ESL-IC-06-11-180

ICEBO2006, Shenzhen, China Building Commissioning for Energy Efficiency and Comfort, Vol. VI-1-1

A New Approach to Commissioning of the VAV Control System Zheng Han Chunhai Xia Yingxin Zhu Guohai Xu Master Doctoral Professor Ph.D. Candidate Candidate Yamatake Tsinghua University Corporation P.R.China Japan [email protected]

Abstract: Commissioning of the HVAC system has A number of researchers have worked on the been practiced in buildings for the purpose of energy diagnose of HVAC system [2][3], but due to the conservation and performance optimization. complexity and diversity of different HVAC systems, Commissioning of the HVAC automation system should some methods are not very practical. In the field of be paid more attention. In this paper, Objective Control VAV system troubleshooting, some researchers Method (OCM) is proposed to analyze the operational mainly focus on the main equipments (AHU, , performance of VAV control system. The approach starts pump, etc.) [4][5], while only a few papers on a with the evaluation of satisfaction of indoor thermal complete system diagnosing have been published. comfort, and then is followed by the performance For example, Harunori Yoshida (Japan) and Jin analysis of different control loops with a graphic chart Xin-Qiao developed some computerized simulation of relations between different parameters. Finally the program to diagnose some typical failure from sensor operation fault is detected. This approach has been and monitor in a VAV system [6][7]. applied and validated in a real VAV control system of a VAV system failure mainly includes: improper commercial office building in Beijing with one year’s system design, facilities failure, sensor failure, signal on-site measured data. By means of OCM, phenomena transfer failure and improper control strategy, etc.. of ‘hunting’ in VAV control system are deeply studied. Existing diagnose method generally deal with As a new commissioning approach of VAV control problems like sensor failure with computerized system, OCM is of great feasibility and convenience. program simulation, and the analysis is based on Key words: VAV ，commissioning , OCM，hunting great amounts of monitored data. While investigation of control strategy and system design in operation 1. INTRODUCTION stage is insufficient. This paper is try to introduce a Building and/or HVAC commissioning in new approach to diagnose system design failure, nowadays sense, however, is understood as the equipment failure, control system failure and signal process to realize the real owner’s project transmission failure, etc. based on long term requirements through building construction stage and commissioning practice, and concludes that Objective continuing to operation and maintenance stage as the Control Method (OCM) is a practical method in life-cycle process in an ideal sense, by defining realizing a complete diagnosis of a VAV system. owner’s project requirements on performance, reviewing, inspecting, verifying and testing a total 2. OBJECTIVE CONTROL METHOD functional performance[1]. Being a type of HVAC (OCM) system, a VAV system has the great potential on Commissioning of VAV system is a step by step energy saving, it also has a complicated control system and multifarious equipments. Therefore, the performance analysis and diagnose for a VAV system would be a very important part for Building HVAC System Commissioning.

Proceedings of the Sixth International Conference for Enhanced Building Operations, Shenzhen, China, November 6 - 9, 2006 ESL-IC-06-11-180

ICEBO2006, Shenzhen, China Building Commissioning for Energy Efficiency and Comfort, Vol. VI-1-1

OCM DIAGN OS E

SAV Meets the Requirement

Ye s No Required SAV Reaches Max/Min Air Valve Opens to Max/Min

Yes N o Ye s No Required SAV Hunting Improper Fa n Speed Inc reas e Fan Valve Ccontrol of /Dec re ase to Max/Min Failure; Required Improper Control Yes No SAV of Fan Valve Yes No Hunting SAT Meets the Required Both Max and Min Problems Requirement Select a opening in different termina ls at Small the s ame t ime Sc ale F an Ye s No Improper Contrl Yes No In charge of different districs; of SAT; S elec t a Small Sc ale Te rm inal; Deficiency of Hunting problems Improper Control ... Water Flow of Fan Speed

