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An experimental solar ejector refrigerant system using HFC134 as working fluid is designed and constructed to study the critical performance in this paper. The relationship between the ejector critical condenser temperature and the system working condition has been proposed. The experimental results show that the COP and ejector entrainment ratio keep almost constant firstly, and then reduce dramatically...
Based on the existing design meteorological data and the relationship of climate and geography, this paper presents a novel method which structures outdoor air design conditions by interpolation. The results show that the method is applicable to hot summer and cold winter regions, and that for those regions the deviations are less than 2 °C.
There are still some important issues related to the implementation of VAV system. One of the most critical issues is coupling which exists in different control loops of VAV system. To solve this problem, a model of VAV air supply system is established based on ventilation network theory, by which the model predictive control is used to control the VAV air supply system. Simulation results show that...
This paper presents information about boiling heat transfer of R417A replacing R22 outside horizontal smooth and enhanced tubes at the saturation temperature of 10°C. A Wilson plot technique was used to determine the refrigerant heat transfer coefficient. The results indicate that boiling heat transfer coefficients of R22 are larger than those of R417A at the same condition of saturation temperature...
Experimental studies of film condensation of R22 on single horizontal smooth tube and five enhanced tubes have been conducted. The objective is to obtain optimum fin density on condensation heat transfer characteristics. The results indicate that the predicted condensation heat transfer coefficients of smooth tube from Nusselt theory agree within ± 10 percent with the experimental data. Experimental...
As an environmentally friendly refrigerant, CO2 is seen as one of the best fluids for a heat pump water heater application system. To investigate the relationships between optimum heat rejection pressure and other related operating parameters, an experimental research has been conducted for a transcritical CO2 heat pump water heater with two throttling valves. It proved that it is relatively reliable...
The energy-saving potential of the demand-controlled ventilation (DCV) has been highlighted in several literatures these years, there are still some important questions related to the implementation of CO2-based DCV. One of the most critical issues is that low CO2 levels alone do not guarantee acceptable indoor air quality (IAQ). In this paper, a simulation model was built to study the on-line control...
Thermal load prediction is essential for optimal operations of heating, ventilation, and air conditioning (HVAC) systems. Usually, the building thermal load is predicted by using artificial neural network (ANN) model based on environmental input variables. Unfortunately, it is not obvious that how many the input items should be or what preprocessing of inputs are best, which can cause significant...
In this paper, a simulation model was built to study the CO2-based outdoor air rate control system in public buildings by PID control and fuzzy-PI control method. It is shown that classical PID algorithm can eliminates steady-state error, but the overtune is big and transitional time is long. The PID algorithm only suits for the case of CO2 concentration changed small. When the CO2 concentration has...
The direct multi-step prediction employs measurement data but not the results of single-step prediction. So it should have a better prediction effect for short-term wind speed. Aiming to the chaotic nature of wind speed data, a novel direct multi-step prediction approach for wind speed has been presented in this paper. This approach was based on chaos analysis and dynamic recurrent neural network(DRNN)...
The acoustic scattering problem is solved and an example is calculated using the finite element/infinite element method. Firstly, the surface velocity is obtained by the incidence acoustic wave and the characteristic of structure. Then the surface pressure is solved using the finite element/infinite element method. Lastly, the frequency of the incidence acoustic wave changes for the error of this...
In this paper, a near- optimal operation strategy, weight priority method, is presented for ice storage air-conditioning systems. How to determine proper proportion between ice storage tanks and chillers to meet buildings load demand is a key factor for the optimal control of ice storage systems. By the priority weight method, the optimization control problem is converted into a sorting problem. Compared...
A new formulation based on a prolate spheroidal coordinate was proposed to describe acoustic pressure in the acoustic field. The radiated acoustic pressures are obtained by means of an expansion of independent functions based on the prolate spheroidal coordinate system. Then the acoustic pressure in the field can be reconstructed by using some measured acoustic pressure signals in the field. The independent...
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