Using large eddy simulation to model buoyancy-driven natural ventilation

The use of Large Eddy Simulation (LES) for modelling air flows in buildings is a growing area of Computational Fluid Dynamics (CFD). Compared to traditional CFD techniques, LES provides a more detailed approach to modelling turbulence in air. This offers the potential for more accurate modelling of low energy natural ventilation which is notoriously difficult to model using traditional CFD. Currently, very little is known about the performance of LES for modelling natural ventilation, and its computational intensity makes its practical use on desk top computers prohibitive. The objective of this work was to apply LES to a variety of natural ventilation strategies and to compile guidelines for practitioners on its performance, including the trade-off between accuracy and cost

Investigating Heat Loss through Vestibule Doors for a Non-Residential Building

The aim of this study was to investigate the effects of air flow movement through high use front entrance doors of a college building with large flows of people. The objectives were to visualize and quantify the resultant energy losses through the entrance doors, coupled with investigating any potential improvements that can be obtained through improved design. The findings of the study suggest that the heat loss from the front entrance design can contribute to up to 2.8% of the buildings’ energy loads. It was also seen that a vestibule creates a tunnel effect for cold ambient air to enter the building without hot air escaping from the vestibule. Rather hot stale air exits through openings at the ceiling height. Potential solutions with entrance design are investigated and their results compared to the outcomes of a similar model designed using Computational Fluid Dynamics (CFD)

Investigating heat loss through vestibule doors for a non-residential building

The aim of this study was to investigate the effects of air flow movement through high use front entrance doors of a college building with large flows of people. The objectives were to visualize and quantify the resultant energy losses through the entrance doors, coupled with investigating any potential improvements that can be obtained through improved design. The findings of the study suggest that the heat loss from the front entrance design can contribute to up to 2.8% of the buildings’ energy loads. It was also seen that a vestibule creates a tunnel effect for cold ambient air to enter the building without hot air escaping from the vestibule. Rather hot stale air exits through openings at the ceiling height. Potential solutions with entrance design are investigated and their results compared to the outcomes of a similar model designed using Computational Fluid Dynamics (CFD)

Adaptive comfort model incorporating temperature gradient for a UK residential building

Thermal comfort field experiments were conducted to acquire thermal comfort data of 119 participants in a test house representative of a typical UK house. This paper compares the performance of popular PMV-based thermal comfort index vs neutral temperature based on Actual Mean Vote. The aim of this research was to incorporate vertical thermal gradient, which is usually a neglected yet highly influential parameter in a residential setting and propose a new adaptive thermal comfort model. The new adaptive model (LPMV) has been developed using a polynomial curve fit method. This method was chosen as it has the capability to correlate indoor environmental parameters with AMV and incorporated them in the generated mathematical model. The model requires temperature gradient and SET* only to determine neutral temperatures which makes it the first of its kind. The LMPV model was rigorously tested against thermal comfort data compiled in this study and against independent/unbiased data (the ASHRAE RP-884 database). LPMV showed up to 0.7°C improvement in predicting neutral temperature of occupants compared to the famous Fanger’s PMV model. This can result in better prediction of a suitable heating setpoint temperature which has great implications on annual energy demand

Evaluation of LES and RANS CFD modelling of multiple steady states in natural ventilation

This paper reports research carried out with the aim of evaluating and comparing the performance of Large Eddy Simulation (LES) and Unsteady Reynolds-Averaged Navier-Stokes (URANS) modelling for predicting the multiple steady states observed in experiments on a buoyancy-driven naturally ventilated enclosure. The sub-grid scales of the flow have been modelled using a Van Driest damped Smagorinsky sub-grid scale model in the case of LES and an RNG k-ε turbulence model has been used for URANS. A novel mesh design strategy was introduced to design the LES mesh to identify an optimum 'well-resolved' mesh, assuming that the flow investigated is free-shear dominated. It was found that the URANS solution eventually settled down into a permanent steady state, displaying no evidence of continuing instabilities or periodic unsteadiness. Both URANS and LES solutions captured the existence of three steady states as observed in experimental studies. However, LES was more accurate in predicting the temperatures inside the enclosure compared to URANS. In the URANS solutions, it was observed that for smaller lower opening areas the average indoor temperature had noticeable discrepancies when compared with experimental results. Unlike URANS, LES correctly predicted different steady state temperatures for different opening areas and the time to reach steady state agreed closely with theoretical predictions

Modelling buoyant thermal plumes in naturally ventilated buildings

The aim of the work reported in this paper was to evaluate the performance of Large Eddy Simulation (LES) for modelling natural ventilation driven by twin plumes. The flow is characterised by an interface height which separates the warm buoyant air above from the cooler air below, and a merging height for coalescence of the two plumes. Comparison between the LES predictions and theory for the interface height and volume flow rate in the merged plumes is good, giving confidence that LES has potential for modelling this important class of flows

