Office Plug Load Metering Study on NTU Campus€¦ · The peak plug load intensities for this...

Office Plug Load Metering Study on NTU Campus

By

Adrian Sansoldi Lamano Wu Xiangyu

Zhou Jian Bharath Seshadri

Sustainable Building Technologies Group Energy Research Institute @ Nanyang Technological University (ERI@N)

17 June, 2015

I

Acknowledgement

This study was made possible because of the support and advice from Mr. Alfred Cheng Ho Ho and Mr. Roger Mun Kok Hin from NTU’s Office of Development and Facility Management (ODFM). The research team would like to thank Mr. Wong Poh Chwee, Mr. Chen Xing, Mr. Mohd.Adnan and Mr. Tan Ah Lim from ODFM for their technical support. The team also would like to thank Kim Yew Contractor and SFMI for their on-site assistance.

Note from ERI@N

NTU does not represent, warrant or guarantee the accuracy and completeness of information and/or opinions in this research report. Any use of information and/or opinions in this research report by you is at your sole discretion and NTU will have no responsibility and/or liability whatsoever to such use thereof. No part of this research report may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of NTU.

II

Executive Summary

The receptacle power demand in building spaces, simply referred to as ‘plug load’, contributes significantly to the total heat gain of a building. The heat gain (and the corresponding building cooling demand) directly impacts the cooling system design, sizing and costs. In commercial office spaces in Singapore, the cooling demand contribution from plug loads can be 15-20% of the total building’s cooling demand. Hence, it is necessary to accurately account for heat gain from plug loads while calculating the total cooling demand of the building and cooling system sizing.

A detailed plug load metering study was conducted in typical office spaces within the Nanyang Technological University (NTU) campus in Singapore to measure the plug load intensities over a 6 month period. 10 typical general offices and research offices with a total metered area of 7,554 m2 were selected for this exercise. 5-minute sampling interval data was collected for each office for 2 weeks.

The peak plug load intensities for this metering exercise range from 7.19 to 10.17 W/m2, and 11 W/m2 could be proposed to benchmark the peak plug load intensities for offices on NTU campus. This value is well below common design assumptions of peak plug load intensity of 16 W/m2 for general office areas recommended by Building and Construction Authority’s (BCA). However, proposed value complies well with ASHRAE standard (10.8 W/m2 for medium load density office) and other international standards.

However, it should be noted that this study is carried out on NTU campus, which is more representative for academic buildings. In the future, the research group plans to extend this metering study for more office spaces in Singapore based on parameters such as function, occupant density and space layout. Hopefully, this study could be a useful guide for building and energy engineers to calculate more accurate building cooling loads and cooling system design capacities. Furthermore, the data gathered during the study could be a good reference for BCA to reconsider the current value of recommended peak plug-load intensities for general offices.

III

Table of Content

Acknowledgement ......................................................................................................................................... I

Executive Summary ...................................................................................................................................... II

Table of Content .......................................................................................................................................... III

List of Abbreviations .................................................................................................................................... V

List of Figures .............................................................................................................................................. VI

List of Tables .............................................................................................................................................. VII

1. Introduction ........................................................................................................................................... 1

1.1. Background ................................................................................................................................... 1

1.2. Objective ....................................................................................................................................... 1

2. Review of Current Plug Load Standards ............................................................................................... 2

3. Methodology ......................................................................................................................................... 5

3.1. Site Assessment and Selection of Office Spaces in NTU ............................................................. 5

3.2. Plug Load Metering ...................................................................................................................... 8

3.2.1. Equipment ............................................................................................................................. 8

3.2.2. On-site Measurement ............................................................................................................ 8

3.3. Data Analysis ................................................................................................................................ 9

4. Results and Discussion ....................................................................................................................... 11

4.1. Data Results ................................................................................................................................ 11

4.1.1. Type 1: General Office ....................................................................................................... 11

4.1.1.1. ODFM Office .............................................................................................................. 11

4.1.1.2. Administration Building Office .................................................................................. 14

4.1.1.3. SPMS CBC Office ...................................................................................................... 18

4.1.1.4. NSS Office .................................................................................................................. 21

4.1.1.5. Summary ..................................................................................................................... 24

4.1.2. Type 2: Research Office ..................................................................................................... 25

4.1.2.1. CTO 06-04 .................................................................................................................. 25

4.1.2.2. EOS block A office ..................................................................................................... 28

4.1.2.3. EOS block B-C office ................................................................................................. 32

4.1.2.4. CTO 06-09 .................................................................................................................. 35

IV

4.1.2.5. CTO 06-11 .................................................................................................................. 38

4.1.2.6. IMI Research Office .................................................................................................... 41

4.1.2.7. Summary ..................................................................................................................... 44

4.2. Office Plug Load Intensities Benchmarking ............................................................................... 45

5. Conclusion .......................................................................................................................................... 46

References ................................................................................................................................................... 47

Appendix I .................................................................................................................................................. 48

Appendix II ................................................................................................................................................. 54

V

List of Abbreviations

ACMV: Air Conditioning and Mechanical Ventilation

ASHRAE: American Society of Heating, Refrigerating, and Air-Conditioning Engineers

BCA: Building and Construction Authority

CBC: Chemical Block

CI: Confidence Interval

CIBSE: Chartered Institution of Building Services Engineers

CTO: Clean Tech One

DB: Dash-board

ECG: Energy Consumption Guide

EOS: Earth Observatory of Singapore

HVAC: Heating, Ventilating and Air Conditioning

IMI: Institute of Media Innovation

IT: Information Technology

NREL: National Renewable Energy Laboratory

NSS: NTU Shared Services

NTU: Nanyang Technological University

ODFM: Office of Development and Facilities Management

PC: Personal Computer

SPMS: School of Physical and Mathematical Sciences

VI

List of Figures

Figure 1. Related studies on plug load intensities for offices. ..................................................................... 4

Figure 2. Three-Phase Power meters ........................................................................................................... 8

Figure 3. On-site Measurement .................................................................................................................... 9

Figure 4. ODFM OfficePlug Load Profile 1st Week .................................................................................... 12

Figure 5. ODFM OfficePlug Load Profile 2nd Week................................................................................... 12

Figure 6. Typical Weekday ODFM OfficePlug Load Profile ....................................................................... 13