Fig. 1 OCM flow figure of pressure independent VAV system process, which includes performance evaluation of shown in Fig. 2. Terminal temperature is the original control system, indoor thermal environment object. If temperature deviation is larger than a fixed evaluation, and energy consumption analysis, etc. value, then it goes to the OCM diagnosis. The first (Fig. 1). The first step is to confirm whether the VAV level question is to judge whether the terminal’s control system is working under the designed supply air volume satisfies the requirement. Based on condition. If “yes”, then evaluate the indoor comfort the answer to the first question the secondary level starts (since the terminal sensor reaching the design questions are whether required air volume reaches the requirement doesn’t illustrate a good indoor thermal max (min) or air valve opens to max (min), the environment); if “no”, then apply OCM to diagnose potential failure reasons for the former one includes the VAV control system and find the failure. Finally system hunting, a smaller terminal, one terminal we analyze the energy consumption and the energy responsible for different zones, insufficient water conservation potential. supply for AHU, improper setting of terminal air Comparation volume, control problem of air supply, etc. and the betw een sensor an d IAQ evaluation work area temp. Emer gu reasons for the latter one includes inappropriate Ye s Co ns u mp tio n Level selection of fan, excessive resistance in air Satisfy the Sensor Adjust OCM Diagnose terminal temp. No (blocked or failed design), system hunting (the reason Fig. 2 Commissioning flow chart of VAV system of hunting is complicated and will be discussed This paper focuses on setting up the OCM flow deeply in the case study), improper control strategy chart for diagnosing a VAV control system. The of fan speed, failure of fan valve adjustment etc.. pre-assumption for this method is the data collected From the OCM logic flow chart, we can see that from control system test and record is free of error, there are various kinds of object to judge. OCM can which means the sensor problem has already been help to detect the definite failure and point out the solved. OCM firstly judges whether the direction of further improvement. For failure facility performance fulfill the design requirement, then or air duct blocked problem, it can be repaired follow the route to the next step according to the immediately; for improper design problem, facilities analysis result, then it repeated the process for several or terminals should be considered to be replaced; for times until find the reason of the failure. data transmission problem, the relative facilities Take a VAV system with pressure independent should be checked and repaired; for control strategy terminal for example, the OCM logic flow chart is problems, an improved strategy should be developed;

Proceedings of the Sixth International Conference for Enhanced Building Operations, Shenzhen, China, November 6 - 9, 2006 ESL-IC-06-11-180

ICEBO2006, Shenzhen, China Building Commissioning for Energy Efficiency and Comfort, Vol. VI-1-1 for water supply deficiency problem, a further 100%, the fan speed will increase; commissioning of water system should be carried out; (3)AHU controller: maintain the required fan for system hunting or problem of one terminal speed and SAT; responsible for different zones, it is hard to be solved (4)Central monitor: record measured data and in short time, we can only reduce its affect by contribute to management. applying some measures. 3.3 OCM APPLICATION 3．CASE STUDY Take SE.P.Z.B in intermediate seasons (AHU A real case is given to explain how to use OCM B12, 2 terminals) for example. Calculate the flow figure to solve problems. temperature and SAV deviation of each terminal between set point and measured value(Table 1). 3.1 INTRODUCTION OF CASE Beijing Fortune Building (Fig.3) is a slap-up office building, which was built in 1980s. The main building is 80m high with the construction area reaching 54490 m2. There are 20 stories up ground and 2 stories underground. 3rd ~21st stories are mainly used as office room, designed with pressure independent VAV system. General stories are divided into two large sections and each section includes 3 zones in Fig.4 (I.Z.A/B-interior zone in section A/B; Fig.3 Elevation drawing of Fortune Building W.P.Z.A-west perimeter zone in section A; N.P.Z.B-north perimeter zone in section B; SE.P.Z.A/B-southeast perimeter zone in section A/B).

