Here is another fantastic project I got to do with my dad, John Mack. When people tell me I'm just like my father, I always consider it the greatest of compliments. I feel my dad is one of the greatest engineers on the planet. The contraption we hold in our hands is not only a work of art, but a very useful upgrade to my solar water heater.
Dad marks the startup date of May 31, 2009
In an attempt to cut down on my carbon footprint, I bought an 80 sq ft solar domestic water heater about 10 years ago. I love it. With 280 gals of storage, I can go 3 days without any sun. However, from November to March, there are still some days I have to consume energy. I did switch from gas to electric to continue lessening my carbon footprint.
"If you bought the system 10 years ago, what are you doing here?", I hear you asking. Well, I'll tell you. The system I bought was badly designed, just like all the other systems out there. Here were the problems:
When the tanks were cold, it would take a whole day of sun to get any hot water.. Now, the second the sun starts shining, the water is hot.
When there was a lot of sun, the water was scalding hot. Now the water never gets too hot, and if we go on vacation in the summer, the system automatically dumps the excess heat at night. No more chance of overheating.
It was unreliable. The check valve failed in 2 years. Now it should last 50 years.
I could not incorporate my wood burning stove. Now I can, and this winter I plan to not use any electricity during those cloudy winter weeks.
The panels were set at a fixed angle so they were only efficient in the winter.
The first part of my redesign was to put the panels on a hinged frame. Now I can aim them up in the summer (see picture) or lay them flat on the roof aiming low into the southern sky for winter.
The re-plumbing part was fundamentally simple, but then I started adding more features. The basic idea is that the water is allowed to circulate through the panel until the water gets up to 120 degrees. At that point, a valve opens and lets the hot water directly into the house. If no one is using hot water, it is pushed backwards through the water tanks making a thermocline. The thermocline is pushed backwards during the day when there is sun, and it moves forward as people use hot water. Normally the water is circulated using a 12VDC pump running off a solar PV panel. However, when the sun is really hot, a thermostat at the panel turns an 110V booster pump which doubles the speed of the water. This helps keep the output temp near the perfect 130 degrees we want. Any cooler, and tomorrows showers are a bit cold. Any hotter and it is a waste of sun energy.
The Chimney Heat Exchanger is a bit of a complication. It takes throw-a-way heat that goes up my chimney when I am having a fire, and heats my hot water for free. Cooling the exhaust gases not only saves me electricity, it also reduces the chance of a fire from hot sparks.
There is one last feature I would like to tell you about. When we are gone in the summer and not using up the hot water, all 280 gals become hot. This means that at the end of the day, hot water is going up to the panel. As the sun sets, the panel actually starts cooling the water and it falls back down by gravity (hot water rises, and cold water falls). This keeps the thermal valve open and the system dumps energy all night to bring the temp down. However, if someone uses even a little water after sunset, a pulse of cold water goes up through the panel and closes the thermal valve.
Note: The Watt thermal values shown here proved to be unreliable. I replaced them with an electrically operated valve and thermostat which will never fail. It is absolutely bullet proof.