Which solar thermal pipes do I insulate anyway?
Solar thermal pipes can only be insulated with solar grade materials but understanding just which pipes can be insulated with standard, domestic grade, materials can save money without impacting performance.
In the previous article we established that most solar hot systems you're likely to encounter are “indirect” systems. We also saw that some pipes operate at different pressures and temperatures.
One thing we didn't cover in much detail was why you need to insulate solar hot water pipes.
Like all other heated pipes, when you apply insulation around solar hot water pipes you stop thermal energy from leaving the pipes. Unlike a conventional gas or oil fuelled boiler, in a solar hot water system this thermal energy is “free” - there's no need to burn fossil fuels to obtain the energy that has been lost.
What's more, during the summer months a typical solar thermal system will produce so much excess hot water that simply can't be used fast enough that preventing the loss of this energy is irrelevant but this isn’t the end of the story.
During the Autumn & Winter things change. Solar systems are rarely sized to fulfil the hot water requirements during these months and users are reliant on back-up conventional water heaters. The less energy lost through the pipework, the less often the conventional back-up system is needed. Indirectly offsetting the use of fuel that would release Carbon.
So, ultimately, the reason why all pipework connected to a conventional hot water system needs to be insulated remains the reason why you should insulate all pipework connected to a solar thermal system. A number of things do, however, make insulating a solar thermal system slightly more challenging.
Too hot to handle
Solar panels are incredibly efficient at absorbing energy from the sun and, in the right conditions, the glycol-water mixture passing through the solar panels can increase to temperatures in excess of 150 degrees. Such temperatures are unusual for a domestic solar thermal system and would require pipework capable of operating at very high pressures but most solar panels or tubes are easily capable of heating the glycol-water mixture to more than 100 degrees.
This creates a challenge because Kaifoam PE, like all other domestic grade polyethylene insulation, melts at just over 100 degrees (every year some people find this out the hard way…). Kaiflex ST is based on Nitrile rubber and fares slightly better - the material won’t melt but it does have an upper temperature limit of around 110 degrees, above which the rubber will begin to harden and experience a reduction in physical integrity.
EPDM rubber is rated for use at temperatures of up to 150 degrees before experiencing hardening and this is why EPDM rubber forms the basis of all Kaiflex materials that we specifically promote for use on solar thermal systems.
The great outdoors
Another challenge presented by solar thermal systems is the sun itself. Most insulation materials simply can’t withstand prolonged exposure to direct UV light but when insulating a solar thermal system at least some of the pipework is likely to be located on the roof next to the panels themselves.
Again EPDM rubber provides a natural solution as it is inherently UV-stable. Kaiflex EPDMplus, Kaiflex Solar EPDM and other EPDM based Kaiflex products are completely suitable for use outdoors on solar thermal systems.
So this leads to a scenario we get asked about at Kaimann at least a few times each summer. You have a solar thermal system and need to insulate the pipework. You know that, for the reasons outlined above, the only way to go is Kaiflex EPDMplus or Kaiflex Solar. Do you need to insulate all of the pipework in your house with EPDM based insulation?
Provided that you have an indirect solar thermal system the answer is no.
In an indirect solar thermal system the pipework connected to the panel acts as the heat source for the hot water cylinder. Only the pipework between the solar panels and the hot water cylinder needs to be insulated with Kaiflex EPDMplus.
The remainder of the pipework on the other side of the hot water cylinder operates just like a conventional hot water system and not at elevated temperatures. This pipework can be safely insulated with conventional domestic pipe insulation like Kaifoam PE or Kaiflex ST.