Feasibility Of Using Thermal Inertia To Shift The Peak Load Of Buildings

In China,the acceleration of urbanization and the improvement of residents’ indoor thermal comfort have led to an increase in the total energy consumption of buildings,which also caused an increase in electricity consumption.In order to satisfy the demand of consumers,ensure a continuous and high-quality electricity supply,reduce the installed capacity of power generation and avoid the expansion of grid,through the way of reducing the unnecessary electrical loads or shifting the peak load to realize the electricity management of buildings.Using thermal inertia,radiators or air conditioning systems can operate during off-peak hours,and the thermal or cold energy is stored in materials,which will be used during peak demand periods.Thus,the peak demand is shifted to off-peak hours.In this paper,numerical simulation is the main research method.Considering the characteristics of heat storage and release about indoor items,the effect of building thermal inertia on indoor thermal comfort and the effect of stored food thermal inertia on storage quality and time limit are investigated in winter heating period and summer high-temperature period,respectively.Furthermore,the feasibility of using thermal inertia to shift peak demand is analyzed.Firstly,the theoretical investigation is carried out,which relates to the analysis method of unsteady heat transfer process on building envelope.The thermal characteristics of building envelope are compared based on harmonic analysis method and transfer function method.The results show that the main thermal characteristics of two methods have the same or similar physical meaning.Secondly,according to the storage temperature range of food,three cases that represent different operation strategies of refrigeration system are studied.The numerical simulation of three cases is conducted on storing pears and beef in a small refrigerated warehouse,respectively.Due to the order of thermal inertia index,stored food > polyurethane wall > closed air,the order of temperature variation is airflow > polyurethane wall > stored food after the refrigeration system stops running.In addition,there is a significant hysteresis on the temperature fluctuations of stored foods,which shows delay in response to the temperature variation of airflow.The refrigeration unit adopts the control strategy of shutting down during peak hours and operating during off-peak hours.During the off-peak hours,the compressor consumes more electricity to increase the cooling capacity,then reduce the air outlet temperature of air cooler.Using the thermal inertia of stored food can realize the reduction of peak electricity demand in refrigerated warehouse,while ensuring the storage quality and storage period of food.Thirdly,according to the comfortable temperature range of the heating room in winter,three cases that represent different operation strategies of radiator are investigated.The numerical simulation of three cases is carried out for an office room.The material of building envelope is reinforced concrete and has a large thermal inertia.After the radiator shut down,the decrease speed of the wall inner surface temperature is lower than the decrease speed of indoor air temperature.During the off-peak hours,the radiator consumes more electricity to increase the indoor heating temperature.Thus,more heat can be stored in walls.The stored heat is released during the peak hours to maintain the indoor thermal comfort.By utilizing the thermal inertia of walls,the radiator adopts a control strategy that shutting down during peak hours and operating during off-peak hours.It is feasible to reduce or shift the heating peak demand of office room without affecting indoor thermal comfort.Finally,a simple economic analysis is performed between the utilization of thermal inertia and without utilization of thermal inertia in refrigerated warehouse.The refrigeration unit adopts the control strategy of shutting down during peak hours and operating during offpeak hours.The investment cost of the compressor increases,but the working time is reduced,which resulting in a decrease in the power consumption and operation cost of refrigerated warehouse.Among which,due to the advantage of the price difference between the peak and off-peak electricity,the proportion of operation cost saving is significantly higher than the proportion of electricity consumption saving.Therefore,using thermal inertia not only shifts the peak load and alleviates the contradiction between power supply and demand,but also saves the operation costs and obtains good environmental benefits.