Study On Optimal Control Strategy Of Ground Source Heat Pump-Radiant Cooling System In Residential Buildings

As a kind of comfortable and energy-saving air conditioning,the radiant cooling system uses high temperature cold water when cooling,which provides a possibility for natural cold source cooling.The combination of radiant cooling system and ground source heat pump system can effectively improve system performance and reduce energy consumption.At present,for the combination of ground source heat pump and different types of radiant terminals,there is a lack of targeted operation strategy,and further research is needed to achieve optimal control.radiant cooling system has various forms.This subject is suitable for capillary radiant cooling system and concrete radiant cooling system of residential buildings.The capillary radiant plate is generally an integrated network composed of polypropylene plastic pipes.The surface area of the grid is large,the water supply pipeline is fine and uniform,which will make the radiant plate surface temperature distribution more uniform,comfortable,and its thermal response faster to achieve immediate control.Water supply pipeline of concrete radiant cooling system is embedded in concrete floor structure.Because of the strong cold storage capability,the operation control strategy is different from the conventional air conditioning system.The high heat storage characteristics of concrete structure make the intermittent operation mode superior.The thermal storage effect can transfer the peak load,and its delay characteristic can make the radiant cooling system play its energy-saving effect on the basis of maintaining indoor temperature stability.This subject takes residential buildings in Xi'an as the research object,and uses TRNSYS to set up the internal and external disturbance parameters according to the characteristics of residential buildings,and builds the system model of ground source heat pump-radiant cooling system.Different control modes are adopted according to the characteristics of different terminal forms.Aiming at the ground source heat pump-capillary radiant cooling system,taking thermal comfort parameters as control parameters,two control modes,i.e.start-stop control of unit at set room temperature and start-stop control of unit at set PMV range,are proposed.By comparing indoor comfort and system energy consumption,a better control mode is selected as the basic control mode of the system,and added in the control mode.In order to improve the system performance and achieve greater energy saving,theoptimization control of direct supply of buried pipeline and frequency conversion of water pump is carried out.According to the concrete radiant air conditioning system,the underground pipe direct cooling system is proposed.By comparing the indoor thermal comfort and system energy consumption of different distribution schemes under different cooling time lengths and the same cooling time lengths,the optimal scheme is selected,and the feasibility of the underground pipe direct cooling system is verified.The main conclusions of this research are as follows:For ground source heat pump-capillary radiant cooling system:(1)Start-stop control with setting PMV range has a slight advantage in thermal comfort,but the difference is very small,only about 2% higher than room temperature control,and both control can meet the indoor thermal comfort requirements.(2)The running time of heat pump unit is shorter under the start-up and shutdown control mode of unit set at room temperature,which reduces the energy consumption of heat pump unit and pump by 298 kW H.Under this control,the average soil temperature only rises by 2.08?,and the stability is good.(3)When the outlet temperature of buried pipes is less than 18 C,the energy-saving rate of the system is increased by 5.7% and the average energy-efficiency ratio of the system is 4.82,which is 22.6% higher than that of the room temperature control mode only.After adding the frequency conversion optimization of the pump,the energy-saving rate reaches 19.9% and the average energy-efficiency ratio of the system reaches 5.81.For the underground pipe direct-supply concrete radiant air conditioning system:(1)Taking indoor operating temperature and PMV value as the thermal comfort evaluation index,it is concluded that the comfort of 8-hour cooling time is the best,and only the energy consumption of water pump is 32.1 kW·h higher than that of 6-hour cooling.(2)The distribution of energy consumption in different cooling periods is basically the same under the same cooling time.The fluctuation of indoor temperature in daytime cooling mode is small,but the frequent start-stop control mode of water pump can increase the cooling capacity of the system,and the cooling effect is better.(3)The soil heating rate increases with the increase of cooling time.The average outlet temperature of underground pipes is about 18?under different cooling time lengths,which proves the feasibility of underground pipes direct cooling system for concrete radiant.