Passive House Saves Big on Energy with Zoning Technology

Joey Conover and husband Jeff Erkelens own Latitude 38, Charlottesville, Virginia, a business dedicated to sustainable building and energy efficiency. They stated, “The key to every Latitude 38 project is whether we feel we would want to live on the street and in the house that we build.” Where do they really live? In one of their own houses, the Sixth St. Passive House.

The Sixth St. Passive House is 3,168 square feet of innovation. The stringent passive house criteria focus on preventing air leakage. The house is so well-insulated that Conover and Erkelens can spend most winter days comfortably inside without the heat on. The electronics and occupants produce most of the needed heat but not all of it. That’s where Mitsubishi Electric US, Inc. Cooling & Heating Division (Mitsubishi Electric) comes in.


Challenge: To install an HVAC system that would complement a passive house design.


Conover and Erkelens called in a Certified Passive House Consultant, John Semmelhack, owner, Think Little, Charlottesville. Semmelhack is a Certified Passive House Consultant. He worked with the couple to ensure that the project would meet all of the passive house criteria. The team solved the cooling and heating factor with an M-Series multi-zone system. “This technology was a given,” Semmelhack said.

Semmelhack has specified variable-capacity heat pump systems “in all of the houses that are of this performance level that I’ve been working on. They give a right-sized system for a better portion of the year.” A key tenet of passive house building is that one cannot install too large of a system. Bigger in this case is not better. “We need systems that are able to ramp down their capacity,” Semmelhack said.

Semmelhack also explained the difficult issue of moisture in tighter houses: “In our climate, in the summertime, it’s very humid. The insulation that helps so much in the winter doesn’t do anything to take out moisture. The [M-Series] system’s variable capacity nature makes it so we’re removing moisture nearly 24/7 throughout the summer.”

Zoning capabilities ultimately became a vital design component. The couple lives in the top two floors of the three-story passive house. The bottom floor is entirely separate, functioning as a rental apartment. It was critical that the tenants of the space control their own cooling and heating. “It’s really nice that the tenants have their own unit,” Conover said.

The team selected Mitsubishi Electric’s system after “look[ing] at the available units from various companies – we looked at the specs,” Semmelhack said. “In terms of performance and local installers’ familiarity with the equipment, Mitsubishi [Electric] just made the most sense.”


Solution: A Mitsubishi Electric multi-zone system provided the exact cooling and heating loads needed.


After two years of living with the system, the homeowners have already seen impressive energy efficiency. Semmelhack reported the average annual energy use for the first two years at 9,881kWh. The net energy use for the first two years (which includes energy production from the Solar PV system) comes in at 4,999kWh.

The U.S. Energy Information Administration’s most recent energy survey shows Virginians consume 25,175kWh per year, making the Sixth St. Passive House’s net consumption a fifth of their neighbors’. “The house is doing well,” Semmelhack said. “It’s right in line with my expectations. I’m very pleased with it.”

He’s not the only one. A handful of organizations have now recognized the Sixth St. Passive House’s energy efficiency, among them the Passive House Institute US, EarthCraft Virginia, ENERGY STAR and the DOE Builder’s Challenge.

The energy savings are deeply important to Conover and Erkelens as well. Conover said they wanted a passive house because “we liked the philosophy of it: to reduce the amount of energy you need in the first place.”