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The performance of ductless personalized ventilation (DPV) was compared to the performance of a typical desk fan since they are both stand-alone systems that allow the users to personalize their indoor environment. The two systems were evaluated using a validated computational fluid dynamics (CFD) model of an office room occupied by two users. To investigate the impact of DPV and the fan on the inhaled air quality, two types of contamination sources were modelled in the domain: an active source and a passive source. Additionally, the influence of the compared systems on thermal comfort was assessed using the coupling of CFD with the comfort model developed by the University of California, Berkeley (UCB model). Results indicated that DPV performed generally better than the desk fan. It provided better thermal comfort and showed a superior performance in removing the exhaled contaminants. However, the desk fan performed better in removing the contaminants emitted from a passive source near the floor level. This indicates that the performance of DPV and desk fans depends highly on the location of the contamination source. Moreover, the simulations showed that both systems increased the spread of exhaled contamination when used by the source occupant.
Performance assessment of a ductless personalized ventilation system using a validated CFD model
(2018)
The aim of this study is twofold: to validate a computational fluid dynamics (CFD) model, and then to use the validated model to evaluate the performance of a ductless personalized ventilation (DPV) system. To validate the numerical model, a series of measurements was conducted in a climate chamber equipped with a thermal manikin. Various turbulence models, settings, and options were tested; simulation results were compared to the measured data to determine the turbulence model and solver settings that achieve the best agreement between the measured and simulated values. Subsequently, the validated CFD model was then used to evaluate the thermal environment and indoor air quality in a room equipped with a DPV system combined with displacement ventilation. Results from the numerical model were then used to quantify thermal sensation and comfort using the UC Berkeley thermal comfort model.
A new large‐field, high‐sensitivity, single‐mirror coincident schlieren optical instrument has been installed at the Bauhaus‐Universität Weimar for the purpose of indoor air research. Its performance is assessed by the non‐intrusive measurement of the thermal plume of a heated manikin. The schlieren system produces excellent qualitative images of the manikin's thermal plume and also quantitative data, especially schlieren velocimetry of the plume's velocity field that is derived from the digital cross‐correlation analysis of a large time sequence of schlieren images. The quantitative results are compared with thermistor and hot‐wire anemometer data obtained at discrete points in the plume. Good agreement is obtained, once the differences between path‐averaged schlieren data and planar anemometry data are reconciled.
Overheating is a major problem in many modern buildings due to the utilization of lightweight constructions with low heat storing capacity. A possible answer to this problem is the emplacement of phase change materials (PCM), thereby increasing the thermal mass of a building. These materials change their state of aggregation within a defined temperature range. Useful PCM for buildings show a phase transition from solid to liquid and vice versa. The thermal mass of the materials is increased by the latent heat. A modified gypsum plaster and a salt mixture were chosen as two materials for the study of their impact on room temperature reduction. For realistic investigations, test rooms were erected where measurements were carried out under different conditions such as temporary air change, alternate internal heat gains or clouding. The experimental data was finally reproduced by dint of a mathematical model.
The human body is surrounded by a micro‐climate which results from its convective release of heat. In this study, the air temperature and flow velocity of this micro‐climate were measured in a climate chamber at various room temperatures, using a thermal manikin simulating the heat release of the human being. Different techniques (Particle Streak Tracking, thermography, anemometry, and thermistors) were used for measurement and visualization. The manikin surface temperature was adjusted to the particular indoor climate based on simulations with a thermoregulation model (UCBerkeley Thermal Comfort Model). We found that generally, the micro‐climate is thinner at the lower part of the torso, but expands going up. At the head, there is a relatively thick thermal layer, which results in an ascending plume above the head. However, the micro‐climate shape strongly depends not only on the body segment, but also on boundary conditions: the higher the temperature difference between the surface temperature of the manikin and the air temperature, the faster the air flow in the micro‐climate. Finally, convective heat transfer coefficients strongly increase with falling room temperature, while radiative heat transfer coefficients decrease. The type of body segment strongly influences the convective heat transfer coefficient, while only minimally influencing the radiative heat transfer coefficient.