Knick's Solar Water Heating System -- Comments

OK, this is obviously a great job that Knick did on this system, but I cannot resist a tiny bit of nit picking:

- I really like both the looks and extra weather protection that the aluminum trim on the outside of the collector provides.  I think this would be a good way to go -- particularly in climates where wood has a shorter life.

- I think its a good idea to use the polyisocyanurate insulation board rather than polystyrene insulation board for insulating the tank -- at least for the layer of insulation that is directly against the EPDM liner.  The polyiso gives more temperature margin in case the tank temperature goes above about 160F.  A side bonus for using the polyiso is that it has a higher R value per inch.
Knick has his controller set to limit the tank temperature to 140F, so the polystyrene insulation will be fine in his case.

- I think that using pipe with a higher temperature capability than the PVC for the piping used for the circulation pump U-tube would be a good idea.  The PVC may be OK, but CPVC or PEX or copper would give more margin for higher temperatures.

- Some have commented that braising rather than soldering would give the riser to manifold joints more strength.  I think that given the great care that Knick used to get a good fit at these joints that the solder is likely to work fine.  Another option for the less skilled among us would be to use reducing T's to go from the 3/4 inch manifold to the riser pipes.  One example of using the reducing T's...
These reducing T's can be expensive, but has a good price in box quantity.

- I would feel a bit better if the pump were mounted down closer to the floor.  The pump manufactures recommend that the water pressure at the inlet of the pump be at or above a certain value.  This varies with pump manufacturer and model, but its usually around 3 ft of water head -- so, mounting the pump down near the floor helps to satisfy this.

- Knick is trying a pump with an iron case, and may change to bronze or stainless later.  I'm doing the same thing on my new system.  While Grundfos and Taco would recommend using a bronze or stainless case for open systems like the $1K system, from what I have seen over the past couple years, iron case pumps may be fine for the $1K systems in which very little new water is introduced after the initial charge.

One final thing is that the notion of using a large collector area that is installed vertically coupled with somewhat larger storage tank volume with the objective getting a good solar fraction right through the winter and still not have an overheating problem in the summer is not (to my knowledge) a fully proven idea.  My new system uses this idea and Knick's does as well -- so, both of us feel that its likely to work well, but it will take a year of performance to be sure.



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Gary May 29, 2010