©2013 Green Building Advisor. From The Taunton Press, Inc., publisher of Fine Homebuilding Magazine.
Energy experts often repeat the cliché, “There’s no such thing as a zero-energy home — just zero-energy homeowners.” Energy monitoring data from two well-publicized Massachusetts homes — the so-called Montague Urban Homestead house  in Turners Falls and the home of Matt and Laura Beaton  in Shrewsbury — prove the cliché to be true.
Energy-use data for the two homes were shared in a presentation by Mike Duclos and Paul Panish at the Better Buildings by Design conference in Burlington, Vermont, on February 8, 2012. Duclos and Panish are energy consultants at the DEAP Energy Group in Newton, Mass.
The first of the two houses, the Montague house, is owned by Tina Clarke and Doug Stephens. It has won at least two awards: the $25,000 Massachusetts Zero Energy Challenge, and NESEA’s $10,000 Zero Energy prize. Energy-use data from the Montague house show that the homeowners used far less energy than predicted by energy models.
The other house discussed by Duclos and Panish, Matt Beaton’s house in Shrewsbury, is the first certified Passivhaus in Massachusetts. Energy use data from the Beaton house show that the homeowners used far more energy than predicted.
The key factor in both cases was occupant behavior.
The Montague house was built by Bick Corsa with help from the homeowners. Construction was completed in 2009.
Here’s a snapshot of the house:
Energy modeling (using REMrate software) predicted that the homeowners would consume 5,479 kWh of electricity per year; in fact they used only 1,959 kWh — that is, only 36% of the projected usage. Average consumption was 163 kWh per month.
The home’s PV array produced 4,892 kWh during the first year — two and a half times as much electricity as the owners consumed.
Of course, there is no secret to low energy use. We all know how to do it: don’t use much hot water, only turn on a light when you really need to, and keep the thermostat low. (Clarke and Stephens reportedly kept the thermostat at 60°F when they were home, and turned off the heating system when they weren’t home.)
After all, the owners had a strong motivation to keep their electricity usage low: they were aiming to win two cash prizes worth $35,000. They succeeded — in part because their modest home has an excellent envelope and extremely efficient HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. equipment, but mostly because they were focused like a laser on energy conservation.
Mike Duclos summed up the situation this way: “These are not normal users.”
Matt and Laura Beaton moved into their new home, the first certified Passivhaus in Massachusetts, in 2011. Since Matt Beaton owns a construction company, he is the builder as well as the owner. The architect was Mark Yanowitz, and the Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. consultant was Paul Panish.
Here’s a snapshot of the house:
According to Panish, who has been monitoring the home's energy use, the owners are using much more energy than predicted. “There is higher than expected cooling demand,” said Panish. “High internal loads are adding to the cooling loads. The default value for internal loads according to the PHPP software is 621 watts continuous, but the actual internal loads at this house are 1,061 watts continuous.”
The data were a surprise to Panish. “Something unexpected is going on,” he said. “Plug loads are sky high.”
It didn’t take long to figure out what was driving the high energy bills. “There is a very large plasma TV, plus a second TV on the porch,” said Panish. “There is a DVR. The two TVs and the DVR use 600 watts when they're on and 100 watts when they are off, and the TVs are on for an average of 6 hours per day. The loads for entertainment and computers are high. There is an old freezer in the basement. There is a basement dehumidifier. The lighting load is 600% of what was predicted. It seems as if all the lights in the house are left on all the time.”
After delving into the data, Panish reached a few conclusions. “You’ve probably seen a bell curve showing energy used by a range of Passivhaus homeowners,” said Panish. “Well, this family is at the high end of the bell curve. They are concerned about energy use, but their concern doesn’t get reflected in their behavior. The implication was that once they built the house with the good envelope, the job was done. But the job was not done.”
There are several points to be gleaned from the monitoring data from these two houses:
Last week’s blog: “The High Cost of Deep-Energy Retrofits.”