Editor’s Note: The title image for this article was provided by Joseph Kennard and reflects a Joseph Kennard Architects house project in Milton, Mass.
Zero Energy Homes help home owners pare energy use and cut costs but getting to that point requires following forward-thinking experts’ check list.
You can cherry pick materials and systems to curtail energy use in a residential and multifamily home and building. But constructing the entire envelope to bring costs down to zero requires a more intensive design and construction process. Originally dubbed Zero Net Energy Homes, the genre was rebranded by the U.S. Department of Energy without the “Net.” The goal remains similar. Despite these types of structures being built around the globe, there’s still confusion about how to achieve best results. Several experienced architects and energy efficient proponents shared these points—six this week and seven next week.
1. Know what it means to “get off the grid.” Zero Energy Homes are tied to a community’s (electric) grid, which tracks a home owner’s energy consumption in the same way a bank calculates a client’s funds. On sunny days, solar photovoltaic (PV) panels on the homes produce energy, and what’s not used is sent to the grid so the home owner gets credit on their account. On cloudy or cold days, the home owner withdraws energy, the equivalent of taking out funds from their account. If the house was designed properly, the owner will hit the goal of a zero balance by year-round. One exception is if they paid for an initial meter hookup, though some communities don’t charge to encourage residents to pare energy consumption, says Joe Emerson, a homeowner in Bend, Oregon, who built his first Zero Energy Home in 2012, and has followed up with several others. He also writes about the topic online at Zero Energy Project.
2. Start with the right site for passive solar gain. The big first step is to choose a site that takes maximum advantage of the sun’s energy to provide the equivalent of “fuel” for a home. That means having few trees and other obstructions that block light on the home’s south side, but having some on the north side to buffer it from cold air and wind entering in winter. The best designs have one of the two long sides along the south so more windows can be placed to capture sunlight, along with properly sized overhangs to block strong rays, says Ryan Shanahan, a senior green building consultant with Earth Advantage in Portland, Oregon, which certifies green-built homes and multifamily dwellings. In making such decisions, good tools and services are available from companies such as Solmetric to measure sun, shade, and test PVA performance results, he says.
3. Do energy modeling for cost-effectiveness. How many energy-conserving features are incorporated, including how many solar PV panels and their size, may be tough to decide. Consider these options. There are an increasing number of software programs that do the work for you. Third-party energy consultants will also model data as a valuable subcontractor on your team, says Shanahan, whose Earth Advantage firm handles such work. If you follow this approach, choose someone who understands local weather conditions. Jacqueline Nunez, a Boston developer with WonderGroup, did so when she started planning her Allandale Street project that will feature 20 town homes and condos in the Boston area and which the Boston Planning and Development Agency board approved last fall. Nunez hired engineer Jeffrey Rhodin’s Sustainable Energy Analytics firm to help drive decisions that would lead to Net Zero, LEED Platinum, and Fortified Construction standards, the latter to withstand severe weather. Architect and founder Ted Flato’s Lake Flato Architects firm in San Antonio is so committed to using as little energy as possible that it has two engineers on staff who specialize in this work.
Architect Joseph Kennard www.jkennard.com, whose eponymous firm is based in Boston, has been interested in sustainability since the firm was founded in 1999. He consults with outside engineers and builders on such challenges as window and door products, layered insulation packages, and mechanical systems. The firm is currently designing a Zero Energy Home in the suburb of Milton, Mass., salvaging materials from a house torn down on the site, and using metal wall and roof products to make it durable for the long term. While built on a tight budget for his clients, the house serves as a prototype for affordable techniques. “We work to determine the right amount of product (return on investment) so the home owners can reduce energy costs without overspending to achieve that goal. Increasing durability and maximizing energy savings will prove beneficial well into the future as costs keep soaring,” Kennard says.
4. Seal and insulate the envelope. Emerson suggests thinking of a Zero Energy Home as a six-sided box that has been sealed and insulated on all sides to avoid letting hot and cold air in and out. To do this requires selecting the best constructed members—walls, floors, ceilings, windows, and doors, and insulating them as another line of defense. Walls should be double thick, and each 1-foot thick with blown-in insulation between them. How much insulation? The R-value depends on an area’s climate. The same rule of thumb applies to insulation used in an attic with the highest possible R-value sought, but again dependent on location. These days triple-pane windows with the best U-value—which in this case is the lowest possible number—offer a gold standard, but some double-pane windows with a very good U value can produce similar results for less money. The best way to know if a package is tight is to have an energy consultant conduct a blower-door test. Sealing and insulation offer another benefit to make a house more durable against moisture, which causes the majority of defects, Shanahan says.
5. Minimize thermal bridging. Energy is also lost through thermal bridging, usually because of poor construction, inferior insulation, or both. Double wall construction with insulation between and rigid foam insulation on the outside of a home’s framing will minimize or remove the possibility, which also leads to mold, Emerson says.
6. Use the sun to heat a hot water system. A thermal hot water system that relies on a storage tank and PV collectors can provide a home’s hot water supply. Choose either an active system that may feature a pump that circulates water directly through the collectors and into the home, or circulates a nonfreezing heat-transfer fluid through the collectors and a heat exchanger, or a passive system that doesn’t include the circulating pump, but is less costly. It’s downside is that it may be less efficient.
Next week, more ideas will follow to fashion a Zero Energy Home.