Solar Thermal psi

Royboy

just about to post a question about sizing expansion tanks for solar systems and thought I'd add it to this thread since it seems directly related.

I use the expansion tank sizing software in Hydronic Design Studio, but am a little unsure of what temps to enter for system max. on one hand there is the stagnation temp of the collectors. if you put that in the formula you end up with really large tanks (and HDS won't even take temps over 250). reality is that you may get stagnation temps in the collector piping but other parts of the system could be relatively cool at the same time.

for instance I am presently trying to see if a tank on a system is too small (it acts like it is). the system has about 9 gal in the collector array and piping, 30 gallons in a storage tank that is really mostly a buffer tank, and another 9 gallons in storage loops in sand beds - which probably never get very hot.

how do the rest of you size solar expansion tanks? rules of thumb?

thanks - Roy

WV EGBERT_2

Question about pressure

So one of my new and latest hobbies is to look at my gauges on my closed loop system when the sun is out (or cloudy) to see how hot fluid is getting.

But always from day one the pressure gauge fluctuates as water is cooled and heated. You would think with the expansion tank P.S.I would stay constant. I'm not sure if I have a problem.

Initially, I filled and pumped up pressure to 2 1/2 bars about 25 psi. Total height from roof to HX is about 15'. I don't see a leak, and I closed vent at highest point on roof thinking leak there.
Is this normal?

Also. I'm moving about 1.5 gpm of fluid, with pump speed set on lowest setting to draw less electrical energy. But, if moving flow at a higher speed, can I get a little better transfer rate from the collector.

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michael_34

expansion tank pressure?

What is your expansion tank pressure set at?

ScottMP

Singh

How much does it fluctuate ?

Do you hae to Add more ? Or does it take care of itself ?

I would check the tank also but I can beat you allready did.

Most hydronic systems will fluctuate 3/4 lbs

Scott

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michael_34

expansion tank pressure?

Try setting expansion tank pressure around 15lbs if your loop psi is around 25.
good luck

Metro Man

solar settings

Singh,

On a closed loop glycol system I would err on faster collector pump speeds or shooting for a delta-T of 15*. When system heats up your slower pump speeds could spell trouble.

Don't worry about the fluctuation of the pressure guage so much. In fact I like the P/G on the output of the pump just so we know it's working. Check pressure when system is off and in morning to compare pressure readings to see if there is a leak. You will eventially go to zero if there is a problem.

We set pressure of x-tank to match the FILL pressure of system @ 70*F.

Once air is out of system close all the vents... they all will leak. A tiny bit of air in system won't kill you. Remember the 7 P's....Proper prior purging plumbing prevents poor performance

Hope this helps..

Metro Man