ASHRAE Journal - May 2011 - 32

Desktop Computer
(W)

LCD Monitor
(W)

CRT Monitor
(W)

Notebook Computer
(W)

Active Wilkins-McGaffin (1994) Wilkins-Hosni (2000) Kawamoto (2001) Moorefield (2008) Hosni (2010) 56 55 55 79 69

Sleep 56 20 25 2 1

Active – – – 34 30

Sleep – – – 1 1

Active 60 55 85 71 –

Sleep 60 0 5 3 –

Active – – 15 31* 28

Sleep – – 3 2 1

* Referred to as idle mode in Moorefield’s study. Active mode was indicated as 75 W, which may have included battery charging.

Table 1: Office equipment loads over time. moto8 and Moorefield9 for some of the most common office equipment. Desktop computers show a trend toward increasing peak energy but the sleep mode has become much more effective over time. This increase in the desktop computer peak wattage has been offset by the lower power consumption of LCD monitors. Using a notebook computer, instead of a desktop computer and an LCD monitor, results in a fairly significant reduction in peak wattage. It is clear that notebook computer’s popularity, flexibility, cost, and computational power have expanded their use and is expected to result in a meaningful reduction in plug load power levels. In the work by Moorefield, four modes of operation for computers and monitors were considered that included active, idle, sleep, and standby. These categories were determined by statistical grouping of the measured data and not based on internal operation of the equipment. Power consumption during what was referred to as sleep and standby was generally low and corresponded to the findings for what was called either idle or sleep mode by Hosni in RP-1482. For the purposes of load calculation discussions, it seems that consideration of only two modes, active and sleep is appropriate. Moorefield also reported periods of notebook computer operation with power levels as high as 75 W, but no explanation for what contributed to this was provided. Notebook computers may introduce a secondary peak condition that could occur when the internal battery is charging while at the same time the notebook is in full use. This condition may increase the power consumption by as much as 10 W during the charging period according to informal measurements by Hosni. The data shown in Table 1 represent the peak for fully charged battery condition. Recognizing that computers and monitors represent the largest share of the plug loads in most conventional office buildings, the power reduction during idle operation will certainly have a significant impact on energy consumption and may be having an impact on the peak cooling load as well. The question to be answered in terms of peak air-conditioning load is how much of the equipment is in sleep mode at the time of peak air-conditioning load. To answer this, diversity factor must be considered.
90% 80% 70% 60% Diversity 50% 40% 30% 20% 10% 0% Sun.
12 p.m.

12 p.m.

Mon.

12 p.m.

Tues.

12 p.m.

Wed.

12 p.m.

Thu.

12 p.m.

Fri.

12 p.m.

Sat.

12 p.m.

Sun.

Figure 2: Desktop computer diversity.
70% 60% 50% Diversity 40% 30% 20% 10% 0% Sun.
12 p.m.

12 p.m.

Mon.

12 p.m.

Tues.

12 p.m.

Wed.

12 p.m.

Thu.

12 p.m.

Fri.

12 p.m.

Sat.

12 p.m.

Sun.

Figure 3: LCD monitor diversity. mation of diversity factor to be calculated. Energy use data were collected from groups of individual items of equipment and then these groups of data were averaged. Diversity is then the average measured energy divided by the peak measured energy. In this case, the peak measured represents the average of the peaks for all equipment of the given type that was in the study. Figures 2 and 3 represent detailed curves for desktop computers and monitors. A single week of data was chosen and presented that represents the higher end of usage. Table 2 represents a summary of this data. The diversity factor for notebook computers in Table 2 was not derived directly from measured data in the same way as was possible with desktop computers and monitors. For the purposes of the table and the
ashrae.org May 2011

Diversity Factors
Diversity factors were not presented in the work by Moorefield, but the data that were collected did allow for an approxi32 ASHRAE Journal



