glycol preheat of water

[wash4me]

I have a boiler with primary secondary piping arrangement to my floor heat glycol system. I am considering adding plumbing and valves so that when I am not in floor heat season I could circulate glycol through the floor heat exchanger and "preheat" my water on the cold side of the hot water tank. It would have a flow switch in the cold line so that it only ran the glycol pump when water was being used. It would also have a thermostat setup that would only run the glycol pumps if there was at least 10 degrees or so difference in the glycol and incoming cold water temperature. Any thoughts?

 

[Earl Weiss]

I think you will be wasting energy. The most efficient liquid for transferring heat is water. The reasons plain water is not used in radiators and floor heat is due to the freeze potential, boiling point and corrosive issues. So, instead of heating water directly which is the most efficient energy use, you will use energy less efficiently to heat the glycol and then the water.

 

[wash4me]

I think you will be wasting energy. The most efficient liquid for transferring heat is water. The reasons plain water is not used in radiators and floor heat is due to the freeze potential, boiling point and corrosive issues. So, instead of heating water directly which is the most efficient energy use, you will use energy less efficiently to heat the glycol and then the water.

I intend to use this idea to "preheat" the water. The actual water heat system will stay the same but hopefully i can raise the temperature of the incoming cold water.

 

[Earl Weiss]

I intend to use this idea to "preheat" the water. The actual water heat system will stay the same but hopefully i can raise the temperature of the incoming cold water.

If I read your OP correctly you would now be using energy to heat the floor heat glycol to heat the incoming cold water . This is energy you would not otherwise use. Lets say the ultimate goal is to raise the hot water temp 50 degrees over the incoming temp. Now you raise it directly witht the Hot water system. You propose to raise the temp 20 degrees at the incoming side and 30 more degrees at the Hot water system . The 20 degree raise at the incoming side thru use of the floor heat system will use more energy that if you just used the Hot water system.

 

[wash4me]

If I read your OP correctly you would now be using energy to heat the floor heat glycol to heat the incoming cold water . This is energy you would not otherwise use. Lets say the ultimate goal is to raise the hot water temp 50 degrees over the incoming temp. Now you raise it directly witht the Hot water system. You propose to raise the temp 20 degrees at the incoming side and 30 more degrees at the Hot water system . The 20 degree raise at the incoming side thru use of the floor heat system will use more energy that if you just used the Hot water system.

I'm having trouble writing it differently. The only energy I am proposing to use would be the glycol pump. I would be pumping glycol from out in the bay floor heat through the exchanger on one side and on the other side would be incoming cold water. So i could potentially raise the temperature 10 degrees if the incoming water was 60 and the floor glycol temperature was 75. Basically using the concrete as a large heat sink.

 

[dogwasher]

Sounds like Geothermal...what about the heat exchanger it might sweat and rot out sooner?

 

[Earl Weiss]

I'm having trouble writing it differently. The only energy I am proposing to use would be the glycol pump. I would be pumping glycol from out in the bay floor heat through the exchanger on one side and on the other side would be incoming cold water. So i could potentially raise the temperature 10 degrees if the incoming water was 60 and the floor glycol temperature was 75. Basically using the concrete as a large heat sink.

OK, now I understand. So, basicaly you wait until the outside temp exceeds the incoming water temp.

In that case I got "Nothing" vis a vis cost to run glycol pump versus savings.