Rock Lake is a seasonal use facility in Algonquin Provincial Park. As such it has a variety of hot water demands, depending on the season. Full campgrounds demand a lot of hot water in the summer months but in winter the building is completely drained of water and shut down. Then there is spring and fall when the campground may not be full during the week and demand is less than average. This varied hot water demand presents some interesting challenges.
Contrary to common belief, the biggest challenge with any commercial solar hot water system is to avoid overheating, not under heating. Over heating causes excessive wear on parts and accelerates the degradation of the heat transfer fluid.
The second biggest challenge is to not over burden maintenance staff with additional annual service requirements from the system. In every commercial facility, the maintenance staff have plenty to do without the solar thermal system imposing onerous tasks on their monthly or annual schedule. If the tasks are onerous there is a good chance they might not get done.
At Rock Lake, we designed a system for all seasons:
A custom designed, closed loop solar water heating system with a heat dump circuit.
Here's how it works:
In the spring and fall when the campground is running at less than full occupancy we also have less sunlight hours. This works well most of the time, but there is still a significant chance of over heating because of low hot water demand and unseasonably sunny weather. During this time of year, the system controller prioritizes heating the water. When the tanks are full, excess heat goes to a dump load.
In the winter, when there is no demand for hot water and the building is shut down and drained of all water, a sensor sends a signal to the controller to tell it to send all the solar heat to the dump load. Our dump load is a bank of radiators. The radiators are located in the basement of the building where they can heat the building. When the water is back on in the spring the system automatically reverts back to normal operation (prioritizing hot water first and heat second).
During the summer the system really shines. In fact, the system was sized specifically for summer campground peak load. In this way, the need to dump heat to the basement, in summer, is minimized. Which is good because nobody likes a hot building in summer.
The key to this system is not just the dump load, but the custom controls to make it all work efficiently in a way that is easy for the park staff to deal with. The last thing any maintenance staff person needs is to spend a lot of time taking care of yet another system. With this system, there is no additional attention required during fall shut down or spring start up. The controls react to the job - not the other way around.