|Neil provides a very detailed description of the solar water heating
system he built for his home in the UK.
This is a very nicely designed and constructed system.
While the system is based on the $1K Solar Water Heating system, Neil has included some unique design changes that might fit your situation.
Thanks very much to Neil for sending this in!!
There are a few highlights of the system below.
|Neil's tank is tall but small in floor area to take
advantage of the space available.
One of the unique features of the tank is that the water proof liner is made from several layers of fiberglass.
The tank also has a number of well thought out design details that might fit your needs.
|Neil did a very nice heat exchanger made from copper
This is a single pass heat exchanger that is used in the same way as the large PEX coil heat exchanger, but since the copper is much more conductive than the PEX, less length and less space is needed for the heat exchanger.
Neil also describes how he interfaced this single pass heat exchange system to his new, efficient combi boiler system.
|The collector uses a single sheet of aluminum under the
copper pipe risers rather than separate fins on each riser pipe.
To thermally bond the sheet to the riser tubes, 3 inch wide strips of aluminum with a U groove to fit snuggly over the riser tubes are snapped over the riser tubes, and then riveted to the backing sheet.
Since the smooth side of the large sheet faces out, this makes for a more visually appealing collector.
Another unique feature of the collector is that the wood frame is protected from the weather by fiberglass.
For the full 26 page detailed detailed description, download this pdf...
Some abbreviations used in the write-up you may not be familiar with:
WBP plywood -- basically exterior plywood -- stands for Weather and Boil Proof
PIR is rigid polyisocyanurate (polyiso) insulation board -- this Xtratherm is the brand Neil used ...
Jubilee clip is regular hose clamp...
Neil will answer questions about the
system here njb-designs AT talk21 DOT com Replace the AT with
an @ and the DOT with a period.
Neil has provided some logged performance plots for the system ...
Clearly, this is a very nicely and skillfully done system, but I'll offer a couple comments/suggestions anyway :)
Two Pumps -- Neil had to use two pumps to achieve the pressure head that is needed at startup in drain back systems to pump water from the storage tank all the way up to the top of the collector. But, once flow is established, one of the two pumps would be sufficient to maintain flow. Some people have handled this by using two pumps at startup with the 2nd pump on a time delay relay that shuts the pump off after a short time interval. This cuts the pumping power in half, but does add a little complexity.
Neil reports that he has experimented with this and was not happy with the flow pattern from a single pump, so this solution may not work in all cases.
Silicone or Epoxy -- Neil suggests that a thermally conductive epoxy might be a better choice for bonding the copper tubes to the aluminum fins. This may be true, but for all the reasons stated here, I still like silicone. If the lower thermal conductivity is a concern, there are thermally conductive silicone caulks made. I plan to test one of these this summer, but for the reasons stated at the link just above, I don't think it will make much difference.
Epoxy might work even better than silicone, but I think there is a little risk involved in using it until someone tries it for a couple years. The lack of flexibility and the lower temperature limits are the areas that bother me a little.
If you have some experience with this, please let me know.
Placement of Tank Temperature Sensor -- Neil found that with the temperature sensor for the differential controller placed at the bottom of the tank that when the tank was temperature stratified and under moderate sun conditions, he could have a situation where cooler water was drawn from the bottom of the tank, sent through the collectors, and come back warmed up some, but cooler than the water in the top of the tank. To avoid this, he moved the sensor to the top of the tank.
To me, this is a tradeoff. If you draw cool water from the bottom of the tank and it comes back warmed up some, but not as hot as the water in the top of the tank, you are still adding heat to the tank, but you are degrading the temperature stratification in the tank. So, if more stored heat is the objective, I'd leave the sensor at the bottom of the tank, but if more temperature stratification is the objective, then you could try moving the sensor up in the tank.
Neil might give us more on this once his logging system is up and running.
Gary May 13, 2010