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Old 11-14-16, 04:27 PM   #1
b420ady
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Default 24000 BTU AC Unit conversion to geothermal well water source

This is my first post ever on this forum so Hello to everybody here.
In my region we get as low as -25 Celsius in the winter and +40 Celsius in the summer, the house that I have to heat is a 67 square meters footprint and 2 levels so 134 square meters. The first level is made of cellular concrete bricks 25 cm thick and the second level is made out of wood panels with an inside glass wool isolation. the whole house will be covered on the exterior in 100 mm thick styrofoam. All the windows are double glazed.
The water well is 44 meters deep, the first layer of water is 13 meters deep and the second layer of water was found at the last meters of the well so about 40 meters. I did measure the temperature of the water and it was 15 Celsius .... I ve test it during the summer but I suppose its pretty constant.
My idea is to convert this AC unit to a well water feed geothermal heater for the house and maybe also adapt a water heater for domestic use.

I m a newbie to this domain but I have very good technical understanding and I m very glad that I have found a proper forum were talk more about it and hopefully get some good advises from you.

TOROS KFR-70W AC Unit
Rated power 2.5 KW
Heating/cooling power 24000 BTU
Refrigerant type: I believe R22 (check the photo with the label )
Refrigerant quantity 2.6 Kg

(I did not manage to find anything online about it so help here if you can, a service manual would be great)

I will get in to the possession of this unit in a few days and I ll open it up so we can see the inside of it.

Anyway what I was thinking is to get a big barrel that I can seal very tight and feed from top with the water line from the pump and also have a second hose at the button to return the water at another depth in the well.... as I told you I don t have experience in this geothermal domain but what I have in my mind an hope its also possible is to save as much power as I can with the water pumping from the well and my idea is that If I pump water from 30 meters depth but I also have a return hose at another depth (bigger or smaller) and the barrel is very well sealed the power requirement of the pump will also bee much lower .... so please anyone tell me if this can be achieved...

Another thing that I don t know at all is what is all about all this types of refrigerants and if I can improve my unit by using something else..... I cannot read very well on the label but i think the refrigerant type is: R22 or 522 ..... but it really looks as 522

I also need someone to help me find the exact length of the copper tube for the coil inside the water barrel that I will have to construct or were can I find this type of information to help me design my coil without reading a 500 pages book )

Also please let me know what how good this unit will be for my situation...I don t truly think one unit will be enough for the whole house but if it covers a whole floor its mission accomplished, if its also heating some water in a boiler its already amazing. From what I understand this unit uses 2.5 KW of power to move 7 KW of heat in its actual air to air setup.... after I will convert it to water to air + water to water for boiler using my 15 degre Celsius water source I suppose the COP will also increase a bit .... its anyone capable of telling me to what to expect....I mean I ve seen commercial 2.5 KW heat pumps that moved 12 KW of heat .... can I get close to that ?

I ve registered to this forum after finding on google some posts made by Renden so you are also very welcome here

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Last edited by b420ady; 11-14-16 at 05:24 PM..
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Old 11-14-16, 06:21 PM   #2
b420ady
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After reading some of you dummy guide here on the forum and reading some more from google searches about refrigerant types I ve discovered that some say that you can replace R22 to R22a and get about 20% less power usage .... this would work for me ? Do you know how can I order to Romania enough to fill my heat pump ? There is another refrigerant that can do the same thing ? Maybe I can find it locally but I could not found R22a , instead I ve found R22 ; R410A ; R407C ; R134A
My ideea is to get the best efficiency out of this unit, so if I can get a 20% improve in power saving just out of chosing the right refrigerant please tell me about it.

Last edited by b420ady; 11-14-16 at 07:44 PM..
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Old 11-14-16, 08:28 PM   #3
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Welcome to the forums! You came to the right place to learn. There are many members who have DIY the type of system you speak of.

The unit you have looks to run off of R-22. If you can get it easily, that would be great. If not, there are other gases you can use instead. They are not the same as R-22, so they will make the unit act a little different.

The unit you took pictures of looks like a Gree or Shinco rebranded unit. I would expect a COP of 2 to 3 out of the unit like it is. If it is a variable speed inverter unit, as the heating/cooling capacity decreases, the COP increases. So at half capacity, you should expect to use less than half the power. Being an air-source unit, as the outdoor temperature changes, so does the capacity and efficiency.

