heat tranfer fluid for evacuated tube system

Glenn Sossin_2

When you add antifreeze to the evacuated tube system, it has nothing to do with the fluid inside the evacuated tube collector. That fluid is permanent and sealed inside each of the tubes. They don't mix with the system antifreeze.

Consult with the manufacture of your collector system for specific recommendations. Checking the anti-freeze concentrations is something that should be scheduled maintenance and done regularly. Check with manufacturer. If you are stagnating excessively, such that you are concerned about these higher temps, perhaps you have too many collectors for your system (tank size).

One option would be to rotate the tubes slightly to maximize performance during winter thereby reducing performance in the summer, and reducing the amount/potential for stagnation. Stagnation occurs when your tank can not absorb any more energy from the panels, and the controller shuts down the pump. More panels is not necessarily a good thing with solar.

Another option, get a second or larger tank. Rotating the tubes would probably be a better option.

Learning this solar stuff, but I believe I'm on track with this question.

My $.02

Glenn

Mike C._4

heat tranfer fluid for evacuated tube system

Does anyone have any specific brand recomendation for glycol (or otherwise) to deal with higher temps of evacuated tube solar system? Nothing I seem to see being used really meets the requirements of the higher temps.

Mike

Ron Huber_2

glycol

Viessmann has Tyfocor (40%glycol and 60% distilled water) or Dowfrost (by Dow) are two of the best high temp glycols out there and the two that Viessmann recomends for their tubes. We use Tyfocor for all our systems, flat plate and tubes.

Mike C._4

heat tranfer fluid for evacuated tube system

My question was specifically for the system heat transfer fluid. I have even talked to suppliers who haven't considered some of these issues.I have an evacuated tube system I will be commisioning in a few weeks and this is one thing that I want to get right. Most of the high end propylene glycol solutions seem to max out at about 325 deg F while stagnation temps can reach 4-500 deg. Sure you can go to mineral/synthetic base heat transfer fluids with wide temperature ranges but then have other problems such as toxicity, flammabilty, low heat carrying content, etc. I am just curious as to what most evacuated tube installs are using.

Thanks for the replies.

Mike

hot_rod

Tyfocor LS

or HTL are high temperature fluids from what I read.

What happens as they adjust the temperatures up in PG is that the toxocity level also goes up. So there is a trade off for higher operating temperatures.

We really want to stay away from double walled HXers to handle fluids that are no longer low oral toxicity. As the trade off for higher operating fluid required less efficient HXers.

hr

Drew_2

Solar Antifreeze

Well said hr.
Before using or recommending high temp antifreezes for solar, check the MSDS sheets for the list of ingredients. Then check that list against the FDA (Food & Drug Admin.) list of food products. If you don't find it listed, be aware that it's not for human consumption.