Research On Indoor Heat And Humidity Regulation And Simulation Optimization Of Floor Radiant Cooling And Displacement Ventilation

Radiant cooling is a superior method to improve indoor thermal environment and reduce energy consumption.By combining with a ventilation system to deal with latent heat load,it can eliminate the risk of condensation on radiant cooled surface,overcome the negative effect of thermal inertia of the radiant terminal,and extend the applicability for climate and building.The advantages and characteristics of radiant cooling system have motivated considerable researches on radiant cooling in terms of comfort,heat transfer analysis,energy simulation,control strategy and system configuration for developing accurate and efficient control strategy,exploiting energy-saving potential and maximizing the use of renewable energy.Therefore,this study used experimental and simulation methods to explore the optimal control strategy of a radiant floor cooling system combined with a ventilation system.An office building in Jinan was selected for experimental test,where measuring points were placed to monitor indoor environmental parameters,supply air temperature and flow rate,and supply and return water temperature and flow rate.The field operational control of radiant floor cooling with a direct-ground cooling source and displacement ventilation systems was studied.The control methods for the composite system were proposed based on three factors including floor surface temperature relative to the indoor air dew point temperature,the range of indoor/outdoor air temperature and humidity,and the indoor thermal and humidity loads to be countered.These factors were considered in three typical scenarios:intermittent operation,variable initial temperature and humidity conditions,and sudden increases in indoor heat gain.The control effects on indoor thermal environment were analyzed to obtain that:(1)The operative temperature was maintained within 26?27°C,meeting ASHRAE standard.(2)The system required that precooling time of the radiant floor cooling system was 2.5?3 times?₆₃ as the time to achieve 63%of the temperature change for intermittent operation on weekends.(3)As for different initial indoor temperature and humidity conditions,when the initial indoor humidity was higher than 75%,the displacement ventilation system started 1?1.5 hours in advance.When the initial indoor humidity was lower than 75%,the displacement ventilation system delayed start time with increase in supply air temperature by 1?2°C.(4)In case of sudden increase of indoor heat source,the supply air flow rate was increased to the maximum value to address the increased indoor heat and humidity load with high efficiency.Therefore,the dynamic optimization control of the radiant cooling system was achieved,contributing to indoor thermal comfort and energy saving.Transient System Simulation(TRNSYS)integrated with the parametric simulation manager j EPlus were used to optimize starting and operation control strategies of a combined radiant floor cooling system and ventilation system.j EPlus was used for setting alternative values of indoor heat gain and system operational parameters to create simulation cases.TRNSYS received the information of simulated cases and simulated 4820 cases.The simulation results were collected by j EPlus and processed according to the thermal comfort constraints defined by the predicted mean vote(PMV)and the objective to minimize energy consumption.The experimental data was used to validate the simulation model accuracy.The simulation results showed that:(1)In the starting stage,the ventilation system was started one hour earlier than the RFC system at an initial indoor humidity of 85%to prevent condensation,whereas both systems were started at the same time at an initial indoor humidity of 75%.(2)In the operation stage,the growing internal heat gain caused a maximum change in total cooling energy of about0.2?0.5k W·h.(3)The increase in the ratio of the sensible heat removed by the RFC system to the sensible heat removed by the ventilation system(S_v/S_R)and the decrease in PMV value resulted in higher energy consumption.(4)The collaborative control strategy of the composite cooling system was proposed.S_v/S_Rwas adjusted according to PMV to achieve dynamic and static control,ensuring PMV within-0.5?0.5 while achieving maximum energy-saving of 26.2%.