The influence of low-temperature surface induction on evacuation, pump-out hole sealing and thermal performance of composite edge-sealed vacuum insulated glazing

Hermeticity of vacuum edge-sealing materials are one of the paramount requirements, specifically, to the evolution of energy-efficient smart windows and solar thermal evacuated flat plate collectors. This study reports the design, construction and performance of high-vacuum glazing fabrication system and vacuum insulated glazing (VIG). Experimental and theoretical investigations for the development of vacuum edgeseal made of Sn-Pb-Zn-Sb-AlTiSiCu composite in the proportion ratio of 56:39:3:1:1 by % (CS-186) are presented. Experimental investigations of the seven constructed VIG samples, each of size 300mm·300mm·4 mm, showed that increasing the hot-plate surface temperatures improved the cavity vacuum pressure whilst expediting the pump-out hole sealing process but also increases temperature induced stresses. Successful pump-out hole sealing process of VIG attained at the hot-plate set point temperature of 50˚C and the approximate cavity pressure of 0.042 Pa was achieved. An experimentally and theoretically validated finite volume model (FVM) was utilised. The centre-of-pane and total thermal transmittance values are calculated to be 0.91 Wm-2K-1 and 1.05 Wm-2K-1, respectively for the VIG. FVM results predicted that by reducing the width of vacuum edge seal and emissivity of coatings the thermal performance of the VIG is improved

Energy simulations of a transparent-insulated office facade retrofit in London, UK

Purpose – Transparent insulation materials (TIMs) have been developed for application to building facades to reduce heating energy demands of a building. The purpose of this research is to investigate the feasibility of TI-applications for high-rise and low rise office buildings in London, UK, to reduce heating energy demands in winter and reduce overheating problems in summer. Design/methodology/approach – The energy performance of these office building models was simulated using an energy simulation package, Environmental Systems Performance-research (ESP-r), for a full calendar year. The simulations were initially performed for the buildings with conventional wall elements, prior to those with TI-systems (TI-walls and TI-glazing) used to replace the conventional wall elements. Surface temperatures of the conventional wall elements and TI-systems, air temperature inside the 20mm wide air gaps in the TI-wall, dry-bulb zone temperature and energy demands required for the office zones were predicted. Findings – Peak temperatures of between 50 and 70°C were predicted for the internal surface of the TI-systems, which clearly demonstrated the large effect of absorption of solar energy flux by the brick wall mass with an absorptivity of 90 percent behind the TIM layer. In the office zones, the magnitude of temperature swings during daytime was reduced, as demonstrated by a 10 to 12 h delay in heat transmission from the external façade to the office zones. Such reduction indicates the overheating problems could be reduced potentially by TI-applications. Originality/value – This research presents the scale and scope of design optimisation of TI-systems with ESP-r simulations, which is a critical process prior to applications to real buildings

Solar energy gain and space-heating energy supply analyses for solid-wall dwelling retrofitted with the experimentally achievable U-value of novel triple vacuum glazing

A considerable effort is devoted to devising retrofit solutions for reducing space-heating energy in the domestic sector. Existing UK solid-wall dwellings, which have both heritage values and historic fabric, are being improved but they tend to have meagre thermal performance, partly, due to the heat-loss through glazings. This paper takes comparative analyses approach to envisage space-heating supply required in order to maintain thermal comfort temperatures and attainable solar energy gains to households with the retrofit of an experimentally achievable thermal performance of the fabricated sample of triple vacuum glazing to a UK solid-wall dwelling. 3D dynamic thermal models (timely regimes of heating, occupancy, ventilation and internal heat gains) of an externally-insulated solidwall detached dwelling with a range of existing glazing types along with triple vacuum glazings are modelled. A dramatic decrease of space-heating load and moderate increase of solar gains are resulted with the dwelling of newly achievable triple vacuum glazings (having centre-of-pane U-value of 0.33 Wm-2 K-1) compared to conventional glazing types. The space-heating annual cost of single glazed dwellings was minimised to 15.31% (≈USD 90.7) with the retrofit of triple-vacuum glazings. An influence of total heat-loss through the fabric of solid-wall dwelling was analysed with steady-state calculations which indicates a fall of 10.23% with triple vacuum glazings compared to single glazings

