but the efficiency of this design would kill it. You would have to build a very tight duct system that would force the air through the radiator first, before entering the heat pump.

The real solution (voiding all warranties of course) is to plumb a refrigerant to water heat exchanger into the refrigerant line just upstream of the heat pump coils. These units DO exist and are designed for just such applications.

Generally, there are 3 types of these heat exchangers
  • tube (a definite DIY possibility)
  • flat plate (very compact)
  • tank (another DIY possibility) Basically a swimming pool heat pump heater without the heat pump.

These heat exchangers don't have to do all the work. They would only assist the coils inside the heat pump compressor unit.

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