Energy-Efficient Homes at Lower Price Point

An affordable housing program gives first-time buyers a chance to own a home—and save money on energy bills.

The lower the cost, the greater the chance of homeownership for low-income buyers. 

That’s the philosophy behind the Energize Delaware ZeMod program, which combines up to $25,000 in payment assistance, and energy costs as low as $0 monthly. According to Russ Huxtable, vice president and CEO of Milford Housing Development Corp. (MHDC), it’s a winning combination of savings.

MHDC collaborated with the Delaware Sustainable Energy Utility (DESEU), Greenwood, Del.-based homebuilder Beracah Homes, Inc., and Vermont Energy Investment Corp. (VEIC) to bring zero energy modular homes to Delaware’s low-income home buyers.

Through the ZeMod program, homeownership is made affordable in part through renewable energy and net metering. The highly efficient modular homes also scored a win for the collaborative, earning a Housing Innovation Grand Award from the U.S. Department of Energy (DOE)’s Zero Energy Ready Home (ZERH) program in 2022.

All homes offered through the ZeMod Delaware program are certified as
DOE ZERHs.

“Our mission is to provide decent, safe, affordable housing solutions to people of modest means,” says Huxtable. “Meeting the high-performance home criteria of the DOE’s [ZERH] program helps ensure we meet these goals.”

Exterior Home Design 101

The first ZeMod home constructed is a 1,209-square-foot, two-bedroom, two-bath, single-story home at Knoll Acres in Lincoln, Del. Lincoln is a neighborhood of small lots with larger shared open spaces under development by MHDC, with sites qualified for low-interest financing through the U.S. Department of Agriculture (DOA) mortgage program.

The solar-powered DESEU State Fair House boasts energy costs as low as $0—a key factor in helping low-income families purchase their first homes. Credit: Energize Delaware’s ZeMod Program and Beracah Homes

With its 5.12-kilowatt (kW) of photovoltaic (PV) panels installed on the roof, the award-winning home—also known as the DESEU Star Fair House—achieved a Home Energy Rating System (HERS) score of 1. Even without PV panels, it would achieve a HERS score of 40, well below the HERS 80 to 90 of new homes built to just meet code.

The home was assembled over a vented, uninsulated crawl space. Framed assemblies were constructed off-site in a factory. Walls are double 2-by-4 framing with a 1-inch gap to create an 8-inch insulation cavity, which is filled with blown fiberglass in the factory. Floors are insulated and sheathed in the modular factory. Windows, siding, and interior finishes are installed in the factory.

The roof comes to the site in two halves, with asphalt shingle roofing and solar panels already factory installed. Roof trusses create a 10-inch raised heel, allowing full R-50 cellulose insulation at the exterior wall top plates. The simple gable roof design is oriented with one side facing south at an optimal angle for solar exposure.

“Constructing the home modules in a factory ensures a controlled environment,  which helps us to control costs, reduce waste, improve quality, ensure consistency, avoid labor and scheduling constraints, and minimize exposure to poor weather conditions for both the materials and the crews,” says Huxtable

The modular construction also helps to avoid ad hoc design improvisation in the field, which can sometimes result in quality and performance compromises. “Quality management is built into the modular process,” Huxtable adds. “No design-build decisions are made during construction. All construction details are designed and documented before the build begins.”

Efficient Temperature Controlled Homes

The double-pane windows have a U factor of 0.25 and a solar heat gain coefficient of 0.20. The vinyl-framed casement style windows have an argon gas fill between the two glass panes, both of which have a low-emissivity coating to minimize heat transfer. Quality control in the factory helped to ensure an airtight envelope and the home was tested after assembly at just 1.5 air changes per hour at 50 Pascals of pressure.

Fresh air is provided using a ventilator equipped with a heat pump to precondition outdoor air. The ventilator provides MERV 13-filtered fresh air to each room. Demand controls respond to measurements of temperature, relative humidity, carbon dioxide, and VOCs within the home. Controls also allow continuous or timed ventilation. In favorable conditions, the ventilator brings in outdoor air to provide free cooling. A recirculation mode provides mixing and filtering of indoor air.

