The Department of Energy’s Build America Program hopes to transform the U.S. residential building market by creating and promoting innovative ways to achieve 50% energy savings in new and existing homes for all U.S. climate regions. It’s an ambitious goal, but they have the bare-knuckled commitment and technological resources achieve it.
This summer, I spent three days at the DOE’s Build America Technical Update conference in Denver. Although the program included eight hours of daily lectures and more than 24 technical presentations, a few dominant themes of interest to Vision 2020 emerged, including:
--What innovations are important to future homes?
--How do we avoid doing harm with high-performance enclosures?
--Why are so many high-performance homes under performing?
--How do advancing codes and standards actually get in the way of performance?
Emerging technology: While some promising new technology was discussed, one theme repeated with almost militant frustration was that U.S. heating and air-conditioning manufacturers are not supplying equipment sizes commensurate with high-performance housing requirements. James Cummings of the Florida Energy Center pointed out that not only were most air-conditioning systems sized for peak demand, resulting in significant over-sizing for 90% of operation time, but that this was exacerbated by high-performance enclosures that typically require smaller equipment than manufacturers offer. “Try get a 1-ton or smaller air conditioning unit and you can’t,” said Cummings.
Cooling systems are also set to respond to sensible, or air temperature controls, when the main burden for most and especially high-performance home air conditioning comes with latent loads, or humidity.
In addition to urging manufacturers to make available the smaller equipment required by high-performance envelopes, Cummings also suggests developing a new generation of variable-capacity heat pump systems that satisfy both latent and sensible loads. Some systems exist currently, but they remain comparatively expensive and complicated to install.
John Straube, a principle at the Building Science Corporation and professor of building science at the Civil Engineering Department of the University of Waterloo, Canada, says the age of dual systems has passed, with one system providing household heat and the other hot water. With the low heating requirements resulting from improved enclosures, energy demands have shifted from space to water heating. His preferred solution would come with combining a high-efficiency, gas, tankless hot water system with a small air handler and a micro-duct system, perhaps made from PVC pipe.
Dave Strecher, who leads IBACOS’s research effort in innovative space conditioning strategies for low-load homes presented a strategy to effectively heat and cool a high-performance shell using equipment available today. In essence, the method involves using the oversize equipment and duct systems available, but eliminating most of the distribution network by removing as many interior walls as possible, and then conditioning this large, loft-like area with a single register. Of course, some rooms will still have walls, such as bedrooms and bathrooms, for which Strecher recommends the use of passive, high- and low-wall vent systems through the interior partitions to enable air transfer.
DEVap systems: One of the more exciting developments at DOE involves research on a “super advanced” desiccant enhanced evaporative air conditioning (DEVap) system
: a compact, cost-effective cooling unit that uses 90% less electricity and up to 80% less total energy than its traditional counterparts, while also efficiently managing humidity so that it can maintain a comfortable atmosphere for building occupants without the need for overcooling. Another development comes with emerging technology in radiant floor air conditioning that promises a complete heating and cooling system that requires no blowers or ducting when coupled with an energy recovery ventilation system devoted exclusively to indoor air quality.
Speakers seemed to agree with Joseph Lstiburek, principle of Building Science Corporation and adjunct professor of Building Science at the University of Toronto, Canada, that the trend toward ever-tighter building envelopes is misguided. Lstiburek, who coined the now-famous adage of high-performance building, “Build tight, ventilate right,” says “build tight” means three air changes per hour at 50 Pascals, not one and half, or even lower, as the Passive House standard requires (0.6 ACH). “There’s no logic behind the tighter standards, and it’s expensive and unbelievably difficult to achieve, especially since you have to over-ventilate to compensate for all the problems created when you construct nearly airtight houses,” said Lstiburek.
All the speakers also agreed that the main problem facing the industry today comes from HVAC installation defects. Nearly 80% of high-performance homes tested recently in a California study were not operating up to standard. Nameplate output standards for heating and air conditioning are based on ideal conditions; actual field operation depends on proper duct sizing and fan tuning, among other adjustments. By and large, the HVAC industry neglects key commissioning procedures that result in missed opportunities for operational efficiency and performance.
At the meeting, the debate came with how to overcome this problem, with some advocating improved training, others law enforcement, and still others improved equipment with a diagnostic dashboard that would make commissioning easier.
Codes and standards: The strongest arguments began with debate on the second half of the Lstiburek famous equation, “ventilate right.” Lstiburek opposes changes in ventilation requirements now in effect under the new ASHRAE 62.2, which he says promotes excessive, inefficient ventilation that results in poor indoor air quality. Inefficient, because the 80% increase in ventilation requirement under ASHRAE 62.2, “cancels all the benefit gained in the last two codes updates of IECC,” said Lstiburek. Especially in humid areas, where the standard forces you to add highly energy-inefficient dehumidification. “Why go through all the effort to tighten a structure and then add the equivalent of a gaping hole?” asked Lstiburek. While ERV systems can temper incoming air, they do not dehumidify it.
On the big picture, Sam Rashkin, chief architect for the DOE’s Building Technologies program, emphasized that technology is only half the solution. “Better technologies don’t always win,” said Rashkin, introducing a discussion on market delivery solutions that would effectively communicate and validate the value of high-performance homes innovation. All speakers agreed that the industry needs a uniform label, such as vehicle miles per gallon to achieve a broad market grasp of high performance vs. code-compliant housing.