ASHRAE Journal - September 2010 - 70

of 4 ft (1.2 m). The results indicate that Interior Perimeter the 4 ft (1.2 m) thermostat should be set 120 120 to 76°F (24.4°C) to ensure an average oc76.4 cupied zone temperature of 75°F (24°C) 76.9 100 100 in the more heavily stratified interior zone. Detailed design tool results from the previous example are listed for Case 1 80 80 in Table 2, as well as several additional cases, which are discussed next. 76.3 75.6 60 60 • Case 1 Demonstrates the impact of thermal decay in a series plenum. 76.0 75.2 The high diffuser supply air tem40 40 perature in the perimeter results ÑToz,avg, 75.0 in increased airflow and reduced ÑToz,avg, 75.0 stratification. For purposes of de20 20 termining the minimum number of diffusers for peak design loads, the 72.9 74.4 0 0 usual approach is to select enough diffusers so that each diffuser is 66.5 69.8 63.0 66.5 operating at or just below its design –20 –20 54 59 64 69 74 79 84 54 59 64 69 74 79 84 airflow rate. However, in the interior zone with 20 occupants, a common, Temperature (°F) Temperature (°F) and preferred, design approach is to assign at least one swirl diffuser Figure 5: Predicted temperature profiles for interior & south perimeter zones for example in Table 1. per person; i.e., per workstation. In Case 1 this results in only 64 cfm (30 L/s) (compared to the potential advantage of developing perimeter diffusers design airflow of 80 cfm [37.8 L/s]) for each swirl diffuser, having reduced vertical throw. thereby contributing to increased stratification. • Case 5 Demonstrates the impact of a common plenum as• Case 2 For this and other cases listed in Table 2, the design sumption. The common plenum assumes that the incoming conditions are the same as those listed in Table 1, except air is mixed equally in the interior and perimeter portions for changes in plenum configuration, diffuser type and of the plenum, and delivers the same average diffuser number, plenum inlet temperature, and average occupied discharge temperature in both zones. This configuration zone temperature setpoint, as indicated. Identical to Case may be a better model for designs with higher plenum inlet 1, except the number of swirl diffusers in the interior zone velocities that create greater mixing. was reduced to bring the airflow per swirl diffuser up to its • Cases 6 and 7 A comparison of results for these two cases design value (77 cfm [36.3 L/s]). This has only a small impact demonstrates the potential error in design airflow calculaof slightly reducing stratification and slightly increasing the tions if plenum thermal decay is ignored and each plenum zone airflow rate. zone is defined independently. In Case 6, the plenum inlet • Case 3 Demonstrates the impact of using reverse series temperatures were reduced until the calculated diffuser plenum configuration. The reverse series plenum delivers supply air temperature for both zones was 67°F (19.4°C). cooler air to the perimeter, resulting in a reduction in airflow This results in an extremely low airflow rate through the of nearly 50%, with increased stratification. Due to the interior plenum (normally, the series plenum allows the higher plenum temperature and higher airflow rate in the total airflow serving both zones to pass through the interior interior, the number of swirl diffusers must be increased to portion) and requires the plenum inlet temperature to be 40. It is likely that this configuration with warmer interior set to 54.9°F (12.7°C). The results for Case 7 show what zone diffuser discharge temperatures will also provide would happen if a designer assumed that 67°F (19.4°C) air comfort improvements in the interior