Kinark Sustainable Living Centre

Heating System

No building in a northern climate is complete without a heating system to keep the space warm and comfortable during the cold winter months. How to do this without burning large quantities of fossil fuels?

Design Intent

1. To utilize as much of the sun’s energy as possible to heat the building
2. To heat mass within the building, and not just the air inside the building
3. To use fossil fuels efficiently, if at all

Materials and Methods

The primary heating system uses a propane fired boiler to heat water that is distributed through tubes. Usually, such a radiant heating system uses tubes laid under the floor of the building. In this case, we used the semi-circular earthbag wall in the middle of the building as a giant radiator, and the radiant tubing is placed between each course of earthbags. The mass of the bags will store the heat and distribute it evenly to the whole building.

The secondary, experimental heating system installed in this building is Annualized Geo Solar (AGS). Warm air is collected from under the steel roof on the south side of the building during the warm months of the year. This air is blown through a long tube that travels deep in the ground under the building (3 meters or 9 feet deep) before returning to the roof to be warmed again. The air warms the mass of the earth beneath the building, and because there is scrap rigid insulation below the tube, this heat begins a slow movement through the soil, toward colder soil, including upwards to the uninsulated floor. It will take approximately 6 months for the heat to finally be released into the building, so early spring’s stored heat becomes early winter’s heat inside the building. The system is turned on in early May and is turned off in late September or October. This system cost less than $500 to install. The thermometer display on the north east side of the building shows the heating tube and floor strata temperatures, so we can monitor its progress. However, the majority of the increase in temperature seen below this building at depth is heat loss from the building to the soil from both the heated wall and from passive solar direct gain, and does not come from AGS.

Further modeling and calculations indicate that the AGS system is suited to warmer climates where the average air temperature (and average soil temperature) is within the range of human comfort, at least 16 C. In southern Ontario the average temperature is 9 to 10 C. If this building were 1000 km south, in the State of North Carolina, AGS would be more feasible.

Questions

Why use the wall instead of the floor for the radiant heat?

Unlike private homes where occupants often don’t wear shoes, public buildings like the Sustainable Living Centre typically have occupants who are wearing shoes or, in the winter, boots on their feet. In this scenario, heated floors are sometimes uncomfortable. The central mass of the earthbag wall is close to all the occupied parts of the building and will reach people at body height. We also wanted to be able to determine how much heat enters the building via the floor from the AGS, which would be impossible if we were also warming the floor with the radiant system.

Why use propane for the radiant system?

Expense and complexity ruled out using thermal solar for the radiant system, and cost and availability ruled out using biodiesel, so we were left to choose a fossil fuel option. The rest of the Kinark facility uses propane, so service and fill-ups would be easy to arrange, and propane is one of the cleanest burning of the fossil fuels, so we chose that option.

Is AGS a proven heating system?

No. There are only a few buildings in the world that use this kind of AGS heating. Anecdotal reports from several of these show that after a few years they provide the majority of the heating requirements. However, the depth of the pipes under the ground, the amount of heat gathered under the roof and the strength of the fans in the pipes can all affect the outcome, as can soil type, ground water levels and many other factors. However, given the ease and low cost of installing the system, it will pay off if we even offset the heating bills by a few percentage points.

Why use air instead of solar-heated liquid in the AGS system?

While water is a more efficient medium for storing and moving heat, the air-based system used here is remarkably simple. A solar water heating system would have been much more expensive and complex, requiring specialty collectors, pumps, tubing and sensors. The air system uses two small fans hardwired directly to their own PV panels, and some inexpensive plastic piping. The system can’t overheat, doesn’t need maintenance and has only two, inexpensive moving parts.

Why turn the AGS off in the winter?

Heat accumulated in the system during the winter will surface inside the building during the summer, when we don’t really want it. The system will also blow cold air into the ground if there is snow cover on the roof or if the ambient air temperatures are very low. It’s just not worth running it during the winter.