We finally got around to repressurizing our hot water solar panels. The process was pretty simple. This is a continuation of the work started February 20th.

First we picked a rainy cloudy day so we didn’t have to worry about the panels overheating. With our brand new pH strips and refractometer we tested the solar fluid in the system.

Solar fluid 9~10 pH

Nominally it is supposed to be between pH 8 and 9. So the fluid hasn’t broken down and become acidic. Tyson’s initial measurement of the propylene glycol concentration was probably wrong. He re-measured it later. The fluid in the system reported ~2F in the refractomer. Looking at the chart on the bucket, 2F should mean freeze protection to -6F, pumpable to -15F, burst protection to -50F. The air temperature only dropped to -13F in February, so it seems likely we didn’t damage the pipes.

Tyson adjusting hoses on the two pump system

For the small volume of fluid we needed to repressurize the system, we used a bucket left over from the original installation. It measured at 10F and pH 8.5. This bucket is probably some of what the plumber used when we first had the pipes freeze.

Final pressure — 25 PSI

To pressurize the system, we hooked up the output of the sump pump to our new 1/2 HP pump. First we just cycled the system to get any air out. Oddly, more fluid fit into the system with the solar pump off than on. We think we were pumping into the pressure expansion tank. Then, to pressurize, we closed the outlet. This time, the pressure on the gauge rose steadily until Tyson closed the input valve at 25 PSI.

The instructions I had gotten from RadiantTec said to pressurize the system to 15 PSI, but Tyson and I weren’t sure if that should be 15 PSI at the panels three stories up, or down in the utility room. Presumably the system is pressurized to increase the boiling point. If that’s the case, we would want 15 PSI up at the panels. And Tyson vaguely recollected that the original pressure when we moved into the house was more like 25 PSI.

Before next winter we should consider increasing the propylene glycol concentration.