3.2 INTRODUCTION OF VAV CONTROL SYSTEM Pressure independent VAV system is designed, and it includes four parts: terminal controller, integrated management unit, AHU controller and central monitor (Fig.5). Main functions of each loop are:

(1)Terminal controller: calculate the required Fig.4 Air-conditioning system zoning supply air volume (SAV) and change the opening of AHU valve by deviation of required and measured SAV; terminal integrated controller management controller (2)Integrated management unit: collect each unit terminal’s measured temperature and SAV, and then central monitor calculate the fan speed and supply air temperature (SAT). Fan speed is calculated by the total required SAV and then verified by the opening of all the terminal valves; For example, if all the valve Temperature sensor openings keep smaller than 80%, the fan speed will Fig. 5 VAV control system decrease; while if at least one valve keeps opening at

Proceedings of the Sixth International Conference for Enhanced Building Operations, Shenzhen, China, November 6 - 9, 2006 ESL-IC-06-11-180

ICEBO2006, Shenzhen, China Building Commissioning for Energy Efficiency and Comfort, Vol. VI-1-1

OCM DIAGNOSE

SAV Meets the Requirement

Yes No

Required SAV Reac hes Max/Min Air Valve Opens to Max/Min

Yes No Yes No Required SAV Hunting Improper Fan Speed Increase Fan Valve Cc ontrol of /Decrease to Max/Min Failure; Required Improper Control Yes No SAV of Fan Valve Yes No Hunting SAT Meets the Required Both Max and Min Problems Requirem ent Select a opening in different terminals at Small the same time Scale Fan Yes No Improper Contrl Yes No In charge of different districs; of SAT; Select a Small Scale Terminal; Deficiency of Hunting problems Improper Control ... Water Flow of Fan Speed

Fig. 1 OCM flow figure of VAV16, transitional season

Tab.1 Terminal performance of B12 deviation is large, required SAV maintains at 1st ,May~31st , May VAV16 VAV17 maximum value and no hunting appears. OCM goes Set air temperature (℃) 25.5 25.5 to analyze SAT.

temperature deviation (℃) 1.4 0.1

温度Tem(p.度 (℃) Volume.风量 ((mm33/ / h h)) SAV deviation (×100%) 0.01 0.02 40 2500 35 Table 1 shows that VAV16 has a big temperature 2000 30 deviation, and OCM is applied to diagnose the VAV 25 1500 20 control system. 15 1000 10 First step: According to table 1, VAV16’s SAV 500 5 meets the requirement well ， and OCM goes to 0 0 08: 00 10: 00 12: 00 14: 00 16: 00 18: 00 estimate whether “SAV reaches maximum or VAV-B12-16 B12 Practical 室内温度 temp B1 2B12送风温度检测 practical SAT VAV-B12-16 B12 Set air temp温度设定 VAV- B12 B1 practical 2 - 16 计测风量 SAV minimum value”. V A VB12-B12-16 Set SAV 要求风量 Second step: According to Fig. 7, required SAV Fig. 3 Curve of indoor parameters（VAV16, May arrived at maximum value during 75% of time, and th 20 ） SAV hunting needs to be analyzed.

VAV-B1VAV0--1B160 P-16erce要n求ta风量累ge of Cu积图mulat(5ed月 Air) Volume Tem温度 p. (℃度) 28 2500 26 24 2000 22 20

3/ h) 1500 18

16 1000 14 风量 (m 12 500 10

Air volume 0 08: 00 10: 00 12: 00 14: 00 16:00 18: 00 0% 13% 26% 38% 51% 64% 77% 90% BB1212送风温度检测 Practical SAT BB1212给气温度设定 set SAT Pe百分rcen比tage

Fig.4 Relationship between practical and set SAT Fig. 2 Accumulative curve of required SAV th (May, 20 ) ( Transitional season, VAV16 ) Forth step: According to Fig. 9, when set SAT is Third step: According to Fig.8 when temperature 12℃, practical SAT is around 15℃, which could not

Proceedings of the Sixth International Conference for Enhanced Building Operations, Shenzhen, China, November 6 - 9, 2006 ESL-IC-06-11-180

