http://www.iol.co.za/index.php?click_id=3027
One critical point which has been omitted from this article is that the problems that have been encountered are entirely with flat plate systems. There has been no mention of that fact that Evacuated tube systems are more than adequately frost tolerant.
We have not had a single problem with the recent cold weather. Said Barry Cribb MD of Sky Power.
As mentioned in the article quite correctly, flat plate systems are notoriously prone to freezing because of their design. The very thin fluid channels in contact with the flat sheet of metal can only be protected by an antifreeze solution, typically propylene glycol and configured in what is referred to as an indirect configuration.
Evacuated tube systems conversely use a similar alcohol within a sealed copper pipe which will withstand temperatures down to minus 30 degrees. This is one reason why they are becoming more popular in the consistently colder climates of northern Europe.
The above two photographs above were taken in Rivonia, Johannesburg.
The tubes can be seen clearly covered in ice. Outside roof temperature was measure at -7 degrees Celcius.
No damage was caused to either of the systems inspite of the fact that the electronic frost protection mechanism had been disabled as proof of resilience.
It is important to understand the difference in performance of the various system designs and not brand all solar water heaters as frost sensitive. The more efficient evacuated tube systems are inherently frost resistant.
It's actually well known by many South African Solar water heater dealers that direct flat plate systems are terribly frost prone and that the frost valves don't work. This is more evidence of dealers being in the market to make a quick buck with no desire to grow the industry.
ReplyDeleteIn the Highveld evacuated tube systems which aren't susceptible to freezing are a better solution. The only alternative is the glycol filled flat plate systems which are less efficient but frost resistant.
Hopefully South Africans will learn this lesson and seek out more competent dealers and not just look for the cheapest product.