When I built my
workshop in 1992 I had planned on someday installing solar hydronic
heating. The slab was designed with in-slab heating right from the start.
Embedded in the slab (Figure 1) is 500' of 3/4" plastic tube in 2
loops which is routed through to the attic where a 5 gallon water heater
is located. That tank has a single 2300 watt electric element to provide
all the heat for the 22x26' building. It works wonderfully. Working in a
shop with the floor slab sitting at 17º C when it's -30º C outside is
something else. The beauty of this system is that it takes no floor space,
is silent and there is no open flame. You don't even know it's there.
With our Premier Ralph Clown's stupid idea of "Piratizing"
the electric utilities, the cost of heating the workshop began to climb
quickly, so in 2002 I finally got my act together and started looking for
solar panels. Guess what? Gas and electricity are CHEAP, so the
solar industry is way behind non-renewable energy sources. There are no
suppliers in Edmonton and the only one in Calgary is primarily photovoltaic,
although they were dealers for Canadian made Thermo
Dynamics products. They use old flat-panel technology, but their product would do
the job. In June I ordered two 4x8' panels and waited. Three months
later, when the panels were supposed to be delivered, I contacted the
dealer again. By the sound of things, my order was lost during a company
merger or something, so I asked them to reorder. Two months later the panels were
lost in shipping and the salesman was not answering the phone, nor were
head office staff. When I finally got hold of them, I gave them another 2
weeks to deliver the order but cancelled it when the excuses continued. It
was obvious they were not in a position to either supply or support solar
hydronic systems so I took my business elsewhere.
I gave the order to Thermomax
in Victoria BC primarily because the rep was very knowledgeable and
helpful. Unfortunately, the product is made in Ireland and it took a while
for the material to arrive in Edmonton. Luckily winter held off
until late December, so the panels were commissioned on December 9th
The way heat is moved from the roof to the floor slab is pretty simple.
Basically the heat from the glycol solution in the solar circuit is
transferred to the floor slab circuit through a small heat exchanger. It
is positioned upstream of the heater tank (Figure 3) so if the circulating
temperature is high enough, the electric backup kicks out and heating is
100% solar. Fluid sent to the floor slab is heated to only 30º C by
electricity and boosted to 40º C by solar heat. The shop temperature is
regulated based on slab temperature with a base temperature of 15º C, but
it is allowed to float higher if solar heat is available for harvest.
One of the main problems with solar heating is access to the sky.
Alberta is one of the sunniest places in Canada, particularly in
winter, so it is ideally suited to solar heating. Mapping the sky is
relatively easy, if you don't mind your neighbours looking at you as if
you are a loony for sitting on the roof with a transit! A map of the solar
sky (Figure 4) can be generated with some neat software called Sundi.
Performance curves for solar panes are just plain baffling. There was
absolutely no way to determine how the panels would perform before they
were installed. After they were installed, it was obvious I needed data.
To gather information on performance through the day I installed two HOBO
data loggers, one 4 channel temperature logger on the heat exchanger and a
3 channel (plus humidity) logger to record slab temperature, inside and
outside air temperature. Knowing the delta temperature across the primary
and secondary side of the heat exchanger I was able to determine the
amount of solar energy gained. Basically, the solar panels are
delivering as much energy as the electric backup whenever the system is
running >60º C (Figure 5) and boosting the slab circuit significantly
whenever the solar side is functioning (greater than 40º C). This cut out
2 months of electric dependency and 25% throughout the worst parts of
winter. On good days the floor slab is warmed sufficiently during the day
that it coasts through the night without needing more energy added.
Sadly, my neighbour 2 doors down has a HUGE willow tree in her back
yard that puts the boots to solar gain for about an hour a day for 2
months (Figure 5), the best hour of the worst months! Overall the panels
are collecting for 70% of the solar day (Figure 6). I will be changing the
angle of incidence to improve efficiency during the winter months since
the shop doesn't need too much heat during the summer. For most of the
summer the floor slab was sitting at 30º C! (Figure 7). Increasing the
angle will help the panels shed snow which is an annoying maintenance
Throughout the year I have been tweeking the system and learning more
about how it operates. One change was the installation of an automotive
expansion tank to accommodate the wide temperature swings (-40 to +100º
C) , scoop entrained air and protect
against header boiling should the power go out. Another change was a big
surprise. As spring approached I was concerned that the system was running
too hot and was worried it wouldn't be able to cope with summer sun
without boiling. As an experiment I added Redline
Water Wetter, a product I use in the engines I run on the dynamometer.
The data logger showed an immediate 15º C decrease in system temperature
and a corresponding increase in delta temperature across the heat
exchanger. The product, which I think is just dish soap, improved the
efficiency of the heat transfer at both the solar panel header, and the
heat exchanger. After that, the panels operated in full summer sun without exceeding 90º C.
Bottom line, is it worth it? Well, gas and electricity are never going
to come down in price (thanks Ralph, you asshole) so solar heating makes
sense. It makes more sense the earlier the system is installed so it can
start paying for itself. My total investment for panels, pumps,
insulation, loggers etc is $8000 CDN (NOTE there is no government rebate
for solar installations!!) so payback at current energy prices is about 10
years. Now if only I had installed the panels when I built the shop in