High Heating Costs Lead to Push for Practices That Promote Energy Efficiency.

With concerns about energy costs on the rise, the pressure is on homebuilders to construct homes that are more energy-efficient. The homebuilding industry is seeking new technologies and practices that will lower the demand for energy while also supplying energy from renewable resources. Builders and remodelers already have many options that can enhance a home’s energy performance—keeping costs under control and stabilizing electricity demand.

Windows of Opportunity

Recent innovations, such as double-glazed, gas-filled windows, provide greater insulating value and improved energy efficiency. Relatively new but already widely used low-emissivity (low-e) coatings can be applied to glass used in double-pane assemblies to control thermal radiation. The type and placement of the coatings varies according to the climate where the window will be used. Low-e coatings consist of microscopically thin metal or metal-oxide layers deposited on the glazing surfaces to diffuse radiated heat by reflecting it, rather than allowing it into the air layer.

Heat Recovery Ventilators

Aside from paying the mortgage, heating and cooling costs can be the most expensive monthly cost of home ownership. While a well-insulated, tightly sealed building envelope can prevent the escape of costly conditioned air, it can also have unintended consequences for indoor air quality. Tightly sealed homes therefore require supplemental ventilation in addition to natural infiltration.

Mechanical ventilation systems allow homeowners to conveniently control the exchange of air, either through automatic controls or with the manual flip of a switch. A heat recovery ventilator (HRV) can also enhance the homeowner’s thermal comfort by tempering incoming ventilation air, and making mechanical ventilation more cost-effective by reclaiming energy from exhausted air.

HRVs use heat exchangers to heat or cool incoming fresh air, recapturing 60 to 80 percent of the conditioned energy that would otherwise be lost. Models that can exchange moisture as well as heat are known as Energy Recovery Ventilators (ERVs). ERVs can reduce moisture loads from hot, humid outdoor air and, when necessary, help retain moisture in the winter.

Sizing Up HVAC Equipment

Homebuilders need to be aware that several rules of thumb used in sizing HVAC equipment can result in improperly sized equipment and unsatisfied customers. Installing oversized equipment can cause frequent, short run times of motors and poor dehumidification during cooling. In contrast, the proper sizing of HVAC equipment can result in cost savings in lower initial and operating costs of mechanical heating and cooling equipment, as well as increased comfort.

Homebuilders can estimate heating and air-conditioning loads by using the Air Conditioning Contractors of America (ACCA) guidelines for sizing HVAC equipment, ACCA Manual J Residential Load Calculation. Several software packages are also available that perform Manual J calculations with user-specified inputs. Using Manual J calculations can be more costly than simply applying rules of thumb, but there are several benefits. Customers are more satisfied and comfortable, since the heating and cooling equipment is designed to provide adequate conditioned air to all rooms with the smallest equipment necessary to do the job.

Tankless Water Heaters

Compact, tankless water heaters provide warm water on demand at remote points of use throughout the home. Energy savings occur by the elimination of standby losses—energy lost from hot water sitting in the tank. Since water heating accounts for approximately 14 percent of the average U.S. household budget, this can be significant.

Tankless water heaters can be used either as supplemental heat, such as a booster to a solar hot water system, or to meet all hot water needs. They employ an electric, gas, or propane heating device that is activated by the flow of water. Large units intended for whole-house usage are usually located in a central spot in the home. In point-of-use applications, the water heater is usually located near an outlet. With either one, once activated, the heater provides a constant supply of hot water. The maximum flow rate and temperature rise that the unit can deliver is determined by the heater’s capacity.

Electric tankless units will draw more instantaneous power than tank-type units—and if electric rates include a demand charge, they may be more expensive to operate. The electronics in tankless water heating systems may also require more maintenance than conventional tank units.

Lighting the Way

The use of compact fluorescent lighting has become more common today, and newer lamps have improved light quality and longevity. Compact fluorescent bulbs use approximately one-quarter of the energy for the same light output as incandescent bulbs. Though some compact fluorescents may still have performance issues, such as reduced light output after a period of years, their energy-related advantages outweigh this concern. Builders, remodelers, and homeowners should consider using these bulbs both inside and outside the home. Other advanced lighting technologies, such as light-emitting diodes (LED), are not yet commonly available for general lighting use, but are making their way into consumer products.

Tom Kenney is director of engineering services at the NAHB Research Center. To contact the NAHB Research Center, email toolbase@nahbrc.org.