solar system operating pressure

hot_rod

12 psi is too low in my mind.

hr

Tom_119

solar system operating pressure

I live in Maine and am installing four 30 tube (double wall evacuated) panels to heat my concrete slab shop floor. I'm not sure what operating pressure would be best. I know that Viessmann recomends 90 psi. but I'm not sure why. Some say 15 psi is enough. I guess I want to be sure that there is enough pressure to keep the glycol from boiling in case of stagnation. would appreciate any insight here.

Tom

hot_rod

90 sounds high?

but the Euros do run much higher pressures than what I've always used.

I notice most of the pump stations from Europe ship with 6 bar (87psi) relief valves.

Yes some of it is to keep the boiling point high, especially with evac tybes being able to reach in excess of 400F.

That high pressure does raise some questions from inspectors when the solar fluid pressure can be much higher, maybe twice what the DHW pressure is. Any leak in the HX will discharge solar fluid into the potable side.

Static fill pressure, which lifts the fluid to the highest point in the system, plus 5 psi should work. Unless the collectors are lower than the tank and pump.

30 psi seems like a nice workable number to me with a relief valve at 1-1/2 times that pressure.

A bunch of solar codes are being written and updated right now including the Uniform Solar Code. Proper fill pressure seems to be a moving target.

The German "Planning & Installing Thermal Solar Systems" a great resource by the way, suggests static pressure plus .5 bar about 7 psi.

hr

Mike C._4

solar system operating pressure

I just installed a 4-30 tube system and used Viessmann directions which used static head plus 4.5-7.0 psi extra. It seems to be working great.

Mike

hot_rod

But I think there should be a min.

pressure setting.

Suppose you have a ground mount array at the same level of the tank, static on that may only be a couple pounds. 8 feet = 3.46 psi.

Maybe a 15 psi min. or static plus 7 would be the best rule?

hr

Mike C._4

pressure setting

Viesmann recommends 22 psig minimum cold fluid pressure + .45 x static head (ft) + 4.5 to 7.5 psig.
A typical one story home with 10 ft head would have a cold fill pressure of 33 psig. A two story home is typically 37 psig.
I don't know what others recommend but this sounded right to me.

Mike

Sorry-the two story number was misprinted before.