Figure 7. Typical Weekend ODFM OfficePlug Load Profile ....................................................................... 14

Figure 8. Admin OfficePlug Load Profile 1st-Week ................................................................................... 15

Figure 9. Admin Office Plug Load Profile 2nd-Week ................................................................................. 16

Figure 10. Typical Weekday Admin OfficePlug Load Profile .................................................................... 17

Figure 11. Typical Weekend Admin Office Load Profile ........................................................................... 17

Figure 12. SPMS CBC OfficePlug Load Profile 1st-Week ........................................................................... 19

Figure 13. SPMS CBC OfficePlug Load Profile2nd-Week .......................................................................... 19

Figure 14. Typical Weekday SPMS CBC OfficePlug Load Profile .............................................................. 20

Figure 15. Typical Weekend SPMS CBC OfficePlug Load Profile .............................................................. 21

Figure 16. NSS OfficePlug Load Profile1st-Week ..................................................................................... 22

Figure 17. NSS OfficePlug Load Profile2nd-Week ..................................................................................... 22

Figure 18. Typical Weekday NSS Office Load Profile ................................................................................ 23

Figure 19. Typical Weekend NSS Office Load Profile ................................................................................ 23

Figure 20. General Office Plug Load Intensities. ....................................................................................... 24

Figure 21. CTO 06-04 Plug Load Profile 1st Week .................................................................................... 26

Figure 22. CTO 06-04 Plug Load Profile 2nd Week ................................................................................... 26

Figure 23. Typical Weekday CTO 06-04 Plug Load Profile ....................................................................... 27

Figure 24. Typical Weekend CTO 06-04 Plug Load Profile .................................................................... 28

Figure 25. EOS block A office Plug Load Profile 1st Week ........................................................................ 29

Figure 26. EOS block A office Plug Load Profile 2nd Week ....................................................................... 30

Figure 27. Typical Weekday EOS block A office Plug Load Profile ........................................................... 31

Figure 28. Typical Weekend EOS block A office Plug Load Profile ........................................................... 31

Figure 29. EOS block B-C office Plug Load Profile1st Week ..................................................................... 33

Figure 30. EOS block B-C office Plug Load Profile 2nd Week ................................................................... 33

Figure 31. Typical Weekday EOS block B-C office Plug Load Profile ....................................................... 34

Figure 32. Typical Weekend EOS block B-C office Plug Load Profile ....................................................... 35

Figure 33. CTO 06-09Plug Load Profile 1st Week ...................................................................................... 36

Figure 34. CTO 06-09Plug Load Profile 2ndWeek ...................................................................................... 36


Figure 36. Typical Weekend CTO 06-09 Plug Load Profile ....................................................................... 38

Figure 37. CTO 06-11Plug Load Profile1stWeek ....................................................................................... 39

Figure 38. CTO 06-11PlugLoad Profile2ndWeek ........................................................................................ 39


Figure 40. Typical Weekend CTO 06-11 Plug Load Profile ....................................................................... 41

VII

Figure 41. IMI officePlugLoad Profile1stWeek ......................................................................................... 42

Figure 42. IMI officePlugLoad Profile2ndWeek .......................................................................................... 42

Figure 43. Typical Weekday IMI office Plug Load Profile ......................................................................... 43

Figure 44. Typical Weekend IMI office Plug Load Profile ......................................................................... 43

Figure 45. Research Office Plug Load Intensities ...................................................................................... 44

Figure 46. Peak Plug Load Intensities of Measured office vs Current Plug Load Standards ................... 45

List of Tables

Table 1. Range of Plug Load Factors for Various Types of Office ............................................................... 2

Table 2. Plug Load Factors for Offices ......................................................................................................... 3

Table 3. List of measured office spaces in NTU ........................................................................................... 5

Table 4.Summary of Office Equipment Inventories .................................................................................. 7

Table 5.Validated Data based on 99% CI .................................................................................................. 10

Table 6. Total Space Types in ODFM Office ............................................................................................... 11

Table 7.Total Space Types in Administration Building Office .................................................................. 15

Table 8. Total Space Types in SPMS CBC Office ......................................................................................... 18

Table 9.Total Space Types in CTO 06-04 ................................................................................................... 25

Table 10.Total Space Types in EOS block A office ..................................................................................... 29

Table 11.Total Space Types in EOS block B-C office ................................................................................. 32

1

1. Introduction

1.1. Background Plug loads are defined as building electrical loads that are plugged into electrical system of a building. Electrical power demand from Desktop computers, notebooks, printers, scanners, fax machines and kitchen/pantry appliances are categorized as plug loads. Office buildings are likely to have high cooling demands because of the impact of plug loads. In an air conditioned office, plug loads can take 50% more power to remove heat that the equipment generates than that used to run the equipment itself (CIBSE Guide F, 1998). The cooling demand contribution from plug loads can be 15-20% of the total building’s cooling demand (P. Komor, 1997). Hence, it is important to accurately predict the heat gain and corresponding cooling demand from plug loads in order to improve the energy efficiency of a building.

Plug loads contribute significantly to the total heat gain of a building which directly impacts the cooling system design, sizing and costs. Plug loads are often over-estimated at the design stage, and this has led to oversized or unnecessary air conditioning (Sheppy et al, 2014). Accordingly it could directly impact on cooling equipment sizing and investment costs that furthermore lead to higher running costs. The common practice of over-sizing building services plant (and air-conditioning systems) can lead to reduced energy efficiency, increased emissions, and higher capital and running costs (CIBSE Guide A, 1999). However, with accurate estimation of plug load (and accurate prediction of internal heat gains), cooling plants cycles less frequently, indoor temperature keep constant and humidity is under better control. With rightsizing of chillers the whole building energy consumption can be reduced by 3% to 4% (Thomas et al, 2007).

Therefore, it is essential to benchmark plug load to avoid arbitrary or incorrect inputs used in energy building analysis (Srinivasan et al, 2011). With more accurate benchmarking data, it would enable rightsizing and design of HVAC systems, which lead to more energy efficient electrical and HVAC systems while saving the upfront capital costs (Sheppy et al, 2014).

1.2. Objective The main objective of this study is to investigate the actual plug load power use in existing offices on NTU campus and to benchmark peak plug load intensities (W/m2) for research offices and general offices.

