Indoor mould growth prediction using coupled computational fluid dynamics and mould growth model

This study investigates, using in-situ and numerical simulation experiments, airflow and hygrothermal distribution in a mechanically ventilated academic research facility with known cases of microbial proliferations. Microclimate parameters were obtained from in-situ experiments and used as boundary conditions and validation of the numerical experiments with a commercial computational fluid dynamics (CFD) analysis tool using the standard k–ε model. Good agreements were obtained with less than 10% deviations between the measured and simulated results. Subsequent upon successful validation, the model was used to investigate hygrothermal and airflow profile within the shelves holding stored components in the facility. The predicted in-shelf hygrothermal profile was superimposed on mould growth limiting curve earlier documented in the literature. Results revealed the growth of xerophilic species in most parts of the shelves. The mould growth prediction was found in correlation with the microbial investigation in the case-studied room reported by the authors elsewhere. Satisfactory prediction of mould growth in the room successfully proved that the CFD simulation can be used to investigate the conditions that lead to microbial growth in the indoor environment

An investigation of air and water dual adjustment decoupling control of surface heat exchanger

The terminal equipment of central cooling system accounts for a significant proportion of the total system's energy consumption. Therefore, it is important to reduce the terminal equipment energy consumption in central air conditioning system. In this study, the difference of the effect of the chilled water flow rate and air supply rate on the surface cooler during the heat transfer process is taken into full account. Matlab/Simulink simulation software is used to model and simulate the heat transfer of surface cooler of the main terminal equipment of air conditioning system. Simulation tests and experimental validations are conducted by using variable chilled water flow rate and variable air supply rate control mode separately. The experiment results show that the simulation model can effectively predict the heat transfer performance of heat exchanger. Further, the study introduced a dual feedback control mode, which synchronously regulates the chilled water flow rate and air supply rate. Also, under certain conditions, the complex heat transfer process of the surface cooler can be decoupled, and single variable control pattern is used to separately regulate the chilled water flow rate and air supply rate. This can effectively shorten the system regulation time, reduce overshoot and improve control performance

Investigation on thermal-hydraulic performance of outdoor heat exchanger in air sources heat pump

A plethora of findings exists on the decreasing heat transfer performance of ASHP under frosting condition. This study investigates, using field and laboratory experiments, the frosting behavior and heat transfer performance of fin-tube exchangers. Findings from our initial observation revealed the severity of frosting phenomenon during winter in hot summer and cold winter zone of China; for avoiding the lower COP, defrosting period of ASHP was not longer than 60 min. The results showed that the basic tube surface temperature decreases with running time and remains stable after 70 min, and an adverse pressure drop ensued. The findings, thereby suggests a 70 min defrosting period in ASHP. Comparing jH/fH and COP between exchangers revealed an improved performance of plain fin-tube exchanger over that of louver fin-tube exchanger in all the test conditions. Therefore, under frosting condition, plain fin-tube heat exchanger provides a superior thermal-hydraulic performance over louver fin-tube heat exchanger. Findings from this study will help designers and facility managers in taking a more informed decision when selecting heat exchanger types for ASHP

Experimental investigation on thermal comfort model between local thermal sensation and overall thermal sensation

To study the human local and overall thermal sensations, a series of experiments under various conditions were carried out in a climate control chamber. The adopted analysis method considered the effect of the weight coefficient of local average skin temperature and density of the cold receptors’ distribution in different local body areas. The results demonstrated that the thermal sensation of head, chest, back and hands is warmer than overall thermal sensation. The mean thermal sensation votes of those local areas were more densely distributed. In addition, the thermal sensation of arms, tight and calf was colder than the overall thermal sensation, which pronounced that thermal sensation votes were more dispersed. The thermal sensation of chest and back had a strong linear correlation with overall thermal sensation. Considering the actual scope of air-conditioning regulation, the human body was classified into three local parts: a) head, b) upper part of body and c) lower part of body. The prediction model of both the three-part thermal sensation and overall thermal sensation was developed. Weight coefficients were 0.21, 0.60 and 0.19 respectively. The model provides scientist basis for guiding the sage installation place of the personal ventilation system to achieve efficient energy use

Heat removal efficiency of stratum ventilation for air-side modulation

Stratum ventilation has significant thermal non-uniformity between the occupied and upper zones. Although the non-uniformity benefits indoor air quality and energy efficiency, it increases complexities and difficulties in the air-side modulation. In this study, a heat removal efficiency (HRE) model is first established and validated, and then used for the air-side modulation. The HRE model proposed is a function of supply air temperature, supply airflow rate and cooling load. The HRE model proposed has been proven to be applicable to stratum ventilation and displacement ventilation for different room geometries and air terminal configurations, with errors generally within ±5% and a mean absolute error less than 4% for thirty-three experimental cases and five simulated cases. Investigations into the air-side modulation with the proposed HRE model reveal that for both the typical stratum-ventilated classroom and office, the variable-air-volume system can serve a wider range of cooling load than the constant-air-volume system. The assumption of a constant HRE used in the conventional method could lead to errors in the room temperature prediction up to ±1.3 °C, thus the proposed HRE model is important to the air-side modulation for thermal comfort. An air-side modulation method is proposed based on the HRE model to maximize the HRE for improving energy efficiency while maintaining thermal comfort. Results show that the HRE model based air-side modulation can improve the energy efficiency of stratum ventilation up to 67.3%. The HRE model based air-side modulation is also promising for displacement ventilation