Research On Effects Of Different Combinations Of Thermal Environmental Parameters On Energy Consumption Of HVAC System

In a room equipped with HVAC system, thermal environmental parameters thataffect the occupants thermal comfort are as follows: air temperature, air humidity, airvelocity, mean radiant temperature, metabolism rate and clothing resistance. Besidesmetabolism rate which is dependent on the occupants’ state of motion and clothingresistance which is related to the occupants’ living habits and different seasons, otherfour parameters are directly related to HVAC system. Correlative studies indicate thatpeople have the same thermal comfort sensation when the thermal comfort index(SET*or PMV) is the same. Different combinations of four thermal parameters canlead to equal thermal comfort sensation, i.e. the same thermal comfort index. In thesame air-conditioned room, the energy consumption of the room is different when thethermal comfort index is kept the same with different combinations of four thermalenvironmental parameters. When people are in a comfortable state, the combinationthat consumes the minimum energy is called the optimal combination of parameters.This paper studies the optimal combination of thermal environmental parametersbased on PMV index.Air temperature, relative humidity, mean radiant temperature and in door windvelocity are four thermal environmental parameters affecting PMV. First, by intuitiveanalysis of orthogonal numerical experiment, the significance of the influence of thefour parameters on PMV is compared and the influencing laws of parameters on PMVare detailed analyzed. Then, based on the envelope surface heat balance and air heatbalance equation, an energy consumption model of HVAC system is established. Onthe basis of the energy consumption model, the influencing laws of parameters onenergy consumption at the same PMV are analyzed. By comparing the energyconsumption of different combinations of thermal environmental parameters at agiven PMV, it is found that there is a big difference between different combinations,which indicates the existence of the optimal combination of parameters. Last but notthe least, by utilizing optimization function for solving nonlinear multivariableconstrained optimization problem in MATLAB optimization toolbox, the optimalcombination of air conditioning system at a given PMV is calculated. The resultsshow that both for convection air-conditioning system and convection plus radiationair conditioning system, the optimal values of air velocity in summer are at the upper boundary. Relative to convection air conditioning system, convection plus radiationair conditioning system can control mean radiant temperature, so, it can lower meanradiant temperature to compensate air temperature rise accordingly. Therefore, theenergy consumption of convection plus radiation air conditioning system in theoptimal combination is less than corresponding convection air conditioning. Underthe same air-conditioning system, the load values of PMV control air conditioningsystem after using the optimal combination and corresponding26℃constanttemperature control system are compared. The results indicate that PMV control airconditioning system after using the optimal combination has great potential for energyconservation while maintaining the same comfort sensation.