To repurpose the unit as water source, some design work has to happen. Rather than a coil of pipe in a bucket, I would suggest a pipe-in-pipe or coaxial heat exchanger. With a bucket, not all the water that flows moves much heat. With a coaxial rig, all the water that flows is in close contact with the refrigerant pipe, so you get a lot more heat transfer per unit of water that you pump. Sizing the heat exchanger is a matter of how much heat transfer you need at what flow rate.

Some pics

Corrugated or convoluted tube is much more efficient than smooth tube and can be ordered to length. Smooth ends make it easy to seal and connect.


Refrigerant through the middle, water around edge.

Manufactured (Packless) unit, 12000 btu size. For reference, overall diameter is 11.5 inches, refrigerant connections are 3/8 inch, water connections are 1/2 inch. This unit contains about 10 feet of tubing.

Heat Pump Coils

Last edited by jeff5may; 11-15-16 at 07:52 AM..
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Old 11-15-16, 04:16 AM   #4
randen
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Default 24000 BTU AC hack

b420ady

Welcome to the forum. The project you have suggested I believe is do-able. The mini-split/heat-pump your looking at may cover most of your needs however on the coldest and windiest nights you will in all likelihood need more heat. If you were to find another 1-2 ton unit these would keep you warm through the coldest days. We have similar seasonal temps.

I would first like to caution you. I'm a realist. I wouldn't want to have you spend all your time developing a geo-thermal heat-pump plus additional money for parts when you could buy an off-the-shelf unit designed to operate efficiently down to your winter extreme temps. Do some home work. Check to see whats available before you begin.

Two thoughts, as Jeff5may had suggested about the barrel heat exchanger. This would be problematic as the heat transfer is dependant on convection and you could experience a totally frozen barrel. The tube in tube heat exchanger is the way to go for you application as the heat is transferred with the fluid being pumped around with its turbulence. Now again we have to be very careful to size this appropriately as this can freeze solid as well. Ask me how I know!!!

The next potential problem will be dumping back to the same well. You will soon exhaust the heat from this well and chill the water within. You require to draw from this well and dump to another collecting the grounds heat as the water moves through the aquifer.

With the pump and dump two issues arise: 1/ The cost of electrical power to move this water and the waters hardness. 2/ The minerals that dissolve in the water will eventually deposit in your heat exchanger. To lift the water 40 m will involve some power and this will be detrimental to your savings. This is why closed loops are a better method as the coolant within will not deposit any minerals into your H/X and you can circulate this coolant with a few watts.

Any thoughts to installing a ground loop?? What is your soil conditions?? You require about 200m / ton of heat. Do you have enough land.

Let us know your thoughts. Keep your sights focused on the goal of staying warm for very few dollars. A proper heat pump will do this without breaking a sweat.

Randen
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Old 11-15-16, 08:46 AM   #5
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Thanks for your fast reply, the project will be on a budget, I will pay just 50 USD to get this AC unit
I don t have were to digg trenches as half of the yard is a valley and on the other half is the house.
My ideea to use the well was exactly because I cannot aford multiple well shafts or trenches.... As water suplly this well is amazing....I have used 30 cubic meters in a day without a problem, and thats why I tought there is plenty heat energy down there and it won t be depleted....the well tube is plastic and about 25 cm in diameter and the water column in the well is about 15 meters i think....the whole 15 meters of water won t act as a huge heat exchanger in the ground ?
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Old 11-15-16, 02:41 PM   #6
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The easiest cheapest most reliable way to do a pump and dump system is drain to the surface. Any time you put water back into the ground, it could travel back to your source, robbing you of your heat advantage and poisoning your efficiency. People who do inject water back underground do it downstream in the aquifer or to another layer that is separate from the source layer. Either way requires a whole lot of testing and faith or courage.

Think of it this way: the ground is huge, but your borehole is not. Injecting nearly freezing water down 40 meters is only going to have 40 meters times the circumference of the borehole worth of surface area. For a 25 cm hole, that equals 31.4 square meters. Standard rules of thumb say 100 to 200 square meters per ton, so your hole is at least 5 times too small. In comparison, drawing from an effectively infinite source layer of heat, you'll have no heat transfer problems at all.

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Old 11-15-16, 07:56 PM   #7
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Quote:
Originally Posted by b420ady View Post
In my region we get as low as -25 Celsius in the winter and +40 Celsius in the summer, the house that I have to heat is a 67 square meters footprint and 2 levels so 134 square meters.
Have you calculated the heat loss at -25 C? You really need that information to properly size the heating system.
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Old 11-15-16, 10:48 PM   #8
b420ady
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Quote:
Originally Posted by jeff5may View Post
The easiest cheapest most reliable way to do a pump and dump system is drain to the surface. Any time you put water back into the ground, it could travel back to your source, robbing you of your heat advantage and poisoning your efficiency. People who do inject water back underground do it downstream in the aquifer or to another layer that is separate from the source layer. Either way requires a whole lot of testing and faith or courage.