ASHRAE Journal - May 2011

Table of Contents for the Digital Edition of ASHRAE Journal - May 2011

ASHRAE Journal - May 2011
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Seismic Restraint
Plug Load Design Factors
Technology Award Case Studies:
State-of-Art School
Green School Lab
Eco-Friendly, Affordable, School
Building Sciences
Special Section
InfoCenter
Solar NZEB Project
Emerging Technologies
IAQ Applications
Washington Report
International Column
Products
People
Classified Advertising
Advertisers Index
ASHRAE Journal - May 2011 - Intro
ASHRAE Journal - May 2011 - ASHRAE Journal - May 2011
ASHRAE Journal - May 2011 - Cover2
ASHRAE Journal - May 2011 - 1
ASHRAE Journal - May 2011 - 2
ASHRAE Journal - May 2011 - Contents
ASHRAE Journal - May 2011 - Commentary
ASHRAE Journal - May 2011 - 5
ASHRAE Journal - May 2011 - Industry News
ASHRAE Journal - May 2011 - 7
ASHRAE Journal - May 2011 - 8
ASHRAE Journal - May 2011 - 9
ASHRAE Journal - May 2011 - 10
ASHRAE Journal - May 2011 - 11
ASHRAE Journal - May 2011 - 12
ASHRAE Journal - May 2011 - 13
ASHRAE Journal - May 2011 - Letters
ASHRAE Journal - May 2011 - 15
ASHRAE Journal - May 2011 - 16
ASHRAE Journal - May 2011 - 16a
ASHRAE Journal - May 2011 - 16b
ASHRAE Journal - May 2011 - 17
ASHRAE Journal - May 2011 - Meetings and Shows
ASHRAE Journal - May 2011 - 19
ASHRAE Journal - May 2011 - Seismic Restraint
ASHRAE Journal - May 2011 - 21
ASHRAE Journal - May 2011 - 22
ASHRAE Journal - May 2011 - 23
ASHRAE Journal - May 2011 - 24
ASHRAE Journal - May 2011 - 25
ASHRAE Journal - May 2011 - 26
ASHRAE Journal - May 2011 - 27
ASHRAE Journal - May 2011 - 28
ASHRAE Journal - May 2011 - 29
ASHRAE Journal - May 2011 - Plug Load Design Factors
ASHRAE Journal - May 2011 - 31
ASHRAE Journal - May 2011 - 32
ASHRAE Journal - May 2011 - 33
ASHRAE Journal - May 2011 - 34
ASHRAE Journal - May 2011 - 35
ASHRAE Journal - May 2011 - State-of-Art School
ASHRAE Journal - May 2011 - 37
ASHRAE Journal - May 2011 - 38
ASHRAE Journal - May 2011 - 39
ASHRAE Journal - May 2011 - 40
ASHRAE Journal - May 2011 - 41
ASHRAE Journal - May 2011 - 42
ASHRAE Journal - May 2011 - 43
ASHRAE Journal - May 2011 - Green School Lab
ASHRAE Journal - May 2011 - 45
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ASHRAE Journal - May 2011 - 47
ASHRAE Journal - May 2011 - 48
ASHRAE Journal - May 2011 - 49
ASHRAE Journal - May 2011 - 50
ASHRAE Journal - May 2011 - 51
ASHRAE Journal - May 2011 - Eco-Friendly, Affordable, School
ASHRAE Journal - May 2011 - 53
ASHRAE Journal - May 2011 - 54
ASHRAE Journal - May 2011 - 55
ASHRAE Journal - May 2011 - 56
ASHRAE Journal - May 2011 - 57
ASHRAE Journal - May 2011 - Building Sciences
ASHRAE Journal - May 2011 - 59
ASHRAE Journal - May 2011 - 60
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ASHRAE Journal - May 2011 - 62
ASHRAE Journal - May 2011 - 63
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ASHRAE Journal - May 2011 - 65
ASHRAE Journal - May 2011 - 66
ASHRAE Journal - May 2011 - 67
ASHRAE Journal - May 2011 - InfoCenter
ASHRAE Journal - May 2011 - 69
ASHRAE Journal - May 2011 - 70
ASHRAE Journal - May 2011 - 71
ASHRAE Journal - May 2011 - 72
ASHRAE Journal - May 2011 - 73
ASHRAE Journal - May 2011 - 74
ASHRAE Journal - May 2011 - 75
ASHRAE Journal - May 2011 - 76
ASHRAE Journal - May 2011 - 77
ASHRAE Journal - May 2011 - Solar NZEB Project
ASHRAE Journal - May 2011 - 79
ASHRAE Journal - May 2011 - 80
ASHRAE Journal - May 2011 - 81
ASHRAE Journal - May 2011 - 82
ASHRAE Journal - May 2011 - 83
ASHRAE Journal - May 2011 - 84
ASHRAE Journal - May 2011 - 85
ASHRAE Journal - May 2011 - 86
ASHRAE Journal - May 2011 - 87
ASHRAE Journal - May 2011 - 88
ASHRAE Journal - May 2011 - 89
ASHRAE Journal - May 2011 - Emerging Technologies
ASHRAE Journal - May 2011 - 91
ASHRAE Journal - May 2011 - 92
ASHRAE Journal - May 2011 - 93
ASHRAE Journal - May 2011 - 94
ASHRAE Journal - May 2011 - 95
ASHRAE Journal - May 2011 - IAQ Applications
ASHRAE Journal - May 2011 - 97
ASHRAE Journal - May 2011 - 98
ASHRAE Journal - May 2011 - 99
ASHRAE Journal - May 2011 - 100
ASHRAE Journal - May 2011 - 101
ASHRAE Journal - May 2011 - Washington Report
ASHRAE Journal - May 2011 - 103
ASHRAE Journal - May 2011 - International Column
ASHRAE Journal - May 2011 - 105
ASHRAE Journal - May 2011 - 106
ASHRAE Journal - May 2011 - Products
ASHRAE Journal - May 2011 - 108
ASHRAE Journal - May 2011 - People
ASHRAE Journal - May 2011 - Classified Advertising
ASHRAE Journal - May 2011 - 111
ASHRAE Journal - May 2011 - Advertisers Index
ASHRAE Journal - May 2011 - Cover3
ASHRAE Journal - May 2011 - Cover4
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