The team hopes that the results and methodology of this study could be a useful guide to conduct similar metering study for other spaces in Singapore, and the results could serve as a good reference for building and simulation engineers to use to accurately calculate the cooling load and right size cooling equipment.

2

2. Review of Current Plug Load Standards

In recent years, there has been several studies focus on office plug load measurement and benchmarking. This section summarizes the key findings of these studies and related standards. Energy Consumption Guide 19 (ECG 19), a British standard, indicated that typical and good practice benchmarks for plug load intensities in office buildings is ranging from 10 to 18 W/m2. Particularly for air conditioned standard office, the good practice and typical practice is 14 W/m2 and 16 W/m2 respectively. For air conditioned prestige office (with server room and/or large kitchen), the good practice and typical practice is 15 W/m2 and 18 W/m2 respectively (ECG 19, 2000). In 2000, Wilkins and McGaffin performed a measurement in 25,550 m2 of fully occupied office space in five buildings in the US. They classified 4 different office types with a subjective description of the type of office space, as shown in Table 1. The results show that the actual heat gain per unit area ranging from 4.75 W/m2 to 11.34 W/m2 with an average of 8.75 W/m2. With the peak load factor of 11.66 W/m2, it is correspondent with medium load density that likely will be appropriate for most standard office spaces. The results also indicate that the plug load intensity can be set lower than 10.8 W/m2. In extreme cases for denser office and without diversity the plug load intensity can be set at 21.5 W/m2. Medium/heavy or heavy load densities may be encountered but can be considered extremely conservative estimates even for densely populated and highly automated spaces (Wilkins and Hosni, 2000).

Table 1. Range of Plug Load Factors for Various Types of Office

Load Density of Office

Load factor

(W/m2)

Description

Light 5.4 Assumes 15.5 m2/ workstation (6.5 workstations per 100 m2) with computer and monitor at each plus printer and fax. Computer, monitor and fax diversity 0.67, printer diversity 0.33.

Medium 10.8 Assumes 11.6 m2/ workstation (8.5 workstations per 100 m2) with computer and monitor at each plus printer and fax. Computer, monitor and fax diversity 0.75, printer diversity 0.50.

Medium/Heavy 16.1 Assumes 9.3 m2/ workstation (11 workstations per 100 m2) with computer and monitor at each plus printer and fax. Computer and monitor diversity 0.75, printer and fax diversity 0.50.

Heavy 21.5 Assumes 7.8 m2/ workstation (13 workstations per 100 m2) with computer and monitor at each plus printer and fax. Computer and monitor diversity 1.0, printer and fax diversity 0.50.

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ASHRAE standard indicated that a medium density office would have a plug load intensities of 10.8 W/m2. The values are correspondent with the study done by Wilkins and Hosni for medium load density office spaces. This standard has been widely used in the industry since the mid-1990s (ASHRAE, 2009). Metzger conducted a detailed study of an office cubicle with area of 74 m2. The ASHRAE equipment schedule was used in this study to estimate annual energy consumption and average usage profiles. The study shows that the plug load intensity was on the average of 9.72 W/m2 with diversity factors taken into account (Metzger et al, 2011). In 2011, Wilkins conducted an update study on plug load factors for offices. They indicated that peak plug load intensities can be as low as 2.70 W/m2, because of advanced technology in energy efficiency and requirements in electronic office equipment with typical diversity factors (Wilkins and Hosni 2011). The study shows that plug load factors range from 2.70 W/m2 to 21.60 W/m2 with a subjective description of the equipment being used in an office space, as shown in Table 2.

Table 2. Plug Load Factors for Offices

Type of Use Load

Factor (W/m2)

Description

100% Notebook – Light 2.70 15.5 m2/workstation, All Notebook Use, 1 Printer per 10, Speakers and Misc.

100% Notebook – Medium 3.56 11.6 m2/workstation, All Notebook Use, 1 Printer per 10, Speakers and Misc.

50% Notebook – Light 4.32 15.5 m2/workstation, 50% Notebook/50% Desktop, 1 Printer per 10, Speakers and Misc.

50% Notebook – Medium 5.40 11.6 m2/workstation, 50% Notebook/50% Desktop, 1 Printer per 10, Speakers and Misc.

100% Desktop – Light 6.48 15.5 m2/workstation, All Desktop Use, 1 Printer per 10, Speakers and Misc.

100% Desktop – Medium 8.64 11.6 m2/workstation, All Desktop Use, 1 Printer per 10, Speakers and Misc.

100% Desktop – 2 Monitors 10.80 11.6 m2/workstation, All Desktop Use, 2 Monitors, 1 Printer Per 10, Speakers and Misc.

100% Desktop – Heavy 16.20 7.9 m2/workstation, All Desktop Use, 2 Monitors, 1 Printer Per 8, Speakers and Misc.

100% Desktop – Full On 21.60 7.9 m2/workstation, All Desktop Use, 2 Monitors, 1 Printer Per 8, Speakers and Misc., No Diversity

More recently, Sheppy conducted a detailed study and measurements in 10 office building in the US. The study shows that average peak plug loads for offices (without laboratories or data centers) is 5.4 W/m2; 6.9 W/m2 for higher education buildings and 9.5 W/m2 for offices with data centers (Sheppy et al, 2014). Singapore’s Building and Construction Authority (BCA) suggested that 16 W/m2 is the nominal value of plug load intensities for general office areas and 22 W/m2 for computer intensive office

4

areas (BCA Green Mark Version 4.1, 2012). This benchmark is correspondent with ASHRAE standards for medium/heavy and heavy load density office.

Figure 1. Related studies on plug load intensities for offices.

Figure 1 summarizes all related studies and standards on plug load intensities use for offices. It can be seen the peak plug load intensities have a wide range from 2.70 W/m2 to 21.50 W/m2, and it seems a decreasing trend from 2000 until present, which is probably due to significant improvements in the energy-efficiencies of office equipment resulting in reduced power demand and resultant heat gains.

