Backward Inverse Simulation Of Enclosure Air And Heat Recovery From Building Ventilation

Several initiative researches, including inverse identification of single or multiple pollutant sources, inverse modeling of turbulent indoor air flows, design of heat pipe heat recovery air conditioning system, indoor airsimulation with heat pipe heat recovery, and PIV measurement of transient pollutant dispersion, have been conducted in the present dissertation, due to the fact that there exist many practical issues, such as reliability of building ventilation, and inhibition of airborne pollutant spread, energy conservation of building air conditioning, enhancement of indoor air environment, to name just a few.Firstly, prompt identification of pollutant locations or pollutant spread routes will greatly contribute to the active control of indoor airborne pollutants. Spatial locations of pollutant sources can be effectively identified by the quasi-reversibility methodology, where spatial distributions of indoor airborne pollutants at any temporal episode can be adopted to identify the pollutant source locations. With the quasi-reversibility methodology, temporal step will be minus in values and a fourth stability term should be added into the transient pollutant dispersion equation to implement stable convergent solutions as time backwards to original one. Additionally, the extra stability term should be maintained enough low in values to ensure the accuracy of time backward solutions.The spatial location of one pollutant source has been inversely identified in a three dimensional displacement ventilated room. Initially, effects of the ventilation flow rate, pollutant source location, and pollutant diffusion property on the indoor airborne pollutant spread have been analyzed with the forward time CFD simulations. Subsequently, pollutant source locations have been identified by the aforementioned quasi-reversibility methodology, according with the temporal episode of pollutant dispersion obtained from the forward time simulations. Effects of supplying air velocity, pollutant source location, pollutant spread time, and pollutant diffusion rate on the quasi-reversibility solutions have been discussed in details.The spatial locations of multiple pollutant sources have also been identified in a two dimensional displacement ventilated room, where one thermal plume interacts with the external forced air convections. As time elapses, effects of supplying air velocity, heating source intensity, pollutant diffusion prosperity and pollutant source locations on the transient spread of indoor airborne pollutants have been investigated. Following that, these spatial locations of pollutant sources can be identified by the quasi-reversibility method and prior-known spatial distributions of pollutants at any temporal episode. The effects of supplying air velocity, heat source intensity, pollutant diffusion rate, and pollutant spread time on the backward time solutions have been discussed in details.Secondly, artificial control and design of indoor air environment strongly depends on the inverse modeling of indoor air convection, which means that initial or boundary conditions will be determined by the final flow state. Here, inverse modeling on indoor air turbulent flows should be solved due to the realistic vented indoor air motion belongs to the turbulent flow. Time averaged turbulent air convection in the slot-ventilated room has been firstly investigated respectively concerning the displacement ventilation and mixed ventilation modes. Heat dissipation rates from the indoor thermal source have been compared in terms of different ventilation modes, covering from the forced convection dominated indoor air flow to the natural convection dominated indoor air flow, which is depending on the variations of Reynolds and Grashof number. In addition, energy flow lines or heat lines defined in turbulent flows have been presented to express the indoor thermal transport routes, and also to indicate the global conservation of average turbulent energy flows in the system. Following that, conjugate gradient method has been adopted to derive the sensitivity and adjoint equations with the couple flows of forced and natural convections. Spatial distributions along one wall in the slot-vented room have been inversely determined with some known temperature measurements within the room. Effects of supplying air velocity, thermal plume intensity, spatial function of wall heat source, and measurement errors on the inverse estimation accuracy and inverse solutions have been analyzed, concerning the aforementioned displace and mixed ventilation modes.Thirdly, heat recovery from exhaust air to preheat entrained fresh air is firstly introduced. It is well known that entrainment of surrounding fresh air will enhance indoor air environment, whereas it will increase the energy consumptions of building air conditioning units, which will directly conflict with the enhancement of indoor air. In the present work, heat recovery from exhaust air will be adopted to preheat the entrained fresh air through the heat pipe heat recovery equipment, and which will completely or partially debate the reheating load and increase the volume of fresh air within the room simultaneously. Upon that, performance experiment on separate heat pipe, defrost of heat recovery air conditioner in winter, and indoor air environment modeling with heat recovery unit were paid attentions as follows,An air conditioner with separate heat pipe heat recovery equipment is firstly constructed, where two phase fluid fills the closed separate heat pipe unit to recovery heat from the exhaust air and preheat the entrained fresh air respectively on the condensation side and evaporation side. Effects of hydraulic diameter and evaporation temperature of separate heat pipe on the upper and lower boundary values of heat pipe filling ratio have been analyzed concerning the present experimental rig system and mathematical modeling. Both experimental and analytical results demonstrate that the heat recovery efficiency of air conditioning unit can be greatly enhanced by the separate heat pipe. Subsequently, frosting process of heat recovery air conditioner in winter has been investigated, concerning unsteady thermal flows of finned heat pipe heat recovery air conditioning evaporator subjected to the external forced air convection. Effects of temperature, relative humidity, and volume flux of mixed air passing through the heat recovery unit on the heat transfer coefficient, frost thickness and air side pressure drop have been investigated to optimize the winter operation of heat recovery air conditioners.Following that, the effect of the heat recovery air conditioner on the slot-vented air environment has been numerically modeled, concerning the double roles of heat recovery unit (heat recovery and pollutant filtration). Indoor air flows and airborne pollutant spread within the heat recovery air conditioning room have been fully modeled. The effects of supplying air velocity, fresh air ratio, filter efficiency, and the thermal plume on the volume average concentration of indoor airborne pollutants and the pollutant diffusion rate on the surface of pollutant source have been discussed in details. Numerical results show that heat recovery air conditioning unit can harmonically resolve the contradictions between indoor air environment and building air conditioning energy consumption, due to this novel unit not only effectively dilute the indoor pollutants through entraining ambient fresh air, and also greatly reduce the energy consumptions of pre-cooling (or pre-heating) fresh air.Finally, temporal spread of indoor airborne pollutants has been prescribed respectively using CFD simulation and PIV measurement. Within few seconds, saturated nano-particle solution was abruptly released into the horizontal water-supplying tube, where a pitch300mm from the port attached to the size reduced model room exists. Temporal developments of nano-particle flows in the slot-pumped enclosure have been illuminated and their scattered lights were recorded by the CCD camera. Since the laser light is continuous, an external signal was programmed to control the camera exposure. Consequently, transient spread of indoor airborne pollutants in the displacement ventilated room can be qualitatively obtained, which can be used not only as the reliable experimental data for indoor airborne pollutant dilution, and also as the validation of the present CFD simulation results.