zone, which can leaving the air handler is the same thing as 67°F (19.4°C) sometimes experience overcooling since there is no means air entering the space through the diffusers. Due to thermal of providing heat (outside of internal loads). decay, the predicted total airflow rate for Case 7 is nearly • Case 4 Identical to Case 3, except the number of linear bar double that for Case 6. grilles in the perimeter was increased (thereby reducing • Case 8 Identical to Case 1, except the average occupied vertical throw) until the maximum vertical temperature zone temperature setpoint was increased by 2°F (1.1°C) to stratification limit was just met (5.2°F [3°C]). This pro77°F (25°C), which still falls within the acceptable range duced the lowest combined total airflow for both zones for operative temperature specified by ASHRAE Standard for all cases in Table 2, except Case 6, and demonstrates 55-2010 for summer clothing. The higher setpoint results
70	 ASHRAE	Journal	
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ASHRAE Journal - September 2010

Table of Contents for the Digital Edition of ASHRAE Journal - September 2010

ASHRAE Journal - September 2010
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Doored Display Cases: They Save Energy, Don't Lose Sales
Energy Storage: Providing for a Low-Carbon Future
Specifying Insulation for Air Terminal Units
Stem Cell Lab
Horticultural Lab
Fume Hood Retrofit
Cooling Load Design Tool for UFAD
AHR Expo Mexico 2010 Show Guide
Emerging Technologies
Building Sciences
Solar Applications
Operations & Maintenance
Washington Report
People
Products
Classified Advertising
Advertisers Index
ASHRAE Journal - September 2010 - Intro
ASHRAE Journal - September 2010 - ASHRAE Journal - September 2010
ASHRAE Journal - September 2010 - Cover2
ASHRAE Journal - September 2010 - 1
ASHRAE Journal - September 2010 - 2
ASHRAE Journal - September 2010 - Contents
ASHRAE Journal - September 2010 - Commentary
ASHRAE Journal - September 2010 - 5
ASHRAE Journal - September 2010 - Industry News
ASHRAE Journal - September 2010 - 7
ASHRAE Journal - September 2010 - 8
ASHRAE Journal - September 2010 - 9
ASHRAE Journal - September 2010 - Letters
ASHRAE Journal - September 2010 - 11
ASHRAE Journal - September 2010 - 12
ASHRAE Journal - September 2010 - 13
ASHRAE Journal - September 2010 - 14
ASHRAE Journal - September 2010 - 15
ASHRAE Journal - September 2010 - Meetings and Shows
ASHRAE Journal - September 2010 - 17
ASHRAE Journal - September 2010 - Doored Display Cases: They Save Energy, Don't Lose Sales
ASHRAE Journal - September 2010 - 19
ASHRAE Journal - September 2010 - 20
ASHRAE Journal - September 2010 - 21
ASHRAE Journal - September 2010 - 22
ASHRAE Journal - September 2010 - 23
ASHRAE Journal - September 2010 - 24
ASHRAE Journal - September 2010 - 25
ASHRAE Journal - September 2010 - 26
ASHRAE Journal - September 2010 - 27
ASHRAE Journal - September 2010 - Energy Storage: Providing for a Low-Carbon Future
ASHRAE Journal - September 2010 - 29
ASHRAE Journal - September 2010 - 30
ASHRAE Journal - September 2010 - 31
ASHRAE Journal - September 2010 - 32
ASHRAE Journal - September 2010 - 33
ASHRAE Journal - September 2010 - 34
ASHRAE Journal - September 2010 - 35
ASHRAE Journal - September 2010 - 36
ASHRAE Journal - September 2010 - 37
ASHRAE Journal - September 2010 - Specifying Insulation for Air Terminal Units
ASHRAE Journal - September 2010 - 39
ASHRAE Journal - September 2010 - 40
ASHRAE Journal - September 2010 - 41
ASHRAE Journal - September 2010 - 42
ASHRAE Journal - September 2010 - 43
ASHRAE Journal - September 2010 - Stem Cell Lab
ASHRAE Journal - September 2010 - 45
ASHRAE Journal - September 2010 - 46
