Solar propylene glycol foaming.

joseph annon

I have a whole house heating system that has three solar panels attached the installer designed the system to be all glycol. My issue is that the glycol is proving very difficult to remove the air from when I purge the system with a charge pump it that the air does not separate easily from the glycol mix and stays in solution. The system has radiant floor for a small part of it and several Buderus radiators for the rest of the home heat. The glycol has good freeze protection now. I have not checked the PH yet but will do that. If it was a small amount of glycol ie the collectors connected to a heat exchanger I would flush and recharge the system with new glycol. However this system will be a challenge to flush all the radiators about fifteen of them and the four zones of radiant floor and the pool HX and DHW tank HX. My goal is to keep the existing glycol if possible.

hot_rod

Yes glycol is tough, tough to get all the air out. But it can be done.

Don't use too high of a percentage is one tip.

You MUST have a good micro bubble air purger, Caleffi of course The air purger needs to be at the hottest fluid portion of the system to do the best job.

A float type air vent at the top of the collector will help get and keep air out.

What pressure on the solar glycol? The higher the pressure you can run the higher the boiling point. In summer stagnation conditions the fluid in the collectors will flash to steam. A flat plate collector can stagnate above 400°F. Vac tubes even higher.

At 12 psi on the collectors they can flash around 244°F

I highly recommend drainback solar thermal to get rid of all the glycol issues. That may not be an option for you?

Sometimes an oversized fill pump will churn up the fluid cause it to foam, like a blender. You should be able to purge pump until the fluid comes back air free, a solid glycol stream.

You need a good volume of fluid to purge back into so you don't keep recirculating the air, at least a 5 gallon bucket, a 10 gallon fill cart works best. Don't put the purge hose near the fill pump suction, you will never get the small air out.

It can take 20 minutes of purging to get a good clean air free fluid coming back, be patient.

We did a video back in 2008 showing how to fill and purge glycol in solar loops, the more air you can get out with the fill and purge, the easier for the air purger to finish it off.

There are some air entrainment chemicals that can be added to glycol. I've seen that used on some of the clear demos at trade shows to help glycol deaerate quicker

joseph annon

This is a hodge podge of a system. No real good air relief in the system. It is tied to a boiler so pressure is running about 20 psi or less. GLycol is good to -10F* So probably fairly concentrated. Trying to get system to operate reliably while customer decides on options. I have spent about 30 minutes on two different days purging into a five gallon bucket using a transfer pump. Going to talk to customer about separating solar from the rest of the system with a HX. I do like drain back systems I do install them when I can. H ere we have flat roofs.

pecmsg

Why -10°? Keep the glycol above the average low temp for freeze point. Big difference between freeze point and BURST temperature!

When pumping to remove air do it slowly, small pump, low GPM. No need having that impeller create bubbles your trying to get rid of!

hot_rod

Also the system should really be cleaned with a hydronic detergent before adding glycol solution.

The assembly process leaves behind solder flux, oil, grease, assembly lube, pipe dope, etc. That can have a bad effect on the glycol blend if it is not cleaned out first. Some fluxes have chlorides are an ingredient, you really want that flushed out with stainless boilers. If you have an over aggressive fluxer on your team... just saying.

Also glycol blended on site should really be with deionized water. Hard or high TDS water will also compromise the glycol. Best to use pre-blended in the bucket if you do not have access to DI water.

joseph annon

I inherited this system hence the -10 rating on the glycol. When I do use fresh glycol I use premixed for the convenience. System is mostly piped in Kitec and is several years old. As for temperatures design temp is here is 10*F I have seen several times in my life here temperatures as low as -15*F overnights with highs in the teens for several days. Thank you for advice. It seems that I need to spend a longer time purging the system.

pecmsg

Delute the mix for 0 - 10* freeze protection. Easier to remove air

pecmsg

Should read 0 - +10*