The Utilization Strategies and Case Study of a Compound Geothermal Heating System

Geothermal energy is a kind of renewable energy source, which is widely employed for heating purpose. There are problems that the temperature of tail water from heating is too high and geothermal energy is not taken full advantage of. Hence, boilers (coal-fired, oil-fired, gas-fired or electric) are often used as supplement to meet the massive heating load in the coldest season. Nowadays, moderately high temperature heat pump is gradually applied to recover heat from tail water thanks to its features of energy savings and environmental protection. Obviously, geothermal heating system, boilers and heat pumps make up of a so-called compound geothermal heating system. This paper presents a feasible operating modulation strategy for the compound system based on dividing the heating period into slight cold period, moderate cold period and severe cold period, as well as a calculating method to determine the operation of each sub-system according to heating system modulation curves. A case study indicates the strategies can make the compound system operate steadily and save energy compared with conventional systems.