ASHRAE Journal - September 2010 - 47
ASHRAE Journal - September 2010 - 48
ASHRAE Journal - September 2010 - 49
ASHRAE Journal - September 2010 - Horticultural Lab
ASHRAE Journal - September 2010 - 51
ASHRAE Journal - September 2010 - 52
ASHRAE Journal - September 2010 - 53
ASHRAE Journal - September 2010 - 54
ASHRAE Journal - September 2010 - 55
ASHRAE Journal - September 2010 - Fume Hood Retrofit
ASHRAE Journal - September 2010 - 57
ASHRAE Journal - September 2010 - 58
ASHRAE Journal - September 2010 - 59
ASHRAE Journal - September 2010 - 60
ASHRAE Journal - September 2010 - 61
ASHRAE Journal - September 2010 - Cooling Load Design Tool for UFAD
ASHRAE Journal - September 2010 - 63
ASHRAE Journal - September 2010 - 64
ASHRAE Journal - September 2010 - 65
ASHRAE Journal - September 2010 - 66
ASHRAE Journal - September 2010 - 67
ASHRAE Journal - September 2010 - 68
ASHRAE Journal - September 2010 - 69
ASHRAE Journal - September 2010 - 70
ASHRAE Journal - September 2010 - 71
ASHRAE Journal - September 2010 - 72
ASHRAE Journal - September 2010 - AHR Expo Mexico 2010 Show Guide
ASHRAE Journal - September 2010 - S2
ASHRAE Journal - September 2010 - S3
ASHRAE Journal - September 2010 - S4
ASHRAE Journal - September 2010 - S5
ASHRAE Journal - September 2010 - S6
ASHRAE Journal - September 2010 - S7
ASHRAE Journal - September 2010 - S8
ASHRAE Journal - September 2010 - S9
ASHRAE Journal - September 2010 - S10
ASHRAE Journal - September 2010 - S11
ASHRAE Journal - September 2010 - S12
ASHRAE Journal - September 2010 - S13
ASHRAE Journal - September 2010 - S14
ASHRAE Journal - September 2010 - S15
ASHRAE Journal - September 2010 - S16
ASHRAE Journal - September 2010 - S17
ASHRAE Journal - September 2010 - S18
ASHRAE Journal - September 2010 - S19
ASHRAE Journal - September 2010 - S20
ASHRAE Journal - September 2010 - S21
ASHRAE Journal - September 2010 - S22
ASHRAE Journal - September 2010 - S23
ASHRAE Journal - September 2010 - S24
ASHRAE Journal - September 2010 - S25
ASHRAE Journal - September 2010 - S26
ASHRAE Journal - September 2010 - S27
ASHRAE Journal - September 2010 - S28
ASHRAE Journal - September 2010 - S29
ASHRAE Journal - September 2010 - S30
ASHRAE Journal - September 2010 - S31
ASHRAE Journal - September 2010 - S32
ASHRAE Journal - September 2010 - Emerging Technologies
ASHRAE Journal - September 2010 - 74
ASHRAE Journal - September 2010 - 75
ASHRAE Journal - September 2010 - 76
ASHRAE Journal - September 2010 - 77
ASHRAE Journal - September 2010 - Building Sciences
ASHRAE Journal - September 2010 - 79
ASHRAE Journal - September 2010 - 80
ASHRAE Journal - September 2010 - 81
ASHRAE Journal - September 2010 - 82
ASHRAE Journal - September 2010 - 83
ASHRAE Journal - September 2010 - 84
ASHRAE Journal - September 2010 - 85
ASHRAE Journal - September 2010 - 86
ASHRAE Journal - September 2010 - 87
ASHRAE Journal - September 2010 - Solar Applications
ASHRAE Journal - September 2010 - 89
ASHRAE Journal - September 2010 - 90
ASHRAE Journal - September 2010 - 91
ASHRAE Journal - September 2010 - Operations & Maintenance
ASHRAE Journal - September 2010 - 93
ASHRAE Journal - September 2010 - Washington Report
ASHRAE Journal - September 2010 - 95
ASHRAE Journal - September 2010 - People
ASHRAE Journal - September 2010 - Products
ASHRAE Journal - September 2010 - 98
ASHRAE Journal - September 2010 - 99
ASHRAE Journal - September 2010 - 100
ASHRAE Journal - September 2010 - 101
ASHRAE Journal - September 2010 - Classified Advertising
ASHRAE Journal - September 2010 - 103
ASHRAE Journal - September 2010 - Advertisers Index
ASHRAE Journal - September 2010 - Cover3
ASHRAE Journal - September 2010 - Cover4
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