ASHRAE Technology Award... Detecting Faults in Hong Kong High-Rise

8/12/2019 ASHRAE Technology Award... Detecting Faults in Hong Kong High-Rise

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A S H RA E J O U RN A L a s h r a e . or g J A N U A R Y 2 0 1 44 6

BY YOUMING CH EN, MEMBER ASHRAE; HAITAO WANG; CARY W. H. CHAN; AND JIANYING QIN, MEMB ER ASHRAE

Detecting Faults In Hong Kong High-Rise

2013 ASHRAE TECHNOLOGY AWARD CASE STUDIES

HONORABLE MENTION

COMMERCIAL BUILDINGS, EXISTING

Maintaining nearly 1,200 VAV

terminals in a 36-story office

building is no easy feat. The

recipients of the Technology

Award Honorable Mention

developed a fault detection tool

that doesn’t require an extra

sensor and works with the

existing energy management

and control system.

ABOUT THE AUTHORS

Youming Chen is a professor of Hunan University in Changsha, Hunan, China. Haitao Wang is a project engineerof Hunan University in Changsha, Hunan, China. Cary W.H. Chan is a general manager at Technical Services andSustainability of Swire Properties Ltd in Hong Kong and Jianying Qin is an assistant building services manager of Swire

Properties Ltd in Hong Kong.

Cambridge House VAV Terminals

Location: Hong Kong

Owner: Swire Properties Ltd.

Principal Use: Office Building

Includes: Retail, restaurant and foyer

Employees/Occupants: 3,000

Gross Square Footage: 317,361

Conditioned Space Square Footage: 282,705

Substantial Completion/Occupancy: 2003

Occupancy: 100%

BUILDING AT A GLANCE

This article was published in ASHRAE Journal, January 2014. Copyright 2014 ASHRAE. Posted at www.ashrae.org. This article may not be copied and/or distributed electronically or in paper form withoutpermission of ASHRAE. For more information about ASHRAE Journal, visit www.ashrae.org.



J A N U A R Y 2 0 1 4 a s h r a e . or g A S H RA E J O U RN A L 4 7

Each floor in the building is served by a single duct

VAV air-conditioning system. Constant air volume boxes

provide 1,377 cfm (650 L/s) of fresh air for each floor.

Fresh air is delivered to the air-handling unit (AHU)

room of each floor by three fresh air fans. Return air is

sent to the AHU room through a ceiling void.

The layout of an air-conditioning system for a typicalfloor is shown in Figure 1. An AHU with monitoring and

control instrumentation provides an adequate fresh

airflow rate, suitable supply air temperature, and supply

air pressure. VAV terminals are used to maintain zone

air temperature at the desired value through regulating

supply air volume into the zones.

VAV terminals are likely to fail after running for several

years. VAV terminal faults cause zone air temperatures

out of the desired values, poor thermal comfort and

more energy consumption.

The 1,186 VAV terminals are dispersed in the closed ceil-

ing void. It is difficult to check all VAV terminals manu-

ally because of the labor involved and issues with access

to tenant spaces. An investigation of VAV terminals for a

similar office building took two technicians almost six

months to complete. Current energy management and

control systems (EMCS) do not diagnose faults of VAV

terminals. But, the effective use of a fault detection and

diagnosis (FDD) tool for VAV terminals can help improve

thermal comfort, increase equipment service life, and

reduce maintenance costs and energy consumption.

For the Cambridge House project, an online FDDtool was developed to find and identify VAV terminal

faults. The FDD tool can analyze the operating data in

an EMCS automatically and provide building operators

with user-friendly fault information of VAV terminals.

The implementation of the FDD tool in Cambridge

House covers two phases: tool development (January

2009 to December 2009) and application trial (January

2010 to present). In the application phase, many VAV

terminal faults were verified and corrected because of

fault reports provided by the tool.

FDD Tool for VAV Terminals The FDD tool for VAV terminals adopts a robust fault

detection and diagnosis strategy. In the strategy, a

residual-based cumulative sum (CUSUM) control chart

is used to detect faults. And, some expert rules derived

from mass and energy balances are designed to find

fault sources in VAV terminals. The FDD tool is installed

in a stand-alone computer. A schematic of the FDD tool

integrated with the EMCS is shown in Figure 2.

The FDD tool has no special operational requirementsfor air-conditioning systems, and doesn’t need an addi-

tional sensor. It relies only on sensor data and control

signals available in a typical EMCS.

The tool has five functions: operating data acquisition,

fault detection, fault diagnosis, automatic generation of

VAV box trend log, and automatic fault report. Figure 3

shows the interface of the FDD tool. On the left is a lay-

out of VAV terminals according to their location in the

building.

