Variable Air Volume Air Research Articles

Experimental study of five different VAV air terminal devices under variable heat gain conditions in simulated office and meeting rooms

Demand control of the air distribution systems is crucial to the satisfactory thermal environment under variable heat gain conditions in an energy efficient manner. In this study, the airflow patterns, ventilation performance and local thermal comfort have been experimentally investigated in mock-up meeting and office rooms with a variable air volume (VAV) system. The Active Diffuser, which had a constant inlet air velocity, was compared with some commonly used diffusers: Rectangular; Swirl-Radial; Swirl-Compact and Multi-Nozzle Diffusers. In the test, there were four different heat gain levels: high heat gain (46 W/m2) in a meeting room setting; high (46 W/m2), medium (24 W/m2) and low (11 W/m2) heat gain in an office room setting, respectively. The corresponding specific supply airflow rates in the high, medium and low heat gain cases were 4.3 L/s m2, 2.1 L/s m2, 1 L/s m2, respectively. Visualized figures showed the effect of VAV on airflow patterns were quite different among different diffusers. The indexes including air velocity, ventilation effectiveness, effective draft temperature, draught rating and so on were therefore analysed. By using the Active Diffuser, the airflow distribution and most of these indexes were more uniform and more stable under the VAV. Although the Rectangular, Swirl-Compact, Swirl-Radial and Multi-Nozzle Diffusers might perform better in one or two cases regarding some indexes, their airflow patterns and performances of indexes were unstable under the VAV. Thus, the Active Diffuser was recommended for the VAV system for the application where heat gains vary significantly.

Assessing the energy performance of VAV and VRF air conditioning systems in an office building located in the city of Florianópolis

Abstract The objective of this study is to analyze the energy performance of two types of water-cooled air conditioning systems, variable air volume (VAV) and variable refrigerant flow (VRF), in terms of their cooling energy use through building simulation. These systems were designed to operate in an office building located in the city of Florianópolis, Brazil. The analysis involved the application of two building use schedules: a) constant and b) variable. Moreover, an analysis of the coefficient of performance (COP) and partial load ratio (PLR), and the percentage of operating hours for each range of cooling COP and PLR for each air conditioning system, allowed the system cooling efficiency to be assessed and the results to be related to the annual energy consumption. The coefficient of performance of VAV and VRF is 6.7 and 5.0, respectively, but the VRF system presented the lowest energy consumption for both schedules. The difference in the cooling energy consumption values for the VRF and VAV systems, for the variable schedule compared with the constant schedule, is mainly influenced by the partial load performance during the hottest period of the year.

Optimization of BuildingsEnergy Consumption by Designing Sliding Mode Control for Multizone VAV Air Conditioning Systems

Variable air volume (VAV) is the most common installation among heating ventilating and air conditioning (HVAC) systems. To maintain the comfort level and lessen energy utilization, there is a pressing need for its effective control. In this study, a lumped parameter model composed of multizone VAV is considered, and sliding mode control (SMC) is designed to guarantee robust operation in the presence of uncertainties. For comparison of the proposed controller performance, a proportional integral derivative (PID) controller is additionally designed. The indoor temperature of zones is controlled by positioning the supply air dampers. Tracking objectives of controllers are inspected via two practical cases of desired temperature setpoints including (a) sinusoidal waveform and (b) the combination of steps. Results obtained using SMC ensure the robust operation of the VAV system against parametric uncertainties. In addition, SMC is more energy efficient than PID in terms of overshoot and settling time.

An identification method for room temperature dynamic model based on analytical solution in VAV system

Variable Air Volume (VAV) system is a typical time delay system with multiple variables, and it is difficult to build a dynamic response model for describing room temperature regulation process. This paper firstly proposes a novel model of dynamic response of room temperature based on the analytical solution of heat balance equation in VAV air conditioning zone. According to the solution, inertia time constant and magnification coefficient of room temperature response can be directly calculated by initial environmental parameters. The model is further extended to a Multi-Input Single-Output (MISO) model with airflow regulating actuators as input and room temperature as model output. Experimental studies are carried out to test practical supply airflow and room temperature response and corresponding model parameters are identified according to the measured data in the VAV experimental platform. The proposed identification method based on analytical solution is validated through simulation and compared with classical identification method. Results indicate that the proposed identification method could describe the room temperature dynamic characteristics of VAV system well, and it can be applied in control simulation and engineering application in future work.

