Investigation of energy-efficient strategy for direct expansion air-cooled air conditioning systems

This paper addresses the energy saving significance of air-cooled direct expansion (DX) air conditioning systems using liquid pressure amplification (LPA) technology along with proposed theoretical-empirical models for the system components. This method utilizes a refrigerant pump in the liquid line to allow the system operation at lower condensing pressure. An actual DX rooftop package is used for data collection. The performance of the proposed method is simulated using transient simulation software. Simulation tool was validated by comparing predicted and measured power consumption of the rooftop package. Results show that up to 42% power savings can be obtained using this approach

A comparative study on the effect of different strategies for energy saving of air-cooled vapor compression air conditioning systems

This paper investigates and compares the energy saving potential of air-cooled vapor compression air conditioning systems by using liquid pressure amplification (LPA), evaporative-cooled condenser (ECC) and combined LPA and ECC strategies. The applicability, limitation and energy performance of these strategies are discussed. For the purpose of this study, an existing direct expansion rooftop package of a commercial building is used for experimentation and data collection. The system under investigation is extensively equipped with a number of instrumentation devices for data logging. Theoretical–empirical mathematical models for system components were developed first, while a numerical algorithm together with monitored data and a mathematical model implemented on a transient system simulation tool is used to predict the performance of each strategy under transient loads. The integrated simulation tool was validated by comparing predicted and measured power consumption of the rooftop package. Comparing between LPA and ECC methods shows that for the ambient temperatures less than 27◦C the LPA is more effective method while for ambient temperature greater than 27◦C the ECC system is more efficient. Our results also demonstrate average energy savings of 25.3%, 18.3% and 44.2%, respectively for LPA, ECC and combined LPA and ECC methods

An innovative solar assisted desiccant-based evaporative cooling system for co-production of water and cooling in hot and humid climates

Although evaporative coolers consume much lower electricity than the vapor compression systems, they are not applicable in humid climates. Combination of desiccant wheels and evaporative coolers, known as desiccant-based evaporative cooling systems, allows evaporative coolers to be used in humid climates, which provide significant energy and environmental advantages with respect to vapor compression systems. However, one of the main disadvantages of evaporative cooling is the high water. Regarding the global water crisis, a cooling system which saves both water and energy will be an attractive alternative to the current cooling systems. To this aim, this paper presents a novel desiccant-based evaporative cooling system for co-production of water and cooling. In this system, the moisture content of exhaust regeneration air is recycled to cover all of the evaporative cooler water consumption, and also part of the domestic water usage. To evaluate the system performance, dynamic hourly simulation of the proposed system as well as a reference vapor compression system was performed for a typical 60m2 building in hot and humid climate of Bandar Abbas, Iran. The simulation results show that the proposed system is able to provide comfort temperature and relative humidity in a hot and humid climate. Moisture harvesting produce about 590L water during a week, which covers all of the evaporative cooler water consumption, and provides an excess amount of 289L for domestic usage. Monthly integrated results indicate that electricity consumption of the proposed system is 60% lower than the reference system, while its natural gas consumption is 30% higher than VCS, which is due to the high regeneration temperature in some hours. In other worlds, this system replace electricity consumption, a high-exergy and expensive energy carrier, with heat consumption. This system leads to 18.7% saving of CO2 emissions over a month. Economic evaluation proves the economic feasibility of proposed system with a payback period of 3 years. In conclusion, proposed system provide a more environmental friendly cooling system for water, energy and carbon saving

A review of different strategies for HVAC energy saving

Decreasing the energy consumption of heating, ventilation and air conditioning (HVAC) systems is becoming increasingly important due to rising cost of fossil fuels and environmental concerns. Therefore, finding novel ways to reduce energy consumption in buildings without compromising comfort and indoor air quality is an ongoing research challenge. One proven way of achieving energy efficiency in HVAC systems is to design systems that use novel configurations of existing system components. Each HVAC discipline has specific design requirements and each presents opportunities for energy savings. Energy efficient HVAC systems can be created by re-configuring traditional systems to make more strategic use of existing system parts. Recent research has demonstrated that a combination of existing air conditioning technologies can offer effective solutions for energy conservation and thermal comfort. This paper investigates and reviews the different technologies and approaches, and demonstrates their ability to improve the performance of HVAC systems in order to reduce energy consumption. For each strategy, a brief description is first presented and then by reviewing the previous studies, the influence of that method on the HVAC energy saving is investigated. Finally, a comparison study between these approaches is carried out

Thermo-economic optimization of rooftop unit’s evaporator coil for energy efficiency and thermal comfort

In this paper, the optimization-simulation approach is proposed to investigate energy saving potential of an air-cooled direct expansion rooftop package air conditioning system by refining the model of the HVAC system components and deriving optimal configuration for evaporator coil subject to technical constraints. In this method the frontal area of the evaporator coil is maintained as constant and the variation of other geometrical parameters on the thermal and economical performance of the system is investigated. An actual air-cooled rooftop package of a real-world commercial building in hot and dry climate conditions is used for experimental data collection. Both inputs and outputs are measured from the field monitoring in two summer weeks. Based on the mathematical models and using collected data, modules incorporating the proposed optimal redesign procedure were embedded in a transient simulation tool. A mixed heuristic-deterministic optimization algorithm was implemented in the transient tool to determine the synthesis and design variables that influence the cost and energy efficiency of each configuration. Available experimental results were compared to predicted results to validate the model. Afterwards, the computer model was used to predict how changes in cooling coil geometry would affect the building thermal comfort, the cost and energy consumption of the system