Mulberry home musings
Greg Kallio studies the efficiency of a local green house
One of my current projects is an energy study of the Mulberry Home—a local green residence built by Laurie Norton and Murray Smith (featured in CN&R’s GreenWays in May 2007). The builders have a reputation locally for building high-quality, affordable green houses, and their passion and commitment to eco-friendly structures extends beyond design and construction; they also want to know how their homes perform once occupied.
Norton contacted Chico State a while back to see if any academic types would be willing to monitor the home as a research project. Not really knowing much about energy monitoring, I took on the project as a learning experience.
The Mulberry Home is a modern two-story, single-family house with three bedrooms, 2 1/2 baths, and a conditioned floor area of 1,970 square feet. Its green features include:
• a 2-kilowatt photovoltaic (PV) array located on the detached garage.
• advanced framing, or optimum-value engineered (OVE) framing, on all exterior walls. (This framing reduces total lumber use and thermal bridging by spacing studs at 24-inch centers rather than 16 inches.)
• wall insulation consisting of R-21 glass fiber batts between studs, plus a continuous 1-inch-thick layer (R-4) of expanded polystyrene around the sunny sides of the house.
• an attic space insulated to R-38 with blown glass fiber.
• a roof consisting of foil-backed sheathing with high-reflectivity composition shingles.
• double-glazed, argon-filled, low-e2 windows with a U-factor of 0.38 and solar heat gain coefficient of 0.37.
• a high-efficiency (0.91 AFUE) natural-gas furnace and a 13 SEER vapor-compression air conditioner for heating and cooling.
With these features, one would expect significant savings in energy bills. But how much? One problem is that I have no “control home” with which to compare the energy consumption. Furthermore, there is great variation in energy use between different families living in the same house in the same climate zone. So, with this limited experimental control, I resigned myself to monitoring the energy consumption for a short time when the house was vacant, followed by a full year when the house was occupied.
I’m particularly interested to find out how well this home performs compared to the Building America Benchmark (a home generally consistent with mid-1990s standard practice), how effectively the solar system reduces peak energy demand, and if the data can be used to validate a building energy simulation math model that I’ve built using commercial software called TRNSYS.
Hi-tech tools Through a Chico State partnership, I have borrowed a sophisticated energy monitor—one that measures and records electricity use (every minute!), electricity generation from the PV system, and natural gas use. The data are transmitted by phone line to a computer, where software “disaggregates” the total electricity use into individual appliances by recognizing their unique power “signature.” Then it’s then sent to me via e-mail. The monitoring has been ongoing since May 2008 and I expect to finish up the analysis this summer. I’m hoping the results will show a significant energy savings over the benchmark home, thereby providing a marketing tool for the builders.