The Department of Energy will spend $11.5 million on 16 research projects aimed at improving the energy performance of building envelopes and HVAC systems in U.S. homes.
The Building America Industry Partnerships will underwrite research in three broad categories: advanced residential envelope and HVAC systems, fault analysis for residential HVAC systems, and how building industry standards affect energy performance.
The announcement came from the Building Technologies Office (BTO), which is part of the Department of Energy’s Office of Energy Efficiency & Renewable Energy.
The average American household spends more than $2,000 a year on energy bills, with U.S. homes accounting for 20% of total energy consumption and 37% of all electricity use, the BTO said. In all, spending on residential energy is $240 billion a year.
“While building materials and HVAC equipment efficiency have improved over recent decades,” the office said, “a number of challenges continue to result in significant energy losses.”
Air sealing houses with an aerosol
One of the technologies on the grant list is the use of an aerosol sealant to plug up air leaks in a building envelope. The promising technique called AeroBarrier was commercialized by Aeroseal, which used research from the University of California, Davis to market a system for sealing air ducts. AeroBarrier was first tested on a single-family house in 2012. The technology was licensed to Aeroseal in 2015. (For a detailed slide presentation on the process, click here.)
AeroBarrier is designed to simplify what is now the painstaking and relatively expensive process of sealing leaks in the building shell with caulk, gaskets, and specialized tapes. Instead, technicians pressurize the house with a blower door and release an aerosol mist through tripod-mounted spray nozzles. Forced out of the house through gaps in exterior walls, floors and ceilings, the atomized latex material seals the exterior within a matter of hours. At least to a point, the longer the system runs, the tighter the house gets.
According to the company, the process is capable of sealing a house well enough to pass the Passivhaus airtightness standard of 0.6 air changes per hour at 50 pascals of pressure (ach50).
As part of the grants just announced, the Center for Energy and Environment (CEE) in Minneapolis will study the use of the technology on existing homes. Dave Bohac, the center’s director of research, said in a telephone call that some of the details of the two-year study are still being worked out. With UC Davis as a partner, researchers will test the process on 22 apartment units and 13 single-family houses — 35 residential units in all — with roughly half in California and the other half in the Midwest. The houses have yet to be selected.
The study will supplement another Building America project in which the process was tested on new construction. In that research, houses in Minnesota were air sealed before the drywall had been installed. Bohac said the AeroBarrier process reduced air leaks by an average of 75% to 80%, with average post-process airtightness of 0.7 ach50. Forty percent of the houses were tested at 0.6 ach50 or below. The houses were mostly production homes.
The new round of study will help determine whether that kind of success can be translated to existing houses. The most logical time to apply the sealant is when the building is being renovated — no furnishings to worry about, no people, and possibly some open walls.
In a test project a few years ago, Bohac said, an early 1900s masonry building was the guinea pig. The building was being divided into smaller units for income-eligible housing and had a leaky envelope testing at 13.4 ach50. The average after sealing was 4.1 ach50, with one unit getting down to 1.4 ach50, an 88% improvement over pre-treatment numbers.
Whether AeroBarrier will be useful to seal houses that are complete — unoccupied but not undergoing any renovation — is another question. Cleaning up the sealant is one issue. The sealant doesn’t seem to stick to vertical surfaces, but it will collect on horizontal surfaces, and because it’s sticky it doesn’t sweep off easily.
With cleanup in mind, Bohac suggested that a logical time to seal an older house is when it’s already undergoing lead abatement. Another possibility is isolating a single room in the house that’s undergoing renovation and misting just that space.
How durable is the seal?
The sealant gradually collects at cracks and holes in the building shell, and within a few hours airtightness improves dramatically. UC Davis has been conducting accelerated durability testing in the lab on ducts that have been sealed with Aeroseal, essentially same process, and so far the results are promising, Bohac said. Researchers are finding that duct seals are more durable (showed a slower increase in leaks over time) than ducts sealed conventionally with mastic and tape.
Preliminary results on accelerated testing of AeroBarrier seals also show very little increase in leakage.
“It’s worked really well for ducts,” he said. “It seems reasonable that it would work well for building envelopes, too.”
