Near-Zero Is Goal of Some Home Builders
February 5, 2007
Have you ever heard of a home with an electricity meter that sometimes runs backwards? That’s just one of the intriguing features of a near-zero energy home. Other interesting features usually include high-performance building envelopes, photovoltaics to harness the power of the sun, and highly efficient heating and cooling systems.
High energy costs have fueled an interest in near-zero energy homes, and while their first cost might still be excessive, consumers are letting builders know that better efficiency and lower fuel bills are on their minds. According to a quarterly survey by the American Institute of Architects (AIA), requests for energy-efficient housing features leaped from 38 to 54 percent between 2005 and 2006. The AIA poll also showed that 90 percent of consumers would be willing to pay $5,000 more for a house that would use less energy.
A near-zero energy home would definitely allow the homeowner to use less energy, but right now, it costs more than an additional $5,000 to build this type of house. That’s not to say that builders aren’t trying to figure out a way to offer customers affordable, near-zero energy homes. In 2005, Ideal Homes, Norman, Okla., constructed such a home for just under $200,000. Perhaps in the not-too-distant future, near-zero energy communities will be popping up around the country.
HISTORY OF EFFICIENCYIdeal Homes has always incorporated many energy-efficient features into its new homes, including ventilation, low-e vinyl windows, and improved insulation systems in walls, ceiling and around the foundation. In addition, the builder uses duct mastic sealings and foil-flex duct work, which reduces the amount of air put into its attics due to leakage on the supply side and being pulled from the attic on the return side. The net effect is Ideal Homes have only 5 percent air leakage to the outside, compared to the 20 to 25 percent leakage that is often found in homes in which conventional methods of sealing with duct tape have been used.
“We’re a production home builder in the starter home category,” said Mack Caldwell, architect, Ideal Homes. “All our homes are EPA Energy Star homes. We build them tight, ventilate them right, and we build them to a very high standard for a starter home production builder.”
Since Ideal already had the advanced energy-efficient construction methods in place, company president Vernon McKown thought that building an affordable, near-zero energy home would be the next logical step for the company. These types of homes are typically in the $1 million range, so building one for under $200,000 would be a challenge.
Near-zero energy homes produce as much energy as they consume, combining energy-efficient construction with renewable energy technology to reach a “net zero” energy consumption over the course of a typical year. “There will be times when the house will not supply enough electricity, but there will be other times when the house supplies more than what is needed, and we’ll sell the electricity back to the utility company. When you average the give and take out at the end of the year, it should come out to near zero,” said Caldwell.
Ideal’s near-zero energy home was built in 2005 and features three bedrooms, two bathrooms, and a two-car garage. The 1,650-square-foot home is based on the builder’s regular floor plan, and it blends seamlessly into its neighborhood community called Valencia in Oklahoma City, Okla. The house is a prototype, and Ideal has no plans to sell it at this time; instead, it is renting out the house and collecting data to substantiate its near-zero energy status.
HIGH-EFFICIENCY FEATURESAs can be expected, a high-efficiency heating and cooling system was needed for this near-zero energy home. Kelly Parker, P.E., owner, Guaranteed Watt Saver (GWS), Oklahoma City, designed the HVAC system, which is all in a day’s work for his company.
“Our job is to work with large and small builders to get them stepped into building a more resource-efficient house,” said Parker. Last year GWS helped over 7,000 homes in four states achieve some sort of energy-efficient certification level, such as EPA’s Energy Star program.
For Ideal’s near-zero energy home, Parker decided to specify a geothermal system. This system made sense from an energy-saving standpoint, plus the builder wanted to try out the technology. The 3-ton ClimateMaster unit required three 200-feet-deep wells, and features an EER of 27 and a COP of 4.5. Parker originally recommended a 2-ton unit, but accepted the 3-ton unit because it has a two-stage compressor. Most of the time the unit will run on the low stage, meaning greater energy savings will be achieved.
The ductwork design is a trunk system with flexible ducts. “The ductwork was installed in an unconditioned space, but it was sealed with mastic for less than 5 percent duct leakage to the outside,” said Parker. “A Venmar variable-speed energy recovery ventilator was installed to provide balanced pressures of incoming and outgoing air. In this climate, we actually want to balance the ERV to provide a positive pressure on the enclosure.”
The house is also well insulated to ensure energy efficiency. For this house, 2 x 6 construction was utilized, and blown-in cellulose insulation was used in the walls with R-38 in the roof. Solar board was installed on the roof to reduce the heat gain and heat loss in the attic. “Our houses are very tightly sealed - I think the air change is about .3 air change per hour (ACH). We go the extra mile in making sure the building envelope is both tightly sealed and well insulated,” said Caldwell.
On the south-facing roof are 28 photovoltaic (PV) panels, which cost approximately $30,000 and produce about 5 kW by capturing energy from the sun. The PV inverter is located in the garage along with several meters, which often run backwards, illustrating the fact that the house produces its own energy.
A tankless hot water system from Rheem heats water instantly when the tap is turned on, conserving energy by not maintaining heated water 24 hours a day. The tankless system was installed in the garage on an outside wall, so it could be vented right through the wall, thus saving the cost of expensive venting up through the roof.
In addition to being a near-zero energy home, this house has the distinction of being the first house in the nation to be certified through the Leadership in Energy and Environmental Design (LEED) Green Building Rating System™. Caldwell had been working on the LEED for Homes committee for four years, so he jumped on the chance to have the first house certified using LEED criteria.
Ideal Homes doesn’t have the final figures for how much energy the near-zero home has been consuming or producing. The National Renewable Energy Laboratory (NREL) is gathering the data and Building Science Corp. is performing the evaluations, which should be available this fall. The good news is that the family currently renting the home hasn’t had any complaints about their comfort.
“We just went through a really frigid spell here, so I would have expected to hear something from somebody, and it’s been quiet,” said Caldwell.
Comfortable occupants, low (or no) energy bills, affordable house ... maybe more builders will see the benefit of constructing near-zero energy homes.
Publication date: 01/29/2007