Research On Thermal Comprehensive Utilization System In Urban Underground Space

Underground space development is an effective approach to solve the City Syndrome and problems on population, resources and environment, and it's also an important way to implement the concept of scientific development and to construct the society with resource conservation and environment friendness. As a major mean to create and maintain built environment and consequently to ensure sustainable development of underground space, HVAC system should be energy-saving and environmentally benign on the premise of indoor air quality. Aiming at resource and environment disadvantages of conventional system, and following the principle of step utilization on thermal energy, the thesis brought up a new concept of thermal comprehensive utilization system (TCUS), using kinds of heat pump as major equipments and considering multiple thermal usage. Furthermore, it gives out an application form of the TCUS using water loop as major characteristics, which takes different building types in concentrated area of underground space into consideration, and hence achieves thermal energy shift and utilization in spatial dimension. To remove heat surplus and fill heat gap of TCUS, it also brought up a water-to-air-to-refrigerant triple-fluid heat exchanger installed in exhaust air shaft.According to the concept of TCUS, mathematics models of involved HVAC system, sanitary hot-water (SHW) system, triple-fluid heat exchanger and air-source heat pump (ASHP), and the whole system were created, in order to study energy performance of water loop and major equipments in the system. The models include (a) air handling process in AHU using -NTU method; (b) refrigeration circulation in chiller, consisting of compressor energy consumption in refrigeration theory circulation and fitted heat loss based on test data; (c) thermal storage water tank based on multinode considering thermal stratification; (d) triple-fluid heat exchanger, both directly air cooling using -NTU method and indirectly evaporation cooling based on thermal balance; and (e) each pipe in TCUS's ridimensional ring network using particle method, focusing on heat balance and mess balance.Using those models, quasi dynamic simulation based on hourly heat balance state for an application case in real area was accomplished, under the data of typical meteorological year of Harbin, Beijing, Xi'an, Shanghai, Chongqing and Guangzhou, respectively. By examining hourly parameter in typical day of each season, average value of each month and statistic data of the whole year of simulation results, from aspects of terminal performance, thermal quantity requirement, energy consumption, water loop performance and main equipment operation, respectively, it's concluded that TCUS can be used in different cities and climate, and the general trend of electricity consumption is Southern higher than Northern and summer higher than winter. Although triple-fluid heat exchanger achieves to remove heat surplus, small temperature difference between inlet and outlet water results in strong temperature fluctuation in water loop and high energy consumption of water pump, and indicates requirement on efficiency improvement.For operation data simulated in case study, evaluation index system on energy performance of TCUS was established, including energy efficiency evaluation and energy saving evaluation. On energy efficiency evaluation, comprehensive EER, thermal comprehensive utilization rate, thermal recovery efficiency and water loop efficiency, was presented from angles of overall energy output/input ratio, usage/generation ratio of indoor remaining heat, the ratio of recovered heat to used energy of recovery equipments and the ratio of carried heat of water loop to consumed energy of its water pump, respectively, together with indices of EER, energy consumption per temperature difference and energy consumption per fresh air volume per person of HVAC system, and EER of SHW system. On energy saving evaluation, saving quantity and/or rate of TCUS compared to conventional system was assessed, in terms of equivalent heat, equivalent electricity and equivalent power coal consumption, respectively. In addition to evaluation on studied case, it's followed by area applicability analysis of TCUS.At last, optimization strategies on the whole TCUS and HVAC system were given out, and their effect were corroborated by former studied case. Introduction of energy management mode into TCUS operation was also put forward.