M.A. Fayazbakhsh

Comprehensive Modeling of Vehicle Air Conditioning Loads Using Heat Balance Method

The Heat Balance Method (HBM) is used for estimating the heating and cooling loads encountered in a vehicle cabin. A load estimation model is proposed as a comprehensive standalone model which uses the cabin geometry and material properties as the inputs. The model is implemented in a computer code applicable to arbitrary driving conditions. Using a lumped-body approach for the cabin, the present model is capable of estimating the thermal loads for the simulation period in real-time. Typical materials and a simplified geometry of a specific hybrid electric vehicle are considered for parametric studies. Two different driving and ambient conditions are simulated to find the contribution and importance of each of the thermal load categories. The Supplemental Federal Test Procedure (SFTP) standard driving cycle is implemented in the simulations for two North American cities and the results are compared. It is concluded that a predictive algorithm can be devised according to the driving conditions, vehicle speed, orientation, and geographical location. By using this model, the pattern of upcoming changes in the comfort level can be predicted in real-time in order to intelligently reduce the overall AC power consumption while maintaining driver thermal comfort.

A Resistance–Capacitance Model for Real-Time Calculation of Cooling Load in HVAC-R Systems

Simulating the real-time thermal behavior of rooms subject to air conditioning and refrigeration is a key to cooling load c alculations. A well-established Resistance-Capacitance (RC) model is employed that utilizes a representative network of electric resistors and capacitors to simulate the thermal behavior of such systems. A freezer room of a restaurant is studied during its operation and temperature measurements are used for model validation. Parametric study is performed on different properties of the system. It is shown that a reduction of 20% in the walls thermal resistivity can increase the energy consumption rate by 15%. The effect of set points on the number of compressor starts/stops is also studied and it is shown that narrow set points can result in a steady temperature pattern in exchange for a high number of compressor starts/stops per hour. The proposed technique provides an effective tool for facilitating the thermal modeling of air conditioned and refrigerated rooms. Using this approach, engineering calculations of cooling load can be performed with outstanding simplicity and accuracy.

A Self-Adjusting Method for Real-Time Calculation of Thermal Loads in HVAC-R Applications

A significant step in the design of heating, ventilating, air conditioning, and refrigeration (HVAC-R) systems is to calculate room thermal loads. The heating/cooling loads encountered by the room often vary dynamically while the common practice in HVAC-R engineering is to calculate the loads for peak conditions and then select the refrigeration system accordingly. In this study, a self-adjusting method is proposed for real-time calculation of thermal loads. The method is based on the heat balance method (HBM) and a data-driven approach is followed. Live temperature measurements and a gradient descent optimization technique are incorporated in the model to adjust the calculations for higher accuracy. Using experimental results, it is shown that the proposed method can estimate the thermal loads with higher accuracy compared to using sheer physical properties of the room in the heat balance calculations, as is often done in design processes. Using the adjusted real-time load estimations in new and existing applications, the system performance can be optimized to provide thermal comfort while consuming less overall energy. [DOI: 10.1115/1.4031018]

Thermodynamic investigation of a typical commercial refrigeration system

In this study, the thermodynamic performance of a typical commercial refrigeration system is investigated and the degradation from design condition is evaluated. A mathematical model is developed to simulate thermal behavior of the refrigeration system and to obtain the coefficient of performance (COP). A number of measuring equipment including thermocouples, pressure transducers, flow meters, and power meters are installed on the refrigeration system to obtain the real-time data for a period of three months. The acquired data is utilized to investigate the thermodynamic behavior of refrigeration system in addition to model validation. A good agreement between the simulation results and the real-time data, with a maximum discrepancy of 9%, is achieved. The results represent a range of 1.1-1.4 for current COP of the refrigeration system under different operating conditions. It is shown that due to degradation, the current COP is lower than design COP by 29%-39% in different duty cycles.

Analytical Modeling of Mist Condensation by Natural Convection Over Inclined Flat Surfaces

Dew formation on a transparent surface creates a pattern that can cause blurred view over it. This fogging phenomenon should be avoided in many applications. Mist condensation of water on a cold surface exposed to humid air is studied in this work. In order to analyze the misting process, the fluid flow and heat transfer of humid air as well as the heat transfer across the solid surface are considered. A dew formation model is used to predict the shape and size of the droplets. Analytical models have been proposed to solve the heat and mass transfer for the simple arrangement of a vertical flat surface. The analytical model is then combined with the dew formation model to introduce an analytical model for mist condensation over vertical and inclined surfaces. Due to the proposed method, complex numerical calculations can be avoided for solving the heat and mass transfer equations.Copyright