Solar Water Heaters
by Kim Kinrade
The sun has been ignored as a major source of energy by almost all the heating supply manufacturers for the simple reason is that oil and natural gas was cheap and clean and electricity was a no-hassle system. However, with oil hitting $150 a barrel these reason not only seem naïve but economically unfeasible. This a domino-effect because the price of oil is escalating inflation, and that means all of our household goods and consumables will be going up in price while our incomes will be teetering at a fixed amount.
We can scale back on a lot of luxuries but food and heat can only be pushed back so far. So now, more people than ever are looking up to the sun for help and are happy to find that there are already systems being manufactured that can alleviate their energy woes. By just adding a simple roof-mounted passive-solar panel your energy savings can drop as much as 40% depending on where you live and much sun is available.
Passive-Solar Heating
If you place a glass of water on a kitchen counter during a sunny day, winter or summer, you would be surprised at how quickly this once-cool liquid has heated up to a lukewarm temperture, and even hot water. This is because the sun's rays are intensified by the glass from the window and the material holding the water. As well, water is a great thermal storage medium which means that it will store and hold heat.
The thermal mass can also be a masonry product such as brick which has great heat storage potential. A room with this type of wall can store the heat and then release it at night when the house cools down. A small fan can then disperse it into other rooms of the home.
Using this principle a passive-solar water heating system uses a heated liquid – glycol – running in a coiled pipe to flow through a water unit and elevate the temperature of tap water so that it can be used for showering, clothes washing and even pool heating.
The Passive-Solar Water Heating System
How a passive-solar system works begins with an array of tubes, or collector, on the south side of the home. The sun's heat is collected and held in the array until the temperature reaches a favorable mark and then a pump directs the glycol fluid into copper coils suspended within a secondary tank, which is usually stored beside the normal wanter tank in the home. This tank contains cold, household tap water from either the well or the civic system and the influx of the heated glycol brings the temperature of the water up, sometimes to the desirable level. Then the glycol is recirculated back to the solar array. This newly-heated water is transferred to the household water heater where it is held for distribution through the home's hot water pipes.
In a "drain-back" system, distilled water instead of glycol is used. This is for use in warm areas of the country or in cottage country where the place is only used in the warmer months and is drained in the winter. The fluid only flows through the system when the processor decides that there is a usable amount of heat being collected in the arrays. Therefore, the pipes are only filled with the glycol when the pump operates and sometimes the pipes are full of air. This prevents the freezing of the heat transfer fluid whereas in the standard system the glycol can sit in pipes and not promote freezing.
Parts of the System
The Solar Array: There are a few types of solar collectors. Copper tubes painted flat-black form the core of one type of collector as, being a great conductor, copper heats up quickly. Another type of array uses collecting fins in vacuum tubes to prevent heat loss from radiation. This is also helped by the glass covering which has a low-emissivity coating.
Controller: This is usually a microprocessor which activates a pump when the temperature is right. This pump can be powered by solar as well and there is usually a photovoltaic solar panel attached to a battery-storage unit.
Storage Tanks: Depending on the system there can be 1 or 2 storage units for the glycol. Usually the transfer tank contains potable water from the tap which is then heated by the glycol running through coiled, copper pipe. Heat transfer takes place and the cooled glycol is then returned to the system. Even on a cold winter day there can be enough heated generated to make a noticeable difference in the hot water tank.
Hot Water Tank: This can be a common electric or gas-fired tank. The heated water from the solar water heating system may be hot enough for home use. If not the heating system in the water tank will top it off.
Although relatively expensive to install ($1000-$3000), with general maintenance they will last 30 years or more. And the savings will have it paid off in less than 5 years.