Greening Your Home
BACKGROUND INFORMATION: INSTALLING SOLAR HOT WATER
Having survived the solar electricity installation, Ethan is by now really getting into his solar projects. In April he embarked on a solar water heating project that he just completed. This particular project took about a year to research, but I can tell you that the amount of pleasure he has derived from it is quite palpable. No visitor to the house is safe from a highly enthusiastic tour. His favorite part of the project seems to be a digital readout of the temperature in the water tank. He enjoys watching the readout change as people use water. He especially likes giving updates to anyone who will listen. It's the small pleasures in life...
SOLAR HOT WATER COMPONENTS
A solar hot water installation has the following components:
- Heat pipes which include copper tubing, evaporator, wick, condensor and refrigerant;
- Hot water tank;
- On-demand hot water heater; and
- Mixing valve
SUNDA HEAT PIPES
The key components of the system are the Sunda heat pipes or double walled glass vacuum tubes that act as solar collectors. This process is about 80-90% efficient. Little House Farm has 16 vacuum tubes on the roof of the house. That is what a four person house requires. Fortunately, the house already had the right pitch for the solar water technology. Sunda happens to be a Chinese manufactured product using German technology.
The inner glass tube is coated which enables it to absorb and convert the maximum of solar radiation and infrared light into heat. Installed within the glass tube is a copper heat pipe containing a small amount of refrigerant. The copper heat pipe captures the heat and with the help of the refrigerant evaporates the liquid to steam. There this steam will be condensed by water flowing through the pipe. Latent heat energy will be released to the process water through this change of vapor to liquid. In vacuum tube solar collectors, the condensation zone is at a higher level than the evaporation zone. The transport medium condenses and returns to the evaporation zone under the influence of gravity. This process is repeated continuously thereby heating the water in the solar loop. When the sun goes down or there is inclement weather the water pumping stops, but the system works with very little light.
BUDERUS HOT WATER TANK
The water that is captured by the heat pipes is transferred by another series of pipes, also installed on the roof, down through a kitchen pantry and into the basement to the Buderus hot water tank. Once the vaporized liquid arrives from the heat pipes, where it can be anywhere over 150 degrees depending on the weather, the Buderus hot water tank stores the water waiting until someone turns on a faucet or shower.
The average home spends about 20%-25% of its total energy dollars heating water. The Buderus tank is insulated with foam to prevent heat loss. It will loose only 1/2 degree every hour if the Rinnai is not taking in heat energy and tranferring it to the Buderus tank. Buderus also makes tanks in different shapes to fit your home's construction. In Little House Farm's case, the basement has such low ceilings that the hot water tank is actually the shape and size of a coffin.
RINNAI ON-DEMAND HOT WATER HEATER
Then the Rinnai on-demand hot water heater takes over. Rinnai is a Japanese company and it is considered the best on-demand system because of its energy efficiency and water flow consistency. [As an aside there is an interesting article in the Sustainable Links section of this site entitled Japanese Putting All Their Energy Into Saving Fuel.]
Most people heat their hot water to about 120 degrees and then the system waits for someone to use it. Picture leaving a car running all day waiting for someone to drive it. These kinds of hot water systems are very inexpensive; they only cost about $300. The real cost ends up being in the fuel or propane used to heat the water. The Rinnai heats the water coming from the Buderus tank if the temperature is below 120 degress. If the water is above 120 degrees the Rinnai does not fire. There is a slight delay as the hot water heats up, but it really takes very little time to get perfectly hot water. The water in the tank on a day with a lot of sun could be over 160 degrees. This is why you need a mixing valve.
MIXING VALVE
The last component of the system is a mixing valve which will force cold water into the system to prevent scalding if the water rises above the preset target of 120 degrees.
ADDITIONAL ENERGY SAVING RECOMMENDATIONS
Other energy savers recommended by the contractor HVCE are: a) to have the hot water pipes insulated to reduce hot water use even more; and b) to insulate the cold water pipes to prevent condensation.
FINAL THOUGHTS
As you can see this is a rather complex system which certainly ended up being a labor of love. It may not be possible or feasible to install such a system, but hopefully this will give you ideas about what you might do in your home.
CONTACT US
Feel free to contact Ethan by e-mail at info@littlehousefarm.com with any questions. As with all of his projects sometimes he's a little gruff, but in the end he loves talking about them and you may even have trouble getting rid of him.