Neural Network Models Using Thermal Sensations and Occupants’ Behavior for Predicting Thermal Comfort

It is important to create comfortable indoor environments for building occupants. This study developed neural network (NN) models for predicting thermal comfort in indoor environments by using thermal sensations and occupants’ behavior. The models were trained by data on air temperature, relative humidity, clothing insulation, metabolic rate, thermal sensations, and occupants’ behavior collected in ten offices. The models were able to predict similar acceptable air temperature ranges in offices, from 20.6℃ to 25℃ in winter and from 20.6℃ to 25.6℃ in summer. The comfort zone obtained by the NN model using thermal sensations in the ten offices was narrower than the comfort zone in ASHRAE Standard 55, but that obtained by the NN model using behaviors was wider than the ASHRAE comfort zone. This investigation demonstrates alternative approaches to the prediction of thermal comfort

Thermal Comfort Analysis of Displacement Ventilation System Coupled with Passive Chilled Beams

Displacement ventilation (DV) has been widely studied in literature, and is currently used in enclosed environments like office buildings. Although DV has been shown to be able to provide better indoor air quality in the occupied zone than conventional mixing ventilation (MV), its capability of removing heat is usually limited. Since it supplies air directly to occupied zone, the temperature of supply air is inevitably higher than that in MV. Meanwhile, passive chilled beams (PCB), which cool occupied space by running chilled water through beams at ceiling level, has been reported to have a high heat removal capability, and can save energy. Thus, a coupled system that combines both DV and PCB has the potential of keeping the advantages of both systems, and was explored in detailed by using experimental and simulation methods. This study focused on investigating the thermal performance of a coupled system of DV and PCB, and compared it with a corresponding DV-only system. Experiment was carried out in a full-scale environmental chamber to measure air velocity and temperature at various locations in the chamber. Moreover, a computational fluid dynamics (CFD) model was used to simulate the air velocity and temperature distributions, which were then validated by the measured data. With the validated CFD model, thermal comfort in the occupied zone were analyzed with the coupled system and the DV-only system. Thermal comfort level was presented by the predicted mean vote (PMV), and percentage dissatisfied people due to draft (PD). The results indicated that the PCB can help to cool down the temperature in the room, and the air temperature stratification was still maintained in most regions. However, due to the cold downward jet generated by the PCB, the region under the PCB had a higher air velocity and lower temperature than that with DV-only system. This resulted in a local zone with less thermal comfort. Based on reported results, this study provided preliminary guidelines for designing of the coupled system with acceptable thermal comfort in occupied zone

Experimental Study on the Impact of Passive Chilled Beam in a Room with Displacement Ventilation

Previous studies have demonstrated that displacement ventilation (DV) can provide better air quality than mixing ventilation (MV), and may save energy in buildings. However, since DV introduces supply air to the occupied zone directly, the temperature of supply air it provides is normally higher than in a MV system, so the ability to remove cooling load is limited with the same amount of air. On the other hand, passive chilled beam (PCB) systems have been shown to be able to remove a large cooling load while saving energy. Therefore, this research studied a coupled configuration that combined DV and PCB, and examined its thermal and ventilation performances through the measurements of airflow velocity, temperature, and contaminant (simulated by sulfur hexafluoride, or SF6) concentration at various locations. Measurement results were compared with those in the same room but with only DV system. A third set of measurements was also conducted to test how sensitive the results were to room layout and ratio of heat removed by PCB. Experimental results showed that PCB increased the overall air flow velocity in occupied zone, although the maximum airflow velocity was still observed at floor level, which was similar as in a DV only system. When both PCB and DV systems were used, temperature gradient was observed in most locations of the room. Meanwhile, contaminant concentration stratification was seen to be destroyed by PCB in this experiment. Similar trend was observed in the third set of measurement which had a different room layout and a lower ratio of heat removed by PCB

Optimal lifting of Levi-degenerate hypersurfaces and applications to the Cauchy--Szeg\"o projection

We consider a family of Levi-degenerate finite type hypersurfaces in $\mathbb C^2$, where in general there is no group structure. We lift these domains to stratified Lie groups via a constructive proof, which optimizes the well-known lifting procedure to free Lie groups of general manifolds defined by Rothschild and Stein. This yields an explicit version of the Taylor expansion with respect to the horizontal vector fields induced by the sub-Riemannian structure on these hypersurfaces. Hence, as an application, we establish the Schatten class estimates for the commutator of the Cauchy--Szeg\"{o} projection with respect to a suitable quasi-metric defined on the hypersurface

The Kohn-Laplacian and Cauchy-Szeg\"{o} projection on Model Domains

We study the Kohn-Laplacian and its fundamental solution on some model domains in $\mathbb C^{n+1}$, and further discuss the explicit kernel of the Cauchy-Szeg\"o projections on these model domains using the real analysis method. We further show that these Cauchy-Szeg\"o kernels are Calder\'on-Zygmund kernels under the suitable quasi-metric

A semi-empirical model for studying the impact of thermal mass and cost-return analysis on mixed-mode ventilation in office buildings. Energy Build

Abstract: Mixed-mode ventilation that combines natural ventilation and mechanical ventilation has great potential to save cooling energy when compared to mechanical systems and is more reliable than natural ventilation systems. This paper investigated the impact of window opening area, insulation, and thermal mass on the cooling energy saving of mixed-mode ventilation for three office buildings in different types of U.S. climates using EnergyPlus simulations. The results show that electricity use can be reduced by 6-91% depending on the climate. In addition to climate, thermal mass has a large impact on the performance of mixed-mode ventilation. This investigation developed a semi-empirical model to predict the impact of thermal mass on energy use, and optimized the thermal mass for maximum monetary return based on the model

Voltage-current characteristics of needle-plate system with different media on the collection plate

Abstract The hybrid electrostatic precipitator and media filtration system is significantly more promising than traditional filtration methods. This paper investigated the electrostatic characteristics of different filter media types used in the hybrid filtration system. The voltage-current (V-I) characteristics of needle-plate system, the collection plate of which is covered by filter media, were measured. Seven types of filter media and collection plate including iron plate, iron grid and activated carbon layer were considered. The glass fiber and polyethylene media reduce approximately 20% of the current value. The bag filter increases the current value because of the back corona effect. Polyester and polyethylene terephthalate materials with activated carbon attached can increase the current value significantly. In addition, this paper studied the effects of cake thickness on V-I characteristics. The results show that the cake layer has little influence on the V-I character when its thickness is not very big