5

3. Methodology

3.1. Site Assessment and Selection of Office Spaces in NTU

i. Categorization of metered office spaces

In this study, 10 different office spaces were selected to represent two major types of offices on NTU campus, namely Research Office and General Office. General office is also known as administrative office, with basic office equipment and typically with a schedule of 40 working hours per week (Monday-Friday). Research offices are usually equipped with high performance computer or even a server room. Researchers tend to work longer and irregular hours during weekdays and sometimes weekends. Among these offices, three different spatial layouts were identified, namely open plan, large cellular and mixed plan. The open plan contains some small cellular; large cellular refers to multi-occupant cellular office; mixed plan is a mixed space type between open plan and cellular spaces.

Table 3. List of measured office spaces in NTU

Table 3 shows the list of 10 typical general and research offices with a total metered area of 7,554 m2. Those offices were selected based on the availability of building information, the accessibility to the buildings, and most importantly they have separated electrical lines for plug load and other end uses (ACMV system and lighting system)at the main dash-board (DB) panel.The building data and specifications for each selected office were collected from ODFM office.

Office Area (m2)

Occupant density

(m2/person)

Type of Office Spatial Layout

ODFM- Office 1100.00 7.3 General Office Mixed Plan Administration Building- Office

475.00 19.8 General Office Mixed Plan

SPMS CBC Office 418.65 27.9 General Office Mixed Plan NSS Office 1,142.70 5.1 General Office Open Plan CTO 06-04 Office 423.00 10.8 Research Office Mixed Plan EOS block A Office

1,196.50 16.2 Research Office Mixed Plan

EOS block B-C Office

2,119.60 17.1 Research Office Mixed Plan

CTO 06-09 Office 153.00 4.8 Research Office Open Plan CTO 06-11 Office 258.00 4.7 Research Office Open Plan IMI Office 267.20 7.6 Research Office Large Cellular

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ii. Equipment Inventory

Walk-through survey was conducted to gather information about space usage and actual operation conditions. These walk-through surveys were conducted at each site between October 2014 and May 2015. The equipment inventory was collected for each office during the survey to further characterize space type. Table 3 lists equipment type and quantity for all studied offices. The equipment comprised of desktop PC/ laptop, high performance PC, common printer/scanner/copier, inkjet printers, fax machine, wide-scanner, LCD screen, projector, 24-hours server room, and multimedia equipment. The remaining others were classified as miscellaneous equipment comprised of microwave, water boiler, refrigerator, and coffee machine.

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Table 4.Summary of Office Equipment Inventories

Remarks: PC: Desktop PC/ Laptop Hi-PC : High performance PC CP : Common printer/scanner/copier IP : Inkjet printers Fax : Fax machine S : Wide Scanner LCD screen P : Projector SR : 24hours-Server room ME : Multimedia Equipment MW : Microwave WB : Water boiler R : Refrigerator C : Coffee Machine

Type of Office

Office Office Equipment (qty) Miscellaneous PC Hi-

PC CP IP Fax S LCD P SR ME MW WB R C

General Office

ODFM Office 150 0 2 0 1 0 0 0 0 0 1 1 1 0 Administration Building Office

24 0 4 16 1 0 0 1 0 1 1 1 1 0

SPMS Chemical Block- Office

29 0 1 6 1 0 0 2 0 2 1 1 1 0

NSS Office 225 0 10 10 1 0 0 0 0 0 1 2 2 0 Research Office

CTO 06-04 Office 39 0 2 3 0 0 2 3 0 0 1 1 1 3 EOS block A Office

74 1 4 10 0 1 2 1 1 1 0 1 1 0

EOS block B-C Office

104 3 4 5 0 0 6 5 2 3 2 2 3 4

CTO 06-09 Office 32 2 1 0 0 0 0 0 0 0 1 1 1 0 CTO 06-11 Office 55 0 1 0 0 0 0 0 0 0 1 0 1 0 IMI Office 35 1 2 2 0 0 1 0 1 1 0 0 0 0

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3.2. Plug Load Metering

3.2.1. Equipment

(a) (b) Figure 2. Three-Phase Power meters

In this study, 2 three-phase power meters were used to gather data on power demand and power factor for each office. Both of those power meters can collect the voltage, current, power, power factor and integrated power (watt-hours). The first power meter is Fluke 1730 Three-Phase Electrical Energy Logger as shown in Figure 2 (a).The second power meter is HIOKI 3169 Three Phase Power Meter as shown in Figure 2 (b). The specifications for both power meters can be found at Appendixes.

3.2.2. On-site Measurement

As-built drawing and single line diagram were studied to gather all the information needed for this study.Total plug load power use was logged at the distribution panel level in order to obtain aggregate plug loads and profiles over time. In the main dash-board (DB) panels, the individual plug load circuit was logged directly by placing the power meters at the panel feeders to record actual power use and energy values at a five-min interval over a 2-week period, as shown in Figure 3.

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Figure 3. On-site Measurement

3.3. Data Analysis

Collected data was further processed to analyze the peak power density for each office, and the steps are as follows:

i. The collated data from the power meters were normalized to nominal occupancy by dividing the power use by the office area, resulting in plug load intensities (W/m2) to assess actual peak power demand.

ii. After normalized, extreme meter spikes were found in some of the offices. These extreme spikes are considered as outliers and not be taken into consideration. Those extreme spikes were happened in certain period of time during occupied hour due to some of the office equipment power use ramps up on the first start. The extreme spikes were validated at 99% confidence interval, as shown in Table 5. And the formula is as follows: a. Upper outer fence = Mean data + (2.576*Standard Deviation)

This value assessed with 99% Confidence of Interval (CI) b. Lower outer fence = Mean data - (2.576*Standard Deviation)

This value assessed with 99% Confidence of Interval (CI)

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Table 5.Validated Data based on 99% CI

Type of Office

Office

Weekday (peak hours)

Weekday (off peak)

Weekend (peak hours)

Weekend(off peak)

Upper bound

Lower bound

Upper bound

Lower bound

Upper bound

Lower bound

Upper bound

Lower bound

General Office

ODFM 10.42 5.88 6.84 0.29 6.79 2.20 5.66 0.62

Admin 10.12 1.90 6.42 -0.45 4.19 0.65 4.25 0.71

SPMS 7.79 4.25 5.51 -0.92 1.28 1.24 1.30 1.23

NSS 9.92 5.31 4.76 0.76 2.72 1.45 2.71 1.43

Research Office

CTO 06-04 7.57 1.79 5.99 -1.04 4.40 0.06 4.18 -0.69

EOS-A 9.16 4.53 10.41 3.14 10.18 6.42 10.64 6.26

EOS-B&C 8.41 1.98 6.51 2.25 6.60 3.06 5.71 3.10

CTO 06-09 14.73 0.33 10.66 1.21 11.11 1.00 10.24 1.03

CTO 06-11 9.63 5.05 5.22 2.02 5.45 2.99 4.21 2.94

IMI 10.32 6.49 8.81 5.12 6.85 5.69 7.59 5.42

iii. The data was further processed to show the profile of weekly plug load intensities for the

first and second week, typical weekday and weekend during occupied and unoccupied hours.

iv. The results are compared against the benchmarks.