The home’s single ductless mini split heat pump provides efficient heating and cooling in all weather conditions. Distribution and mixing of the heated or cooled air is assisted by the ventilator’s fresh air ducts and recirculation mode.

Appliance Power

Water heating in the all-electric home is provided by a 50-gallon heat pump water heater with a coefficient of performance (COP) of 3.45. The water heater is in a utility room within the home, where it derives heat from the condensing clothes dryer also located in the utility room. In addition, the room is supplied with conditioned air by the ducted ERV.

The home is equipped with high-efficiency, all-LED lighting and ENERGY STAR refrigerator, dishwasher, clothes washer, and clothes dryer. Several of the home’s plumbing fixtures are EPA WaterSense rated for water efficiency. The electric panel has room to add an electric vehicle (EV) charger if desired by the homeowners in the future. 

As an EPA Indoor airPLUS certified home, all cabinets, flooring, paints, countertops, and doors are low-emission products.

Energy metering was installed in the home to determine energy performance during occupancy. Circuits that are metered include the major appliances (the clothes washer, clothes dryer, and refrigerator), the HVAC, water heating, and bedroom plug loads. This energy usage data will be analyzed to identify opportunities for further savings and to support changes to the design of future ZeMod homes.

The home’s design and layout is compact and simple to minimize details, help control costs and take best advantage of the benefits of modular construction. Credit: Energize Delaware’s ZeMod Program and Beracah Homes

Home Design Priorities

According to Huxtable, the driving forces behind the design of a ZeMod home are affordability, comfort, health, and zero energy. All are equally important.

“The design and layout of the house were meant to be compact and simple, to minimize details, to help control costs and take best advantage of the benefits of modular construction,” Huxtable says.

A simple form factor can help avoid costly problems associated with maintenance, he notes. For example, reducing the likelihood of water damage at roof valleys and around windows further supports affordability. “The size of the home is modest, again supporting the goal of affordable ownership,” Huxtable says.

This particular award-winning home was actually first assembled as a model at the Delaware State Fair. But the ZeMod program has three standard designs to choose from: two different 2-bedroom, 2-bath models, and one 3-bedroom, 2-bath model. To be eligible to purchase a ZeMod home, the family must earn less than 120 percent of the median income. As of May 2022, four such homes have been purchased.

“We are hoping to attract those who likely did not think that homeownership, let alone ownership of a zero-energy home, was possible,” Huxtable says. “The success of the ZeMod program will be measured by the number of low-income families who can own and reside in a zero-energy home.”

Key Home Features

Air sealing: 1.5 ACH50; modular components are sealed together on site

Appliances: ENERGY STAR refrigerator, dishwasher, clothes washer, clothes dryer

Attic: Vented. R-50 of 7.25 inches of dense-pack fiberglass and 7.75 inches of loose-fill
fiberglass; 10-inch raised heel energy trusses

Energy management system: Rooftop photovoltaic solar panels. Energy production and usage at specific end uses are monitored

Foundation: Vented crawl space: Concrete masonry unit (CMU) walls. R-30 fiberglass batts in 2-by-10 floor joists

HVAC: Ductless heat pump, 11 HSPF, 26 SEER, variable-speed compressor

Hot water: Heat pump water heater, 50 gallon, 2.78 EF

Lighting: 100 percent LED lighting, large windows

Roof: Gabled rafter roof, 2-by-8 ceiling joists, coated oriented strand board (OSB) with taped seams, asphalt shingles

Solar: 5.12-kW rooftop panels

Ventilation: Ducted conditioning energy recovery ventilation (ERV) with MERV 13 filters; 2.6 CFM/watt. Controls based on temperature, relative humidity, CO_2, and volatile organic compounds (VOC) sensors. Continuous or timer-based settings

Walls: Double wall, R-33.5 total: two 2-by-4 walls, 1 inch apart, dense-packed fiberglass; coated OSB; vinyl siding. Wall panels and house sections constructed in factory

Water conservation: EPA WaterSense-labeled fixtures

Windows: Double-pane, argon-filled, low-e, vinyl-framed, U=0.250, SHGC=0.18

Other: Low-emission cabinets, flooring, paint, counter tops, doors; hard floors that minimize particulates. Modular construction.

Credit: Energize Delaware’s ZeMod Program and Beracah Homes