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Drake Landing Solar Community Thrives in Canada

Credits: ©2009 Drake Landing Solar Community

Drake Landing Solar Community is 52-house subdivision with all space and water heating supplied by solar energy. The solar energy is captured year round by 800 panels mounted on all the garages in a large array. A combination of seasonal and short-term thermal storage (STTS) facilitate the collection and storage of solar energy in the summer for use in space heating in winter. In addition, borehole thermal energy storage (BTES) is provided by an in-ground heat sink for seasonal energy storage. Short-term thermal storage (STTS) tanks are a central hub for heat movement between collectors, district loop (DL)/houses, and the borehole storage system. The district loop moves heat from the STTS to all of the houses. The community is in Okotoks, Alberta, Canada at 1084 m elevation. Winter low temperatures are around -33 C, and in summer high temperatures average 28.3 C. Drake's Landing won the 2011 Energy Globe World Award, represented by more than 40 nations at the Energy Globe World Award Ceremony in Wels, Austria.


Drake Landing Garages with Panels

An array of 800 solar panels located on garage roofs throughout the community generate 1.5 mega-watts of thermal power during a typical summer day and supply heat to the district heating system for Drake Landing Solar Community in Canada. ©2007 Drake Landing Solar Community

Capturing the Solar Thermal Energy
An array of 800 solar panels located on garage roofs throughout the community generate 1.5 mega-watts of thermal power during a typical summer day and supply heat to the district heating system.

From sunrise to sunset, the solar panels absorb the Sun’s energy and heat a glycol solution running through an insulated piping system, or collector loop, that connects the array of collectors.

The heated glycol travels along the roof overhang, down the end of the garage, and underground through a shallow buried trench system until it arrives at a heat exchanger within the community’s Energy Centre.

The heat exchanger transfers heat to the water stored in a short-term storage tank. The glycol solution carries on through its loop back to the solar collector system.

Storing the Solar Thermal Energy
During the warmer months, the heated water is distributed from the short-term storage tank to the borehole thermal energy storage (BTES) system via a series of pipes. The pipes run through a collection of 144 holes that stretch thirty-seven meters below the ground and cover an area thirty-five metres in diameter.

As the heated water travels through the pipe-work, heat is transferred to the surrounding earth. The temperature of the earth will reach 80 degrees Celsius by the end of each summer.

To keep the heat in, the BTES is covered with sand, high-density R-40 insulation, a waterproof membrane, clay, and other landscaping materials.

The water completes its circuit of the borehole system and returns to the short-term storage tanks in the Energy Centre to be heated again and repeat the same process.

Distributing the Solar Thermal Energy
When winter arrives and the homes require space heating, the heated water in the BTES passes to the short-term storage tank in the Energy Centre and is then circulated to the homes through the district heating loop.

Reaching each home the heated water passes through a heat exchanger within a specially designed, low-temperature air handler unit located in the basement. A fan, also within the unit, blows air across the warm fan coil. Heat is passed from water to air and then distributed throughout the house via the home’s ductwork.

When the temperature of the home’s thermostat is met, an automatic valve in the basement shuts off the heat transfer between the district heating loop and the air handler unit.

Heat Transfer throughout the System
The system only initiates heat transfer when the temperature within a preceding component rises higher than the temperature within a succeeding component. For example, as the sun rises and the solar collectors heat up, the collector loop is turned on once the glycol temperature rises above the temperature of the water in the Energy Centre’s short-term storage tanks (STTS). Energy is then transferred from the collectors to the STTS.

Similarly, after the water temperature in the STTS rises above the BTES temperature, the BTES pump is turned on to transfer heat from the STTS to the BTES.

The collectors will heat up the STTS about twice as fast as the BTES can remove heat from the STTS. Consequently the collector pump will shut off when the sun goes down while the BTES pump will run most of the night.

When the houses need heating in the wintertime the heat from the collectors will be directed from the STTS into the district heating loop, and not transferred to the BTES.

The district heating loop temperature varies with outdoor air temperature. As it gets colder outside the district heating loop temperature is raised. This temperature is regulated by the heat exchanger between the STTS and the district heating loop.

Solar Collection
The solar thermal collection system consists of 800 flat plate solar panels organized into four rows mounted on the detached garages behind the homes.

An antifreeze solution - a mixture of water and non-toxic glycol - is pumped through the solar collectors and heated whenever the sun is out. The 800 collectors are connected via an underground, insulated pipe that carries the heated solution to the community’s Energy Centre. Once there, the heated solution passes through a heat exchanger, where the heat is transferred to the water in the short-term storage tanks. While the flow rate through the collectors is constant, the flow rate on the water side of the heat exchanger is automatically adjustable, allowing the control system to set a desired temperature rise.

The solar collectors for DLSC were manufactured by Enerworks.

* 800– 2.45m x 1.18m flat-plate glazed collectors

* 50% propylene glycol antifreeze

* Mounted on four rows of garages, with two rows of collectors per garage

* Azimuth – south; tilt – 45°