Net-Zero Buildings and Geothermal Heating and Cooling
Another potential tool in developing net—zero buildings is geothermal heating and cooling.
The term “flat load profiling” means matching a facility’s energy use curve with its production curve. Most mechanical systems that use air as the medium for transferring heat (either in or out) decrease in efficiency as the temperature of the air digresses from the intended set point. In other words, when it is 20 F outside and the building interior needs to be 70 F, the energy it takes to bridge that temperature gap increases not only because of the higher rate of heat loss through the building surface, but also because the equipment becomes less efficient. Geothermal uses the constant temperature of the earth in any given locale to ensure that equipment efficiency is not affected by the digression of the outdoor ambient temperature. It works for cold climates in the Arctic Circle, hot climates of the desert Southwest, and everywhere in between.
The static earth temperature (starting point for heat energy transfer) is typically equal to the annual average temperature for that latitude. It could be 50 F in the northern states or 78 F in the extreme South, but it stays relatively close to that temperature year round. Swings in outdoor ambient can affect the first 10 feet of soil depending on location. With geothermal wells reaching lower depths, a geothermal system only has to use the energy that it takes to get from, say, 65 F earth to a 70 F building and that temperature spread changes very little on a properly designed system.
Geothermal systems typically tap the constant temperature and huge mass of the earth to stabilize one side of the system. In some cases, a system can also use a body of water like a pond, lake, or even the Gulf of Mexico or the ocean. This mass, whether made of soils (sand, clay, rock, etc.) or water, can be used like a thermal battery to store heat energy, in some cases for long periods of time. Heat energy that is put in during a hot August can be stored and reused in January or February to heat the building. Implementing a geothermal system can significantly reduce the cost of photovoltaic installations or other energy capital that must be spent to achieve net—zero energy.
Like LEED certification, net—zero energy is not a passing wave, but the viable next step in sustainable building practices. Fortunately, a variety of optimization solutions exist that can be achieved without breaking the bank.
R. Stephen Spinazzola, PE, LEED AP, is KCI Technologies’ regional practice leader for MEP/FP in the northeast. Craig E. Pullyblank, PE, is the firm’s lead electrical engineer on solar design projects. Gregory M. Tinkler, CGD, is KCI’s practice leader with 20 years of experience in the design of all types of geothermal systems.
Marine Corps Building Aims for Net—Zero Energy
The Child Development Center in Parris Island, S.C., is the Marine Corps Base Recruit Depot’s first facility that was designed to achieve net—zero energy use.
The 25,775—square—foot building serves a staff of 65 and about 250 children. The building has more than 1,100 photovoltaic panels that together are capable of producing 387,581 kWh per year, as well as hydronic heating and cooling via a variable flow geothermal closed loop system.
To capitalize on the renewable energy generation capabilities, efficiency was built into many aspects of the facility, including the building envelope, high—efficiency electric appliances, and LED lighting.
Sustainability guided the choice of water—saving plumbing fixtures and products that contain high percentages of recycled content as well as materials that were manufactured locally and regionally.
The facility also plays a role in achieving the Department of Defense Education Activity (DODEA) 2030 goal of achieving energy independence in all of its buildings, as well as the U.S. Navy 2020 mandate that 50 percent of energy requirements be met using renewable resources.
— R. Stephen Spinazzola, Craig E. Pullyblank, and Gregory M. Tinkler