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SOLAR HEATING SYSTEM CONSTRUCTION LOG
February 20, 2003: Over pressure fix
(see UPDATE Jan. 10, 2005 below)
At this time of year I occasionally have more heat than I need since I now have 4- 4X8ft Sun Earth collectors (added 2 last year). I have gotten various suggestions for solutions to this issue, including a thermostatic 3 way valve that dumps heat to an outside radiator, and boat covers for the extra collectors. I have yet to implement these suggestions.
Excess temperature in my storage tank drives the pressure over 100psi, at which point the P/T valve at the top of the tank dumps hot water all over the place! (I now have a bucket in place under the outflow!).
I figured that if I could just back the pressure off a bit somehow, that I could continue to store more hot water. I was able to do this manually by turning up the thermostat for the radiant floor loop, the excess heat is then dumped to the floor and the pressure plummets in a few minutes. When the tank measures 165F at the top( outflow), and 90psi, the water coming out the bottom is no more than 75-80F before it goes into the heat exchanger, this is due to the deliberate temperature stratification in the tank. I figure I could squeeze more heat into the tank if I could just dump the pressure.
My solution is
to replace the pressure gauge at the top (outflow) of my storage tank with
a gauge that has an adjustable electrical set point. Now, when the
pressure reaches 90psi the set point closes. I wired it in parallel
with the radiant floor loop thermostat so that hot water is dumped into
the slab. The result is that in less than 5 minutes the pressure
is down below 90psi in the tank. The gauge will continue to cycle
on for a few minutes throughout the afternoon for a minute or so on very
Since the heat dumped to the floor is negligible (it takes 3 hours to see a temperature rise at the thermostat for the radiant floor) the solution works fine for the occasional spring and fall warm days. I believe that this allows me to store extra heat in the tank.
I still plan to drain and flush the collectors when the weather turns hot, but this seems like a viable interim measure.
Above are images
of the gauge installed at the top of my tank. I got the gauge
Surplus in Pasadena CA for about $20.00. (Unfortunately C&H no longer
sell the same gauge ore any other suitable gauge with set points. I'm not
sure where you would find a similar one at this point)
UPDATE: January 10, 2005
April 2, 2005