ICEBO2006, Shenzhen, China Building Commissioning for Energy Efficiency and Comfort, Vol. VI-1-1

meet the requirement. Therefore, the failure may be OCM DIAGNOSE result from insufficient water flow rate of AHU. SAV Meets the Requirement

Fifth step: Analyze other possible failure Yes No As shown in Fig. 10, VAV17’s temperature Required SAV Reaches Max/Min Air Valve Opens to Max/Min Yes No Yes No sensor locates in a separated small room when Required SAV Hunting Improper Fan Speed Increase Fan Valve Ccontrol of /Decrease to Max/Min Failure; Required Improper Control VAV16’s in a large-span room. VAV17 is designed to Yes No SAV of Fan Valve Yes No Hunting SAT Meets the Required Both Max and Min Problems Requirem ent Select a control air temperature in both large-span room and opening in different terminals at Small the same time Scale Fan small room. But in practice, small room always has a Yes No Improper Contrl Yes No In charge of different districs; of SAT; small load and needs small SAV when large-span Select a Small Sc ale Terminal; Deficiency of Hunting problem s Improper Control ... of Fan Speed room’s load is large and large SAV is needed. Water Flow Because VAV17’s SAV is determined by Fig.6 OCM flow figure of VAV18, winter season temperature sensor in the small room, practical SAV First step: According to table 2, deviation of for the large room is insufficient. Therefore, large SAV is 4%，and OCM goes to estimate whether SAV SAV and low SAT of VAV16 are required to offset reaches maximum or minimum value. insufficient capacity of VAV17. Second step: According to Fig. 12, required SAV arrived at minimun value during 50% of time, and SAV hunting needs to be analyzed.

VAV-B10VAV-B10-18要求风量累计图-18 P ercentage of Cumulated Air Volume 2500

2000

1500

1000 风量(m3/h)

500 Air volume 0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Per百分比centage

Fig.5 Position of temperature sensor of VAV16 and Fig.7 Accumulative curve of required SAV VAV17 (B12) ( winter season, VAV18 ) Results of Diagnose: 1. Insufficient water flow Third step: According to Fig. 13, required SAV of AHU; 2. Sensor location is not reasonable. is hunting at most time.

温度(度)Temp. (℃ ) Volume.风量(m3/h) (m3 / h ) 3.4 Hunting Analysis 32 3000 30 28 2500 Hunting is a prevalent problem in VAV control 26 24 2000 22 system, which is also considered in OCM (Fig.2). 1500 20 18 1000 Take B10 in winter (I.Z.B, 6 terminals) for example. 16 14 500 Table 2 Terminal performance of B10 12 10 0 VAV 12 13 18 19 20 21 08:00 10:00 12:00 14:00 16:00 18:00 VAV-B10-18 B10-18Practical 室内温度 temp B10送风温度检测 B10-18 practical SAT Set air temperature (℃) 25 25 25 25 25 25 VAV-B10-18 B10-18 Set air温度设定 temp VAV-B10-18 B10-18 practical 计测风量 SAV VAV-B10-18 B10-18 Set SAV要求风量 Deviation of temperature 0.0 0.0 -0.8 0.5 0.5 0.5 (℃) Fig.8 Curve of indoor parameters（VAV18, Jan Deviation of volume 26th） 0.02 0.010.040.020.02 0.02 (×100%) Results of Diagnose: Hunting problem. Table 2 shows that VAV18 has a big deviation of As seen in Fig.14, all VAV terminals’ set air temperature, so enter the OCM diagnose system. temperatures are 25℃, and SAV is nearly close to minimum value. On the other hand, SAT varies between 22 and 28 ℃ , that means the system

Proceedings of the Sixth International Conference for Enhanced Building Operations, Shenzhen, China, November 6 - 9, 2006 ESL-IC-06-11-180

