Smart windows: Thermal modelling and evaluation

Copyright @ 2014 The Authors. Published by Elsevier Ltd. This is an open access article shared under the CC BY license (http://creativecommons.org/licenses/by/3.0/).A numerical investigation of the performance of a multi paned smart window integrated with water-cooled high efficiency third generation GaAsP/InGaAs QWSC (∼32% efficiency) solar cells illuminated by two-axis tracking solar concentrators at 500× in the inter pane space is presented. Optimising system parameters such as optical concentration ratio and coolant (water) flow rate is essential in order to avoid degradation in system performance due to high cell temperatures and thermal stresses. Detailed modelling of the thermo-fluid characteristics of the smart windows system was undertaken using a finite volume CFD package. Results of this analysis which considered the conductive, convective and radiative heat exchange processes taking place in the interior of the smart window system as well as the heat exchange to the internal and external ambient environment are presented.Engineering and Physical Sciences Research Counci

Energy efficient vacuum glazed window: A system design and investigations on hermetic sealing materials

Predictions by Fang et al (2010) indicate that triple vacuum glazing can theoretically achieve a centre of pane thermal transmittance of less than 0.26 W/(m2.K). To date two materials indium and solder glass have been used for sealing the edges the glass sheets in a vacuum glazing. Indium is a low temperature sealing material (157C) but is very expensive. Solder glass is a high temperature sealing material (around 450 C). One of the main hindrance to the manufacture of vacuum glazing at the industrial level is the cost. In this poster presentation, a vacuum glazing system for production at a laboratory scale using a modified evacuation pump-out sealing technique is presented. A number of samples have been fabricated using existing and new sealing materials that achieve a vacuum pressure less than 0.001Pa in the cavity of the vacuum glazing samples. An experimental performance verification of samples using new cost effective sealing materials will be executed in a hot box calorimeter to measure thermal transmittance performance of the samples. Issues associated with degradation of the vacuum pressure inside the cavity can be addressed by introducing non-evaporable getters

Heat load and solar gain prediction for solid wall dwellings retrofitted with triple vacuum glazing for selected window to wall area ratios

In much of the developed world there is a large stock of solid wall dwellings that require intervention to improve their energy performance. Heat loss through the windows of solid wall buildings is one of the factors contributing to high energy consumption for space heating resulting in excessive carbon emissions which lead to climate change. In this paper the heat load and solar gain are analysed for a room in a solid wall dwelling with single, double air filled, triple air filled, double vacuum and triple vacuum glazings at 5.49%, 12.36%, 13.19%, 20.6%, 24.72% and 32.96% window to wall area ratios (WWR’s). Simulated results are presented and the influence on energy required for space heating and solar energy gain in winter months (Dec, Jan and Feb) are analysed. The costs for space heating energy are calculated and show that replacing single glazed windows with triple vacuum glazed windows in the simulated room of a solid wall dwelling could save £36.07 annually. Assuming a dwelling consists of 6 simulated rooms, considerable energy and cost savings could be realised. It was also shown that for low heat loss glazings it is possible to significantly increase the window to wall area ratios with little increase in room heat load

Predicting the Solar Energy and Space-heating Energy Performance for Solid-wall Detached House Retrofitted with the Composite Edge-sealed Triple Vacuum Glazing

Existing UK solid-wall houses, which have both heritage values and historic fabric, are being improved but yet they tend to have preventable heat loss through windows. 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 the retrofit of the thermal transmittance (U-value) of a new composite edge-sealed triple vacuum glazing i.e. 0.33 Wm-2K-1. 3D dynamic thermal models (timely regimes of heating, occupancy, ventilation and internal heat gains) of an externally-insulated solid-wall detached house with a range of existing glazing types along with triple vacuum glazing with frame areas are modelled. The 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% (EUR 49.2) and 15.31% (EUR 105.4), respectively, were obtained with a 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

An investigation on edge sealing materials for the fabrication of vacuum glazing

This study aims at experimental durability investigation of low-temperature edge sealing material for the fabrication of vacuum glazing. A new technique offers a number of advantages in terms of cost for direct glass to metal sealing over conventional methods such as indium based vacuum glazing. The present study shows the results of three samples that were fabricated with different techniques and sizes. Sample A-170mmx170mm achieved a vacuum pressure of less than 0.001Pa. Sample B-400mmx400mm achieved a vacuum pressure of down to 0.1Pa. Sample C-300mmx300mm achieved a vacuum pressure of 0.088Pa. The edge seal bond was proven to be rigid; the small leakage around the edge can be avoided by improving the seal material uniformity around the periphery. A crack at one of the sides of the glass occurred due to the intense tensile stress resulting from the hot plate surface temperature of 120°C

Design and fabrication of vacuum glazing units using a new low temperature hermetic glass edge sealing method

