ASHRAE Journal - August 2008 - (Page 45)

Temperature for Climate Locations, °F Design Day Cooling Design Day Design Temperatures Dry Bulb Dew Point Wet Bulb Dry Bulb Dew Point Wet Bulb Atlanta 93 68 75 88 73 77 2,991 5,038 Albuquerque, N.M. 96 26 60 83 60 68 4,425 3,908 Boston 91 65 73 87 70 75 5,641 2,897 Fort Worth, Texas 100 64 75 92 74 79 2,304 6,557 Miami 91 72 77 87 78 80 200 9,474 Minneapolis 91 65 73 88 71 76 7,981 2,680 Washington 95 68 76 89 76 79 4,707 3,709 Latent Design Day HDD 65 CDD 50 Table 3: Design conditions. each component and dividing the combined sensible capacity by the combined total capacity. The latent and sensible cooling provided by the enthalpy exchanger varies with outdoor conditions; as the outdoor humidity increases, so does the latent capacity of enthalpy recovery. In this way the SHR of enthalpy recovery adjusts automatically to changing outdoor conditions. This characteristic allows for the introduction of additional outside air without negatively impacting the SHR balance. Figure 10 compares the SHR of the building load (from the examples in Figures 7 through 9) with the combined SHR of a unitary air conditioner with an enthalpy recovery exchanger. (The modeled SHR of the unitary air conditioner alone, as indicated by the dotted line, is typical of commercially available products, while the latent and sensible effectiveness of the ERV are both modeled at 70%). The figures show a close match of SHR across a range of humid weather cooling conditions, leading to stable humidity levels in the indoor space. Conclusion 0.8 0.7 Sensible Heat Ratio 0.6 0.5 0.4 0.3 0.2 0.1 0 SHR of Unitary Building Cooling Load SHR Combined SHR of Unitary and ERV Sensible Latent Shoulder Sensible Latent Shoulder Design Design Design Design Miami Boston Figure 10: Comparison of the building SHR with the combined unitary + ERV SHR. 3. Shirey, D.B. 2003. “Understanding the Dehumidification Performance of Air-Conditioning Equipment at Part-Load: Test Results.” Seminar 40 at 2003 ASHRAE Annual Meeting. 4. ARI. 2003 Guideline for Calculating the Efficiency of Energy Recovery Ventilation and its Effect on Efficiency and Sizing of Building HVAC Systems. Arlington, Va: Air Conditioning and Refrigeration Institute. The evolution of ASHRAE standards and building technology over the past 30 years has resulted in a mismatch between the SHR of the typical unitary air conditioner and that of the typical commercial building load. The resulting loss of indoor humidity control can cause structural, comfort, and health problems. Enthalpy recovery ventilation systems can address these issues by allowing standard unitary packaged cooling equipment to closely match building SHR, while conserving energy and reducing peak demand. References 1. Amrane, K., G. Hourahan, and G. Potts. 2003. “Latent performance of unitary equipment.” ASHRAE Journal 45(1):28 – 31. 2. Henderson, H.I. 2003. “Understanding the Dehumidification Performance of Air Conditioning Equipment at Part-Load Conditions: Background and Theory.” Seminar 40 at 2003 ASHRAE Annual Meeting. August 2008 www.info.hotims.com/16017-42 ASHRAE Journal 45 http://www.wrightsoft.com http://www.wrightsoft.com http://www.info.hotims.com/16017-42

Table of Contents Feed for the Digital Edition of ASHRAE Journal - August 2008

ASHRAE Journal - August 2008 Contents Commentary Industry News Letters Meetings and Shows Maintain to Sustain—Delivering ASHRAE’s Sustainability Promise Ultraviolet Germicidal Irradiation: Current Best Practices Improving Humidity Control With Energy Recovery Ventilation Single- or Two-Stage Compression Data Center Cooling: Using Wet-Bulb Economizers Building Sciences InfoCenter Practical Pointers Products Emerging Technologies Washington Report People Special Products Classified Advertising Advertising Index

ASHRAE Journal - August 2008

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