ICEBO2006, Shenzhen, China Building Commissioning for Energy Efficiency and Comfort, Vol. VI-1-1 alternates between cooling mode and heating mode. tested and gathered by system monitor are error free Under cooling mode, some terminals’ practical (the data in the case study are tested and corrected temperature are lower than set air temperature and before analysis). Practically, the troubleshooting of SAV can’t be reduced, so SAT needs to be increased sensor failure relies on actual measurements during until higher than 25℃. Then it turns to heating mode the operation stage, sometimes it is possible that the when SAT higher than 25℃. Under heating mode, performance test of the sensor and the OCM of the some terminals’ practical temperature are higher than HVAC control system should be carried out set air temperature so SAT needs to be reduced until simultaneously, which is a more complicated lower than 25℃. Then it turns to cooling mode ,when problem and needs further research. SAT lower than 25℃. In this case, hunting of SAT appears and it 5．ACKNOWLEDGEMENT results in hunting of fan speed, water valve, and The work of on-site testing and data collection terminal valve etc.. has obtained great support from Beijing Fortune Building Facility Department. The author would like 温度(度)Temp. (℃ ) Volume.风量(m3/h) (m3 / h ) 35 120 to take the opportunity to acknowledge their support! 30 100 25 80 20 60 REFERENCES 15 40 10 [1] Nakahara, Nobuo. Study and practice on HVAC 5 20 system commissioning. Proceedings of the 2003 - 0 0 8:00 10:00 12:00 14:00 16:00 18:00 4th International Symposium on Heating, B10给气温度设定 B10 Set air temp B10送风温度检测B10 practical SAT Ventilating and , 2003: 44-61 VAV-B10总要求风量 B10 Set air volume VAV-B10总控制状态B10 control state B10风机转速控制 B10 Set fan speed B10水阀开度控制B10 control of water valve [2] J. Hyvarinen, S. Karki. Building optimization and Fig.9 Curve of AHU parameters（B10, Jan 26th） fault diagnosis source book. IEA Annex (1996) 25 This case illustrates that hunting problem always [3] H. Yoshida, T. Iwami, H. Yuzawa, M. Suzuki. appears when cooling and heating requirement Typical faults of airconditioning systems and fault existing at the same time for the terminals linked to detection by ARX model and extended Kalman the same AHU. Filter. ASHRAE Transactions, 1996, 102 (1): There are three situation may result in the 557–564 problem: 1. small terminal load (always in [4] D. Ngo, A.L. Dexter. A robust model-based transitional season or interior zone); 2. Each VAV approach to diagnosing faults in air-handling units. terminal has a big deviation in set air temperature; 3. ASHRAE Transactions, 1999, 105 (1): 1078–1086. Improper zoning. [5] L.K. Norford, J.A. Wright, R.A. Buswell, D. Luo, C.J. Klaassen, A. Suby. Demonstration of fault 4．SUMMERRIZE detection and diagnosis methods for airhandling This paper introduced OCM to analyze the units, HVAC&R Research, 2002, 8 (1): 41–71 operation performance of VAV control system. OCM [6] Harunori Yoshida, Sanjay Kumar1, Yasunori Morita. will help to figure out the definite reason of a VAV Online fault detection and diagnosis in VAV air system’s failure and point out the direction for further handling unit by RARX modeling. Energy and improvement. The author explains how to use OCM Buildings, 2001,33: 391–401 logic flow chart in a VAV system with pressure [7] Jin Xin-Qiao, Du Zhi-Min, Sun Yong. Principal independent terminals through a case study. For other component analysis (PCA) based fault detection forms of HVAC system, some loops can be omitted, method for sensors in (VAV) but the main principle is the same. Furthermore, the air-conditioning system. Shanghai Jiaotong Daxue author analyzes the hunting problem in the case study Xuebao, 2005, 39(8): 1222–1225.(In Chinese) and summarizes several reasons of it. OCM is based on the assumption that the data

Proceedings of the Sixth International Conference for Enhanced Building Operations, Shenzhen, China, November 6 - 9, 2006