This section is a brief review of solar hot water systems and concepts.
Solar hot water collectors are the moderately complex to install.
Best use: domestic hot water
Secondary use: storage and space heat
Cost: low to moderate
Installation: usually roof mount, also ground mount or directly to the side wall of the house
Solar hot water collectors can be more complex to install. Solar hot water collectors are connected together with copper piping and use a pump to move the water from the collectors into a storage tank. The pump is turned on by a controller.
There is a solar "Hot Box" design for a solar water collector with a tank inside the collector housing. The water tank is essentialy sitting inside a superinsulated box. This is a passive solar design where city or well water pressure supply the movement of the water through the tank. Water passes through the solar hot box enroute to the regular domestic hot water tank when the faucet is opened. The water is pre-heated with solar. Most hot box installations have to be ground mounted due to the weight.
Solar Hot Water System -
A Typical Installation Model for Residential Rooftop
Most solar water collectors are about 4 feet wide and 8 feet long.
The solar collectors need to be facing south with a steep incline to maximize the exposure during the winter months.
There are two main installation designs for hot water sytems;
closed loop or drain back.
Closed loop systems include a 50:50 mixture of glycol and water running through the pipes between the solar collectors and the water tank. The closed loop system needs to have the glycol tested for acidity or water freezing effectiveness every few years. This is a simple procedure done with commonly found pH strips or a radiator freeze tester tube.
Drainback system designs mean that when the pump stops running during the day, the water will "drain back" into the holding tank. All the pipes for the drainback system will have a declining slope so the water will rapidly drain towards the tank. These systems can be more efficient in harvesting heat, but can not always be installed due to where the collectors are mounted.
Solar Hot Water Components Diagram
The solar components of a hot water system include; collector, pump, copper piping, control system, tank and heat exchanger.
The pump is sized acording to the number of collectors and total length of the piping. Larger systems with storage for space heat will have more than one pump.
The piping is insulated to reduce the heat loss between the collectors and the tank.
The control system is a "temperature differential controller" which uses sensors to compare solar storage tank temperature and collector temperature. When the collector temperature is warmer than the tank temperature the pump is turned on to move the heat. Hot water systems sometimes use multiple controllers to manage the pumps between the tank, collectors and heat exhanger.
The heat exchanger is a specially designed copper pipe that allows the transfer of heat without the direct contact of water. Solar storage tanks will often have an interior (water-to-water) heat exchanger. A water-to-air heat exchanger is like a radiator where air is passed over a water pipe surrounded by fins (such as a convector or furnace coil).