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4. Results and Discussion

4.1. Data Results

4.1.1. Type 1: General Office

For this type of office, the metering was conducted in four offices, namely ODFM office, Administration Building office, NTU Shared Service (NSS) office and School of Physical and Mathematical Sciences (SPMS) CBC office. The official schedule operation of these 4 offices is 40 working-hours per week (Monday to Friday), starting from 8:30 am to 5:30 pm.The plug load intensities profiles were generated over every 1 week period, and typical weekday and weekend profiles were also extracted to illustrate the contributions of plug loads throughout the day and week.

4.1.1.1. ODFM Office

ODFM office is a mixed-plan office located at level B2 of block N2.1. This office is occupied with 150 employees and with a total metered area of 1,100 m2. It is composed of several space types such as cubicles, cellular office spaces, print room, reception area and pantry. Table 6

summarizes the total number of space types in ODFM office. The equipment used for this office includes desktop computer/laptops, common printers, fax machine, and some pantry appliances.

Table 6. Total Space Types in ODFM Office

Space Type Total Cubicle 140 Cellular Office Space 10 Print Room 1 Reception Area 1 Pantry 1

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Figure 4. ODFM OfficePlug Load Profile 1st Week

Figure 5. ODFM OfficePlug Load Profile 2nd Week

13

Figure 4 and Figure 5 show the weekly plug load intensity profile over 2 weeks the plug load intensities range from 1.31 to 10.17 W/m2 during this period. It can be seen there is a repeated pattern during weekdays corresponding with general office working schedules. The plug load intensities range from 2 to 4 W/m2 during off peak hours, indicating that some office equipment may be still operating during weekends.

Figure 6. Typical Weekday ODFM OfficePlug Load Profile

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Figure 7. Typical Weekend ODFM OfficePlug Load Profile

Figure 6 and Figure 7 show the typical weekday and weekend profile. For a typical weekday, the plug load intensities peak at 10.17 W/m2 during 8:30 am-9:30 am, and gradually decreasing to 4.38 W/m2 around 6 pm. During off peak hours, the plug load intensities range from 2.04 to 5.93 W/m2, indicating some office equipment may be still operating during night time. This is also observed for weekends when the office is not occupied. On a typical weekend profile, it shows the plug load intensities range from 1.98 to 6.15 W/m2.

4.1.1.2. Administration Building Office

Administration building office is a mixed-plan office with a total metered area of 475m2. It is located at level 2 of Administration building. It is occupied with 24 employees and composed of several space types such as cubicles, cellular office spaces, print room, meeting rooms and pantry. Table 7 shows the total number of space types. The equipment used for this office includes desktop computer/laptops, common printers, inkjet printers, fax machine, projector, multimedia equipment, and some pantry appliances.

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Table 7.Total Space Types in Administration Building Office

Space Type Total Cubicle 16 Cellular Office Space 8 Print Room 1 Meeting room 3 Pantry 1

Figure 8. Admin OfficePlug Load Profile 1st-Week

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Figure 9. Admin Office Plug Load Profile 2nd-Week

Figure 8 and Figure 9 show the weekly plug load intensity profile over 2 weeks theplug load intensities ranged from 1.76 to 10.02 W/m2 during this period. It can be seen there is a repeated pattern during weekdays corresponding with general office working schedules. It is also observed there is a flat profile with some spikes on weekends, indicating some office equipment maybe still running but no occupants are in the office.

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Figure 10. Typical Weekday Admin OfficePlug Load Profile

Figure 11. Typical Weekend Admin Office Load Profile

18

Figure 10 and Figure 11 show the typical weekday and weekend profile. For a typical weekday, the plug load intensities peak at 10.02 W/m2 during 8:00 am- 9:00 am, and gradually decreasing to 4.36 W/m2 around 5:30 pm. During off peak hours, the plug load densities range from 1.93 to 5.99 W/m2, indicating some office equipment may be still operating during night time. This is also observed for weekends when the office is not occupied. On a typical weekend profile, it shows that the plug load intensities range from 1.76 to 4.18 W/m2.

4.1.1.3. SPMS CBC Office

SPMS CBC Office has a floor area of 418 m2. It is occupied with 15 employees and composed of several space types such as cubicles, cellular office spaces, print room, reception area, filing rooms and meeting rooms. Table 8 shows the total number of space types in SPMS CBC office.The equipment used for this office includes desktop computer/laptops, common printers, inkjet printers, fax machine, projectors, multimedia equipment, and some pantry appliances.

Table 8. Total Space Types in SPMS CBC Office

Space Type Total Cubicle 12 Cellular Office Space 3 Print Room 1 Meeting room 2 Reception Area 1 Store/Filing Room 3

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Figure 12. SPMS CBC OfficePlug Load Profile 1st-Week

Figure 13. SPMS CBC OfficePlug Load Profile2nd-Week

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Figure 12 and Figure 13 show the weekly plug load intensity profile over 2 weeks the plug load intensities ranged from 1.00 to 7.19 W/m2 during this period. It can be also seen there is a repeated pattern during weekdays corresponding with general office working schedules. A nearly constant value of 1.7 W/m2 was observed during office peak and weekends, indicating that some office equipment may be always operating. However, the plug load intensities are much lower than that in ODFM office and Administration Building office.