Think of it this way: the ground is huge, but your borehole is not. Injecting nearly freezing water down 40 meters is only going to have 40 meters times the circumference of the borehole worth of surface area. For a 25 cm hole, that equals 31.4 square meters. Standard rules of thumb say 100 to 200 square meters per ton, so your hole is at least 5 times too small. In comparison, drawing from an effectively infinite source layer of heat, you'll have no heat transfer problems at all.
Thank you so much !
That s why I ve registered to this forum, thank you for opening my eyes so I don t end up doing extra work and expenses. So what I think I can try is to make another bore at a lower depth and a bit downhill like 10-15 meters away were the valley begins , can this work ?


JRMichler
Thank you very much for your pipe-in-pipe and coaxial heat exchanger information, for sure I will have to fallow that path but I ll have to construct it on my own at a budget so I ll start researching for some designs that I can replicate, if you have knowledge of an homemade one with good efficiency please share it with me and the rest of the readers


About your last reply, I did not do heat loss math as I don t know how do that , even thou indeed I really need it, I also have a much bigger problem now like having funds before snow comes to do the exterior styrofoam isolation and final rendering...
I don t expect this unit will match my heat requirements, but I expect to live with it this winter which is coming very fast....we already have frost, and funds are very limited so I ll have to do my best on a budget and replace my 2 KW electric radiator and 2 KW heating fan that can barely heat the space around my bed with something a bit more comfortable, and in my head this project will be another story compared to what I m running now here beside my laptop
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Old 11-16-16, 06:44 AM   #9
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You are VERY smart to concentrate now on exterior styrofoam and insulation. Any energy saving mechanisms such as heat pumps are MULTIPLIED by your increase in insulation.

What I might do is spent your resources (money +time) on insulation now and research the water source heat pump this winter. I realize how badly you want to have that heat, but efforts spent on tightening up a structure by adding more insulation and cutting down in infiltration is by FAR the best money spent.

Only after that do the energy saving source of heat.

The worst thing we could do is advise you on starting a project in a house that can't save energy as it is too poorly insulated.

Does this make sense?

Steve
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Old 11-16-16, 08:17 AM   #10
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I agree with Steve on improving the envelope of the home first. If you haven't done a blower door test yet, you REALLY need to! It is much more economical to seal up a leaky home that leaks air everywhere than to insulate without sealing leaks first. Yes, insulating is important as well, but if the walls and ceiling leak badly, the insulation loses its effect whenever the wind blows. This air barrier may or may not count as a vapor barrier, which is also important in the insulation project. Airflow carries heat with it, and heat not lost counts as energy you don't need to provide.

Downstream in the aquifer may or may not be downhill on the ground. Check with a geologist or water utility in your area, they will definitely know what exists underground. It may or may not be against the law to dump water back into the natural source: again, the pro's in your area will know the details. Also remember that cold water is heavier than warm water, so if you pump cold water back in, try to inject it deeper than your source well.

The effect of recirculating cold water through your well may not show up immediately. Usually it takes a few seasons of use to happen. What happens is after a few years of use, your source water temperature may change (for the worse) a few degrees. This trend will slowly continue with use until the ground can make up the difference. If you are heating and cooling throughout the year, these modes cancel each other out to the extent of duty cycle. For example: if you extract 2000 tons of heat in the heating season, but only add back 1500 tons during cooling season, the net loss of 500 tons will have an easy time being made up by the Earth. If you only heat with the system, there will be 4 times more heat to extract from underground.

Making your own evaporator is not all that difficult physically. The main difficulty in building is making everything not leak. The more difficult aspect lies in the design of the heat exchanger. Making absolutely sure the materials and configuration will handle your loading requirements (in a worst-case situation) on paper before you build anything is super important! Some fail-safe elements must be included in the control system as well. In your application, when something goes wrong, the heat exchanger will try to freeze the water flowing inside. This event is usually catastrophic, so failure mode analysis and control is absolutely necessary. Making sure your design can handle whatever the world throws at it before it is built can mean the difference between a unit that tries to flood your basement (while you aren't there to stop it) and one that does what it should for years.


Last edited by jeff5may; 11-16-16 at 08:36 AM.. Reason: words
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