Based on actual utility usage:

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  Kilowatt-hour use has been reduced an average of 45.4 percent (Figure 1). Monthly electrical demand essentially has flat-lined.

FIGURE 1. Electricity use at Wausau West High School.

• Despite the fact the building essentially is uninsulated and was converted to deliver 100-percent outdoor air when occupied, overall natural-gas use has been reduced an average of 59.8 percent over the last nine years (Figure 2).

FIGURE 2. Natural-gas use at Wausau West High School.

• Total energy use has dropped an average of 60.5 percent from the baseline year and been improving steadily (Figure 3). This can be attributed to the school staff learning to better use the technology.

FIGURE 3. Total energy use at Wausau West High School.

• Annual energy savings peaked at $420,349 during the 2005-2006 school year and were $373,040 for the 2007-2008 school year (Figure 4). Actual energy savings to date total $2,547,761.

FIGURE 4. Actual vs. equivalent baseline costs for Wausau West High School.

• Annual cost benefits of the modifications ranged from 60 cents per square foot (2001) to $1.34 per square foot (2005) from 1999 to 2007 (Figure 5).

FIGURE 5. Utility-cost savings of Wausau West High School.

Pre-modification air-quality testing was performed by an independent agency hired by Wausau School District. Post-modification air-quality testing was performed by the State of Wisconsin Division of Health. Those tests demonstrated that typical-classroom carbon-dioxide levels were, on average, reduced to the 700-to-750-ppm level (Table 3).

TABLE 3. Carbon-dioxide concentration, parts per million.

During the summer of 2000, lighting was upgraded from T12 lamps and magnetic ballasts to T8 lamps and electronic ballasts. After a 50,000-sq-ft addition was completed in 2001, no apparent increase in energy use was observed, and the new boiler plant, reduced 60 percent in size, still was functionally 40-percent oversized.

RECOGNITION RECEIVED

In 2000, the DOE recognized Wausau West High School for the performance of its HVAC systems, citing the facility as “an excellent example of how to achieve energy savings while improving IAQ.” The DOE requested permission from the engineer to submit the strategy to the International Energy Agency (IEA) Energy Conservation in Buildings and Community Systems (ECBCS) program for the “Annex 36: Retrofitting of Educational Buildings” project (www.annex36.com).

In 2002, Wausau West High School was featured in the DOE's Energy Smart School calendar.

In June 2008, following a visit by then-American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) President Kent W. Peterson, PE, Wausau School District was featured on ASHRAE's home page for its energy-reduction achievements.

SUMMARY

The Regenerative Dual Duct System disproves several beliefs on which the HVAC industry is built:

• Recirculation of air is necessary for economical operation.

• High performance always increases first costs.

• Evaporative processes are high maintenance and have little merit outside of arid environments.

In addition to being highly efficient, the Regenerative Dual Duct System is flexible and dynamic in operation. This allows it to be relatively small in size, meeting the needs of high-density-occupancy and ventilation-dominant applications, improving air quality and thermal performance.

NOTE

1. “Regenerative Dual Duct System” is a registered trademark and service mark of Lentz Engineering Associates Inc.

For past HPAC Engineering feature articles, visit www.hpac.com.

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The president of Lentz Engineering Associates Inc. (www.lentzengineering.com) and a member of HPAC Engineering's Editorial Advisory Board, Mark S. Lentz, PE, is nationally recognized for having successfully developed, tested, and proven several advanced HVAC-system strategies designed to exceed the performance requirements of ANSI/ASHRAE/IESNA Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings, while meeting or exceeding the requirements of ANSI/ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality. He is the recipient of numerous national engineering awards, including an American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Energy Award, an ASHRAE Symposium Paper of the Year Award, and an ASHRAE Distinguished Service Award.

Regenerative Dual Duct

The Regenerative Dual Duct System substantially reduces inefficiency associated with the provision of ventilation. Air-to-air energy-recovery and evaporative processes are employed to amplify the recoverability of both heating and cooling potential, while the combination of direct and indirect evaporative cooling effectively eliminates the need for refrigeration for much of the cooling season.

Based on full-range, multistage air-to-air energy recovery, the strategy strips energy for reheat from exhaust air, depressing both dry- and wet-bulb temperature and amplifying the recoverability of cooling energy. Adiabatic evaporation is the primary cooling process, making mechanical cooling the process of last resort. In hot and humid weather, the use of building exhaust air instead of outdoor air amplifies the effectiveness of the indirect-evaporative precooling process by 200 to 250 percent. During heating season, energy-recovery effectiveness is a controlled parameter, with performance as high as 97 percent documented through submetering in prototype installations.

The Regenerative Dual Duct System is configured to minimize the number of system elements and parasitic fan energy, maximize system turndown, and effectively manage ventilation to the individual-room level. One-hundred-percent outdoor air is conditioned and distributed in a manner allowing both ventilation and thermal needs to be met. The volumetric flow of air delivered to a space is measured and actively controlled.

To learn more about the Regenerative Dual Duct System, visit www.lentzengineering.com.

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