Modeling and Optimization of a CoolingTower-Assisted Heat Pump System

Abstract

Abstract:To minimize the total energy consumption of a cooling tower-assisted heat pump (CTAHP) system in cooling mode, a model-based control strategy with hybrid optimization algorithm for the system is presented in this paper. An existing experimental device, which mainly contains a closed wet cooling tower with counter flow construction, a condenser water loop and a water-to-water heat pump unit, is selected as the study object. Theoretical and empirical models of the related components and their interactions are developed. The four variables, viz. desired cooling load, ambient wet-bulb temperature, temperature and flow rate of chilled water at the inlet of evaporator, are set to independent variables. The system power consumption can be minimized by optimizing input powers of cooling tower fan, spray water pump, condenser water pump and compressor. The optimal input power of spray water pump is determined experimentally. Implemented on MATLAB, a hybrid optimization algorithm, which combines the Limited memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm with the greedy diffusion search (GDS) algorithm, is incorporated to solve the minimization problem of energy consumption and predict the system's optimal set-points under quasi-steady-state conditions. The integrated simulation tool is validated against experimental data. The results obtained demonstrate the proposed operation strategy is reliable, and can save energy by 20.8% as compared to an uncontrolled system under certain testing conditions.

Experimental Study on the Heat Release Operational Characteristics of a Soil Coupled Ground Heat Exchanger with Assisted Cooling Tower

“…It is shown that starting up the cooling tower when the temperature is within 8-12 • C could effectively lower the ground temperature rise and reduce energy consumption. Wei et al [22] come up with a novel hybrid optimization algorithm to find the optimized set-points of the power cost. It is concluded that the optimized system could greatly decrease energy consumption in the cooling mode.…”

Model-based optimal operation of heating tower heat pump systems

“…Due to the high demand of building heating supply in cool or cold regions, researchers proposed to replace the chillers with heat pumps and coupled them with the heating towers to fulfill the heating demand. The mean coefficient of performance (COP) of the heating tower heat pumps (HTHPs) in winter varied from 2.24 to 4.12 for different climate zones [4,5] And in summer, the HTHP could function as a water-cooled chiller with high efficiency [6]. The HTHP has shown significant advantages over the conventional heat pumps.…”