Solar Piping Question

Paul Rohrs_4

I am working with a solar contractor who provides and installs his own collectors. He also provides his own drainback tanks that I am to pipe to.

His request for this project is for me to:

Provide & Install 2-120gal storage tanks, 1 thermostic mixing valve, boiler backup, tie on a recirc, and connect to his two drainback tanks.

This is DHW only and I am thinking I am close on my diagram but it seems like it still could be a matter of controls. (The solar contractor uses an "Eagle 2" differential control.)

This is a 48 unit hotel and my understanding is that it's usually completely full, or totally empty. I do not want a "not enough hot water" call, as do most contractors.

As a sequence of operation, I want to make sure I am engaging the boiler at the appropriate time. If there is heat available at the collector, but not enough to satisfy quick recovery, I will still default to the boiler. The upside is that we are taking it to 160°F and then mixing it down.

My thought is to make the solar the 1st stage, and boiler the 2nd stage. I will need to limit the differential on the 1st stage so that if it falls behind, 2nd stage assumes total control. Yes? I want pump operation to be NO/NC with the boiler pump or the drainback tank pumps. The addendum to that would be that if the tank falls to below 130°F, to then bring on the boiler.

The scenario in my mind is that if the solar drainback falls behind, 2nd stage engages for boiler operation, boiler pump comes on-line, hydraulicly locking the drainback tank pump out along with dropping power to drainback tank pump, leaving boiler to produce until satisfied.

I thought about a hydroseparator simplifying the piping, but that would have to be bronze or non-ferrous.

Is there a better way?

Regards,

Paul

hot_rod

why

the two drainback tanks? Do they have coils in them to keep the db water and potable separate?

Suggest a solar controller that has all of the functions built into it. Plenty out there, you need one with two outputs. Caleffi I-solar plus is one example.

The control needs to keep looking back at the solar, so when the array has enough horsepower the boilers drop out.

Be sure the boiler can cover the entire load without any solar of course. Have someone sign off on the amount of DHW you intend to provide if they don't give you the spec. You don't want to be blamed for insufficient DHW.

Recirc piping with a thermostatic is critical. I have a schematic for commercial recirc with mixers I will dig out.

hr

hot_rod

check valve

location (both) is critical. Recirc mid tank if possible to keep solar performing best.

hr

Paul Rohrs_7

DHW

The drainback tanks he is providing do have internal coils. I am still waiting for more info about the system but my thought is that he needs two drainback tanks because of the large array.

I will check out the I-solar plus controller. I piped it similar to a modcon for space heat and dhw and didn't know if this was the norm for boiler backup.

Thanks,

Paul

hot_rod

HTP has large drainback tanks

up to 60 gallons, with or without the coil inside. That would save some piping. I used an Ergomax tank for my drainback. It has a lot of copper coil inside, and they now have additional taps for buffer or solar connections.

I-dronics 3 has some piping options for that system, there will be more in I-dronics 6, due any day now.

The main thing is to not heat the solar tank with the boiler, looks like you have the concept correct. The right control makes it easy to control, data log. etc.

hr