Quote:
Originally Posted by roosterk0031
Problem is going to be weight, takes a lot of mass to hold fairly few BTU. Water holds 1 btu per lb per degree F temperature change. To hold 1 gallon worth of LP BTU's (91,500 btu/gallon) assuming a 140(70-210) degree temperature difference in the water/antifreeze you'd need 657 lbs of water (79 gallons). My furnace is 80,000 btu so that would be 68 minutes or run time. I think my last LP fill was $1.25 a gallon but has been over $3 in the past.
So I'd need 2 (40) gallon hot water heaters sized tanks, an heat exchanger in the exhaust (wrap exhaust pipe with copper tube and insulate), an expansion tank and a circulating pump.
Then a way to put the heat into house (already have some radiant hot water floor heat in part of my house so that part would be easy for me. Park in the garage, hook up 2 hoses and turn on the 12v circ pump.
I don't know the specific heat of brine or how that would change things.
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Somebody below linked to a site that presumably explains phase change.... We are NOT talking about brine here, but phase change of a salt from solid to liquid. The principle is the same as melting ice. It takes approximately 80 times as much energy to change ice to liquid water, as it does to raise the same amount of water one degree C. Molten salts or eutectic salts if you will, are engineered to have the phase change of the salt from solid to liquid at the temperature you need it.... this would presumably be around 180F, or a bit lower. The latent heat of fusion of these salts probably is not as high as water, but even at 1/2 that, you would need only a fraction as much as you would need water.
The only reason for having an actual brine, is for mobility in the solid state, and faster distribution of the energy through the mass of salts.
H.W.