IMPACT OF RISKS ON IJV PERFORMANCE IN PAKISTAN: MEDIATING ROLE OF EMC

The ongoing growth of the infrastructure development and construction industry in Pakistan in recent years has attracted foreign investors and firms to undertake Joint Ventures (JVs) in this emerging market, especially in the context of CPEC. The IJV paradigm is however quite complex and it is a general perception that usually the performance of JVs remains below the desired expectations. International construction businesses usually embody grave social, economic, and political implications in developing countries like Pakistan, where the problems of IJVs become more accentuated due to a host of other external as well as internal factors. Besides being an emerging trend, very few studies are available with regards to IJVs performance in Pakistan. This research is hence aimed at (1) Exploring the impact of Environment, Project and Partner's Risks on IJVs performance (2) Develop a matrix for explaining the impact of risk factors and mediating role of Effective Management Control in IJV paradigm (3) To test the postulated hypothesis through quantitative methods. For this, a questionnaire-based survey has been conducted in which the feedback and perceptions from local and foreign firms and professionals have been recorded and analyzed using SPSS software. The study finds out that there are negative effects of Risks on IJV performance however, with Effective Management Control, the impact of risks are mitigated

Investigating performance of solid desiccant dehumidification in an evaporative cooling system

Desiccant evaporative cooling (DEC) systems are still at early stage of utilisation and commercialise development. The primary focus of this study is to analyse the simulated performance of DEC in hot and humid climates. Four configurations of one-stage solid desiccant dehumidifiers with two-stage evaporative cooling systems have been simulated using TRNSYS simulation software for a typical test room. The psychrometric process and the coefficient of performance (COP) for each configuration is presented and configurations for the most efficient system have been identified

Performance assessment of Fanger’s PMV in a UK residential building in heating season

Traditionally there are two approaches to thermal comfort studies in the indoor environment. The first approach is to conduct tests in fully controlled climate chambers located in laboratories which help in maintaining desired environmental conditions for the experiments. However, the thermal physics of climate chambers are very different to that of real buildings. Additionally, the numbers of participants in such studies are also limited. The alternate/second approach is to place sensors and collect data in a set of homes and offices over a period of time where researchers have virtually no control on the thermal environment. This approach does involve a large set of participants however the large variations in thermal environmental parameters make the data not very reliable to elucidate trends. This paper reports on an original approach that combines the advantages of both these methods. In this research thermal comfort studies were conducted in a test house representative of a real residential building and a large set of participants. The thermal environmental parameters and heating strategies inside the test house were also fully controlled by researchers. The aim was to assess the performance of Fanger’s thermal comfort model (PMV) in predicting the actual thermal comfort of occupants (AMV) during heating season using two different types of heating emitters. A total of 119 participants between the ages of 19 and 21 years took part in these experiments. AMV of the occupants was determined by conducting surveys whilst PMV was calculated using sensors installed in the living room. Thermal neutral temperatures were calculated and compared for both AMV and PMV indices. It was found that there is a strong and directly proportional relation of both AMV and PMV with the operative temperature in the room. It was also observed that PMV would typically overestimate the neutral temperature compared to the statistically derived neutral temperature which the occupants would consider thermally comfortable

Temperature sensitivity analysis of thermal comfort in a UK residential building

This research focusses on investigating the sensitivity of thermal comfort to temperature in a heated space. Thermal comfort test sessions are conducted in a test house representative of a typical UK house during the winter season. A total of 119 participants took part in the series of tests conducted in the test house’s living room. Operative temperature in the heated space was maintained within the comfortable range recommended by CIBSE for a living room area in a UK house. Two different heating emitters were used for heating during the tests in order to examine their effects on occupant thermal comfort. Conventional radiators supplemented by a gas boiler and an electric fan heater were investigated in the presence and absence of a circulation fan running in the corner of the room. Thermal comfort sensation of occupants was calculated using sensors installed in the living room (Fanger’s Predicted Mean Vote). At the same time the occupants were asked to fill in surveys which were used to record their Actual Mean Vote. From the test sessions conducted it was found that AMV predicted a neutral temperature of 23.5°C whilst PMV predicted a neutral temperature of 24.0°C thus PMV over predicted the occupant’s thermal sensation compared to AMV. For the four heating scenarios it was found that a convective fan heater with a circulation fan causes the smallest temperature gradient (1.0oC) between ankle and head height for a seated occupant according to ISO7730 standards. The highest temperature gradient was measured for fan heater without a circulation fan (7.3oC). Occupants reported to be most uncomfortable if the convector heater without a circulation fan was used