In today’s home building industry, heating and cooling loads are being significantly reduced thanks to the integration of well-sealed and highly insulated building enclosures, along with the use of efficient lighting and appliances. Although these advancements have been extremely beneficial to the industry, oversized conventional and fixed-capacity heating and cooling equipment is still commonly used for small homes, which is causing an increase in first costs and operating costs.

Cost is not the only challenge the industry is facing with heating and cooling equipment. This Building America project identified several space-conditioning issues unique to high-performance homes that impact energy use and comfort. To address these challenges, research was conducted in partnership with three equipment manufacturers who were also striving to understand the conditioning profiles of low-load homes. Researchers evaluated the performance of these three emerging strategies using variable-capacity systems to maintain whole-house comfort in low-load, mechanically vented homes:

• A centrally ducted, small-duct, high-velocity, variable-capacity heat pump
• A centrally ducted, minisplit heat pump with cassette air handling unit
• A ductless multisplit system using transfer fans to control temperatures in bedrooms.

Research sought to validate system approaches for the energy-efficient management of temperature and relative humidity in low-load homes located in hot and humid climates. This is particularly challenging in homes with whole-house mechanical ventilation provided at ASHRAE 62.2 levels, such as the test homes in this research. A few of the recommendations from this project for manufacturers concerning the improvement of equipment performance that came out of this project include:

• Extending consistent run time of cooling systems during low-load hours will address high latent loads in low-load homes
• Delivering low sensible heat ratio (and thus cold-supply airflows) during operation will help to control indoor relative humidity
• Extending manufacturer’s standard operating airflow ranges and developing special low-airflow modes is essential to improving dehumidification and system efficiency in low-load homes
• Refining the low-flow accuracy and control algorithm will lower coil airflow so that low capacity and long runtimes can be achieved without overcooling.

Read more about this success story in the technical report.

This project explored the development and demonstration of a roof/attic energy retrofit solution using nail-base insulated panels for existing homes for which traditional attic insulation approaches are not effective or feasible.

For this study, prefabricated panels were installed above the existing roof deck during a reroofing effort. Vented attics were converted to unvented attics and mechanical systems were installed in the attic. These types of retrofits have been shown in older, existing homes to improve energy savings and comfort as well as air quality. This project made a number of key findings demonstrating the efficiency and durability that comes with using this type of retrofit panels:

• Estimated heating/cooling energy savings were approximately 23% heating and 13% cooling for Michigan, and 11% heating and cooling for Georgia.
• Overall house tightness improved by 29% for Michigan and 12% for Georgia.
• The data set collected showed that moisture conditions at retrofit panels and existing roof decks were well within acceptable limits.

The potential energy-savings impact of this technology in the market is large. The current reroofing cycle is 21 years for the average house, and 5.7 million houses had a whole-roof replacement in 2016. If the portion of existing houses with these attic types homes was 10%, the number of candidate houses for the installation of retrofit panels would be 570,000 annually, at an estimated annual heating/cooling energy savings of 10%–15% or more.

Read more about this success story in the technical report.

Home Innovation Research Labs studied the extended plate and beam wall system during a two-year period from mid-2015 to mid-2017 to determine the wall’s structural performance, moisture durability, constructability, and cost-effectiveness for use as a high-R enclosure system for energy code minimum and above-code performance in climate zones 4–8.

Project activities included structural lab testing, construction observation of two demonstration houses built in Grand Rapids, Michigan, 12-month moisture monitoring of the Oriented Strand Board sheathing and wood framing within the walls of those field tests, and moisture and heat transfer simulations.

The successful field-test demonstration of the extended plate and beam wall system provided positive results and data that will be used to support a code proposal, optimize fastening schedules and framing configurations, fine-tune computer simulations, and publish a construction guide. This wall system will reduce construction complexities, improve cost-effectiveness, and spur adoption in the market, helping more builders transition to high-performance wall assemblies that provide better than code thermal performance.

Read more about this success story in the technical report.

This project sought to address an existing need in the home building industry for innovative new approaches to space-conditioning technology, such as improved air delivery (i.e., duct) systems. The goal of this project was to develop a simplified residential air delivery system that is a solution to air distribution and comfort delivery issues in low-load, production-built homes.

