Shengwei Wang

Supervisory and Optimal Control of Building HVAC Systems: A Review

HVAC systems are the major energy consumers in buildings. Operation and control of HVAC systems have significant impacts on the energy or cost efficiency of buildings besides their designs. Buildings nowadays are mostly equipped with comprehensive building automation systems (BASs) and building energy management control systems (EMCSs) that allow the possibility of enhancing and optimizing the operation and control of HVAC systems. Supervisory and optimal control, which addresses the energy or cost-efficient control of HVAC systems while providing the desired indoor comfort and healthy environment under the dynamic working conditions, is attracting more attention of the building professionals and the society and provides incentives to make more efforts in developing more extensive and robust control methods for HVAC systems. This paper provides a framework for categorizing the main supervisory and optimal control methods and optimization techniques developed and/or utilized in the HVAC field. The application characteristics of each control method and optimization technique are also identified and compared. A comprehensive overall review of the state of the art of the research and development, as well as application of supervisory and optimal control, in HVAC systems is also presented.

Model-based optimal control of VAV air-conditioning system using genetic algorithm

Abstract A control strategy using a system approach based on predicting the responses of overall system environment and energy performance to the changes of control settings of VAV air-conditioning systems is developed. Incremental dynamic models with ‘self-tuning’ of the VAV system are developed and used. A genetic algorithm is used by the strategy to solve the on-line optimisation problem of multiple parameters. The strategy is tested and evaluated in a simulated ‘living’ environment under various weather conditions.

Dynamic simulation of building VAV air-conditioning system and evaluation of EMCS on-line control strategies

Abstract Dynamic models are developed to simulate the thermal, hydraulic, environmental and mechanic characteristics and energy performance of a building and VAV air-conditioning system under the control of EMCS. Three on-line supervisory strategies and programs based on integrated EMCS stations are developed to optimise the VAV static pressure set-point, AHU outlet air temperature set-point and outdoor ventilation air flow set-point, The strategies and programs are commissioned and evaluated under the simulated ‘real-life’ environment. This paper presents the dynamic models, the control strategies and the simulation exercises for commissioning and evaluation of the strategies.

Dynamic simulation of a building central chilling system and evaluation of EMCS on-line control strategies

Abstract Dynamic models of centrifugal chillers, heat exchangers, seawater and chilled-water networks, cooling coil, actuator, sensor, variable-speed pump and DDC controller of EMCS are developed to simulate the dynamics of a seawater-cooled chilling system controlled by EMCS on-line strategies. The thermal, hydraulic, energy and control performances of the system are simulated. The on-line control strategies (i.e. adaptive and derivative strategies) developed for the central chilling system are tested and evaluated by applying them to control the simulated living chilling system under different AHU dynamic loads. This paper presents the models, system dynamic simulation of the chilling system, chilling system performance monitoring, validation of simulation, EMCS on-line control strategies and evaluation of the strategies.

Integrating Building Management System and facilities management on the Internet

Abstract Recently, it is of great interest to adopt the Internet/Intranet to develop Building Management Systems (BMS) and Facilities Management Systems (FMS). This paper addresses two technical issues: the Web-based access (including database integration) and the integration of BMS and FMS. These should be addressed for accessing BMS remotely via Internet, integrating control networks using the Internet protocols and infrastructures, and using Internet/Intranet for building facilities management. An experimental Internet-enabled system that integrates Building and Facilities Management Systems has been developed and tested. This system integrated open control networks with the Internet and is developed utilizing the embedded Web server, the PC Web server and the Distributed Component Object Model (DCOM) software development technology on the platform of an open control network. Three strategies for interconnecting BMS local networks via Internet/Intranet are presented and analyzed.