Figure 14. Typical Weekday SPMS CBC OfficePlug Load Profile

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Figure 15. Typical Weekend SPMS CBC OfficePlug Load Profile

Figure 14 and Figure 15 show the typical weekday and weekend profile. For a typical weekday, the plug load intensity peaks at 7.19 W/m2 during 11:00 am - 11:30 am, and gradually decreasing to 4.71 W/m2 around 6 pm. During off peak hours, the plug load intensities range from 1.00 to 4.18 W/m2, indicating some office equipment may be still operating during night time. This is also observed for weekends when the office is not occupied. It shows that the plug load intensities range from 1.25 to 1.28 W/m2 on a typical weekend profile.

4.1.1.4. NSS Office NSS office is an open plan office space with an area of 1,142m2. It is occupied with 225 employees and composed of cubicles, meeting area, and pantry without partition wall.The equipment used for this office includes desktop computer/laptops, common printers, inkjet printers, fax machine, and some pantry appliances.

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Figure 16. NSS OfficePlug Load Profile1st-Week

Figure 17. NSS OfficePlug Load Profile2nd-Week

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Figure 16 and Figure 17 show the weekly plug load intensity profile over 2 weeks the plug load intensities ranged from 1.85 to 9.64W/m2 during this period. It can be also seen there is a repeated pattern during weekdays corresponding with general office working schedules. A nearly flat profile was also observed during off-peak hours and weekends.

Figure 18. Typical Weekday NSS Office Load Profile

Figure 19. Typical Weekend NSS Office Load Profile

Figure 18 and Figure 19 show the typical weekday and weekend profile. For a typical weekday, the plug load intensities peak at 9.64 W/m2 during 9:00 am - 9:30 am, and gradually decreasing

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to 3.67 W/m2 around 6pm. During off peak hours, the plug load intensities range from 2.07 to 4.61 W/m2, indicating some office equipment may be still operating during night time. This is also observed for weekends when the office is not occupied. On a typical weekend profile, it shows that the plug load intensities range from 1.78 to 2.71 W/m2.

4.1.1.5. Summary

All of the 4 measured general offices have similar load intensity profiles. A repeated pattern was found during weekdays corresponding with general office working schedules. The plug load intensity ramped up in the morning as staff come to office to work and gradually decreased after work hours typical general offices.

Figure 20. General Office Plug Load Intensities.

Figure 20 summarizes the range value of plug load intensities for general offices over 2 week period. The plug load intensities for general offices range between 1.31 and 10.17 W/m2. It can be seen that the peak plug load intensity varies as different offices with maximum value of 10.17 W/m2 found in ODFM office.

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4.1.2. Type 2: Research Office

The metering was conducted in six research offices, namely Clean Tech One (CTO) 06-04, 06-09, 06-11, Institute for Media Innovation (IMI), Office and Earth Observatory of Singapore (EOS) block A Office, and block B-C Office. This type of research office is categorized as a computer intensive office. Some of the measured offices contain server room that run 24 hours. The official operation schedule of the research office is more than 40 working-hours per week and also during weekend. The plug load intensities profiles were generated over every 1 week period, and typical weekday and weekend profiles were also extracted to illustrate the contributions of plug loads throughout the day and week.

4.1.2.1. CTO 06-04

CTO 06-04 office has a floor area of 423 m2 office. It is a mixed plan office and occupied with 39 employees. It is located at level 6 of Clean Tech One building. It is composed of several space types such as cubicles, cellular office spaces, print room, reception area, meeting rooms and pantry. Table 9 shows the total number of space types in CTO 06-04. The equipment used for this office includes desktop computer/laptops, common printers, inkjet printers, LCD screens, projector, and some pantry appliances.

Table 9.Total Space Types in CTO 06-04

Space Type Total Cubicle 37 Cellular Office Space 2 Print Room 1 Reception Area 1 Meeting Room 4 Pantry 1

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Figure 21. CTO 06-04 Plug Load Profile 1st Week

Figure 22. CTO 06-04 Plug Load Profile 2nd Week

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Figure 21 and Figure 22 show the weekly plug load intensity profile over 2 weeks the plug load intensities ranged from 1.05 to 7.45 W/m2 during this period. It can be seen there is a repeated pattern during weekdays and weekend corresponding with research office working schedules. The plug load intensities range from 1 to 4 W/m2 during off peak hours, indicating that some office equipment may be still operating during weekends.

Figure 23. Typical Weekday CTO 06-04 Plug Load Profile

Peak: 7.45

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Figure 24. Typical Weekend CTO 06-04 Plug Load Profile

Figure 23 and Figure 24 show the typical weekday and weekend profile. For a typical weekday, the plug load intensity peaks at 7.45 W/m2 around 8:30 am, and gradually decreasing to 3.13 W/m2around 6pm.During off peak hours, the plug load densities range from 1.08 to 4.95 W/m2, indicating some office equipment may be still operating during night time. This is also observed for weekends when the office is not occupied. On a typical weekend profile, it shows that the plug load intensities range from 1.05 to 4.27 W/m2.

4.1.2.2. EOS block A office

EOS block A office is a mixed-plan office located at level 1 of block N2. This office is occupied with 74 employees and with a total metered area of 1,196 m2. It is composed of several space types such as cubicles, cellular office spaces, print room, reception area, meeting rooms, server room, filing room, common lounge and pantry.

Table 10 shows the total number of space types in EOS block A office.The equipment used for this office includes desktop computer/laptops, high-performance desktop, common printers, inkjet printers, wide scanner, LCD screens, server room, projector, multimedia equipment and some pantry appliances.

Peak: 4.27

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Table 10.Total Space Types in EOS block A office

Space Type Total Cubicle 56 Cellular Office Space 16 Print Room 1 Reception Area 1 Meeting Room 2 Common Lounge 1 Server Room 1 Store and Filing Room 4 Pantry 1

Figure 25. EOS block A office Plug Load Profile 1st Week

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Figure 26. EOS block A office Plug Load Profile 2nd Week

Figure 25 and Figure 26 show the weekly plug load intensity profile over 2 weeks the plug load intensities ranged from 4.53 to 9.11W/m2 during this period. It can be seen there is a repeated pattern during weekdays and weekend corresponding with research office working schedules. The plug load intensities range from 4 to 10 W/m2 during off peak hours, indicating that some office equipment may be still operating during weekends.