A numerical investigation into the heat transfer and melting process of lauric acid in a rectangular enclosure with three values of wall heat flux

A numerical study of melting of Lauric acid in a vertical rectangular cross-section enclosure was performed with FLUENT 18.2. The enclosure was subject to a constant heat flux on one side of 500, 750 and 1000 W/m2. For model validation purposes simulations were initially performed of experimental systems in the literature with predicted values compared to experimental measurements. Predictions indicate that during the initial stage of melting, conduction is the dominant mode of heat transfer, subsequently replaced by convection when there is sufficient liquid PCM. The simulations show that as the magnitude of heat flux is increased, average wall temperature increases and melting time reduces. The predicted results indicated that melting time decreases by 28.5 % as the wall flux increases by 50 % from 500 to 750 W/m2. The time required for melting reduces by about 50% when the wall heat flux is increased from 500 to 1000 W/m2

Predicting the solar energy and space-heating energy performance for solid-wall detached house retrofitted with the composite edge-sealed triple vacuum glazing

© 2017 The Authors. Published by Elsevier Ltd. Triple-Vacuum-Glazing is regarded as evolutionary step in minimising the space-heating loss. This paper takes a comparative analysis approach to envisage space-heating supply required for achieving thermal-comfort temperatures and attainable solar energy gains to households with retrofit of composite edge-sealed triple-vacuum-glazing. Predictions of varying window-to-wall ratios on space-heating energy and solar energy gains for winter months are analysed. The notable winter and annual space-heating energy savings of 14.58% and 15.31%, respectively, were obtained with solid-wall detached-house retrofitted with triple-vacuum-glazed windows compared to single-glazed-windows. The heat-loss calculations show a prominent reduction from 12.92% to 2.69% when replacing single-glazed windows to triple-vacuum-glazed windows

A comparative study of the effect of wall heat flux on melting and heat transfer characteristics in phase change material thermal energy stores arranged vertically and horizontally

An experimental investigation was carried out to analyse the heat transfer characteristics during melting of phase change material (PCM) RT44HC in thermal energy stores arranged vertically and horizontally to assess the effect of different values of wall heat flux on the development of melt fraction, solid/liquid interface location and temperature distribution. A test cell consisting of a rectangular cross section enclosure was constructed from polycarbonate sheet, copper plates and mica heaters. Both left and right sides of the store were subject to uniform wall heat fluxes of 675, 960 and 1295 W/m2. Thermocouples were used to measure the temperature at different locations inside the phase change material (PCM) and on the surface of the copper plates. The study included visualization of the melting process and measurement of the temperature distribution at the vertical mid-plane of the store. Images of the melting process were analysed with an image processing technique to determine the melt fraction at selected times. It was observed that as the heat flux input increased the total melting time reduced, the reduction in melt time for the horizontally oriented store was about 12.5-15.0% when compared to the vertically oriented store as a result of the intensification of natural convection flows. Heat conduction was the dominant mode of heat transfer during the early stage of melting, followed by short transition period after which convection dominates during the rest of the melting process. The experimental results provide a set of benchmark data for validation of numerical codes

A study of a eutectic salt of lithium nitrate and sodium chloride (87–13%) for latent heat storage

Latent heat storage in salt mixtures has attracted much attention as it can store a large amount of heat within a small temperature range in a small volume compared to sensible heat storage. In this paper, the eutectic salt of LiNO3–NaCl (87–13%) was investigated to evaluate its potential for latent heat storage for medium temperature range applications (290 kJ/kg). Its thermal decomposition temperature was tested using a Thermogravimetric Analyser (TGA). The salt mixture exhibits an excellent chemical stability below 400 °C with no changes after tests of multiple cycles with DSC and TGA. The main factors affecting the economic feasibility for this eutectic salt were also discussed