Research On Application Of Ground-Sink Direct Cooling And Heat Pump Complex System

With the growing demand for energy and increasing requirements of energy conservation and emission reduction,it is imperative to exploit the clean renewable energy and improve the energy utilization effiency.As a clean and renewable energy technology,ground source heat pump(GSHP)system has been paid more and more attention in recent years.In summer,if the outlet temperature of ground heat exchangers(GHEs)is low enough,the cold energy extracted from GHEs can be directly distributed to the indoor terminals(such as the capillary network)without using the heat pump units,which can greatly increase the performance coefficient of cooling system.Combined with the experiment and numerical simulation,this paper attempts to analyze the reliability and adaptability of ground-sink direct cooling(GSDC)system in the view of the life cycle.First of all,this paper analysed the working principle of the GSDC and GSHP system in summer and winter which was built in a small travel building in C hongqing and compared a series of parameters and characteristics of the GSDC and capillary network systems.The indoor and outdoor environment parameters,the inlet and outlet temperature of GHE,the temperature of the soil around GHE and performance parameters of system are mearsured.From the data we can see,with the system of GSDC in summer,the indoor air temperature was controlled within a reasonable range which ensures the indoor thermal comfortableness,while the outlet temperature of GHE is controlled below 20 degrees Celsius.The maximum diurnal average energy efficiency rate of system was up to 8.77,which shows the great potential of GSDC in energy saving in certain regions.After 3 weeks of GSDC experiment,the average soil temperature rises up by 0.31 degrees Celsius than before and there was no obvious heat accumulation.For winter,this paper compared the indoor environment parameters of capillary radiant heating with different water supply temperatures,and analysed to determine an optimal water supply temperature of capillary radiant heating system,which ensured the high system effiency and comfortable indoor environment.Meanwhile,compared with the air source heat pump with fan coil system,it was found that the complex system had great advantages in indoor thermal environment and system efficiency.Secondly,with the Fluent softwear,a three-dimensional heat transfer model of GHE was built to simulate the temperature of the soil and the water,whose accuracy was validated by the measured data.Based on local typical meteorological year data,the whole year hourly dynamic loads of different air conditioning s ystems were simulated by DeST which were used to verify the outlet temperature and prove the reliability of system.It was shown that heat accumulation of soil was very weak in the GSDC system running mode.Most of the time,the outlet temperature of GEX was below 20 degrees Celsius while the highest was 21 degrees Celsius.In response,the experiment with 21 degrees Celsius supply water temperature was made and results showed that indoor temperature still met the requirements.In addition,a series of operation strategies were put forward to help prove the GSDC system viable in some regions.Finally,combined the experimental building and related literature,four models(heat pump unit,air-source heat pump,VRV and split air-conditioner)were established to calculate the whole year energy consumption.It is shown that compared with air-source heat pump,VRV and split air-conditioner,ground-sink direct cooling and heat pump complex system can attain 39.8%,26.6%,38.1% relative energy saving rate respectively.What's more,in order to analyze the economics,the life cycle cost evaluation model was set up to compare the life-cycle costs and annual costs.The results indicate that the ground-sink direct cooling and heat pump complex system has its own economical advantages.