This is the third in a series of blogs by Paul Kuenn describing energy-efficiency improvements to his home in Appleton, Wisconsin. To read the first blog in the series, click here.
By the spring of 2011, I was hot to finish this long project. Even with another damaged solar thermal collector shipped to us, I was sure we would succeed.
Planning for a fourth hot water collector, I had spent most of the previous hot and humid summer adding support to the roof of the house and garage. The new collector would add more thermal storage by increasing the incoming water/glycol temperature.
I realized that having three separate tanks — two for floor heating and one for domestic hot water — would be the most efficient approach. Any overheating during the summer would be diminished by a dump-load radiator in our cool and damp basement. In other words, during the warm season, hot water from the two floor-heating tanks would be cycled through a wall radiator and a homemade copper dryer for gloves and shoes, thereby cooling both tanks down.
At the Habitat for Humanity ReStore, I found a used 5-year-old 50-gallon hot water tank identical to my first tank. This third tank would become the domestic hot water (DHW) tank and receive the first heat-exchanged fluid from the collectors, then pass it on to two floor heating tanks.
Rob Ryf of Solar Heating Services added a separate heat exchanger with a pump and plumbed it between the floor heating tanks. When the water temperature in the larger (#1) tank dropped below that of the smaller (#2) tank, sensors would start the 12-volt pump and exchange the heat in #2 to the water just before it entered a new Thermolec electric mini-boiler. The Thermolec would replace our on-demand gas-fired Rinnai water heater.
In the end the system looked like this: Four solar collectors on the roof send a water/glycol solution through all three tanks — the 50-gallon domestic hot water tank first, then the 80-gallon tank for radiant heating, and finally the 50-gallon tank also used for radiant heating. Water from the floor tanks passes through the Thermolec mini-boiler before passing through the floor circulating pump. (A diagram of the hot-water system is shown in Image #4, below).
Pulling the plug on fossil fuel
I chose the very efficient Thermolec boiler because it has multiple heating elements. If the incoming water from the solar storage tanks is at the desired floor heating temperature of at least 110°F, the elements are not active. It can read water temperatures and activate one to three elements as needed.
Having the Thermolec enabled me to make my final fossil fuel-free call to We Energies and ask them to remove the gas line and meter. There was no cost to do this but they certainly questioned me. By this time, I was getting a yearly call from We asking me whether I’d changed anything on my solar contract. I’d simply say no, and they wouldn’t call back until the following year.
But now, the improvements we had made in the system were going to allow us to take a big step. On more than one previous occasion, I had watched the temperature in tank #1 drop from 140° to 85° with 120° in tank #2. With the exchanger between tanks 1 and 2, the water could be boosted to 110° to minimize use of the boiler.
We celebrated by disconnecting the gas line from the house.
Time for a new roof
If this wasn’t already enough, we decided to replace the roofing on both the house and garage. Many strong hailstorms had damaged the 10-year-old asphalt shingles. Ordinarily, this would mean removing all the original hot water panels on the house as well as the PV array on the garage. I had a different idea.
Using old climbing ropes and anchors, I built a floating frame that I could slide up and down the roof pitch so that roofing work could be done above and below as a one-man operation. I was able to slide each array onto this horizontal frame without sacrificing security in the face of an oncoming storm. Using newer quick-mount hardware rather than the old L brackets made replacing the array easy and certainly made the attachment point more waterproof.
Recycled rubber and plastic slate tiles were ideal and would give us clean runoff for garden water storage. The garden pump would be powered by the old 12-volt portable PV system.
The house had to wait until everything was in place for the new roofing. The only knowledgeable roofing contractor was busy due to recent storms and associated insurance claims, so we were pushed off until November. Leftover EcoStar slate from a church project helped reduce the cost of the roofing job.
Once again I found my favorite season, winter, approaching too quickly. The PV modules had sat since spring waiting to see the sun. Because of limited space I had to make some of my own PV racks, using a mix of national brands. I still wanted to tilt the garage-mounted PV array seasonally while the house array would remain at a fixed tilt, and I wanted to avoid any shading.
Another setback took place when I removed the AirTap heat pump from the 80-gallon tank (where it couldn’t keep up with demand). I accidentally broke the copper heating tube. The manufacturer replaced it, but in the meantime I hooked up the 240-volt element in the DHW tank. This seemed to work fine as we overproduced on the electrical side and wouldn’t really see an increase in the bill.
Once the heat pump was fixed, we planned to use it to heat water in the third tank for domestic hot water, powering it with the PV battery system. There was always excess power during the day when nothing but the fridge is running. I consider the floor pump as having negligible energy use (13 watts at 1-2 gallons per minute — enough to keep the floors warm).
By November 2011, the fourth matching thermal collector was found by Heliodyne and shipped to me without charge, making up for the year’s delay.
Enjoying warm floors
We had our last two cold showers when a couple of events caused problems. (I accidentally disconnected some wiring, and soon afterward the heating element in the DHW tank was turned off due to a faulty overheat sensor.) But soon thereafter, the new AirTap heat pump arrived and there was no need for the DHW tank-heating element.
It was a warm and sunny spring just before a cloudy plunge in temperature. The early quarter of 2012 was very mild as winters go in Wisconsin and bills were next to nothing, with more checks in the mail that were double those of the previous five years ($15 to $35 checks each month from February to November). Our bills in December and January were only in the $5 to $10 range.
In the spring of 2012, I used the remaining slate tiles to re-roof the garage. I was able to lift each section of both PV arrays to lay underlayment (leftover Ice & Water Shield) and nail down the tiles without removing any electrical wiring or the PV modules. I also buried a used 750-gallon water tank from a fire truck in the front yard and a used 500-gallon farm tank in the back yard for rainwater collection.
The AirTap works great for the 50-gallon domestic hot water tank. It’s rarely used as it only takes a few hours in winter to heat this tank to 125°F with the solar collectors.
My mitten and ski boot dryer works great. Using the differential sensor’s “pump on” switch for tanks #2 and #3, I can run hot water from the flooring manifold. The differential control will turn the heat dump on when tank #2 reaches 155°F and off when it falls below the temperature of tank #3. In summer, the sensors measure when water in the tanks is too hot and run water through the boot/glove dryer as a heat dump and into a baseboard heating unit to cool the water down. It also keeps the basement at 72°F and has minimized the need for a dehumidifier (which used to run 24/7). The basement still feels cool when it’s hot and humid outside.
Yes, it was a costly change to the home. No, we would never turn back. Just on the original 2006 PV array we had saved the earth from I don’t know how many pounds of carbon. Actually, we do: the Fronius PV grid-tied inverter display reads 9,010 tons saved as of December 2012. With additional PV modules and solar thermal collectors, we have more cash on hand and now enjoy warm feet, no dust bunnies, and no drafts. After riding the bike home from work in the winter and cross-country skiing, I love to stretch and just lie on the floor. It feels great!
In my next blog installment, I’ll discuss another (and I hope last) round of insulation updates.
The fourth installment of Paul Kuenn’s blog series is here: One Man’s Quest for Energy Independence — Part 4.
Paul Kuenn lives in Appleton, Wisconsin. He is a past owner of a climbing school and guide service who has studied environmentally sound building practices, along with plumbing and electrical. He’s a graduate of solar thermal and photovoltaic installation programs at the Midwest Renewable Energy Association. In the last eight years Paul also has worked as a third-party inspector for fire and rescue apparatus. In his spare time, he helps homeowners use the least amount of fossil fuel energy possible.