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Old 02-28-14, 08:58 AM   #1
nokiasixteth
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Default What would be more efficient cheapest to run

What would be use the least amount of electricity. A geothermal unit lets say for comparison a geothermal unit 2 tons. Or a mini split 2 tons also . But the mini split have a radiator on the side that the air comes in with well water flowing through at what ever gpm it needed. Im not a math tech or nothing like that on knowing how much water it would need.

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Old 02-28-14, 10:28 AM   #2
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The unit that has the higher SEER (seasonal EER) or HSPF will be the most efficient. Most new geothermal units are in the SEER range for AC of about 30-35 (some as high as 45-50). Mini splits typically have a SEER in the upper teens to low 20's. But at a lot less cost.

For example, let's compare an AC unit that has a EER of 15 and compare it to another with a EER of 30.

The second unit (higher EER) will put out twice the amount of cold BTUs for a dollar of electricity. Or, the second will put out the same amount of cold BTUs for half that amount of electricity. Think of EER (or SEER) as 'gasoline mileage" on a car/truck.

The EER is simply the quotient of the BTU output and the electrical power to run the heat pump.

With an open loop geothermal system, you need about 2-3 gallons per minute of water per ton to get an adequate temperature difference (10 F) across the unit. A 2 ton unit will need about 4-6 gallons per minute when the geothermal compressor is on.

Inside every geothermal heat pump is a relay and a set of 24 V AC wires that controls a 24 V AC electric water valve (open loop water). When the compressor turns on, these wires are energized and the electric water valve opens allowing water flow to go through the unit. When the compressor turns off, the value is closed.

It is not as simple as just putting the mini split evaporator in a running stream of water - sure wish it was!

Hope this helps,

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Old 02-28-14, 04:35 PM   #3
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Borrow a trick from the window shakers. They use a "sling blade" on the outdoor coil to grab the cold evaporator water and sling it all over the condenser. The hotter it gets outside, the better it works. Hotter outdoors + more humidity = more condensed water to feed the hot coil. That's how the window shakers keep blowing ice cold air even when it's blazing outside.

I made the mistake of not sealing up a hole I drilled in my drain pan last year. In heating mode, the water built up and froze in the pan. The unit took forever to defrost. To fix it, I drilled a hole in the pan, and defrost times took a nosedive. The following summer, the unit lost cooling capacity when it got hot outside. After taping up the hole I had drilled, the cooling capacity immediately returned.

With your mini-split unit, you can stick a drain pan where your indoor unit drains outside. Simply stick a fountain pump in the pan and plumb it to a mini spray nozzle that sprays on your outdoor unit intake. You will be recycling the cold water your indoor unit has produced. This is how the newer portable a/c units dispose of the condensate they produce. The water is dripped onto the condenser fan and blown out the window after being reheated by the condenser.
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Old 02-28-14, 04:48 PM   #4
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That looks like a good idea. Run the drain hose from mini split inside unit to the outdoor and use that. What i was thinking on is being my water table here is 9ft during rainy and about 16ft constant and its around 60 or so degrees constant. Was when it got to the extremes here . Heating below the 35s or 100s cooling. Fix a water pump with a piggy back on the fan to turn on a switch to turn on a water pump to circulate the water summer comein in 60 goin out 65 or 70 and winter have a switch 60 goin in and 55 goin out. But havent been sure it would even be worth doing.
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Old 03-01-14, 01:57 PM   #5
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Ok, let's think about this for a minute.... It all depends on how much the unit runs and how hard and fast. If the unit is running pretty hard, the water can only help. If the unit is not struggling, it may not help too much. During cooling season, it's a no-brainer.

During heating season, the method you employ will make a big difference. If it's not too cold, say above 40 degF outside, you can simply spray water onto the coil to improve performance. But when you dip into "defrost territory", spraying water onto the coil will only help a little. The reason is not related to defrost or freezing so much, but is related to the saturated suction temperature (SST).

When it gets cold outside, the evap coil pressure and SST follows the air temperature change. This limits the capacity of the heat pump "from below" at the decreased suction pressure entering the compressor. With an air heat exchanger, there is no way around this limit, since the refrigerant gas will always be colder than the outdoor air as it leaves the hx. Adding water to the air coil only makes it unstable.

