From the Ground Up

The Zero Place project showcases how to efficiently heat a multifamily home with geothermal energy.

Content courtesy of the U.S. Department of Energy. Edited by Green Builder staff.

A first glance at Zero Place, a four-story mixed-use apartment building in New Paltz, New York, reveals what appears to be eye candy. The 63,320-square-foot multifamily project sports a rooftop deck with seating and views, plus 688 photovoltaic (PV) panels on the roof and south-wall awnings capable of producing 270,000 kilowatt hours (kWh) of power per year.  

What’s underneath the building is even more impressive. Fifteen ground-source heat pump wells reach deep into the earth below the building to draw heat from the temperate ground. The ground-source heat pumps provide space and water heating for tenants in the building’s 46 apartments and six commercial spaces.

Affordable Housing Concepts’ Zero Place apartment building in New Paltz, New York utilizes ground-source heat pumps to provide space and water heating for tenants.

This is the second ground source-heated multifamily building for developer Keith Libolt of Affordable Housing Concepts. It’s the first structure that he has certified through the U.S. Department of Energy (DOE)’s Zero Energy Ready Home (ZERH) Program.

Ground-source heating was just one of several innovations convincing the judges for DOE’s 2023 Housing Innovation Awards competition that Zero Place was worthy of Grand awards in the “Blazing the Trail” and “Total Package/Best All Around” categories.

The building, like every home certified through the DOE Zero Energy Ready program, met the criteria of Energy Star Certified Homes Version 3.1 or 3.2 and the U.S. Environmental Protection Agency (EPA)’s Indoor airPLUS program. 

Builders must also meet other efficiency requirements, such as those for hot water distribution through the EPA’s WaterSense program; the insulation requirements of the 2015 International Energy Conservation Code; HVAC and water heating efficiencies; third-party verified air sealing targets; installation of Energy Star appliances, windows and lighting; and ducts in conditioned space. In addition, homes are required to have PV panels installed or have the conduit and electrical panel space in place for future installation.

To meet the envelope requirements of the DOE certification, Libolt chose a building material not often seen in multifamily construction, insulated concrete form (ICF) blocks. Rigid foam (2.625 inches thick) and plastic spacers create hollow blocks, which are stacked together to form walls. Steel rebar is laid horizontally and vertically through the spacers. The 6-inch-wide space is filled with concrete that hardens in place for an R-22 wall that is 11.25 inches wide and is resistant to hurricanes, fires, pests, and mold. The ICF blocks form the crawlspace and basement foundation walls where they are covered with a waterproofing membrane. 

Above ground, the ICF blocks are covered with house wrap and brick veneer on the first three floors and engineered wood siding on the fourth floor. The ICF walls are inherently airtight but additional caulking or foaming was done at all rough openings around windows and doors, around plumbing and electrical holes, and at the edges of the drywall on party walls and wallboard behind showers and tubs. These measures yielded an airtightness of 1.9 air changes per hour at 50 Pascals pressure differential, better than the 2.5 ACH 50 required by Energy Star.

The building’s flat roof consists of open-web steel joists at 48 inches on center with corrugated metal and poured concrete decking and adhered rubber roofing membrane.

The underside of the metal deck is covered with 4 inches (R-28) of closed-cell spray foam, which itself is covered by 12 inches (R-42) of open-cell spray foam.

The triple-pane windows, another unusual feature for multifamily housing, provide exceptional performance with a U-value of 0.17 and a solar heat gain coefficient of 0.27.

The rooftop has space for half of the building’s photovoltaic (PV) panels. The PVs provide occupants with free power over the course of the year.

Heating Things Up

While the building envelope is impressive, the mechanicals are the real story. Heating and hot water are provided by ground-source heat pumps. Builders often have difficulty siting these items because the piping used to extract heat from the ground is often installed as large loops of tubing buried 5 feet or deeper across several hundred feet of ground to the side of the building, thus requiring a site with a large amount of open space. 

In this case, the builder dug the 15 wells straight down, 400 feet into the ground before starting the building. Each well contains a separate pipe loop that connects directly to a manifold in the equipment room, so if a well were to fail, it could be closed off with a valve without impacting the rest of the system. 

By digging the wells within the building’s footprint, no additional yard space was needed. Excavation costs were reduced because excavation was already planned there for the building’s footings and crawlspace.

