Buildings with small, discrete, functional spaces- think schools- can achieve net-zero energy use by using all electric, distributed heating and cooling. Think heat pumps.
The legitimacy of distributed, all-electric heating and cooling was recently discussed in a webinar by one of the gurus of high-performance buildings: Jim Straub of RDH. If nothing else, the fact that Jim and his coworkers are designing high-performance buildings in Canada while I have it easy in eastern Maine gives them a lot of street cred with me.
By coincidence, we are just completing renovating a 10,000-square foot warehouse building into a daycare facility. The major rooms are from 450 square feet to about 1,000 square feet: classrooms, an indoor play room, a cafeteria. We looked at a number of heating and cooling options. Central water-source heat pumps, gas-fired boilers with rooftop condensers, VAV air handlers with reheat coils, unit ventilators with DX cooling, and others. Our priority was first cost, since this was a budget-driven project. Some options were suggesting combined mechanical/plumbing costs north of $50 per square foot.
We ended up choosing a scheme with nine heat pumps (about 1,100 square feet per pump), plus a central energy recovery unit with electric duct heating for ventilation air. The photograph above shows the heat pumps arrayed on the back side of the building.
One of the nicest features of distributed heat pump, all electric buildings, and one which RDH emphasized in their webinar, is the level of control it gives to end users, namely the classroom teachers. Each teacher has a control. Ventilation air is controlled by a schedule, but temperature is controlled by the end user. Supplemental heat comes from electric baseboard heaters. In private offices, electric baseboard is the only heating source.
We did not use top of the line heat pumps. These are entry-level units, with less energy efficiency than more expensive ones. Thankfully, we were able to double the wall and roof insulation from what existed in this pre-engineered metal building.
We have designed two all electric buildings this year, and I think we will see more in the future.