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Old 02-26-20, 02:04 PM   #1
Sadashi
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Default Heat pump idea ? Or maybe not !

Hi folks , my name is Alex and I'm from Romania . I would like your opinion about a heat pump that I want to build in the near future . We now have a diy air to water heat pump , converted from a Gree split ac unit ( 24000 btu or 2 ton ) that heats our house of 125 sqm ( 1345.489ft ) which is connected to slightly larger radiators . It works very good for us , we keep 22C ( 71F ) inside the house and the electricity consumption is around 6000 kWh for the whole heating season with domestic hot water included ( the 6000 kWh are just for heating and hot water ) . What I want to build is a geothermal heat pump style that doesn't have any loops or any boreholes . I was thinking of getting a cheap ac unit ( 7000 btu or 0.58 ton ) on R32 or R410a that I will convert it into an air to water heat pump . This small pump will be connected to a 100 litres ( 3381.402us fl oz) water tank that will serve as an evaporator for the " ground source heat pump " that I want to build . The refrigerant in the " ground source heat pump " will be R134a , because of the higher output temperatures . The water tank will have a mixing valve , so that I can adjust the water temperature that goes in the evaporator of the " geothermal heat pump " . What do you think about this idea ? It's basically a geothermal heat pump for those who don't have the necessary space or the money for the boreholes . I don't know if it makes sense from an economic point of view ( electricity consumption ) . Thanks and hope to get some replies from the more experienced users out here and not only

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Old 02-26-20, 08:33 PM   #2
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Ok, I'm not exactly sure what you hope to accomplish, but it sounds like you are looking for a free lunch. You are trying to convert a window air conditioner into a supplemental heater? Air to air indoors? And some sort of evaporator submerged in a garbage can of water outdoors?
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Old 02-27-20, 02:57 AM   #3
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Hi Jeff and thanks for your reply . What I want to achieve is a ground source heat pump that is using the heat for vaporization from a smaller air to water heat pump instead of boreholes or ground loops . The small air to water heat pump will feed a water tank and from the water tank the water which will have 50-60 F ( i will use a mixing valve to set the desired flow temperature ) will go to the ground source heat pump heat exchanger ( evaporator ) . For the ground source heat pump I want to use R134a because of the higher temperatures achieved by this refrigerant .
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Old 03-01-20, 12:48 PM   #4
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Default Ground Source with no Ground?

It would help if you included a diagram of your proposal.

I may not understand correctly what you want to do.

I can say this, the great efficiency of a Ground Source Heat Pump is that it is able to pull heat from the ground or air, and bring it into a house. It's main feature is that it doesn't 'make' heat, rather it moves existing heat from the ground or air to your house or water heater, or whatever. Ultimately, the heat from the ground or air is heat from the sun that has shined on the ground, and warmed the ground up. There are cases when there are shallow geothermal hot spots. I have also discovered that rain falling on the earth also brings heat with it that can warm the earth.

For heat to flow from one place to another, the heat will flow from hot to cold. For instance, if your Heat Pump heated up water in a tank, to a temperature above 20C, like 85C heat would flow from the tank to the house until the temperatures were close to equal, then no more heat flow.

However, I can see one situation where you might have a very, very large water reservoir to use for heat storage, and you could use a small heat pump to extract heat from this tank. By using a powered heat pump, you could extract heat from this storage tank, to a point that was well below 20C, even down to nearly 2C or 3C.

Is this your idea??
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Old 03-04-20, 10:44 AM   #5
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The advantage of the ground source heat pump is pulling heat out of the ground that is at a higher temperature then the air.

If you are using an air source heat pump to heat the tank that feeds the water source heat pump, you are getting no advantage. You would have a loss of efficiency.

Could you make a mini DIY bore field and get your ground source? Sounds like you have the skills
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Old 03-07-20, 01:08 AM   #6
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Thank you Ac and gadget for your answers . Want I want it to know it was your opinion about the idea . I must admit that I'm not very good when it comes to thermodynamics and that's why i was asking for your opinion . Maybe the the best would be to see if I can find a solution for boreholes done as cheap as possible , maybe a diy solution . I was quoted around $7000 for two boresoles , each 150 metres deep . It's way to much and I can not afford that at the moment , I rather keep my diy air source heat pump .
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Old 03-07-20, 01:34 AM   #7
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I still don't understand what you are trying to do here. Are you trying to directly heat indoor air with your machine? Or are you building some sort of cascaded device, using the water tank as an intermediate heat store? Gadget has been contemplating a device somewhat like this, only he is using tandem units to heat up a tank at different power levels, using batteries and solar panels for some of the electricity.
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Old 03-07-20, 04:32 AM   #8
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Hi Jeff , gadget said it better than me and I will quote him here : "If you are using an air source heat pump to heat the tank that feeds the water source heat pump, you are getting no advantage. You would have a loss of efficiency." Sorry that I didn't explain my idea good enough , but that is what I wanted to do : use a small air to water heat pump that will feed a water tank , the water from this tank will serve as the heat source for may "ground source heat pump" ( not so much ground source as it will get the heat needed to evaporate the refrigerant from.the water tank ) .
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Old 03-07-20, 05:55 PM   #9
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Ok I get where you are going now. I tend to think outside of the box though. There is a definite advantage to your idea in certain areas and circumstances. Don't know about your heat load or local climate, so I will just throw out some ideas.

The water tank add on works well with solar assistance. While normal solar panels can be directly plumbed into the house, insulation and high water temperature are absolutely necessary for the system to function. When combined with a heat pump, these restrictions are lifted. The solar collector panels don't have to work hard to heat up the water, so don't need as much insulation. In certain conditions, the solar collector panels can even absorb heat at night, once the water temperature in the tank falls below ambient.

The extreme application of this solar assist is to eliminate the air source hx and the water tank, and run your refrigerant straight through the solar collector. I believe sunpump made some of those.

Yep, here is the link:
http://thinkmechanical.com/residenti...e-do/sun-pump/

Last edited by jeff5may; 03-07-20 at 07:49 PM..
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Old 04-07-20, 05:11 AM   #10
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Frankly, I use with success a small geothermal pump, but you need to stay in a proper area for this kind of thing, they are not like solar panels plug and go. They are good, even RenewablePedia.com admit it, but geographic position counts more than 60% from my point of view.

I wish you success with your project!

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