Cost-effective optimal design of groundwater source heat pumps

Abstract

By analyzing the operating characteristics of the groundwater heat pump, this paper puts forward an integrated optimal mathematical model with an objective function of the annual total costs according to technical and economic optimal principle. A computation program is also developed. On the premise of ensuring that the unit will fulfil the heating and cooling requirements of buildings, this model is used to calculate and optimize some key operating parameters and components according to different temperature and depth of the groundwater. It combines the reliability and economy of heating and cooling and achieves the most optimal match of each part of the system. The present method will lead to a greater improvement in the performance of the heat pump than the traditional method.

Introduction

In recent years, the groundwater heat pump (GWHP) is achieving its rapid development in some parts of China. This type of heat pump that uses groundwater drawn from a deep well and injected into another simultaneously is an ideal unit for space heating and cooling applications. The groundwater is its heat sink for cooling in summer, and heat source for heating in winter [1], [2]. Because of the effect of heat insulation and accumulation of the soil, the temperature of groundwater is nearly constant in a year and is generally 1–2 °C higher than the local annual mean air temperature [3]. Therefore, the groundwater is an ideal heat source/sink for heat pumps. It is obvious that the abundant and steady groundwater resource is necessary for this unit. In practice, the performance of the GWHP is affected seriously by such facts that the property of the well (temperature of groundwater, water level, etc.) varies with places and the proportion of heating load to cooling load also varies with buildings. In order to ensure its reliability and improve its economy, it is important to design the system properly according to the property of the wells and the actual needs of the buildings.

The optimum design of the GWHP is to realize optimal cooperation for all components, and to consider the running costs and first investment simultaneously under present technical and economic conditions.