Predication control for indoor temperature time-delay using Elman neural network in variable air volume system

Aiming at the prediction control for indoor temperature time-delay in variable air volume (VAV) air conditioning system, this paper presents an indoor temperature prediction control method based on Elman neural network multi-step prediction model. Firstly, this paper introduces basic control principles of pressure-dependent and pressure-independent VAV terminal through comparable analysis and points out significance of indoor temperature prediction control based on pressure-dependent VAV terminal. Then, Elman neural network multi-step prediction model and corresponding indoor temperature prediction control method for pressure-dependent VAV terminal are proposed based on the fundamental principle of periodic prediction control for time-delay system. Finally, the effect of proposed prediction control method is validated by the experimental study according to the test data of supply air volume regulating process, provided that the supply air volume control loop adopts constant static pressure control method. Experimental results indicate the proposed indoor temperature prediction control method based on pressure-dependent VAV terminal could change the conventional regulating mode of the VAV air conditioning system, which will be benefit for improving the control stability of indoor temperature control loop and other corresponding control loops.

Fault diagnosis and energy consumption analysis for variable air volume air conditioning system: a case study

Several common faults and their causes in variable air volume (VAV) air conditioning system are presented, and the principle of fault diagnosis of air conditioning system is briefly described. The VAV air conditioning system was modeled in TRNSYS, and five typical faults of the cooling mode were simulated. The comparative analysis of the respective under normal operation and fault operation had been made, and the impact of each fault on the energy consumption was also analyzed. The actual operating characteristics of air conditioning system was then evaluated. Further, some parameters under fault operations were compared with those under the normal operation, from which the changing characteristics of parameters could be discovered, and the characteristics can be used to diagnose faults. The simulation results demonstrate that fault can affect the energy consumption of VAV air conditioning system, and the impact of each fault is different. In addition, monitoring the change of energy consumption and operation parameters is helpful in fault diagnosis, and the effective fault diagnosis has great significance to energy-saving of the air conditioning system.

Novel cylindrical induction controller and its application in VAV air conditioning system in an office building

High performance variable air volume (VAV) air-conditioning systems can be as energy efficient as systems based on water or refrigerant, while first and life-cycle costs of such systems are significantly lower. The paper presents experimental test results of a novel cylindrical induction VAV controller and simulation results of energy consumption and thermal comfort in an office building with such controllers. A method for estimation of the minimum induced airflow required to avoid cold air dumping and a method for induction controllers and diffusers selection and sizing are proposed. To compare the VAV system with induction controllers and two other popular air conditioning systems, in terms of energy consumption and thermal comfort in an office building, the IDA Indoor Climate and Energy simulation tool was applied. The comparison was made for moderate climate conditions of Krakow, Poland, typical of Central and East Europe. The results showed that the total consumption of the electric energy used in cooling season for cooling and media transportation was similar when using a VAV system with induction controllers, a system with air chilled beams or a fan coils system. Similar thermal conditions were also observed.

A robust fault detection and diagnosis strategy for multiple faults of VAV air handling units

Fault detection and diagnosis (FDD) is critical to reliable operation and energy efficiency of variable-air-volume (VAV) air-conditioning system. In this paper, a robust fault detection and diagnosis strategy is presented for multiple faults of air handling units by using the residual-based exponentially weighted moving average (EWMA) control chart method and the rule-based fault diagnosis method. Residual-based EWMA control chart with designing chart limits is used to detect faults of air handling units. In order to provide a level of robustness with respect to modeling errors, control limits are determined by incorporating uncertainty information into EWMA control chart. Furthermore, the rule-based fault diagnosis method is extended to isolate simultaneous multiple faults of VAV air handling units in the mechanical cooling operation mode. Twenty-six expert rules consisting of system behavior rules and energy related rules are used to diagnose twenty-two faults of air handling units. The fault detection and diagnosis strategy was validated by using the operating data from real VAV air-conditioning systems involving multiple artificial faults. The results of validation show that residual-based EWMA control chart with designing control limits is a robust tool of fault detection for air handling units. The rule-based fault diagnosis method presented is efficient to isolate multiple faults of air handling units.

