Freeport School Saves Before & After with Air Source Heat Pumps
The Merriconeag Waldorf School in Freeport, Maine recently built this beautiful building to house their Arts and Crafts classes. Their building is a wonder of modern building science and was built to amazing standards. reVision heat was brought in to supply the heating system. In this case, the entire building is being heated by two 18,000 BTU Mitsubishi Hyper Heat air source heat pumps.
Typically, a well insulated building without access to Natural Gas would use and install a high efficiency Propane boiler. Which would all be well and good, except Propane is a derivative of Crude Oil just as Oil is, and we’re running out. Not to mention the fact that like oil it’s expensive.
Not only is the fuel expensive, but so is the boiler. A typical new, high efficiency gas boiler costs around $9,000 to install and that’s just in the basement. In new construction, a distribution system needs to be included, easily pushing the final cost above $15,000.
Indoor Output Unit for Air Source Heat Pump
The Merriconeag Handcraft building is being heated by two heat pumps, one in each room. The system cost about $10,000 to install, significantly less than the propane boiler option. And, to boot, will cost considerably less to operate.
Propane, at $3.50 a gallon, run at 90% efficiency, costs $41 per Million BTU’s. Interestingly, resistive electricity costs $44 per Million BTU’s. Propane is almost as expensive as Electricity for heat now. By contrast, the air source heat pump will run at a seasonal efficiency of better than 300%. Which means that it will cost about 1/3rd less to operate, at $14 per million BTU’s.
Where the Magic Happens - Outdoor Compressors
The fact that heat pumps were an option at all in this project owes to the excellent work on the building envelope by the Waldorf School. If the building needed 50% more heat, it would have required another heat pump. While the building would most likely do fine without any back up, they’ve installed resistive electric back up radiators just in case. In the end, they have effectively taken money out of the mechanical system and put it into the walls. A solution that will create long term savings for the school.
Interesting Side Note: The engineer who specked this system specified a system twice as big. I looked at the heat loss numbers and proposed a smaller, much less expensive system that better matched the heating demand for the building. The folks at the Waldorf School got quotes based on the engineer’s design, which were significantly higher, as bigger heat pumps cost more to install. It turns out the engineer’s design included Air Conditioning load for the Summer months. In their case, the building will not be in use in the summer and will not need a larger system to accommodate air cooling during those months. It’s telling, however, that heat pumps require well insulated buildings to be a cost effective option.
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