CO 2-Based Occupancy Detection for On-Line Outdoor Air Flow Control

This paper presents a dynamic method for detecting the actual occupancy in indoor spaces by measuring the carbon dioxide concentration of the return air and the outdoor air flow rate. The accuracy and response speed are tested and compared with the steady-state detection method. An on-line outdoor air flow control strategy using the dynamic detection method and the validation of the strategy are presented. The indoor air quality and energy performance of the demanded ventilation using this strategy, two CO2-based demanded control strategies and the strategy of constant outdoor air flow, are compared and evaluated under various occupancy and outdoor weather conditions in simu lation.This paper presents a dynamic method for detecting the actual occupancy in indoor spaces by measuring the carbon dioxide concentration of the return air and the outdoor air flow rate. The accuracy and response speed are tested and compared with the steady-state detection method. An on-line outdoor air flow control strategy using the dynamic detection method and the validation of the strategy are presented. The indoor air quality and energy performance of the demanded ventilation using this strategy, two CO2-based demanded control strategies and the strategy of constant outdoor air flow, are compared and evaluated under various occupancy and outdoor weather conditions in simulation.

Experimental Validation of CO2-Based Occupancy Detection for Demand-Controlled Ventilation

On-line ventilation control based on carbon dioxide (CO2) measurement and the dynamic CO 2 balance in indoor spaces has been validated using a dynamic algo rithm for two existing buildings. Occupancy profiles esti mated using the dynamic algorithm were compared with the true occupancy profiles and the occupancy profiles estimated using a steady-state algorithm based on the steady-state CO2 balance. The dynamic algorithm esti mates the changes of occupancy without significant de lay. The steady-state algorithm is comparable only at a high air change rate and shows a considerable delay when the number of air changes per hour in a space is small. This phenomenon was investigated using com puter simulation.

Sensor validation and reconstruction for building central chilling systems based on principal component analysis

This paper presents an automatic and online FDD (fault detection and diagnose) and sensor reconstruction scheme that can be used in a building energy management and control system to detect and diagnose sensor faults and reconstruct faulty sensors in building central chilling systems. The scheme is based on principal component analysis to build a model that captures the correlation among the flow meters and temperature sensors installed in the chilling systems. The model is employed to reconstruct an assumed faulty sensor. The square prediction error based on the model and the sensor validity index based on the construction are employed, respectively, to detect the sensor fault and identify the faulty sensor. An existing building central chilling system is simulated to test and validate the developed scheme online. Four types of sensor faults are introduced, respectively, during the simulation to validate the sensor FDD and sensor reconstruction scheme.

A robust fault detection and diagnosis strategy for centrifugal chillers

This paper presents a robust fault detection and diagnosis (FDD) strategy for centrifugal chillers. The strategy consists of a model-based chiller FDD scheme and a sensor fault detection, diagnosis, and estimation (FDD&E) scheme, which handle chiller faults and sensor faults, respectively. The sensor FDD&E scheme uses a PCA-based method (principal component analysis) to capture the correlations among the major measured variables in centrifugal chillers, as it performs well even in the presence of typical chiller faults. The chiller FDD scheme has been developed based on six physical performance indices, which are capable of describing the health condition of centrifugal chillers and, thus, indicating chiller faults. Only after all the sensors whose measurements are crucial to the chiller FDD are validated by the sensor FDD&E scheme is the chiller FDD scheme used to conduct the chiller system FDD. The strategy was validated using laboratory data from ASHRAE RP-1043 and field data from a centrifugal chiller in a real building.

Transient heat flow calculation for multilayer constructions using a frequency-domain regression method

A frequency-domain regression method is developed for transient heat flow calculation of multilayer constructions, which estimates a simple polynomial s-transfer function of transient heat conduction in a building construction on the basis of its theoretical frequency characteristics. This simple polynomial s-transfer function is completely equivalent to the hyperbolic s-transfer function in terms of frequency characteristics. First, the frequency characteristics of the total transmission matrix are calculated within the frequency range concerned. Then, a set of linear equations is solved to yield a simple polynomial s-transfer function for internal, cross and external heat conduction, respectively. Finally, the response factors or CTFs are obtained simply by applying inverse Laplace transforms or Z-transforms on the polynomial s-transfer function. The validations and comparisons show that this method has high accuracy and efficiency and has no stability problem.