Energy efficiency interventions for residential buildings in Bloemfontein using passive energy techniques

Thesis (M. Tech. (Mech. Eng.)) -- Central University of Technology, Free state, 2010The purpose of this research is to minimize the use of active systems in providing thermal comfort in single-family detached, middle to high income residential buildings in Bloemfontein. The typical case study house was selected according to the criteria as reviewed by Mathews et al., (1999). Measurements were taken for seven days (18 – 24 May 2009). The measurements were carried out in the winter period for Bloemfontein, South Africa. Ecolog TH1, humidity and temperature data logger was used in doing the measurements. These measurements included indoor temperatures and indoor relative humidity. Temperature swings of 8.43 ºC and thermal lag of 1 hour were observed. For the period of seven days (168 hours), the house was thermally comfortable for 84 hours. Thermal analysis for the base case house was done using Ecotect™ (building analysis software) and the simulated results were compared with the measured results. A mean bias error (MBE) of between 10.3% ≤≤11.5% was obtained on the initial calibration. The final calibration of the model yielded error between0.364% ≤≤0.365%. The final calibration model which presented a small error was adopted as the base case. Passive strategies were incorporated to the Ecotect™ model (final calibrated model) singly and in combination; then both thermal and space load simulations were obtained and compared to simulations from the original situation (base case) for assessing improvements in terms of thermal comfort and heating, ventilation and air conditioning (HVAC) energy consumption. Annual HVAC electricity savings of up to 55.2 % were obtained from incorporating passive strategies in combination. Incorporating passive strategies resulted in small improvements in thermal comfort

Thermal performance of heavy-weight and light-weight steel frame construction approaches in the central Pretoria climate

Published ArticleThe purpose of this paper is to analyse the thermal performance of two buildings. The one has a large thermal mass and the other a highly insulated low thermal mass. A typical 120 m2 suburban building was modelled in Ecotect. As part of the model infiltration rate, wind sensitivity and a central Pretoria weather file were used. New material composites were introduced in the materials database to represent typical building materials used in the construction of heavy and light-weight buildings in South Africa. The thermal characteristics of these new materials were then calculated within Ecotect. Ecomat was used to calculate thermal lag which was used as an additional input into Ecotect. The research indicates that a low thermal mass and highly insulated building have been shown to use 18.3% less annual space heating and cooling energy when compared to the high thermal mass building. The good thermal performance results of the light-weight building will help in clearing scepticism to adopting this construction technology in southern Africa where high thermal mass masonry is still predominant

Performance evaluation of a plate encapsulated salt hydrate PCM mixed with a gel

Abstract : An alternative method of cooling is required to meet cooling demands and simultaneously decrease conventional energy consumption. The current research aimed to investigate the feasibility of using a phase change material (PCM) in the form of a salt hydrate mixed with a CSIR-developed gel for PCM based cold storage that used nighttime cold to cool ambient air during the day. The experiments were conducted over a time period of three hours between 12:00 pm and 15:00 pm in the afternoon. The total temperature drops were found to be 3.8, 2.9 and 2.6 degrees for air flow rates of 0.03, 0.05 and 0.06kg/s respectively. The total energy transferred for each of the mass flow rates averaged 140.9, 144.4 and 158.9J for air flow rates of 0.03, 0.05 and 0.06kg/s respectively

Experimental analysis for thermal storage performance of three types of plate encapsulated phase change materials in air heat exchangers for ventilation applications

Due to climate change and rising global temperatures, energy demand associated with commercial and office building cooling, is projected to increase. Passive-cooling, based on phase change materials, can assist to moderate this increase, however relatively few modelling equations to describe its operating behaviour exists. In this experimental investigation the melting performance of three commercially available encapsulated phase change materials were evaluated for passive cooling applications in air ducts systems. Two paraffin type phase change materials and one salt hydrate phase change material with melting temperatures in the range of 22 °C and 28 °C were considered. Vertical orientated plate type encapsulations with a thickness of 10 mm and a pitch of 15 mm were tested for air inlet temperatures ranging from 30 °C to 35 °C and upstream air velocities ranging from 0.4 m/s and 0.9 m/s. The average effectiveness, cooling power, energy absorption, and phase transformation durations were determined. It was found that the average thermal effectiveness decreased with increased velocities and that the cooling power, which was inversely proportional to the phase transformation duration, increased with air flow rate and inlet air temperature. Based on the data a new empirical correlation model was developed which describes the cooling capacity of the in-duct phase change material plates.https://www.elsevier.com/locate/jobehj2020Mechanical and Aeronautical Engineerin

