Chilled Water Outlet Temperature Research Articles

Multi-bed regenerative adsorption chiller — improving the utilization of waste heat and reducing the chilled water outlet temperature fluctuation

A multi-bed regenerative adsorption chiller design is proposed. The concept aims to extract the most enthalpy from the low-grade waste heat before it is purged into the drain. It is also able to minimise the chilled water temperature fluctuation so that downstream temperature smoothing device may be downsized or even eliminated in applications where tighter temperature control may be required. The design also avoids a master-and-slave configuration so that materials invested are not under-utilised. Because of the nature of low-grade waste heat utilization, the performance of adsorption chillers is measured in terms of the recovery efficiency, η instead of the conventional COP. For the same waste heat source flowrate and inlet temperature, a four-bed chiller generates 70% more cooling capacity than a typical two-bed chiller. A six-bed chiller in turn generates 40% more than that of a four-bed chiller. Since the beds can be triggered into operation sequentially during start-up, the risk of ice formation in the evaporator during start-up is greatly reduced compared with that of a two-bed chiller.

Neural networks?a new approach to model vapour-compression heat pumps

The aim of this paper is to model the steady-state performance of a vapour-compression liquid heat pump with the use of neural networks. The model uses a generalized radial basis function (GRBF) neural network. Its input vector consists only of parameters that are easily measurable, i.e. the chilled water outlet temperature from the evaporator, the cooling water inlet temperature to the condenser and the evaporator capacity. The model then predicts relevant performance parameters of the heat pump, especially the coefficient of performance (COP). Models are developed for three different refrigerants, namely LPG, R22 and R290. It is found that not every model achieves the same accuracy. Predicted COP values, when LPG or R22 are used as refrigerant, are usually accurate to within 2 per cent, whereas many predictions for R290 deviate more than ±10 per cent. Copyright © 2001 John Wiley & Sons, Ltd.

Modelling of vapour-compression liquid chillers with neural networks

A new approach to steady state modelling of vapour-compression liquid chillers is presented in this paper. The model uses a generalised radial basis function (GRBF) neural network to predict chiller performance. The GRBF chiller model is developed with the objective of requiring only those input parameters that are readily known to the operating engineer, i.e. the chilled water outlet temperature from the evaporator, the cooling water inlet temperature to the condenser, and the evaporator capacity. The GRBF chiller model predicts relevant performance parameters of a chiller, especially the coefficient of performance. The neural network is applied to two different chillers operating at the University of Auckland, New Zealand and the agreement is found to be within ±5%. It is inferred that neural networks, in particular the generalised radial basis function, can be a promising tool for predicting the chiller’s performance for fault detection and other diagnosis purposes.

Analysis of Dynamic Behavior of an Absorption Chiller Heater. 2nd Report. Experimental Validation of the Mathematical Model of Evaporator and Absorber.

This paper presents an experimental validation of the mathematical model of an evaporator and absorber, which are components of a water/lithium-bromide absorption chiller heater. The experimental cycle employs a gas-fired, 176 kW (50 RT) machine, which is mainly used in individually distributed air conditioning systems. One of the features of this model, described in the 1st report, is prediction of both static and dynamic characteristics of the machine, especially transient response to rapid change in external conditions. In this experiment, an immediate change in chilled water flow rate is the input signal. Output signals for comparison with predicted data are transient responses of chilled water outlet temperature, evaporating pressure and cooling capacity derived from chilled water temperature and its flow rate. From comparison between experimental data and values predicted using the model, steady-state analytical error is less than ±3%, and dynamic behavior can be predicted within ±10% analytical error of response time.

Computer Simulation of Triple Absorption Cycles. NH3/LiNO3, NH3/LiNO3+H2O/LiBr Absorption Cycle.

This work presents a computer simulation of two types of triple absorption cycles, employing the refrigerant absorbent combinations of NH3/LiNO3 low-pressure type and NH3/LiNO3+H2O/LiBr binary two-stage type. The system involves coupling two conventional absorption cycles so that the condenser and absorber of the high-temperature-side cycle produce a heating source for circulation in the generator of low-temperature-side cycle. The performance of the absorption systems was investigated through cycle simulation to obtain the system characteristics with the cooling water inlet temperature, chilled water outlet temperature and the temperature loss which was lost by the absorber during the cycle. The most important characteristic of the system is that it obtains a coefficient of performance higher than the sum of the performance coefficients of its parts operating independently. The efficiencies of the different triple cycles have been studied and the simulation results show that a higher coefficient of performance could be obtained for the NH3/LiNO3+H2O/LiBr binary two-stage-type cycle.

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.

Numerical Simulation of Advanced Adsorption Refrigeration Chiller with Mass Recovery

This paper investigates the thermodynamic framework of a three-bed advanced adsorption chiller, where the mass recovery scheme has been utilized such that the performances of this chiller could be improved and a CFC-free-based sorption chiller driven by the low-grade waste heat or any renewable energy source can be developed for the next generation of refrigeration. Silica gel-water is chosen as adsorbent-refrigerant pair. The three-bed adsorption chiller comprises with three sorption elements (SEs), one evaporator and one condenser. The configuration of SE1 and SE2 are identical, but the configuration of SE3 is taken as half of SE1 or SE2. Mass recovery process occurs between SE3 with either SE1 or SE2 and no mass recovery between SE1 and SE2 occurs. The mathematical model shown herein is solved numerically. In the present numerical solution, the heat source temperature variation is taken from 50 to 90ºC along with coolant inlet temperature at 30ºC and the chilled water inlet temperature at 14ºC. A cycle simulation computer program is constructed to analyze the influence of operating conditions (hot and cooling water temperature) on COP (coefficient of performance), SCP (specific cooling power), η (chiller efficiency) and chilled water outlet temperature. Keywords: Adsorption; COP; SCP; Mass recovery; Silica gel-waterDOI: 10.3329/jname.v3i2.920 Journal of Naval Architecture and Marine Engineering 3(2006) 59-67