Hybrid Car – More Fun with Less Gas

Venting Pressure from Solar Collector

register ::  Login Password  :: Lost Password?
Posted by RDuke on October 18, 2005, 4:51 am
 
Hello.  I am installing a solar collector to preheat water for my
electic tank.  This is an active direct system.  I am concerned about
the presure in the hot water system reaching 150PSI.  There are 150PSI
relief valves on the water heater and holding tanks and I am planning
on installing another 150PSI relief valve on the roof at the collector.
 My concern is what happens in the summer when the panel makes more hot
water that I can use.  What if I leave for a couple of days and thinks
heat up?  I assume one or more of the pressure relief valves will blow.
 Is this OK?  How much water will I loose?  Is it OK for pressure in
the system to get up to 150PSI?  I didn't this it was rated that high?

Thanks


Posted by Rob Dekker on October 22, 2005, 1:55 am
 


Hi RDuke,

I asked the same question a month ago or so in this forum.

The answer is that the pressure/temp relief valve on the collector
will take care of this, and no, you will not loose too much water.
Just a small sprinkle of almost boiling water when you leave it unattended
in the blistering summer sun.

Alternatively, you can cover your collectors with tarp or so if you
leave for vacation...

Rob



Posted by Brian Graham on October 24, 2005, 8:12 pm
 By buddy performed an experiment. He turned off his hot water system and let it
cool. He then noted the system pressure. The he turned it back on. The pressure
remained constant. Thus, the increased volume from heat expansion was clearly
being sent back to the city. (There was no expansion tank in the system)

Therefore his PTRV will never blow because of pressure.

Temperature may be another story, though.  You may want to tarp it off or drain
it when not in use..
--
Brian


Hello.  I am installing a solar collector to preheat water for my
electic tank.  This is an active direct system.  I am concerned about
the presure in the hot water system reaching 150PSI.  There are 150PSI
relief valves on the water heater and holding tanks and I am planning
on installing another 150PSI relief valve on the roof at the collector.
 My concern is what happens in the summer when the panel makes more hot
water that I can use.  What if I leave for a couple of days and thinks
heat up?  I assume one or more of the pressure relief valves will blow.
 Is this OK?  How much water will I loose?  Is it OK for pressure in
the system to get up to 150PSI?  I didn't this it was rated that high?

Thanks




Posted by daestrom on October 24, 2005, 8:57 pm
 

The key to your friend's experiment is, he was on municipal water supply
with no check valves.  The water was free to expand 'backwards' into the
city water main enough to not change system pressure.

If he was on a private well with a pump, check valve, and pressure tank, the
results could have been different.  The check valve usually seats pretty
well in such systems, otherwise the pump has to keep restarting to recharge
the pressure tank.  In that case, the pressure *could* rise significantly.

The OP didn't mention city water or private well, so we can't know for sure.

But in either case, if the valve pops on high pressure, it would most likely
immediately reseat after discharging < 1 gallon of water.  If it lifts on
high temperature, it will discharge water until the temp drops below the
reseat point.  This could be a significant amount of water (how long can you
run the faucet before the tank runs out of hot water?).

daestrom



This Thread
Bookmark this thread:
 
 
 
 
 
 
  •  
  • Subject
  • Author
  • Date
please rate this thread