For space heating, each of the 46 apartments has its own unitary ground-source water-to-air heat pump; nine more heat pumps provide heating and cooling for the corridors and common areas. The heat pumps have an average rated efficiency of 3.4 coefficient of performance (COP), which means they are 3.4 times more efficient at heating air than a standard electric furnace. 

The building’s water loop employs variable speed pumping, which uses only as much power as needed. The system makes automated variable speed adjustments relative to the amount of heating and cooling needed and the number of heat pumps operating. Pump power has been measured at 3.6 kW/year (or approximately 3 percent of the annual total ground-source heat pump system energy use).

Ground wells also provide heat for domestic hot water for the building via two water-to-water ground-source heat pumps. These heat water in four 162-gallon storage tanks. The domestic hot water is distributed from these tanks via risers on each floor to each line of apartments. 

Each dwelling unit has its own manifold that distributes the hot water to each fixture. A recirculation pump and loop is installed to minimize wasted water while waiting for hot water to reach the faucet.

The domestic hot water system gets another boost in efficiency from excess heat that is pulled from the apartments when their air handlers are operating in cooling mode. This occurs more than one would expect for a building in IECC Climate Zone 6A; energy load calculations determined the building is cooling dominant.

Although heating and hot water are included in the monthly rent, tenants are encouraged to conserve and can track their usage on a mobile app. There is a surcharge for usage over a high threshold. While the thermostats are in each unit, the actual mechanical equipment for each apartment (including the heat pumps and energy recovery ventilators [ERVs]) is installed in common mechanical rooms accessible from the corridors. This allows easy access for building operations and maintenance staff to repair and maintain the equipment without needing access to the dwellings.

Airflow Advantages

Each apartment has its own ERV. A dedicated fresh air supply is integrated into the return side of each unitary HVAC air handler so the ducted HVAC systems can distribute fresh air to every room of the dwelling unit. Dedicated exhaust terminals are in each bathroom, the kitchen, laundry, and mechanical room. 

Regular operation of the ERV provides an exhaust airflow of 20 to 30 cubic feet per minute (CFM) continuously per bathroom. A manual controller was installed in each bathroom to boost the ERV speed to 45 CFM for 20, 40 or 60 minutes. CO₂ sensors in each unit enable the system to adjust ventilation levels based on CO₂ levels. Occupants can also control the ERV to prevent excessive ventilation during periods of high exterior humidity, extreme temperatures, or wildfire smoke.

The kitchen exhaust terminal also operates continuously at 30 CFM constant speed, and air flow can be increased to 45 CFM at the push of a button when needed. A re-circulating fan in the range hood over the stove operates to remove grease and other cooking particles from the air.

Like all DOE Zero Energy Ready certified homes, this building meets the requirements of the EPA’s Indoor airPLUS program, which include a whole-house ventilation system like the ERVs described above, the use of low-and no-VOC paints and finishes, and good water management practices. 

In addition, the builder chose to make Zero Place a completely emission-free project. There is no gas line into the building and no gas backup heating system. The all-electric building relies on the ground-source heat pump system for all of its water and space heating needs.

To enhance indoor air quality, induction stoves were installed, offering a cleaner cooking alternative to gas stoves. The project also incorporated heat pump clothes dryers, which significantly reduced the energy consumption typically associated with in-unit laundry. ENERGY STAR-rated lighting, ceiling fans, refrigerators, and dishwashers add to energy savings. Even the elevator is energy saving—it uses a unique regenerative power mechanism during descent to effectively offset its energy demands.

The builder installed a comprehensive energy monitoring system that has the ability to measure energy usage down to individual loads in each unit, enabling the detection of improperly functioning equipment to help identify excess energy consumption and address issues before they escalate. 

For example, by employing sensors on the domestic hot water circulation system, they were able to identify the possibility of slowing down the circulation pumps, resulting in a 20 percent reduction in energy usage.

“Combining ICF, geo and solar to create a high-performance building system is incredibly effective,” Libolt says. “ICF walls require a lot less attention to detail in the field than other wall assembly systems to achieve the same or greater levels of air sealing and insulation performance.”

Geothermal is readily available and is two-to-three times more efficient than the next best system for relatively the same costs after incentives are capitalized. 

For Libolt, the project has been the fulfillment of a lifelong commitment to better housing, especially for the underserved. “I grew up in a very poor urban setting,” he notes. “Providing environmentally clean, safe places for people to live has always been important for me.”