This project developed a new design methodology for the plug-and-play duct system to replace existing design methods that are not appropriate for the plug-and-play “homerun” approach (an approach where a series of same-sized ducts that terminate in rooms throughout the home return to a central manifold). Lab testing and modeling was completed to determine the appropriate materials and duct diameters that are needed to adequately condition homes built to the IECC 2009 and 2012 enclosure requirements. A time and motion study was also completed to determine the labor and material costs of the plug-and-play system compared to a traditional trunk-and-branch system. A few key outcomes of the project include:

• A new design methodology was developed where a designer uses a calculation spreadsheet to assist in selecting the number of equal-sized ducts needed to condition each zone.
• Lab testing and modeling found most homes up to 4,200 ft² in climate zones 3–5 could be adequately conditioned with 3-in.-diameter smooth ductwork.
  • Smaller homes could be conditioned using 2.5-in. or 2-in. smooth ductwork.
• The plug-and-play systems require only 5 different components, compared to the 18 needed for a trunk-and-branch system, making it much easier to manufacture, stock, order, and process the necessary components.
• If the piping is made of a thinner-walled pipe in the schedule 10-15 range, this could potentially reduce the material costs.
• Plug-and-play systems are better positioned to avoid the additional cost of return air by using door undercuts as a means of return air transfer.
• The industry feedback received on the plug-and-play duct concept involved a real interest in the technology, specifically where this technology could help builders improve performance and increase the bottom line.

Read more about this success story in the technical report.

Whole-house mechanical ventilation is a critical component to a comprehensive strategy for good indoor air quality. Smart ventilation controls balance energy consumption, comfort, and indoor air quality by optimizing mechanical ventilation operation to reduce the heating and/or cooling loads, improve management of indoor moisture, and maintain indoor air quality equivalence according to ASHRAE 62.2. Three approaches to smart ventilation control were investigated:

• Seasonal temperature-based smart ventilation control
• Occupancy timer-based smart ventilation control
• Real-time weather-based smart ventilation control.

The results of this project show potential for smart ventilation controls; however, currently only a small selection of smart ventilation systems is on the market. To enable savings and indoor air quality improvements from smart ventilation controls, a concerted commercialization effort needs to be undertaken by manufacturers and other stakeholders such as builders, contractors, and standards organizations.

However, the potential market size for smart ventilation controls is growing and could be as high as 600,000 to 700,000 homes per year, including new site-built code homes, new Housing and Urban Development-code manufactured homes, and newly weatherized low-income units. This research helped increase awareness of the potential of smart ventilation controls and prime the industry for eventual device development and implementation.

Read more about this success story in the technical report.

The research from this project examined the moisture characteristics of high-R wall systems as part of a broader effort to offer solutions that increase builders’ confidence with the adoption of energy-efficient technologies. The high-R walls feature increased wall insulation levels, reduced wall air leakage, and often reduced permeance of material layers. Wall assemblies were subjected to various moisture loads, such as bulk water, built-in moisture (construction moisture), water vapor, and capillary transport through materials in contact with water or in contact with the ground. Some recommendations from this project include:

• Because polyethylene continues to be used as an interior vapor retarder by builders in colder climates, it should be accompanied with air sealing details and drainage plane details so as to avoid or minimize the potential for water leaks and moisture accumulation.
• Walls that rely on the combination of exterior insulation and a Class II vapor retarder show promise for increased R-value (with minimum impact to construction practices).
• For walls without exterior sheathing and an interior vapor retarder in climate zone 4A or 4C, control of the interior relative humidity levels should be integrated into the house design strategy.

Read more about this success story in the technical report.

In this study, researchers with the Building America team IBACOS built on research previously done in two new-construction unoccupied test houses—one in Pittsburgh, Pennsylvania, and one in Fresno, California. Specific traditional central air distribution systems were installed in each of these low-load homes. The cold-climate new-construction unoccupied test house in Pittsburgh was additionally modified to test the performance of a heating, ventilating, and air-conditioning system with varied airflow and small-diameter ducts.

The main goal of the small-diameter duct system is to simplify the task of bringing ductwork inside conditioned space, particularly on the single-story slab-on-grade type of home that is prevalent in the South and Southeast. Comparisons were made between variable-capacity heat pump operation modes with three constant airflow rates to determine the ideal tradeoff between maximizing thermal comfort and minimizing fan energy consumption.

Based on this project, lower airflow rates combined with longer system runtime would provide superior occupant comfort because of less air stratification and lower peak room air velocities. This work has shown that duct configuration and zone temperature control issues remain. Future work is suggested using data measured in this study and a detailed whole-house TRNSYS computer model to further understand the impact of the small-diameter duct system operating in different climate zones and house types.

Read more about this success story in the technical report.