Experimental study on a novel fuzzy control method for static pressure reset based on the maximum damper position feedback

In variable air volume (VAV) systems, conventional control methods reset the supply air static pressure based on the exact mathematics model of the controlled objects which are often difficult to be founded, because the VAV controlled systems have the characteristics of nonlinear, multivariable and long delay times. In order to develop a simple inference process for real-time applications, this paper presents a novel fuzzy control method for static pressure reset with no using of the mathematics model. The proposed fuzzy control method is developed based on the maximum damper position feedback using Mamdani-type fuzzy rule and functioning fuzzy subset inference (FFSI). This study provides the detail implement process of the proposed fuzzy control method. Supported by the experimental data, the proposed method is compared with optimal fixed changing step method in an integrated control test rig for a VAV air conditioning system. Experimental results show that the proposed method has better energy efficient and control performance. A minimum of 7% energy saving of the proposed fuzzy control method is shown through experimental study.

A Review of Static Pressure Reset Control in Variable Air Volume Air Condition System

For the sake of energy saving of variable air volume (VAV) system, this paper presents the a review of static pressure control around the optimization problem of static pressure reset in VAV air conditioning system. Then, main control methods of static pressure reset are described, and existing problems are analyzed and concluded. Finally, it is pointed out that the critical technology and the development trend of static pressure reset control. This overview is not intended to be an exhaustive survey on this topic, and any omission of other works is purely unintentional.

Energy Performance Simulation Study on VAV Air Condition System at SPSU Campus Office Building with EnergyPlus

Based on the air condition systems theorem, by EnergyPlus7.0 the office building models were built up with the variable air volume (VAV) and constant air volume (CAV) systems separately at SPSU campus in the USA. The weather datum from Department of Energy US were used to simulate the energy consumption performance both daily and annually. Results show that the VAV system saves the sensible cooling rate 19.25% compared with the CAV one in the hottest day. The VAV system saves the sensible cooling rate 8.95% and reduces the outdoor infiltration sensible heat gain about 35.06% yearly. The VAV terminal-damper position doesnt change linearly as the outdoor climate temperature for the complex system in heating, ventilating, and air-conditioning (HVAC). Though the outdoor temperature is the same, the system sensible cooling rate is greatly different in autumn and spring day.

Design of Terminal Controller of VAV Air-Conditioning System Based on BAS3000 DDC

The terminal device (VAVBOX) is the key part in variable air volume (VAV) air conditioning system, by which we can adjust air output, compensate indoor load change, keep room temperature to be constant. The control effect of VAV system depends largely on the performance of terminal device and the coordination between terminal device and the whole system. In this paper, BAS - 3520 DDC produced by Advantech corporation is used to design VAV air conditioning pressure independent terminal controller. Experiments show that the terminal controller based on DDC can well satisfy the system control requirement, the transition time and overshoot of the indoor temperature achieve good improvement. At the same time , with Webaccess introduced, VAV BOX operation condition can be monitored by host computer, what makes the daily management of the VAV BOX more intelligent.

Online model-based fault detection and diagnosis strategy for VAV air handling units

An online model-based fault detection and diagnosis (FDD) strategy is presented in this paper to diagnose abrupt faults of variable-air-volume (VAV) air handling units (AHU). The FDD strategy proposed adopts a hybrid approach integrating model-based FDD method and rule-based FDD method. Self-tuning model is used to detect the faults in AHU systems. Model parameters are adjusted by a genetic algorithm-based optimization method to reduce the residual between prediction and measurement. If the residual exceeds the corresponding fault detection threshold, it indicates the occurrence of fault or abnormality in AHU systems. Meanwhile, an online adaptive scheme is proposed to estimate the fault detection threshold, which varies with system operating conditions. Furthermore, three rule-based fault classifiers are developed and utilized to find fault sources. The FDD strategy proposed was tested and validated on real VAV air-conditioning systems involving multiple faults. The validation results show that the FDD strategy proposed can provide an effective tool for detecting and diagnosing the faults of air handling units.

