A question of balance

Rodney Summers

I've gotten so much plumbing help here in the past, hoping for a bit more.

I recently converted my electric baseboard heat to oil fired and installed a G115 with the fancy controller. I've plumbed in the necessary connections to allow for solar assist on the one floor of radiant I have designed for 95F. I'm installing a large storage tank and have picked up 7 used solar panels. I'm going to replace the piping in the panels with some new guts I've found on line that come with absorber plates connected to the risers. Frames and glass are in great shape.

Here's the question. 3 panels are 4x8 and 4 are 3x7. Do I have to be concerned about balancing the flow between the different sizes? That is, if I connect all the input tubes in series, will the larger panels get starved due to higher resistance?

Larry Weingarten

Some thoughts

Hello: If the headers in all of the panels are the same size and that will allow adequate flow, I'd consider plumbing them all as one bank using reverse return. Another (likely more precise) option is to plumb them in two banks with a balancing valve on each bank so that when things are up and running you can temperature balance the banks. That is closely matching outlet temperatures by adjusting flow.

Yours, Larry

Rodney Summers

Thanks Larry

What do you mean by plumbing them with reverse return? I'm not a plumber so the term is getting by me.

I've looked for balancing valves before and all I seem to find are shower balancing valves. Can you point me to a brand/model?

flange

reverse return is a setup that allows the return loop of various loads to mix to allow for more even return temps. In essence you pipe the system so that the first panel supplied is the last panel returned. you do this by having a riser that start at the first panel, picks up all the next panels in the loop, then returns to the storage tank. if done correctly it will look as if there is a thre pipe system at the panels, the supply and reverse return water run in the same direction, until the last panel where the reverse return loops back 180 degrees and becomes the reurn with water running back the opposite way.

Brendan_2

Not an expert on solar. However there are many variables involved such as.

What type of system are you installing,is there freeze protection involved such as DRAINBACK,CLOSED LOOP with antifreeze etc.

how are the collectors plumbed are the serpentine(series) or parrallel(large headers with smaller connecting tubes)

Keep in mind that the colder the water you send to each collector the more efficient it will be. I would pipe them in parrallel but maybe some of the guru's will chime in.

PS size your pipeing with future expansion in mind.

Larry Weingarten

Another way...

... to describe reverse return is; say you put cold water in at the lower left corner... than hot would need to exit at the upper right corner. All collectors are tied together at their headers, making essentially one big collector. No matter what system type you build, install the collectors so they can be fully drained (lower at the cold inlet side) and make the hot return from the panels the shorter line so that it has less opportunity to lose heat. Balancing can be done with standard ball valves, but allow time to get the adjustment right. Once the adjustment is perfect, remove the levers and strap them to the pipe. Otherwise it's trouble waiting to happen.

Yours, Larry

ALH_4

balance

The flow rates are relatively low and the difference in length between the tubes is only 1 foot. The difference in head loss is probably negligible for practical purposes. Reverse return piping is probably unnecessary.

At least as important is how you are going to integrate the solar heating with the boiler. Are you planning drainback or glycol? Are you using injection mixing or a mixing valve? Is the storage tank sized to match your panels? What kind of heat exchanger are you going to use in the storage tank?

-Andrew

Rodney Summers

Thanks for help

I've been using the RetScreen software to size the system. I'll be using 700 gallon storage tank and ~320 ft^2 of panel. I'm using the FM241 card on the Buderus G115 with two motorized mixing valves, one NO one NC. Those will allow me to integrate water from the solar tank via a HX. I'm only using it on the radiant loop I have in the house that has a design temp of 95F and a loss of ~10K. It's also only designed for an outside temp of 20F. Figure it should give me a supplement of 15-20 hours if I can get the tank to 125F. Attached is a diagram of the plumbing.