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Figure 27. Typical Weekday EOS block A office Plug Load Profile

Figure 28. Typical Weekend EOS block A office Plug Load Profile

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Figure 27 and Figure 28 show the typical weekday and weekend profile. For a typical weekday, the plug load intensity peaks at 9.11 W/m2 around 10.00 am- 10:30 am, and gradually decreasing to 5.79 W/m2 around 6 pm. During off peak hours, the plug load densities range from 4.72 to 10.26 W/m2, indicating that office equipment still operating during night time. This is also observed for weekends. On a typical weekend profile, it shows that the plug load intensities range from 6.42 to 10.11 W/m2. The team then identified that there was a server room that run 24-hours throughout the week.Hence, the weekly plug load intensity profile over 2 weeks remains steady throughout the week.

4.1.2.3. EOS block B-C office

This research office with a total metered area of 2,119 m2 office is occupied with 124 employees. It is a mixed plan office and composed of several space types such as cubicles, cellular office spaces, print room, reception area, meeting rooms, server room, filing room, common lounge and pantry. Table 11 shows the total number of space types in EOS block B-C office.The equipment used for this office includes desktop computer/laptops, high-performance desktop, common printers, inkjet printers, LCD screens, server rooms, projector, multimedia equipment and some pantry appliances.

Table 11.Total Space Types in EOS block B-C office

Space Type Total Cubicle 83 Cellular Office Space 26 Print Room 1 Reception Area 1 Meeting Room 3 Working Room 7 Computer Room 2 Common Lounge 3 Server Room 2 Store and Filing Room 4 Pantry 2

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Figure 29. EOS block B-C office Plug Load Profile1st Week

Figure 30. EOS block B-C office Plug Load Profile 2nd Week

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Figure 29 and Figure 30 show the weekly plug load intensity profile over 2 weeks the plug load intensities range from 3.44 to 7.39 W/m2 during this period.It also can be seen there is a repeated pattern during weekdays and weekend corresponding with research office working schedules. The plug load intensities range from 3.5 to 7 W/m2 during off peak hours, indicating that some office equipment may be still operating during weekends.

Figure 31. Typical Weekday EOS block B-C office Plug Load Profile

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Figure 32. Typical Weekend EOS block B-C office Plug Load Profile

Figure 31 and Figure 32 show the typical weekday and weekend profile. For a typical weekday, the plug load intensity peaks at 7.39 W/m2 around 4.30 pm - 5:00 pm, and gradually decreasing to 5.82 W/m2 around 6 pm. During off peak hours, the plug load densities range from 3.54 to 5.95 W/m2, indicating that office equipment still operating during night time. This is also observed for weekends. On a typical weekend profile, it shows that the plug load intensities range from 3.77 to 6.45 W/m2. The team then identified that there were2 server rooms and 3 high-performance computers that run 24-hours. Hence, the weekly plug load intensity profile over 2 weekswas steady throughout the week.

4.1.2.4. CTO 06-09

CTO 06-09 is an open plan office space with area of 153 m2. It is occupied with 32 employees and composed of cubicles office and pantry area without partition wall.The equipment used for this office includes desktop computer/laptops, high-performance computers, common printerand some pantry appliances.

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Figure 33. CTO 06-09Plug Load Profile 1st Week

Figure 34. CTO 06-09Plug Load Profile 2ndWeek

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Figure 33 and Figure 34 show the weekly plug load intensity profile over 2 weeks the plug load intensities ranged from 5.28 to 13.91 W/m2 during this period. It can be seen there is a repeated pattern during weekdays and weekend corresponding with research office working schedules. The plug load intensities range from 5 to 12 W/m2 during off peak hours, indicating that some office equipment may be still operating during weekends.


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Figure 35 and Figure 36 show the typical weekday and weekend profile. For a typical weekday, the plug load intensity peaks at 13.91 W/m2around 11.00 am - 11:30 am, and gradually decreasing to 6.11 W/m2 around 6 pm. During off peak hours, the plug load densities range from 5.28 to 9.74 W/m2, indicating that office equipment still operating during night time. This is also observed for weekends. On a typical weekend profile, it shows that the plug load intensities range from 5.12 to 10.57 W/m2. The team then identified that there were 2 high-performance computers that run 24-hours throughout the week. Hence, the weekly plug load intensity profile over 2 weeks was steady throughout the week.

4.1.2.5. CTO 06-11

CTO 06-11 is an open plan office space with area of 258 m2. It is occupied with 55 employees and composed of cubicles office and a pantry without partition wall.The equipment used for this office includes desktop computer/laptops, common printers and some pantry appliances.

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Figure 37. CTO 06-11Plug Load Profile1stWeek

Figure 38. CTO 06-11PlugLoad Profile2ndWeek

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Figure 37 and Figure 38 show the weekly plug load intensity profile over 2 weeks the plug load intensities ranged from 3.21 to 9.90 W/m2 during this period. It can be seen there is a repeated pattern during weekdays and weekend corresponding with research office working schedules. The plug load intensities range from 3.5 to 6 W/m2 during off peak hours, indicating that some office equipment may be still operating during weekends.


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Figure 39 and Figure 40 show the typical weekday and weekend profile. For a typical weekday, the plug load intensity peaks at 9.90 W/m2 around 12.00 pm - 12:30 pm, and gradually decreasing to 4.86 W/m2 around 6 pm. During off peak hours, the plug load densities range from 3.21 to 4.80 W/m2, indicating that office equipment still operating during night time. This is also observed for weekends. On a typical weekend profile, it shows that the plug load intensities range from 3.43 to 4.89 W/m2. The values during weekend were significantly lower than weekdays, indicating that only some of the office equipment were operated during that period of time.

4.1.2.6. IMI Research Office

IMI Research office is a large cellular office space with area of 267 m2. It is occupied with 35 employees and composed of 7 large cellular office and printing area. The equipment used for this office includes desktop computer/laptops, high-performance computers, common printer, inkjet printer, LCD screens, server room and multimedia equipment.

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Figure 41. IMI officePlugLoad Profile1stWeek

Figure 42. IMI officePlugLoad Profile2ndWeek

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Figure 41 and Figure 42 show the weekly plug load intensity profile over 2 weeks the plug load intensities ranged from 5.63 to 9.71 W/m2 during this period. It also can be seen there is a repeated pattern during weekdays and weekend corresponding with research office working schedules. The plug load intensities range from 6 to 8 W/m2 during off peak hours, indicating that some office equipment may be still operating during weekends.