This poster aims at presenting experimental investigations for the fabrication of vacuum glazing using a new low temperature (less than 200C) based hermetic edge sealing method, as shown in Fig. 1. To date two materials indium and solder glass have been used for sealing the edges of the glass sheets in a vacuum glazing. Indium is a low temperature sealing material, melts at 157C, but is very expensive. Solder glass is a high temperature sealing material, melts at around 450C, but has limitation of using low-e coatings and a tempered glass. One of the main hindrances to the manufacture of vacuum glazing at the industrial level is the cost. In this poster presentation, a vacuum glazing system for production at a laboratory scale using a modified evacuation pump-out sealing technique is presented. The vacuum pressure measurements are performed using a combined transducer consists of Micro Pirani and miniaturised hot cathode ionisation gauge. The vacuum pressure of less than 0.046Pa in the cavity of the vacuum glazing samples was recorded. An experimental performance verification of samples can be executed in a hot box calorimeter to measure thermal transmittance performance of the samples

Fabrication of Energy Efficient Vacuum Glazing using a Novel Edge Sealing Material

This poster aims at presenting an experimental investigations for the fabrication of vacuum glazing using a novel low-temperature edge sealing material, melts at around 200 C, as shown in figure 1. To date two materials indium and solder glass have been used for sealing the edges of the glass sheets in a vacuum glazing. Indium is a low temperature sealing material, melts at 157 C, but is very expensive. Solder glass is a high temperature sealing material, melts at around 450C, but has limitation of using low-e coatings and a tempered glass. One of the main hindrance to the manufacture of vacuum glazing at the industrial level is the cost. In this poster presentation, a vacuum glazing system for production at a laboratory scale using a modified evacuation pump-out sealing technique is presented. A number of samples have been fabricated using a novel cost effective edge sealing material that achieves an evacuation pressure less than 0.046 Pa in the cavity of the vacuum glazing samples. An experimental performance verification of samples using new cost effective sealing materials will be executed in a hot box calorimeter to measure thermal transmittance performance of the samples. Issues associated with degradation of the vacuum pressure inside the cavity can be addressed by introducing non-evaporable getters

A new low-temperature hermetic composite edge seal for the fabrication of triple vacuum glazing

High performance low-cost vacuum glazing is a key development in the move to more energy-efficient buildings. This study reports the results of experimental and theoretical investigations into the development of a new low-temperature (less than 200˚C) composite edge seal. A prototype triple vacuum glazing of dimensions 300 mm x 300 mm was fabricated with a measured vacuum pressure of 4.8x10-2 Pa achieved. A three-dimensional finite-element model for this prototype triple vacuum glazing with the composite edge seal was also developed. Centre-of-pane and total thermal transmittance values for this small prototype of the triple vacuum glazing were predicted to be 0.33 Wm-2K-1 and 1.05 Wm-2K-1, respectively. It was predicted using the developed model that the thermal performance could be improved by reducing the width of the composite edge seal and by the use of soft low-emissivity coatings on the glass surfaces. Detailed three-dimensional isothermal contour plots of the modelled triple vacuum glazing are presented

Similarity solutions for unsteady shear-stress-driven flow of Newtonian and power-law fluids : slender rivulets and dry patches

Unsteady flow of a thin film of a Newtonian fluid or a non-Newtonian power-law fluid with power-law index N driven by a constant shear stress applied at the free surface, on a plane inclined at an angle α to the horizontal, is considered. Unsteady similarity solutions representing flow of slender rivulets and flow around slender dry patches are obtained. Specifically, solutions are obtained for converging sessile rivulets (0 < α < π/2) and converging dry patches in a pendent film (π/2 < α < π), as well as for diverging pendent rivulets and diverging dry patches in a sessile film. These solutions predict that at any time t, the rivulet and dry patch widen or narrow according to |x|3/2, and the film thickens or thins according to |x|, where x denotes distance down the plane, and that at any station x, the rivulet and dry patch widen or narrow like |t|−1, and the film thickens or thins like |t|−1, independent of N

Presentation, management, and outcomes of cauda equina syndrome up to one year after surgery, using clinician and participant reporting: A multi-centre prospective cohort study.

BACKGROUND: Cauda equina syndrome (CES) results from nerve root compression in the lumbosacral spine, usually due to a prolapsed intervertebral disc. Evidence for management of CES is limited by its infrequent occurrence and lack of standardised clinical definitions and outcome measures. METHODS: This is a prospective multi-centre observational cohort study of adults with CES in the UK. We assessed presentation, investigation, management, and all Core Outcome Set domains up to one year post-operatively using clinician and participant reporting. Univariable and multivariable associations with the Oswestry Disability Index (ODI) and urinary outcomes were investigated. FINDINGS: In 621 participants with CES, catheterisation for urinary retention was required pre-operatively in 31% (191/615). At discharge, only 13% (78/616) required a catheter. Median time to surgery from symptom onset was 3 days (IQR:1-8) with 32% (175/545) undergoing surgery within 48 h. Earlier surgery was associated with catheterisation (OR:2.2, 95%CI:1.5-3.3) but not with admission ODI or radiological compression. In multivariable analyses catheter requirement at discharge was associated with pre-operative catheterisation (OR:10.6, 95%CI:5.8-20.4) and one-year ODI was associated with presentation ODI (r = 0.3, 95%CI:0.2-0.4), but neither outcome was associated with time to surgery or radiological compression. Additional healthcare services were required by 65% (320/490) during one year follow up. INTERPRETATION: Post-operative functional improvement occurred even in those presenting with urinary retention. There was no association between outcomes and time to surgery in this observational study. Significant healthcare needs remained post-operatively. FUNDING: DCN Endowment Fund funded study administration. Castor EDC provided database use. No other study funding was received