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Greenhill Contracting Case Study

Net-Zero Energy Homes Optimized with Solar PV and Geothermal Systems

Background

Green Acres
Green Acres was one of the first developments of
exclusively net-zero energy homes in the nation.
Credit: Dave Toder

Anthony Aebi is building homes of the future right now in Hudson Valley. These new homes are designed to be highly efficient, incorporate solar photovoltaic (PV) as well as geothermal technologies, and are competitively priced with conventionally built homes of similar size in the area. But a big attraction for homeowners goes beyond environmental stewardship. Energy efficient design coupled with a process called net metering will reduce energy use in these homes to a point where annual utility costs could be reduced to zero. Typical homes of similar size constructed in this location incur annual utility costs estimated to total $2,500 or more. It is also a possibility that the homeowner will receive a surplus check from their utility company for generating an excess amount of electricity.

Aebi is the president of Greenhill Contracting in New Paltz, NY, which is about 70 miles north of New York City. In New Paltz, he has developed New York State’s first two residential developments that are exclusively committed to constructing “net-zero energy” homes. A net-zero energy home produces as much electricity as it draws from the electricity grid, so utility bills balance out to zero over a 12-month period. Net metering allows excess electricity generated during the day to be sold to the utility, with its value credited back to the homeowner for future use during the evening or other higher-use time periods.

The net-zero developments in New Paltz are among the first in the country. Green Acres, a fully customized development of three-bedroom homes each on one-third acre lots, began in 2008. It is the first single-family home development in New York State in which every home was designed to achieve net-zero energy performance. Homes range from about $500,000 to $600,000. The Preserve at Mountain Vista is the second net-zero energy development in the State. Opening in 2013, the development was geared toward selling at a lower price range ($375,000 to $450,000) and house lots range from two to 10 acres. Homes in both developments range from 2,000 to 3,000 square feet.

Challenge

Preserve at Mt Vista
Homes in The Preserve at Mountain Vista are extremely
energy-efficient and designed to achieve net-zero energy
performance and be competitively priced with
conventionally built homes in the area.
Credit: Michael Hill

Adding solar PV or geothermal systems to existing homes can lower utility bills, but installing those systems in homes designed and built from the ground up to maximize efficiency is the key to net-zero energy home performance. John Wright, vice president of Hudson Solar in Rhinebeck, NY, worked with Greenhill Contracting as part of the team that designed these net-zero energy residential developments. Building cost-competitive homes that are sustainable and energy-efficient requires optimizing many facets of the homes, according to Wright. Most important, he explained, is creating an air-tight building envelope that allows the homeowner to control heating and cooling costs, while incorporating ventilation that supports energy efficiency and maintaining a healthy living environment.

Solution

Largely based on Colonial-style architecture, these homes were designed, constructed, and performance tested to ensure that they meet New York ENERGY STAR® Certified Homes standards, a program administered by NYSERDA. Several steps are taken to create an energy efficient, durable, and resilient building shell. First, a layer of insulating foam was spray-applied to isolate the home’s concrete slab from the ground underneath. Next, interlocking foam blocks are used to make forms for the home’s foundation and insulate it. The forms are then filled with concrete to create the home’s foundation and exterior walls, extending to the underside of the roof assembly. The underside of the roof has 12 inches of spray-applied insulating foam to complete the building’s envelope. Wright explained that the only possible way for air to get in would be around the doors and windows, but the triple-paned windows are sealed on the outside with specialty adhesives and caulk, and then sealed on the inside with spray-applied foam. The heat-recovery ventilation system delivers fresh air into the home while retrieving heat from air which is then vented to the outside. The system can also help to control humidity levels within the home.

Roof-mounted solar PV arrays are designed to generate sufficient electrical energy to power each home over the course of the year—and then some. Hudson Solar installed systems with a rated capacity of 7.4 kW. These systems are projected to annually generate about 8,500 kWh, which is typical expected usage for homes of this size. To boost energy generation, roofs face south for maximum sun exposure with no shading from trees and each house’s 28 panels have the optimum tilt of 38 degrees to capture the maximum amount of sunlight throughout the year. In addition, this roof pitch enables the first hint of sun to heat up the panels to melt the snow and ice so it quickly slides off the roof and the panels can keep producing electricity.

Geothermal systems supply exceptionally efficient space heating and cooling along with domestic water heating. Wells are drilled vertically into the ground, allowing groundwater to be circulated through the geothermal system. A geothermal pump operates in the same manner as a conventional air-source heat pump, but instead of relying on ambient air, the pump uses deep wells in the ground as a source for heating during the winter and cooling during the summer. Lloyd Hamilton of Verdae LLC, located in Rhinebeck, NY, installed the geothermal systems in both Green Acres and The Preserve at Mountain Vista.

Results

Green Acres Back View
Because of optimized construction, homes in Green Acres
often produce more energy than they use.
Credit: Candace Roulo

Long-term savings on utilities have attracted people to purchase homes in the developments. Technical support and incentives offered to support construction of New York ENERGY STAR Certified Homes is provided through NYSERDA’s Low-rise Residential New Construction program, which can be coupled with federal tax credits intended to encourage construction of high performance homes and support the builder’s engagement of RESNET Home Energy Raters. “The verification and testing provided by the Home Energy Rater follows nationally-recognized procedures and allows me to demonstrate to buyers and lenders the advanced energy efficiency my homes deliver,” said Aebi of Greenhill Contracting. Pasquale Strocchia of Integral Building and Design was the Home Energy Rater for both Green Acres and The Preserve at Mountain Vista. Although the solar and geothermal systems add to the home construction costs, State and federal tax credits, up to $25,000 per home on this project, as well as NYSERDA incentives through NY-Sun Initiative, help to offset the costs considerably.

And those surplus utility checks can add up for some homes. Green Acres homeowner David Shepler has received two—$80 in the first year and $172 for the second year—from his local utility for the excess energy his home produces.

Last Updated: 01/07/2014