Introduction: Gravity Solar Water Heater, Commercial Size
Problem, to have a cost effective solar hot water heater large enough for PlayaLindaHotel.com , a 10 suite hotel built to keep us occumpied for our retirement. Additional issues to have water available in the case of extended power outage. As this building is located in the south of Mexico we have no freezing days so no need for glass covered frost protected collectors.
Solution, to use solar pool heaters with water storage above the solar heaters all located on the roof. Because the storage is above the solar collector sun heated water being lighter rises into the storage tank, at night the coldest water stays settled in the collector.
Step 1: Sizing
Calculated, based on free Ret Screen Software, http://www.nrcan.gc.ca/energy/software-tools/7465 to have hot but not boiling water. Some sizing allowance could be made by adding or reducing number of collectors. Also we used pressure balanced mixing valve faucets and shower controls in the bathrooms for better and safer control of the hot water.
Based on calculations I ended up ordering 8 of the 2x12 solar pool collectors.
Additional considerations, a gravity system provides slightly under 1/2 psi water pressure per foot drop from storage tank (.42 lbs) so standard shower heads would not work well. This we solved by using a Oxygenics.com Delrin nonclogging shower heads meant for gravity systems, a special request item, the work on as little as about 2 to 3 pounds pressure.
Step 2: Materials and Placement
. Materials, 2 of 1100 litre tanks for Cold Water, 2 for hot water. Water enters 1 tank at top and flows to other tanks via outlet at bottom, the cold bottom of solar collectors, as well as being the cold line to building, Bulkhead fittings 4 polypropylene-1" pipe, 2 placed 25% up the 2 hot water tanks, these are for the hot water returning from the Solar Collectors, cold line to collectors is under the collector. The additional 2 bulkhead fittings are placed about 50% up the 2 hot water tanks so allow up to 500 litres each of hot water. If depleted due to extended power outage there is still available water for flushing toilets. All drinking water is handled by a separate reverse osmosis water system fed from the cold water roof mounted storage tank.
Step 3: Ongoing Maintenance
Maintenance, reverse flushing of collectors twice a year by shutting off cold line to collector and undoing a clamp so hot water flushes tubes, could be made simpler with a T in piping and valve. Painting of support structures steel as required, In use since 2009.
Step 4: Final Notes
Hot Water Heater uses gravity to circulate water within system but a electric pump is used to push water 40 feet up into the tanks. You must plan to separate hot from cold water so a minimum of 2 tanks are required, one does require an angled roof line for the solar collectors, if you don't have this a "Galera" is recommended. In Mexico this is a metal roof covering often used for hanging clothes etc and protecting the main roof from direct heat of sun.It would also be a great place to have your solar electric panels.
I would like to add Solar Electric Panels and perhaps a wind turbine but we are located at the beach and salt corrosion in a hot humid environment is incredible, Galvanized steel is not enough, it must be Epoxy Coated. Aluminum likewise corrodes and should be Anodized to survive a reasonable time.The UV of the sun likewise is very harsh on Plastics. Consequently I have my doubts as to if a solar electric panel could have a pay back here before failure but would love for someone to prove me wrong. Owners, PlayaLindaHotel.com