Dark side of the universe in the Stephani cosmology

We investigate the late time acceleration of the universe in the context of the Stephani model. This solution generalizes those of Friedmann-Lemaitre-Robertson-Walker (FLRW) in such a way that the spatial curvature is a function of of time. We show that the inhomogeneity of the models can lead to an accelerated evolution of the universe that is analogous to that obtained with FLRW models through a cosmological constant or any exotic component for matter.Comment: 8 pages, 2 figure, many improvements; to appear in European Physical Journal

The effects of air permeability, background ventilation and lifestyle on energy performance, indoor air quality and risk of condensation in domestic buildings

Effective and efficient ventilation is essential when improving energy performance and Indoor Air Quality (IAQ) of buildings. Reducing air permeability can considerably improve the energy performance of buildings; however, making the buildings more airtight may result in lower rates of natural ventilation which may in turn increase the risks of condensation and unacceptable IAQ. This study evaluates the effects of different air permeability rates, background ventilation and occupants’ lifestyles on the energy performance as well as the risk of condensation and CO2 concentration in domestic buildings. Dynamic computer simulations were conducted in EnergyPlus. Results indicated direct relations between the ventilation rates, energy performance and IAQ. Higher air permeability along with background ventilation resulted in considerably better IAQ while energy consumption increased by up to four times. Occupants’ lifestyles were identified as a major contributor to the risk of condensation.This is the final version. It was first published by MDPI at http://www.mdpi.com/2071-1050/7/4/4022

Improving Thermal Comfort of Low-Income Housing in Thailand through Passive Design Strategies

In Thailand, the delivery of adequate low-income housing has historically been overshadowed by politics with cost and quantity being prioritised over quality, comfort and resilience. In a country that experiences hot and humid temperatures throughout the year, buildings need to be adaptable to the climate to improve the thermal comfort of inhabitants. This research is focused on identifying areas for improving the thermal performance of these housing designs. Firstly, dynamic thermal simulations were run on a baseline model using the adaptive thermal comfort model CIBSE TM52 for assessment. The three criteria defined in CIBSE TM52 were used to assess the frequency and severity of overheating in the buildings. The internal temperature of the apartments was shown to exceed the thermal comfort threshold for these criteria throughout the year. The internal operating daily temperatures of the apartment remain high, ranging from a maximum of 38.5 °C to a minimum of 27.3 °C. Based on these findings, five criteria were selected to be analysed for sensitivity to obtain the key parameters that influence the thermal performance and to suggest possible areas for improvement. The computer software package Integrated Environmental Solutions—Virtual Environment (IES-VE) was used to perform building energy simulations. Once the baseline conditions were identified, the software packages SimLab2.2 and RStudio were used to carry out the sensitivity analysis. These results indicated that roof material and the presence of a balcony have the greatest influence on the system. Incorporating insulation into the roof reduced the mean number of days of overheating by 21.43%. Removing the balcony increased the number of days of overheating by 19.94% due to significant reductions in internal ventilation

Evaluating the thermal performance of low-income housing in Thailand

This research investigates potential areas for improving the thermal performance of low income, government-provided housing designs in Bangkok, Thailand. In a country that experiences hot and humid temperatures throughout the year, buildings need to be adaptable to the climate in order to improve the thermal comfort of inhabitants. The current housing typologies include a prevalence of high density, low-rise condominiums with a large brick and concrete composition. As an initial step, the performance of the building was determined according to adaptive comfort standards using IES (VE) software. The results from the baseline model were analysed according to the adaptive comfort CIBSE TM52 guidelines. The zones under consideration within the case study housing unit were observed to exceed the acceptable limits of what is deemed appropriate for naturally ventilated buildings. The critical zone of concern is the living room with this zone exceeding the upper limit for overheating by a maximum of 11 hours annually. The main sources of the low thermal performance were identified as resulting from: thermal storage effects, the lack of sufficient natural ventilation through the living zones and excessive heat gains through the roof. The internal operating temperatures of the apartment remain high throughout the day and night, ranging from a maximum of 38.5° to a minimum of 27.3°

Assessing the Risks of Dampness and Mould Growth in Renovated Properties

A large portion of the UK housing stock was built before the introduction of the 1989’s building regulations in which insulated cavity walls became mandatory. It is estimated that 65% of the UK housing stock have uninsulated walls and 49% have single glazed leaky windows making them inefficient in terms of energy performance. There have been great efforts during the recent years to improve the quality and energy performance of such buildings through retrofitting/refurbishment not only to improve the living standards of their occupants but also to achieve UK’s carbon emission targets for 2050. Refurbishing such buildings to improve their quality/energy performance may, at the same time, increase the risk of poor indoor air quality (IAQ), condensation, dampness, and mould growth in these buildings. Many refurbished housing stock in the UK are facing similar problems. Damp and mould issues affect between 30-50% of new or refurbished buildings. There is therefore a need for appropriate design strategies not only to improve the quality and thermal performances of such buildings but also to reduce the aforementioned risks through better design, construction detailing, methods, and management processes. This paper reports on the first phase of a joint university/industry Knowledge Transfer project to address the above issues in renovated student accommodations in North West England. Temperature, relative humidity, CO2, and meter readings are measured and recorded in three case study buildings. Results revealed a direct relationship between energy consumption, IAQ, and occupants’ behaviours in the buildings. CO2, Temperature, and RH levels were more acceptable in one of the case study buildings; however, its energy consumption was 7 times higher when compared with a similar building

Effects of Manual and Automatic Natural Ventilation Control Strategies on Thermal Comfort, Indoor Air Quality and Energy Consumption

Occupants of naturally ventilated buildings can tolerate wider ranges of temperature and Indoor Air Quality (IAQ) if they have more control over their environment. Meanwhile, due to the complexity of advanced natural ventilation (ANV) strategies, introducing some form of automatic control is essential despite the fact that they limit the occupants’ control over their environment. Therefore, it is essential to understand the performance of ANV systems and occupants’ behaviours in order to identify a balance between automatic and manual controls to enhance the performance of ANV systems while maintaining the occupants’ comfort. The aim of the work reported in this paper is to evaluate the effects of a retrofitted ANV system with manual and automatic controls on thermal comfort, indoor air quality and energy consumption in an open-plan office building in the UK. Physical measurements were used to study the building performance in terms of thermal comfort, IAQ and energy consumption. The results revealed that occupants were much more aware about thermal comfort compared to IAQ. Therefore, relying on the occupants to control the ventilation system would considerably increase the risk of poor IAQ in buildings. Moreover, introducing automatic controls did not affect the thermal comfort conditions for those who understood and actively controlled the ANV system, while the situation improved for those occupants who were not active. Results of this study showed that introducing automated natural ventilation helped to reduce energy consumption by 8%