What you have to do is reduce or eliminate the airflow to the heat exchanger, while making sure you have an ample supply of warm enough water. The easiest way to do this is to change heat exchangers, thus removing air from the outdoor side of the system. The not-so-easy way is to slow or stop the fan blower and substitute airflow for water flow. As long as the refrigerant leaving the evap coil is warmer than outdoor air, the unit will provide better heating than "stock" operation.

Last edited by jeff5may; 03-01-14 at 02:06 PM.. Reason: words
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Old 03-02-14, 02:47 PM   #6
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Also consider the EER on a GEO unit isn't affected by outdoor temps nearly as much as air to air units are.
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Old 03-02-14, 08:02 PM   #7
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Quote:
Originally Posted by jeff5may View Post
Ok, let's think about this for a minute.... It all depends on how much the unit runs and how hard and fast. If the unit is running pretty hard, the water can only help. If the unit is not struggling, it may not help too much. During cooling season, it's a no-brainer.

During heating season, the method you employ will make a big difference. If it's not too cold, say above 40 degF outside, you can simply spray water onto the coil to improve performance. But when you dip into "defrost territory", spraying water onto the coil will only help a little. The reason is not related to defrost or freezing so much, but is related to the saturated suction temperature (SST).

When it gets cold outside, the evap coil pressure and SST follows the air temperature change. This limits the capacity of the heat pump "from below" at the decreased suction pressure entering the compressor. With an air heat exchanger, there is no way around this limit, since the refrigerant gas will always be colder than the outdoor air as it leaves the hx. Adding water to the air coil only makes it unstable.

What you have to do is reduce or eliminate the airflow to the heat exchanger, while making sure you have an ample supply of warm enough water. The easiest way to do this is to change heat exchangers, thus removing air from the outdoor side of the system. The not-so-easy way is to slow or stop the fan blower and substitute airflow for water flow. As long as the refrigerant leaving the evap coil is warmer than outdoor air, the unit will provide better heating than "stock" operation.
I think during summer time im going to run a water line to the mini and drill little holes so it sprays on the fins and play with it a little to help when it gets really hot if it doesnt cool the whole house like it does at 77 degrees today..

I had wanted to put a sandpoint right close to the mini and do sorta like a open looped Have a radiator with that 65 degree water in it so when the fan kicks on itd suck in the heated air instead of running water . But way its sounding . I wouldnt be able to do that.
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Old 03-04-14, 04:07 PM   #8
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Did find this on the net . The guy runs water through the radiator from a creek to help cool his house.

Im having a hard time figureing out why it wouldnt work if i built a small covering over it a building with a big enough hole to allow enough CFM of air through the radiator that the mini split would have enough air but also cool the air therefor raising the temp of the air before comeing into the mini split at times when the unit would be sucking in say 30 degree air . Instead the 30 degree air would come through the radiator first with the well water at 65 degrees warming it up to say 45 or 50 degrees. Then the 50 degree air goes through the mini split ? What am i missing ? If it wouldnt work at all what would be the reasons.
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Old 03-04-14, 05:29 PM   #9
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Yes, it would work. How well depends on how much you "Tim Taylor" it.

If you let the outdoor unit do the sucking, this drags down the airflow thru your heat exchangers. If you add enough water pump to the radiator, you might break even. If the outdoor unit has a variable speed fan, it will work against the radiator. I.e. more water>warmer air>fan slows down>same heat extracted.

If you add a fan, both heat exchangers will have more air going thru them. If you pump enough water and air, you might break even. Same effect as above.

During awful weather, the radiator will help the most. More delta T from well water temperature = more capacity for help.

In comparison, spraying a small fraction of the water you would normally pump through the radiator directly on your dx coil will have the effect of a nitrous oxide boost on your heat pump. Just a little spray has lots of energy in it. Only this way, the fan cannot react fast enough to help. I.e. spray water>coil defrosts and warms>massive BTU surge>compressor and/or metering valve must slow the flow to avoid overheat condition. If no over heat condition exists, unit runs balls out until satisfied.

Either way will work. Try it both ways. Just don't drown your new unit.

Last edited by jeff5may; 03-04-14 at 05:39 PM.. Reason: pondering
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Old 03-04-14, 06:02 PM   #10
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I tried the spraying water on the outside when it went into defrost . Made the ice go away very quick melted soon as i put the spray to it.

Do plan on diggin a seperate water well where water table is at highest so i can run through the radiator. Then later on maybe doing like a closed loop . If it actually saves me money. If not . Prob not. When summer comes i do plan on sprayin some water on the coils if i havent got the radiator rigged up yet.

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