I enjoyed reading the article entitled “Platinum PV” in HP158. It was interesting to see where the designers didn’t agree with the LEED standards. I would like to take issue with another of the design decisions made in this house—the choice of an electric furnace instead of an air-source heat pump.
The article mentions that it was less expensive to add PV modules to cover the electricity of the electric heat than to install a heat pump. While this may be the case, it doesn’t take into account the electricity used to power the heat. Electricity is used in real time—the utility isn’t storing our PV-produced power for us to use later. This electric heat unit will likely run mostly at night and during cloudy weather. This means that it will be using electricity largely produced by coal, nuclear, or natural gas—not PV-produced electricity.
So this design choice has a heating system that uses more electricity than a heat pump. And this electricity is most likely coming from conventional (nonrenewable) energy sources. It seems that a Platinum-certified LEED house would strive to use less energy overall (even if offset by PV production) and certainly less from fossil fuels. Installing an air-source heat pump would have met both of these goals and provided air conditioning for the home.
Matthew Huffman • Swoope, Virginia