ASHRAE Journal - August 2008 - (Page 42)

Lighting 0.6 3 Power Density, W/ft2 Office Equipment Solar Heat Gain Coefficient 0.45 Atlanta Albuquerque, N.M. 2 0.3 Boston Fort Worth, Texas Miami 1 0.15 Minneapolis Washington 0 1970 1975 1980 1985 1990 1995 2000 0 1970 1980 1990 2000 Figure 4: 90.1 maximum solar heat gain coefficient over time. Figure 5: 90.1 maximum lighting power density (for office space) and estimated office equipment power density. Required Outdoor Ventilation Air, cfm/ft2 Offices 0.140 0.140 0.140 0.035 0.150 Conference Room 1.00 1.00 1.00 0.30 1.50 Reception/Lobby 0.90 0.90 0.90 0.15 0.30 Weighted Average* 0.292 0.292 0.292 0.073 0.300 some of the reduction of allowed lighting power use. Estimated office equipment power densities are also plotted in Figure 5. As is the case with envelope requirements, the Standard 90 requirements to reduce internal loads addresses sensible load only. Analysis of a Typical Medium-Size Office Building Version of Standard 62 62-2001 62-1999 62-1989 62-1981 62-1973 A hypothetical medium-size (~50,000 ft 2 [~4645 m 2]) office building was Table 1: Weighted average ventilation per floor space required for office building. designed, as shown in Figure 6, to evaluSE Isometric Plan ate the total impact of these changes in U-values, lighting power density, and 50 m ventilation on the total building sensible and latent cooling loads. North 25 m As indicated in Figure 6, the model No Windows Zone rth Zo office building has two stories with a ne 50 m So square footprint, 50 m (164 ft) on a side. Zo uth ne The building has four space conditioning South zones, the north and south halves of each Zone floor. The breakdown of floor space of the building was assumed to be 80% offices, 10% conference rooms, and 10% recep- Figure 6: Model office building configuration. tion/lobbies. Table 1 summarizes the calculation of the average ventilation per square foot required within the U.S. Lighting and office equipment power densities by each revision of Standard 62. Note that ventilation airflow are taken from Figure 5. rates were reduced in the 1980s in response to the energy crisis When these changes are accounted for in the cooling load of that era, but were then restored to previous levels (approxi- model of a typical office building (using the DOE EnergyPlus mately) when cases of sick building syndrome and ongoing building energy simulation software), the increase in humidity IAQ research recognized the need for increased amounts of loading (reduction in the SHR) since the 1980s is dramatic, as ventilation airflow. illustrated in Figures 7 to 9, which plots this building cooling load SHR trend for seven cities, at three cooling load design Evolution of Envelope and Lighting Specifications Over Time conditions. These three figures give the SHR at three design Table 2 summarizes the input values of the envelope speci- points—a high outdoor temperature/high coincident wet-bulb fications for the load model calculations in each of the seven temperature day, a high outdoor humidity (high latent load) cities that were chosen to represent different climate zones day, and a high humidity shoulder day. These three design 42 ASHRAE Journal ashrae.org August 2008 * Based on 80% offices, 10% conference rooms and 10% reception/lobbies. http://ashrae.org

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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