Simulation comparison of VAV and VRF air conditioning systems in an existing building for the cooling season

Performance of two widely used air conditioning (AC) systems, variable air volume (VAV) and variable refrigerant flow (VRF), in an existing office building environment under the same indoor and outdoor conditions for an entire cooling season is simulated by using two validated respective models and compared. It was observed that the indoor temperatures could not be maintained properly at the set temperature by the VAV no-reheat boxes. However, it could be maintained by the VAV boxes with reheat with a significant energy consumption penalty. It was found that the secondary components (indoor and ventilation units) of the VRF AC system promised 38.0–83.4% energy-saving potential depending on the system configuration, indoor and outdoor conditions, when compared to the secondary components (heaters and the supply fan) of the VAV AC system. Overall, it was found that the VRF AC system promised 27.1–57.9% energy-saving potentials depending on the system configuration, indoor and outdoor conditions, when compared to the VAV AC system.

Simulation of a VAV air conditioning system in an existing building for the cooling mode

In this study, simulation of a variable air volume (VAV) air conditioning system in an existing office building is presented for the cooling mode. A building simulation package was used for the simulation [DOE, EnergyPlus Engineering Document, Version 1.3., U.S. Department of Energy, Washington, DC, 2005]. The design information of the existing office building, the actual number of the internal load sources such as occupants, lighting, office equipments and the manufacturer's data for the existing rooftop unit (RTU) and the VAV boxes were used in the building simulation package. The simulation results; RTU power consumption, indoor zone temperature and relative humidity, were validated with the data obtained from the on-site measurements performed in the existing office building under the same outdoor conditions. It was found that 71.1% of all simulated power consumption data falls within ±15% range from the experimental data. The reason for the existence of some data out of band is due to the possible errors associated with the difference in the solar data used for the location 40 km away from the experimental location. It was found that 90.6–94.7% of the indoor temperature experimental data fall within ±1.5 °C range from the simulated data, and 88.3–91.3% of the indoor relative humidity data fall within ±18% range from the simulated data.

Optimization of Energy Conservation Potential for VAV Air Conditioning System using Fuzzy based Genetic Algorithm

The objective of this study is to present the test results of variable air volume (VAV) air conditioning system optimized by two objective genetic algorithm (GA). The objective functions are energy savings and thermal comfort. The optimal set points for fuzzy logic controller (FLC) are the supply air temperature (Ts), the supply duct static pressure (Ps), the chilled water temperature (Tw), and zone temperature (Tz) that is taken as the problem variables. Supply airflow rate and chilled water flow rate are considered to be the constraints. The optimal set point values are obtained from GA process and assigned into fuzzy logic controller (FLC) in order to conserve energy and maintain thermal comfort in real time VAV air conditioning system. A VAV air conditioning system with FLC installed in a software laboratory has been taken for the purpose of energy analysis. The total energy saving obtained in VAV GA optimization system with FLC compared with constant air volume (CAV) system is expected to achieve 31.5%. The optimal duct static pressure obtained through Genetic fuzzy methodology attributes to better air distribution by delivering the optimal quantity of supply air to the conditioned space. This combination enhanced the advantages of uniform air distribution, thermal comfort and improved energy savings potential. Keywords—Energy savings, fuzzy logic, Genetic algorithm, Thermal Comfort

Experimental Analysis of a Genetic-Fuzzy Inverter DX VAV A/C System for Automatically Ventilated Buildings

