Solar Water Heating
A solar water heating system is dollar for dollar one of the best investments a person can make in a renewable energy technology. A properly designed and installed system will produce the equivalent of 2,000 to 10,000 Kwh or more each year, even in Western Washington/Oregon's wetter climates. In addition, a solar water heater will prevent tens of thousands of pounds of carbon dioxide from entering the atmosphere.
With new design and technology, solar water heaters are taking on a greater role in many new and upgraded homes. From simple single tank applications to large scale radiant floor and forced air applications, modern systems are providing significant cost savings for both water and space heating needs.
Solar water heater systems boil down to three elements: collection, storage, and distribution. Once the sun's thermal energy has been collected and stored, there are several options for distribution systems. For the collection and storage of a solar water heater; there are three systems commonly installed: drainback, closed loop glycol, and thermosyphon. Each one has been proven reliable assuming they are installed properly according to location, climate and demand. In the northern hemisphere, this means systems should be installed no more than 45 degrees East or West of South. In addition, shading by trees or other obstructions should be kept to a minimum, and sizing of the system should minimize overheating during the summer months.
A closed loop glycol system utilized a heat exchanger, collector(s), pump(s), and a glycol solution. The glycol/water solution prevents the system from freezing, and the heat exchanger ensures the fluid used to do the heating does not mix with potable water. Similar to a drainback system, the thermal controller will start a small circulating pump when the collector(s) are warmer than the body of water being heated. As the glycol loop is under a small amount of pressure, an expansion tank, pressure relief valve, and pressure gauge are needed as supplemental safety items. Glycol systems are excellent for cold locations, ore where pipe runs would not make a drainback system operate properly. This type of system has proven reliable for many years, but will require periodic changing of the glycol solution.
In addition to washing or bathing, solar heated water useful for some space heating through the use of radiant floor heating, and some new heat pumps and HVAC systems. For example, with radiant floor heating it possible to use the solar heated water to circulate throughout tubing in the home to provide the space heating.
With the use of a water to air heat exchanger, solar heated water can be used to add supplemental space heat to a standard forced air system. The heat exchanger is placed in the home's duct work, and the movement of the air through the heat exchanger allows the solar heated water to heat the air that is then passed into the home.
Another application would be the use of old fashioned cast iron radiators. If enough solar hot water can be collected and stored, with a small pump it can then be circulated through the radiators adding a quiet, comfortable heat to a space.
By Mike Hewitt, E2 Powered
2007/8 Green + Solar Building Oregon magazine |
