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Heating System

Historical Baseline

Prior to installing the wood/solar system, we had lived in the house since it was built 19 1989. During that time, we heated the house, hot water, and hot tub using a 120,000 BTU/hr oil boiler. Our oil usage was 20gal/month for hot water and 600 gal/year for heat and hot tub, for a total annual oil usage of about 740 gallons.

Basic Operation, winter of 2005/2006

The Orlan wood boiler is installed 'as delivered'. There is no external heat storage and no solar panels. The TS-7260 controller does not exist yet.

The wood boiler was initially installed in parallel with an existing oil boiler, with a manual process to switch between them. The house has three zones of hot water baseboards, a zone for domestic hot water, and a zone which heats a hot tub. There is a circulator pump for each boiler feeding a common manifold with motor operated zone valves for each zone.

While the wood boiler is rated at 80,000BTU/hr, in practice it seems to deliver between 45,000 and 50,000BTU/hr averaged over a typical fire. As a consequence, hot water and/or hot tub recovery takes longer with the wood boiler.

The wood boiler has it's own controller, which controls fan speed in order to maintain the selected water jacket temperature. If the temperature is above 65°C (about 150°F), the circulator pump is turned on. There is a manual switch that selects either wood or oil operation.

First Season Results

In the first heating season, fuel consumption was about 3.2 cords (11.6m3) of wood (and virtually no oil) between November 21 and March 15.

While the first season's experience with this boiler was satisfactory, there were several opportunities for improvement:

  • There was no heat storage other than the thermal mass of the house. This meant that hot water would quickly run out if the boiler was not operating, and it meant that a fire had to be built every day.
  • There is not very much baseboard - only 52' for the whole house. This is nowhere near enough to absorb the full heat output of the boiler. This meant that the boiler would have to throttle back, which is less efficient. It also means that it takes a long time to raise the temperature of the house.
  • Baseboards are designed to operate at 80°C, and the controller shuts off the circulator at 60°C. However, domestic hot water and the hot tub zones could use water down to 50°C or even lower. This means that there is residual heat energy that is lost or not available for use every time the boiler shuts down.
  • Switchover to oil heat was a manual process - a switch had to be thrown to activate a relay to make the necessary changes to control signals.
  • There was no convenient way to know that the boiler needed more wood, or that the gasification / combustion process was working optimally.
  • Since it's not desirable to fire up the wood boiler in warm weather, hot water has to be heated with oil starting in March.

Solar hot water, summer of 2006

During the summer of 2006, there were two significant additions: the storage tank and the controller. The addition of the storage tank provided the opportunity to use the solar panel during the summer. On sunny days, the panel was able to provide approximately 30,000 BTU per day, or about half of our hot water needs.

Basic Operation, winter of 2006/2007

In addition to the storage tank and TS7260 controller, a pair of mixing valves were installed at the outlet of the domestic hot water tank. This greatly extends the time that a single tank of hot water can support the household - to the point where we can go three days between fires and have plenty of hot water. More discussion on hot water here.

This season lasted much longer due to mother nature and the fact that we could now store heat. Heat storage meant we cold build a fire on a cool day and provide hot water for several days. Our first fire was October 22, 2006 and our last fire was on April 18, 2007. This means our heating season was approximately two months longer than the previous year. Again, we burned virtually no oil during this time - about 4 gallons to heat the house when we were away for a few days.

Wood consumption was just over 4 cords.

Solar hot water, summer of 2007

During the summer of 2007, there were two more significant additions: a set of three glazed panels which were added to the existing unglazed pool heater, and software improvements that made more efficient use of heat stored in the external tank. The glazed panels effectively doubled the output of the solar heating system, producing output temperatures in excess of 170°F. Details are availaible in the section on solar hot water.

In summary, for the 5 months after the glazed panels were installed, the oil burner came on an average of 13 times per month compared to a historical average of 65 times per month. Oil consumption averaged 4 gallons per month compared to 20 gallons per month in the past - an 80% reduction in oil consumption!