In recent years, the quest has been focused on energy efficient building design. To achieve this in terms of high efficiency air conditioning schemes for hot climate cooling, the combination of variable refrigerant volume (VRV) with variable air volume (VAV) systems have become popular. In this paper, attention is focused on achieving good thermal comfort and indoor air quality (IAQ) combined with energy savings by using multi-zone VAV air conditioning (A/C) that incorporates a genetic based fuzzy logic controller (FLC). Experimental analysis based on a combined demand controlled ventilation (DCV) with economizer cycle (EC) was performed on an inverter driven multi-zone direct expansion (DX) VAV A/C system integrated with a fuzzy logic controller and optimized by a genetic algorithm (GA). The opening of the VAV box damper was controlled using the fuzzy logic controller. Based on the test results, the proposed fuzzy logic operated system maintained supply air temperature close to 13°C and an occupant zone at a consistent temperature of around 24 °C. In DCV mode, the concentration of CO2 was maintained between 950 ppm and 1040 ppm while, when the system was operated under a combined DCV-EC ventilation scheme, the CO2 concentration was maintained at between 350 ppm and 970 ppm. The experimental results suggested that CO2 concentration obtained experimentally was well within the permissible limit for the varying load conditions. Under the combined DCV-EC mode of ventilation, using a fuzzy-genetic algorithm, the maximum power obtained for the supply air fan and variable speed compressor was 415 W and 3.4 kW respectively. The compressor was totally turned OFF during the economizer cycle thus contributing to total power savings. The energy savings potential of the proposed fuzzy controlled multi-zone DX VAV A/C system yielded 70% and 89% under DCV and combined DCV economizer cycle ventilation modes respectively when compared with a constant air volume (CAV) A/C system operated under the DCV technique. The test results suggested that it was feasible for this fuzzy control methodology, integrated with the developed genetic algorithm, to provide a proper control of IAQ, thermal comfort and energy conservation.

Performance improvement of VAV air conditioning system through feedforward compensation decoupling and genetic algorithm

VAV (variable air volume) control system has the feature of multi-control loops. While all the control loops are working together, they interfere and influence each other. This paper designs the decoupling compensation unit in VAV system in the method of feedforward compensation. This paper also designs the controller parameters of VAV system by means of inverse deducing and the genetic algorithm. Experimental results demonstrate that the combination of the feedforward compensation decoupling and the controller optimization by genetic algorithm can improve the performance of the VAV control system.

Development of a dynamic model for a DX VAV air conditioning system

Abstract A direct expansion (DX) variable air volume (VAV) air conditioning (A/C) system consists of a VAV air distribution subsystem and a DX refrigeration plant. This paper reports on the development of a representative and complete dynamic mathematical model for the DX VAV A/C system having a variable speed compressor and pressure independent VAV terminals. The model is component based and takes into account the dynamic behaviors of both the DX refrigeration plant and the VAV air distribution subsystem simultaneously. The dynamic model has been developed based on the principles of mass and energy conservation and using correlations describing the operational performance of some of the system’s components, which are either field tested or available from manufacturers. An experimental rig has been set up for the DX VAV A/C system, and experimental work has been conducted to obtain the system’s responses to the step change of compressor speed. The dynamic model developed was then validated using the experimental data obtained. Steady state and transient responses for five major operating parameters obtained from both the model and the experiment were compared and found to be in good agreement.

06/00786 Predicting the viscosity of liquid refrigerant blends: comparison with experimental data: Royal, D. D. et al. International Journal of Refrigeration, 2005, 28, (3), 311–319.

Fault detection and diagnosis (FDD) is critical to reliable operation and energy efficiency of variable-air-volume (VAV) air-conditioning system. In this paper, a robust fault detection and diagnosis strategy is presented for multiple faults of air handling units by using the residual-based exponentially weighted moving average (EWMA) control chart method and the rule-based fault diagnosis method. Residual-based EWMA control chart with designing chart limits is used to detect faults of air handling units. In order to provide a level of robustness with respect to modeling errors, control limits are determined by incorporating uncertainty information into EWMA control chart. Furthermore, the rule-based fault diagnosis method is extended to isolate simultaneous multiple faults of VAV air handling units in the mechanical cooling operation mode. Twenty-six expert rules consisting of system behavior rules and energy related rules are used to diagnose twenty-two faults of air handling units. The fault detection and diagnosis strategy was validated by using the operating data from real VAV air-conditioning systems involving multiple artificial faults. The results of validation show that residual-based EWMA control chart with designing control limits is a robust tool of fault detection for air handling units. The rule-based fault diagnosis method presented is efficient to isolate multiple faults of air handling units.