He continued: “What we’ve been seeing on new construction, it’s not so much the big leaks that are causing the problems, but the narrower leaks that are just kind of ubiquitous — say, the leak between sheathing and the top plate or the bottom plate. There are just hundreds of feet of that kind of gap. Normally, it would be incredibly labor-intensive to seal that kind of leak, but the nice thing is you don’t even have to go around and find them. This approach just finds them itself.”
Another topic of interest will be the potential energy savings. Preliminary number crunching suggestions that an 80% reduction in air leaks could result in a 20% reduction in heating and cooling costs.
The solid panel ‘Perfect Wall’ building
Another grant recipient is the University of Minnesota, which will look at ways to speed up adoption of a solid panel wall system. The “Perfect Wall” building system yields a “studless” house that is more energy-efficient, tighter, and of higher quality than conventionally built houses, developers said.
The idea is that a single contractor uses structural engineered panels to construct a rigid, structural shell before adding insulation, air-control, and cladding on the exterior. The shell consists of two layers of cross-laminated engineered wood sealed with a peel-and-stick membrane in advance of two layers of rigid insulation, a vented rainscreen and cladding.
From start to finish, the construction process should take about two weeks.
The university, in partnership with two affordable housing developers, has built a half-dozen of the houses since 2016 with several more planned this year. Energy modeling predicted a 40% energy savings over Minnesota code-compliant houses, and 30% energy savings over Energy Star Version 3 houses. (Actual performance data is coming in now.) Airtightness of the first Habitat for Humanity house was 0.26 ach50, according to a summary of the project.
This new round of Building America funding, about $700,000, will pay for structural testing at the Home Innovations Research Laboratory over the next 2 1/2 years, said Patrick Huelman, associate extension professor and the Cold Climate Housing coordinator at the university.
“The primary purpose of the new grant is to nail down the structural behavior of the two-ply panel,” he said by telephone. “It’s just to get all the engineering in place.”
Outperforming conventional construction
Exterior walls are built with two layers of 1 1/8-inch-thick OSB manufactured by Huber Engineered Woods using essentially the same formula as the company’s well known Advantech sheathing. The first 8-foot by 24-foot panels, each weighing about 750 pounds, are craned into place at the corners of the building. Panels run vertically from the foundation to the roof trusses.
Once those are in place, the next course of panels is set horizontally on the inside of the walls and glued and screwed to the corner pieces. Floor trusses set on top edge of the first horizontal course make up the floor system for the second floor.
Development of the system dates back to the 1990s, involving not only the university but some outside partners, including a company called Monopath, Huelman said. The idea was to bring down the cost of the structural portion of the house and put more money into water, vapor, and thermal control layers on the outside.
“That dollar savings gets invested in the control layers, and when we get all said and done we have a more robust, better wall at approximately the same cost as traditional or conventional construction,” he said. “That was the goal. We aren’t quite there yet.”
Huelman has no doubts the houses perform as intended, with one recent example scoring a 39 on the HERS Index (meaning it is 61% more efficient than a comparison code-compliant house).
“We’ve knocked that one out of the park,” he said. “It’s just that we have not been able to get enough cost savings in the framing materials and the framing labor to get us back to even.”
Completing structural testing and finishing engineering studies could help make the technology appealing to a wider audience and settle any potential misgivings about using relatively thin wall panels to support all the structural loads of a house.
Other projects on the funding list
The Department of Energy also is funding these projects:
- Residing: Researchers at the New Jersey Institute of Technology will field test a technique for residing existing homes with graphite-infused rigid insulation combined with a liquid flashing and sealing product, according to the DOE. The project is aimed particularly at houses in Climate Zones 3, 4, and 5. GBA requested details about the project, but a spokeswoman for the institute said no other information about the grant would be made available until the formal start date of the project in late April or early May. The DOE also was unable to provide any further details.
- Heating and cooling: Steven Winter Associates Inc. will conduct research to develop a new integrated heating, dehumidification, and air conditioning system for high-performance houses. The prototype will provide 1 ton of space conditioning for energy-efficient multifamily dwellings and low-load single-family homes.