The icon color of VAV terminals is changed in real time

according to the terminals’ operating status. Green

means normal; red means faulty; magenta means erro-

neous data communication for the terminal; yellow

means a special requirement for the terminal; white

means unused or no data.

The center of the interface shows detailed informa-

tion for a selected terminal. On the right is an array of

floor-switching buttons. Clicking other buttons gener-

ates reports such as a fault report for the day and a fault

report for fault verification and repair. Trend logs of ter-

minals can help operators assess the original design of

LEFT Cambridge House in Hong Kong saved 13% on its electrical bill by installing afault detection tool to help building operators identify faults and make repairs beforethey could waste energy.




2013 ASHRAE TECH NOLOGY AWARD CASE STUDIES

VAV terminals and further look into fault sources in VAV

terminals. Operators can set a tenant special require-

ment for a VAV terminal. The FDD tool can be easily

extended to any other VAV air-conditioning system by

VAV Terminals and AHUs

LAN

DDC

SQL Server

The FDD Tool The EMCS CentralControl Station

Request ing Data from SQL Sending Data Per 5 Minutes

FIGURE 2 Online implemention of the FDD tool in EMCS.

FIGURE 1 Layout of air-conditioning system for a typical floor.customizing the interface according to the number and

location of VAV terminals.

Innovation The online FDD tool is probably one of the first EMCS

tools to diagnose the VAV terminal faults in a commer-

cial building. Extensive tests have been conducted on

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2013 ASHRAE TECH NOLOGY AWARD CASE STUDIES

site to verify the performance of the tool. The

main innovations include:

A site survey study on the faults of VAV termi-

nals was conducted in Cambridge House and 13

main faults were identified. The fault diagnosis

tool was developed to address these faults. A residual-based CUSUM control chart is used

to detect faults. It improves the accuracy of fault

diagnosis through removing adverse effects of

serial correlation in data, but also enhances the

robustness of fault diagnosis through reducing

the impacts of normal transient changes.

Some expert rules, derived from mass and

energy balances, are used to find the fault sources

in VAV terminals. These rules are easy to understand,

which can help to convince operators to use the FDD tool.

The tool shows the operating condition of VAV termi-

nals and the source of the fault. The tool uses the rated

parameters of terminals as well as the sensor and con-

trol signals that are commonly available in an EMCS.

The FDD tool can provide fault statistics and generate

a fault report for verification. Faults of VAV terminals are

separated into different grades according to the severity

of faults. The fault list can facilitate fault rectification and

improve the efficiency of maintenance and management.

Special tenant requirements are considered in the tool

to reduce false alarms. Special requirements include

vacation, interior design work, renovation projects, etc.

FIGURE 3 Interface of the FDD tool.

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J A N U A R Y 2 0 1 4 a s h r a e . or g A S H RA E J O U RN A L 5 1

Operation and Maintenance The tool checks and analyzes the operating data in the

EMCS automatically, and provides building operators with

clear fault information of VAV terminals, which improve

the quality of VAV operation and maintenance. Operators

can work quickly with the FDD tool, as its operation issimple. The FDD tool checks the operating status (on/off)

of VAV terminals and AHUs automatically. The operating

status has no effect on the operation of the tool, which can

operate continuously without any maintenance or cost.

Energy Benefits The implementation of the FDD tool has significantly

improved the energy efficiency of Cambridge House.

The monthly cooling load for weekdays in 2009 and 2010

(8 a.m. to 6 p.m., Monday through Friday, and 8 a.m. to

2 p.m. on Saturday, excluding the rest of the weekends

and public holidays) are listed in Table 1. The total cool-

ing load of Cambridge House was 6,430,883 kWh in

2010, a decrease of 980,250 kWh from the previous year.

The total annual electricity of air-conditioning systems

decreased by 13.23% after applying the FDD tool.

Conclusion The FDD tool has provided an effective approach to

detect and diagnose VAV terminal faults, which improved

thermal comfort, service quality, and reduced mainte-

nance costs and labor. Annual electric savings is 13.23%.

Table 1 Monthly cooling load of Cambridge House for weekdays in 2009 and2010 (based on the data from EMCS).

MONTH 2009 COOLI NG LOAD (KWH) 2010 COOLING LOAD (KWH)

January 307,454 254,106

February 455,624 267,892

March 431,875 399,369April 450,375 370,491

May 657,499 594,552

June 883,080 649,638

July 946,323 823,336

August 950,534 845,983

September 911,237 825,909

October 665,992 599,282

November 454,377 460,675

December 296,763 339,652

TOTAL 7,411,133 6,430,885

SAVING 13.23%

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ASHRAE Technology Award... Detecting Faults in Hong Kong High-Rise