Air-conditioning Control Strategies Research Articles

Developing a validated simulation model of micro-zonal air-conditioning to evaluate thermal comfort parameters

ABSTRACT Micro-Zonal Occupant-Centric Control (MZOCC) helps in reducing building energy consumption by conditioning only the occupied regions in a room. For this, MZOCC divides a large room such as open-plan offices into virtual micro-zones to allow independent diffuser level control. But, unplanned MZOCC can lead to heavy thermal gradients and deflection of air jets, leading to thermal discomfort. To evaluate thermal comfort at different regions of a room under MZOCC, there is a need to accurately model parameters of thermal comfort. Field studies, exploring the transient variations in air temperature, humidity and velocity at different regions of the room due to MZOCC, are limited. At the same time, developing validated simulation models or digital twins using experimental data helps in exploring micro-zonal strategies to arrive at the best strategy. The aim of this study is to create a digital twin of an open-plan office and model the parameters required to estimate thermal comfort. This study senses transient variations in air temperature, velocity and humidity using a wireless sensor network and develops a computational fluid dynamic (CFD) model that can accurately model the sensed transient variations. Field data, constituting external surface temperatures captured using thermal images, variations in air-conditioning control strategy, dynamic occupancy and location, are periodically updated in the digital twin. The CFD model accurately predicts the trends in variations in indoor temperature, velocity and humidity at different regions of the room. The developed digital twin can be used in future studies to evaluate thermal comfort and plan MZOCC control strategies.

A modelling method for large-scale open spaces orientated toward coordinated control of multiple air-terminal units.

The temperature distribution is always assumed to be homogeneous in a traditional single-input-single-output (SISO) air conditioning control strategy. However, the airflow inside is more complicated and unpredictable. This study proposes a zonal temperature control strategy with a thermal coupling effect integrated for air-conditioned large-scale open spaces. The target space was split into several subzones based on the minimum controllable air terminal units in the proposed method, and each zone can be controlled to its own set-point while considering the thermal coupling effect from its adjacent zones. A numerical method resorting to computational fluid dynamics was presented to obtain the heat transfer coefficients (HTCs) under different air supply scenarios. The relationship between heat transfer coefficient and zonal temperature difference was linearized. Thus, currently available zonal models in popular software can be used to simulate the dynamic response of temperatures in large-scale indoor open spaces. Case studies showed that the introduction of HTCs across the adjacent zones was capable of enhancing the precision of temperature control of large-scale open spaces. It could satisfy the temperature requirements of different zones, improve thermal comfort and at least 11% of energy saving can be achieved by comparing with the conventional control strategy.Electronic Supplementary Material (ESM)the Appendix is available in the online version of this article at 10.1007/s12273-022-0942-8.

A novel multistage constant compressor speed control strategy of electric vehicle air conditioning system based on genetic algorithm

This study establishes a passenger cabin-coupled air conditioning model that the heat exchangers adopted in the air conditioning model, are calibrated by testing, during which the parameters for establishing the passenger cabin model are measured. The cabin temperature simulation results of the air conditioning model proposed in this paper fit well with the test results, with a maximum difference of 3 °C. A genetic algorithm (GA) optimization-based multistage constant-compressor speed (MCCS) air conditioning system control strategy is proposed. This control strategy sets the cabin temperature as the input control factor and the compressor speed as the output factor, and different cabin temperature ranges correspond to the MCCSs, which are optimized by the GA. The presented strategy is contrasted with the most commonly used on/off controllers and the proportional integral derivative (PID) controller, and an engineering-applied (EA) air conditioning control strategy. The proposed controller can maintain passenger cabin thermal comfort and save energy simultaneously, and it can be easily applied in engineering. Based on the simulation results, the MCCS controller can save 17.5, 7.5, and 5.8% more energy consumption than the on/off, PID, and EA controllers. Moreover, it can improve the coefficient of performance of the air conditioning system by 5.3 and 3.9% more than the PID and EA controllers. Therefore, the proposed MCCS controller can increase the operation efficiency of electric vehicles AC system.

Study on the uneven distribution of vertical space humidity in a rocket testing workshop

In view of the problem of inconsistent air-conditioning delivery and uneven distribution of vertical space humidity in a rocket testworkshop at a coastal launch site, this paper analyzes the cause and mechanism of the problem based on the characteristics of high space air distribution, test plant structure and air-conditioning system. And puts forward the specific measures such as adjusting high-rise space air delivery target, optimizing the air-conditioning control strategy and improving the unit’s dehumidification capacity. These measures provide support for the solution of the problem and the optimal design and transformation of air-conditioning.

