Image Credit: All photos: Paul Kuenn Photovoltaic panels on both the garage and house were instrumental in allowing the author to remove all of his fuel-burning appliances. A heat dump dryer dries gloves and shoes while simultaneously dumping excess heat from solar collectors. In the summer, the dryer and a length of radiator keep the basement air dry, eliminating the need for a dehumidifier. Three tanks store hot water for the author's radiant-floor distribution system and the domestic hot water supply. Hot water is produced by four rooftop solar collectors, an electric boiler, and a heat pump, although not all components are used all the time. Photovoltaic panels on the house and garage roofs provide the electricity to run the system.
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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.
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12 Comments
Interesting solar collectors verses more PV's to make hot water
Ive been following your blogs and have a question, with the falling cost of PVs why the solar collectors
I have installed a 4.2kwh Sunpower system in July, the local Con Ed owned utility gave me grief and foot dragging to get the system in, so in the end we had a company install it for us so we would get the system we needed and they had to do all the work.
Anyway Im now at stage 2, planning that is, we have a unshaded south facing roof outside of NYC, and have plenty of space left after the 16 panels went in, the hot water boiler we have heats the house as well.
So my question, cost wise I had the idea of doing something similar to what you did, install a few solar collectors to run a feeder tank to keep the hot water storage tank at a level where the gas boiler doesnt kick in as much, or the other idea was to install 2 extra panels and install a small electric feeder tank to do the same as the collectors.
The down side of the collectors is the various tanks, glycol mix, pumps etc that I can see, the downside of the solar pump I see is some way to make it shut off once the sun goes down and then the gas boiler takes over, how that is accomplished I dont know, maybe someone out there has done this or knows of a product that can do it
Great blogs and you deserve a few beers when done
Response to Darren Fitch
Darren,
Like you, I'm interested to hear Paul's response. My guess is that he hasn't invested in more PV modules because his local utility no longer offers net metering.
If you are lucky enough to have an electric utility that offers net metering, it's hard for a solar thermal system to compete with PV. A PV system usually yields greater savings per dollar invested, and is far simpler (from an installation and maintenance perspective).
For more information on this issue, see Solar Thermal Is Really, Really Dead.
Don't forget
Paul did most of the work 3-4 years ago, when PV was more costly than it is today.
Reply to Darren
And thanks guys for jumping in so fast to help. Long day for year end at work. Here it goes.
Solar thermal is much more expensive nowadays thanks to copper prices. I had a super deal at the time during a warehouse sale. Also, GE and others did not have their hot water heat pumps on the market yet. As I work full time, it took up to two years after to install. So now, PV panels are much less costly and so are other methods to heat water and air.
If the house is properly sealed and insulated, it's hard to beat a minisplit as you'll see in many blogs.
I would never give up the hot water though. It's just something about toasty feet that's so welcoming when coming in from the cold. If you have room and a large enough storage tank (s), one could save enough hot water to heat the house most of the winter, proven by friends in Fairbanks, AK. Only one pump is needed for the solar thermal & one for the floor. DC pumps last 30-50 years. The one running in my first earth home above Boulder, Co I put in 1982 and the folks there said it still works fine.
As to how it works, the PV run DC variable speed pump runs fast or slow depending on the sun which is great. Clouds overhead, then the water moves slower to gain more heat on the way through the panels. At night it is off. A separate pump for interior heating (can't beat the Grundfos Alfa) would be set to turn on with the thermostat. Does my drawing help? So much easier with two larger tanks than 3 smaller ones.
I'm actually redrawing the plan for the future as you can get super inexpensive but huge stainless steel tanks from dairy farm auctions. As long as the DHW tank is small, you can save all the otherwise wasted heat from summer in a huge tank. I also always suggest the most efficient exterior tank heat exchangers rather than the tanks with tubing coils in them. If the water/glycol is cooler off the roof than the water in the tank, it won't adversely affect the temp of the water in the tank as the two liquids travel opposite directions in the exchanger. Remember hot only travels to cold. You can use differential switches to prevent tank cooling but it's better to trust physics.
PK
Martin's right as usual
"My guess is that he hasn't invested in more PV modules because his local utility no longer offers net metering."
Correct as well. I do have a very limited budget and have to save years for each project. I love Craig's list! I see at least 4 postings for decent solar thermal panels for next to nothing in the Milwaukee area. Probably not as efficient as Heliodyne, but water is easy to heat with the sun.
Heat exchangers
Paul,
The sketch of your solar water heating system shows external heat exchangers on 2 of the water tanks. Who makes those? I'm planning/exploring heating system options for a house to be built in spring 2016. I'm planning radiant heat in basement and first floor. Have about 10K solar PV coming, so am looking for ways to use it to heat both domestic and radiant heat water. Yet to find source for electric water tanks with heat exchangers.
heat exchangers
Good day Fred!
These are both over 8 years old and were made by Heliodyne. The Helio pak hx ss sw cl liquid to liquid heat exchanger is double walled because we have it mated to the domestic hot water supply. It was a tube & shell design with fins for extra efficiency. Not sure if you need that by code when dealing with just floor heating. They also may not make those anymore with their new compact systems. However, it's always worth searching for. For floor heating alone, the HXP 193 and AIC plate and frame exchangers are very efficient as well.
heat pump
Your sketch also shows a AirGen (spelling?) heat pump next to the 50 Gal. DHW tank. Is that heat pump inside the house, or outside? Is it heating the domestic hot water or other? I'm looking around for air source water heaters with external heat pump.
Airtap heat pump
This one is for interior use only. The Airtap is made by Airgenerate. It sits on a shelf above the DHW tank. So it is inside and does slowly cool down the basement when the clouds are heavy Nov-Dec. With the basement between 58 & 68F year round, the COP is high as the higher temp air makes it more efficient than if it was outside at 0F. Most of the year it doesn't run as the sun does 80% of the heating. It's worked flawless for 3 years now. The refrigerant tubing comes out the backside and is about 16 feet long in a coil. You have to feed it very carefully down into the tank at the hot port. It comes with a brass T so the hot water tubing can continue up and past the insert. It would be considered noisy (fan) if it wasn't in a basement. We can't hear it because of the insulated floors.
Diagram
Been studying your nice hand drawn/color flow diagram. It seems to me that the water in #1 80 gallon storage tank is common with both the floor loops and the DHW tank. It looks the only source of 'cold' water into the DHW tank is from the #1 80 gallon tank. Put perhaps the green 'squiggly' line in the center of #1 tank means the radiant floor loop water is contained in a loop/coil of pipe inside the tank, and thus the return loop from the floor heat is 'preheating' the domestic water but not mixing with it, as also the solar heated water is doing. That must be it.
my goal
To share my goal ... am planning for an external wood boiler as 'primary' heat source, and then probably 2 electric water heaters as 'backup' for times we're not home to stoke the fire. So am pondering ways to transfer the heat from the external boiler loop to the electric water heaters. Was planning to circulate the boiler water thru the electric heaters, and then also have circ pump drawing water from them thru radiant loops. The DHW heater will be separate from this, probably with external exchanger on it to heat that water from wood boiler, when it's on.
Sorry it stopped sending me notices so long ago.. or I would have answered. How did your project turn out. On my system, only water from DHW tank is shared from tank to tank. The heated floor loop is self contained and travels through the coils in the largest tank. Although I do have the external heat exchanger help if the last #3 tank is hot. I could send some photos. Contact me at: https://kuennllc.com/
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