Figure 43. Typical Weekday IMI office Plug Load Profile

Figure 44. Typical Weekend IMI office Plug Load Profile

Figure 43 and Figure 44 show the typical weekday and weekend profile. For a typical weekday, the plug load intensity peaks at 9.71 W/m2 around 11:30 am, and gradually decreasing to 8.70

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W/m2 around 6pm. During off peak hours, the plug load densities range from 6.07 to 8.07 W/m2, indicating that office equipment still operating during night time. This is also observed for weekends. On a typical weekend profile, it shows that the plug load intensities range from 5.96 to 6.79 W/m2. The values during weekend were significantly lower than weekdays, indicating that only some of the office equipment were operated during that period of time.

4.1.2.7. Summary

Six of the measured office had similar profiles and could represent typical research office spaces. There are repeated patterns during weekdays and weekend corresponding with research office working schedules of more than 40 working-hours per week and also during weekend.

Figure 45. Research Office Plug Load Intensities

Figure 45 summarizes the range value of plug load intensities for research offices over at least a 2 week period each. The plug load intensities for research offices range between 1.05 and 13.91 W/m2.

All research offices have a plug load intensities lower than 10.17 W/m2 with an exception of the CTO 06-09 office, which has a peak value of 13.91 W/m2. This is because there are 2 high-performance computers run 24-hours throughout the day. Hence, the plug load intensity is much higher compared with other offices during peak hours and off-peak hours.

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4.2. Office Plug Load Intensities Benchmarking

It is essential to benchmark office plug load intensities for building cooling system design and energy analysis. Figure 46 provides a summarized comparison between the findings of this study and other benchmarking research studies and international standards for peak plug load intensities, such as ECG 19, Metzger et al, BCA and ASHRAE standard.

Figure 46. Peak Plug Load Intensities of Measured office vs Current Plug Load Standards

The peak plug load intensities of all the metered offices range between 7.19 W/m2and 10.17 W/m2, with the exception of the CTO 06-09 office (13.91 W/m2). The CTO 06-09 office is an exception because, in addition to regular office equipment, it houses 2 high-performance servers (24X7 operation) with an occupant density of only 4.8m2/person. Typically these servers are located at an IT rack room from where they are accessed remotely.

The results complied well with similar benchmarking studies and international standards, such as ECG 19 (for standard office), Metzger et al and ASHRAE (for medium load density office) with nominal values of 14 W/m2, 9.72 W/m2 and 10.8 W/m2 respectively. It also indicates that peak plug load intensities are well below common design assumptions and BCA Green Mark’s recommended peak plug load intensity of 16 W/m2 (BCA Green Mark Version 4.1, 2012).

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5. Conclusion

Heat gain from office equipment is an important contributor to the overall heat gain of an office space, and it is essential to use accurate plug load intensities for cooling load calculation and ACMV system sizing.

From this study, on average the peak plug load intensities of 9.45 W/m2 was found for 10 offices metered on NTU campus, and it range between 7.19 and 10.17 W/m2 with an exception of CTO 06-09 office, which has a peak value of 13.91 W/m2, as explained in Section 4.2.1.7. It is concluded that 11 W/m2 should be the peak plug load intensities for offices on NTU campus, for design and sizing purposes. This value is below the reference value of peak plug load intensity of 16 W/m2 for general office areas recommended by BCA, while it complies well with ASHRAE standard (10.8 W/m2 for medium load density office) and other international standards.

However, it should be noted that this study is carried out on NTU campus, which is more of a representative for academic office spaces, and may not necessarily apply to office spaces outside of NTU. There is definitely a need to conduct further studies to set recommended peak plug load intensities for general office spaces in Singapore based on parameters such as function, equipment selection, occupant density and space layout.

The authors hope that the results of this study will be a useful guide for building owners, engineers and energy modelers to accurately calculate building cooling loads, hence ‘right size’ cooling system capacities and reduce whole-building energy use.

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References

ASHRAE. 2009. 2009 ASHRAE Handbook-Fundamentals, Chapter 18.

BCA Green Mark Version 4.1. 2012. Certification Standards for New Buildings. Building and Construction Authority, Singapore.

CIBSE. 1998. CIBSE Guide F: Energy Efficiency in Buildings, 1st edition. London: The Chartered Institution of Building Services Engineers, 1998.

CIBSE. 1999. CIBSE Guide A: Environmental Design, London: The Chartered Institution of Building Services Engineers, 1999.

Energy Consumption Guide (ECG) 19. 2000. Energy efficiency in offices. Accessed March 7, 2015: www.actionenergy.org.uk.

Komor, P. 1997. “Space Cooling Demands from Office Plug Loads”. ASHRAE Journal 39, December, pp. 41-44.

Metzger I., A. Kandt and O VanGeet. 2011. Plug Load Behavioral Change Demonstration Project. NREL. Accessed March 7, 2015: www.nrel.gov/docs/fy11osti/52248.pdf.

Sheppy, M., Torcellini P. and Gentile-Polese, L. 2014. An Analysis of Plug Load Capacities and Power Requirements in Commercial Buildings. NREL. Accessed March 7, 2015: www.nrel.gov/docs/fy14osti/61528.pdf.

Srinavasan, R.S., J. Lakshmana, D. Srivastav and E. Santosa. 2011. “Benchmarking Plug-Load Densities for K-12 Schools.” Proceeding of Building Simulation 2011, 12th Conference of International Building Performance Simulation Association, November 2011, pp. 2746-2752.

Thomas, P. C. and S. Moller, 2007. “HVAC System Size: Getting It Right—Right Sizing HVAC Systems in Commercial Systems.” Cooperative Research Centre for Construction Innovation, pp. 11.

Wilkins, C. and Hosni, M.H. 2000. “Heat Gain from Office Equipment.” ASHRAE Journal 42, June, pp. 31-39.

Wilkins, C. and Hosni, M.H. 2011. “Plug Load Design Factors.” ASHRAE Journal, May, pp. 30-34.

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Appendix I

Fluke 1730 Three-Phase Energy Logger

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Appendix II

HIOKI 3169 Three Phase Power Meter

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