by Jeffrey J. Garriga and Pat ‘Sherman’ Morss, Jr.
Photo © www.bigstockphoto.com
Buildings account for as much as 40 percent of all energy consumed in the United States according to the Energy Information Administration (EIA). If the country is to address carbon emissions and its contribution to climate change, this needle must move. Recognition of this has led to a growing emphasis on the concept of net zero energy (NZE). NZE buildings generate energy onsite using clean renewable resources over the course of a year that is equal to, or greater than, the total amount of energy consumed onsite.
State and local government programs increasingly promote NZE usage in public buildings as the ultimate in sustainability. The following eight principles would help the project’s design team to meet the challenging goal of NZE.
1. Define goals and establish parameters
The first step is to establish energy use goals for the site. Case studies and reviews of best practices in sustainable design should be assembled to provide benchmarks for the design team.
Tax incentives and rebates offered by the government or utility companies must be identified. These incentives can help offset potential budgetary concerns for sustainable technologies.
Detail and consider factors such as climate, location (urban or rural), orientation, water usage, and occupancy, relative to the established energy use targets.
Once the initial priorities and goals are established, all stakeholders and agencies must agree on the goals.
2. Assess alternative building configurations
Numerous building configurations (orientation, footprint, shape, and massing) must next be considered for placement on the site.
A building’s orientation dictates access to natural light, ventilation, and sun exposure. Conventional wisdom is that a building on an east-west orientation with a shallow north-south depth is best to take advantage of natural light, ventilation, and sun exposure. This configuration may not always be possible due to site constraints, particularly in dense urban areas.
Computer modeling suggests the compact massing of a cube-shaped building with lightwells may be more energy efficient because this shape encloses the most volume with the least perimeter, and the lightwells can direct light in ways that minimize glare.
The building’s function and use need to be considered when developing the interior space plan. For instance, will it be a 24/7 operation with related power and occupant comfort considerations?
3. Set the energy use intensity goal
The design team and building owners must be on the same page regarding expectations for energy consumption. A starting point for determining energy reduction is a comparison of the energy use intensity (EUI) of the proposed building design with a base industry standard.
These standards are accessible through various online portals including the Energy Star portfolio manager that provides baseline EUI information for many building types, including those with mixed uses. Another possible industry standard for an energy-efficient building is the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings.
4. Determine strategies for energy reduction
The design team should look at multiple energy conservation measures (ECMs) to reduce energy consumption prior to exploring onsite renewable resources. These may include the following.
Site optimization
Orientation of the building and placement of glazing affect energy use.
Solar shading
Exterior architectural features shade window openings from the sun at specific times. Deciduous trees can be planted strategically to create shade.
Daylight and artificial lighting
High windows with light shelves bounce light deep into floor plans. Reducing reliance on artificial light means less heat is produced by fixtures. Also, energy-efficient light-emitting diode (LED) luminaires with intelligent controls that react to daylight entering the space reduces reliance on air conditioning for cooling.
Natural ventilation
Operable windows and mechanically controlled dampers can effectively move air through spaces, allowing for the removal of hot air during shoulder and cooling seasons, thereby decreasing the loads on mechanical conditioning equipment.
Façade and roof design
Air sealing, additional roof and wall insulation, double or triple glazing in high performance framing systems such as fiberglass, and reflective or vegetated green roof can reduce energy gains and losses by at least 30 percent and as much as 90 percent in the most stringent designs.
Ground source heat pumps
Liquid pumped through wells in a closed loop from mechanical equipment helps raise indoor temperatures in the winter and lower them in the summer. Subgrade soil temperatures range by location, falling between 7 to 24 C (45 to 75 F), but remain constant independent of changing above grade air temperature changes.
Displacement air supply
Large spaces are more efficiently climate-controlled by providing temperature-controlled air directly to the area of human use in the zone 2 to 2.4 m (6 to 8 ft) above floor level.
Education
Occupants should be educated about the sustainable design of the building and how to inhabit it comfortably while saving energy.
5. Determine renewable energy strategies
The design team should assess onsite renewable energy strategies to offset anticipated energy use. The degree to which energy can be produced onsite, as opposed to being drawn from a utility grid, will determine the project’s success. Here are some renewable energy resources.
Solar photovoltaic (PV) panels
Cost has fallen at a dramatic rate since systems produce more energy per panel thus reducing cost and at the same footprint projects produce more energy.
Solar thermal panels
These panels use solar energy to pre-heat domestic hot water. Tube arrays may also be tied into a hot water heating system.
Unglazed transparent collector
Collectors pre-heat outside air and deliver it to air-handling units (AHUs) of the heating system. The collectors are highly efficient in cool climates.
Biomass boilers
Solid, liquid, or gaseous biofuels can be derived from biological materials such as feed stocks, wood, and algae. Boilers serving the HVAC system would be conventional.
Biofuel tri-generation plant
Cogeneration efficiently produces electric power and heat from natural gas or a biofuel. The waste heat from generating the electricity is recycled to provide heating for boilers or cooling for absorption chillers.