Research on Air-Conditioning Control Strategy of Textile Mill Based on Bidirectional Fuzzy Dynamic Decoupling Compensation

This paper introduces the main problems in the air conditioning system of China’s textile mills. Due to the coupled line problem of temperature and humidity affecting each other in the temperature and humidity regulation system, it is difficult to adjust the air conditioning system in the textile mill, and it is also more difficult to adjust the air conditioning system in the textile mill because of the influence of region, season, human activities and so on. In view of this situation, the air conditioning control system of textile mill based on TMS320F28335 was designed by dynamic decoupling control method. The reasonable adjustment and control of the equipment of the air conditioning system can achieve the stable control of the temperature and humidity of the workshop of the textile mill and reduce the energy consumption of the air conditioning control system. The practice shows that the system has good dynamic performance, high control precision and remarkable energy saving effect, and has a broad application prospect in air conditioning control in textile enterprises.

A new model predictive control scheme for energy and cost savings in commercial buildings: An airport terminal building case study

Predictive control technology for heating, ventilation and air conditioning (HVAC) systems has been proven to be an effective way to reduce energy consumption and improve thermal comfort within buildings. Such methods rely on models to accurately predict the thermal dynamics of a specific building to achieve the optimal control. Implementing a predictive control at the building level faces several challenges, since buildings’ thermal dynamics are nonlinear, time-varying, and contain several uncertainties. This paper presents a hybrid model predictive control (HMPC) scheme, which can minimise the energy and cost of running HVAC systems in commercial buildings. The proposed control framework combines a classical MPC with a neural network feedback linearisation method. The control model for the HMPC is developed using a simplified physical model, while the nonlinearity associated with HVAC process is handled independently by an inverse neural network model. To achieve the maximum energy saving, the proposed MPC integrates several advanced air-conditioning control strategies, such as an economizer control, an optimal start-stop control, and a load shifting control. This approach has been tested at the check-in hall of the T-1 building of the Adelaide Airport, through simulations and a field experiment. The merits of the proposed method compared to the existing control method are analysed from both the energy saving and cost saving points of view. The result shows that the proposed HMPC scheme performs reasonably well, and achieves a considerable amount of savings without violating thermal comfort.

Method and Realization of Central Air-Conditioning Control Strategy Communication Based on STM32

Abstract. With the SIEMENS S7-200 PLC and HMI based on KingView being the master, a slave station of STM32F103C8T6 microcontroller is developed based on MODBUS protocol. The establishment and program designing of communication protocol using RS485/RS232 between master and slave is introduced firstly. Then the process of debugging between the microcontroller and PC, the microcontroller and the PLC is elaborated. Thus serial communication is implemented based on MODBUS protocol in RTU mode. The system will be applied in central air-conditioning control system. A good control effect will be obtained as the controlling strategy and main algorithm can be computed in the STM32 slave station.

A study on the potential of natural ventilation and cooling for large spaces in subtropical climatic regions

The potential of natural ventilation and cooling due to stack effects was investigated for large spaces with high ceilings. Different opening area ratios with respect to floor area were studied. Parameters of stack effects that consider floor heights were analyzed. Performance of natural ventilation was evaluated with cooling effects and indoor air quality for different months of the year. Three cities in northern, middle and southern Taiwan were used to represent typical subtropical weather types. It was found that opening ratio above 0.9％ is sufficient to provide fresh air to meet IAQ requirement. Two different temperature control strategies, fixed indoor temperature (FIT) and operative indoor temperature (OIT) were proposed and studied. A sensible cooling potential, f pc, was proposed. Different levels of f pc, namely, strong, medium, weak and not available were used to evaluate the number of days for which natural cooling, hybrid ventilation, mechanical air conditioning are to be applied to satisfy the cooling requirement. The research results presented can be used in the design of openings for large spaces, and also the air-conditioning control strategies for different seasons of the year.

Air-conditioning control strategies : Computer simulation for a commercial building in Hong Kong

This paper presents a transient simulation method for simulating an air-conditioning (AC) system in a commercial building. Using the simulation program, a typical air-water cooling system in a commercial building was simulated with real data from Hong Kong. The impacts of several different control strategies (start/stop, continuous, start/stop with night ventilation, economiser) on energy saving were computed and the energy consumptions were compared. The effects on energy saving of the control mode before the occupied period and the chilled water outlet temperature from the chillers were also simulated. The computational results show that the control strategy has a significant effect on the energy consumption of an air-conditioning system and that there is an optimal range of chilled water outlet temperature within which the system energy consumption is a minimum.