A review of passive thermal comfort energy efficiency interventions in residential buildings of Bloemfontein

Published ArticleThe paper presents a critique of passive and active thermal comfort strategies. Extensive review of literature on passive thermal comfort energy efficiency interventions and their benefits was under taken. The paper explains the correlation between climatic comfort and energy efficiency. The applicability of the energy management process in ensuring energy efficiency is presented. Passive thermal comfort energy efficiency interventions have been seen to provide thermal comfort as well as energy efficiency. Their major shortcoming is their disability to work in all kinds of weather, heating in the winter and cooling in the summer. There is need to optimize passive thermal comfort energy efficiency interventions so that they provide heating in the winter and cooling in the summer

Development of a design tool for PCM based free comfort cooling system in office buildings in South Africa

Space cooling energy demand is projected to increase due to climate changes. For example, the South African climate change model projected warming to reach around 3 to 4°C along the coast, and 6 to 7°C in the interior. Such temperature increases will significantly increase the energy demand by building cooling applications. Thus, there is an urgent need to improve the energy efficiency in buildings and to reduce the peak cooling loads. Various studies for building free cooling using phase change materials have shown to reduce or avoid the need for mechanical space cooling. Very few of these studies covered Southern African climatic conditions and no research was found reporting a comparison of free cooling thermal performance of different PCM types for an individual climate scenario. The purpose of this study was to experimentally evaluate and compare the cooling performance of three PCM materials in plate-air heat exchanger modules subjected to Southern African climatic conditions and to use the data to deduce empirical correlations that can be used by thermal designers to determine the number of modules required to maintain an objective cooling load within the range of operating conditions. In this experimental investigation the cooling (discharging) performance of plate encapsulated Phase Change Materials (PCMs) for passive cooling applications were evaluated as measured by its average effectiveness, cooling power, energy absorption and phase transformation duration. A test facility that mimics a PCM-air heat exchanger module installed in a ventilation duct was used to consider the impact of varying air flow rate and inlet air temperature. PCM plate encapsulations with a thickness of 10 mm orientated vertically and spaced at a pitch of 15 mm were investigated. The thermal storage characteristics of three commercial PCMs were considered. Two paraffin type PCMs with melting temperature ranges of 25 °C to 28 °C and 22 °C to 26 °C and one type salt hydrate with a phase change temperature range 24 °C to 25 °C were used in air flows ranging in temperature from 30 °C to 35 °C and duct air velocities ranging from 0.4 m/s to 0.9 m/s. The results indicated that average effectiveness of the PCM modules decreased with increasing convective air mass flow rate. Increasing air mass flow rate (at constant inlet air temperature) or increasing the inlet air temperature (at constant air mass flow rate) increased the average cooling power. The phase transformation durations of the PCMs decreased as both the air flow rate and inlet air temperature increased. The salt hydrate (SP24E) module had the highest energy absorption capacity for all experimental conditions. The rate of energy absorption increased with inlet air temperature. From a design standpoint the desirable thermal performance of PCM is to have a high instantaneous heat absorption capacity and also extended over a longer period. Paraffinic PCMs met the first condition of high instantaneous heat absorption but did not meet the second condition of extended heat absorption duration. SP24E met the condition for extended heat absorption duration but had a lower instantaneous heat absorption capacity than the paraffin. Empirically-based correlations for determining the number of modules to maintain an objective cooling load were developed using a multiple regression analysis technique. From this, air conditioning system designers can determine the number of modules (installed in parallel) required to maintain an objective cooling load within the range of operating conditions tested.Dissertation (MSc)--University of Pretoria, 2017.Mechanical and Aeronautical EngineeringMScUnrestricte

Towards a successful free senior high school policy in Ghana: the role of non-profit organisations

This paper seeks to understand the significant challenges of Ghana’s free senior high school (SHS) policy and the roles that non-profit organisations play in addressing them. Findings reveal non-profit interventions such as establishing new school buildings, providing teacher training, addressing inequality issues, equipping graduates with employable skills and evaluating the policy. Such public–non-profit partnerships can help the government achieve its vision of free SHS education for all young Ghanaians.</jats:p