Storage tanks

Weil

I was asked to assess a solar system for a government apartment building. System had 22 Steibel Eltron Sol 25 Plus C flat plate collectors running through a brazed plate exchanger which serves two 500 gallon domestic storage tanks. The glycol is burnt. Since repairs are going to be made they want the system redesigned. They want to eliminate one of the storage tanks and use it for storage of high temperature glycol which can then be used as stage one to heat domestic water into the evening. This will require a lot of glycol. Is their a better way to do this? I have installed only a few solar systems and they were all engineered. Your input is greatly appreciated.
Weil

Tom in Maine

Since the system started out as a glycol system, it will likely have to remain one. How long has the glycol been in the system?
I would suspect the plate hx is undersized or one of the pumps is undersized. The glycol cooked probably because the solar loop was overheating. Making the storage smaller might not be a great move. Depends on where you are and the system usage.
How many units does this system serve? It could be the system is oversized for the usage.

tom@americansolartechnics.com

matt_sunwaysolar

Sounds familiar. This in Chicago by any chance? I just serviced/ retrofitted a 24 collector Stiebel Eltron system with a similar set up in Chicago. There's a bunch of bad S-E systems installed around the city.

SWEI

Tom in Maine said:

Since the system started out as a glycol system, it will likely have to remain one.

I would tend to agree -- though I always at least consider the option of converting to drainback.

hot_rod

It may be possible to convert to a drainback. Are the collectors above the tank and mechanicals? Really all you need to do is have the collectors drainback, as long as you leave it a glycol system, it becomes a drawback with glycol for added protection.

Run the system with water, turn the pump off and see how much drains back.

If chronic over-heating is an issue, the you need to consider some type of protection mechanism. Controls can do a lot, dump zones are next, or a drainback.

It is possible to use a single tank as storage and drawback, pressurized or not. To minimize glycol content, use a HX, and you can drawback thru a plate HX.

matt_sunwaysolar

Stiebel Eltron's are serpentine style. No DB option here.

SWEI

Right, now I remember that. We were hoping we could make use of their landscape format collectors on a job before we found out.

Would a steamback design work?