Figure 1. The NightBreeze system is based on a simple principle. When the outside temperature has dropped sufficiently to cool the home, a damper opens to let in outside air, and a high-efficiency, electrically commutated blower motor introduces cool, filtered fresh air into the home.

The CEC's Public Interest Energy Research (PIER) program has been working to develop possible solutions, including the use of ventilation cooling to reduce compressor-cooling energy consumption. After several years of research by Davis Energy Group and other collaborators, the NightBreeze system was developed to integrate ventilation cooling with heating and air conditioning, as well as to provide fresh-air ventilation for maintaining indoor air quality (IAQ).

"It has become common practice for California home builders to install air conditioning equipment in all new homes, even in mild coastal climates where air conditioning is typically only needed a few days of the year," said Jerry Best of Advanced Energy Products (AEP), a new business venture for Davis Energy Group, lead investigator for the PIER project.

"Building simulation modeling has demonstrated that NightBreeze can significantly reduce cooling energy costs and peak load, and that it can reduce or completely eliminate the need for supplementary air conditioning in relatively dry climates with diurnal temperature swings of 30 degrees or more."

Project investigators have shown that careful attention to house design combined with ventilation cooling can eliminate the need for conventional air conditioning in six of California's 16 climate zones. Outside of California, NightBreeze could be considered an attractive cooling system alternative in such states as Colorado, Idaho, Oregon, Washington, Montana, Nevada, New Mexico, upstate New York, North Dakota, Washington, Wyoming and portions of Arizona.

AEP began offering a system that uses a variable-speed air handler early this year, and will introduce a product that operates with variable-speed furnaces before the end of this year. "The new product also integrates zone control, thereby offsetting the costs of separate fresh-air ventilation and zone control systems," said Best.

Simple But Effective

While open windows have been used for ventilation cooling for centuries, homeowners use windows less now because of their concerns about security, outdoor noise, dust, and pollen.

"When the outside temperature has dropped sufficiently to cool the home, the NightBreeze system's controller automatically opens a damper and starts the high-efficiency, electrically commutated (EC) blower motor to introduce cool, filtered fresh air into the home," explained Best. "What is unique about the system is that it adjusts both the ventilation rate and the temperature to which the house is cooled, depending on current weather conditions."

The system is compatible with conventional cooling systems, and the furnace or air handler is designed to provide high-efficiency heating. According to Best, IAQ is enhanced in summer by the nighttime ventilation, and in winter the system is designed to deliver a measured amount of outside air to precisely meet ASHRAE 62.2 requirements.

For high-volume production housing developments, the system's incremental costs are estimated at $1,500, said Best. At this price, he said monthly energy cost savings would exceed the increase in the monthly mortgage payment, resulting in a positive net cash flow for the buyer.

The PIER-funded Alternatives to Compressor Cooling project that developed the NightBreeze system included researchers from the University of California and Lawrence Berkeley National Laboratory, as well as industry partners RCS/ZTECH and EnviroMaster International. Pacific Gas & Electric Company's Technical and Environmental Services Laboratory provided testing of early prototypes. Davis Energy Group has led the development effort since 1999.

Figure 2. Simulated NightBreeze energy and demand reductions. Building simulations were run in six California climate zones to compare the energy demand requirements of a home compliant with the basic California energy code (Title 24) to those of the same home using the NightBreeze ventilation cooling system. In each of the simulated climate zones, which represented a range of climates and geographic locations, the NightBreeze system provided significant energy demand reductions.

Features And Benefits

On a typical 95 degree summer day, the Livermore house used about 80 percent less cooling energy than a "control" house of identical floor plan located in the same development. Moreover, all of the cooling energy consumed by the NightBreeze system occurred during off-peak hours, so the system contributed significant demand reduction as well, said Best.

The researchers used these monitoring results to calibrate a building simulation model, which predicts significant energy and demand savings in most of California's 16 climate zones. (See Figure 2.)

"The combination of improved house design and ventilation cooling obviated the need for conventional air conditioning at the Watsonville house," said Best. "At the Livermore house, the cooling load was reduced to the extent that only two tons of cooling capacity was needed to maintain comfort, raising the sizing ratio to over 1,500 square feet per ton."

The system employs a thermostat with a graphical interface that provides feedback on the consequences of user settings, even telling the homeowner if the current settings are likely to result in air conditioner operation on the following day. The single thermostat also integrates heating, cooling, and ventilation functions, and provides for adjustment of blower cfm, eliminating the need for motor tap settings, said Best.

"The control interface provides information to the user about optimal comfort settings and adjusts ventilation rates to minimize fan energy use, thereby avoiding overcooling, and minimizing air conditioner operation," explained Best.

The air handler-based system uses an electrically commutated motor (ECM) that operates at high efficiency throughout its speed range. According to Best, this is designed to allow the unit to deliver quiet, variable-speed heating, cooling, and ventilation "with fan energy consumption that is less than half that of typical furnaces." The furnace-based version couples to furnaces that incorporate the same ECM type.

"Ventilation cooling using the NightBreeze system is one of the many solutions we need to improve residential building performance in hot, dry climates, and is being used in the Department of Energy's Building America program to meet the aggressive goals set forth by that program," concluded Best.

The California Energy Commission reports documenting this project may be downloaded at www.energy.ca.gov/pier/final_project_reports/500-04-009.html. A paper on the project was also presented at the 2005 Denver ASHRAE conference.

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