Trevor Hyde

Experimental characterization and detailed performance prediction of a vacuum glazing system fabricated with a low temperature metal edge seal, using a validated computer model

Current multi-pane windows have a very low heat loss but their solar transmittance is low resulting in a loss of daylight and solar gains. Multi-pane windows also require framing arrangements that are difficult to retrofit to existing apertures in many existing buildings. A contiguously sealed evacuated double-glazing with low long-wave radiative emittance coatings on its internal surfaces, no heavier than conventional double-glazing, with good visual transmittance suitable for retrofitting to existing buildings, has been analyzed experimentally. Measured heat transfer coefficients and visual transmittances of laboratory fabricated evacuated glazing samples, along with theoretical predictions of center of glazing thermal conductance are presented.

A comparison of the estimated natural ventilation rates of four solid wall houses with the measured ventilation rates and the implications for low-energy retrofits

To reduce energy consumption and carbon dioxide emissions in existing houses in heating-dominated climates, there is a drive to reduce ventilation heat loss by tightening the building envelope. Energy-efficient domestic retrofits, which neglect ventilation requirements or assume without enquiry that adequate ventilation rates have been met, have the potential to impact negatively on the health and well-being of occupants by creating unhealthy indoor environments. The natural ventilation rates of UK dwellings created by building envelope air leakage is commonly estimated by applying a rule-of-thumb to the air flow required to create a pressure differential across a building envelope of 50 Pa using a fan pressurisation technique. To analyse the appropriateness of the rule, a tracer gas concentration decay technique was used on four Victorian solid wall houses to ascertain their natural ventilation rates created by building envelope air leakage. Results indicate that applying the rule overestimated the natural ventilation rates of the four houses tested. These findings have the potential to impact on retrofit ventilation strategies for existing houses.

Refurbishing the UK's 'hard to treat' dwelling stock: Understanding challenges and constraints - the work of Project CALEBRE

Project CALEBRE (Consumer Appealing Low Energy technologies for Building REtrofitting) is a four year £2 million E.ON/RCUK funded project that is investigating technologies and developing solutions for the UK’s solid-wall houses to offer energy demand reduction, energy efficient heat generation and energy management combined with user appeal. Understanding how technical solutions can be aligned with householder lifestyles is central to the CALEBRE project. The technologies include: vacuum glazing to achieve exceptionally low U-values whilst being capable of retrofit in existing window frames; advanced gas and electric air source heat pumps that operate at the temperatures needed for integration with existing domestic radiator systems; innovative surface materials for buffering moisture, humidity and temperature; retrofit mechanical ventilation with heat recovery (MVHR) to manage ventilation and its associated heat loss. The technologies are being trialled in facilities that include the University of Nottingham E.ON 2016 House, a highly instrumented replica construction of a1930s dwelling. Alongside development and trialling, business case modelling of technologies is being conducted to establish mass roll-out strategies, as well as modelling to identify bespoke packages of measures for house refurbishment. This paper introduces Project CALEBRE, its content and scope, and reports some of its initial findings to highlight the challenges and constraints involved in the process of refurbishing the UK’s domestic stock.

The influence of emittance of low-emittance coating on the thermal performance of triple vacuum glazing

The thermal performance of the triple vacuum glazing was simulated using a finite volume model. The simulated triple vacuum glazing comprises three 4 mm thick glass panes with two vacuum gaps, with one to four internal glass surfaces coated with a low emittance (lowe) coating. The two vacuum gaps are sealed by an indium based sealant and separated by an array of stainless steel pillars with a height of 0.12 mm and a diameter of 0.3 mm spaced at 25 mm. The simulation results show that increasing the emittance of the low-e coatings from 0.03 to 0.18 increases the total glazing heat transmission Uvalue by 50% for a 0.5 m by 0.5 m triple vacuum glazing; while for 1 m by 1m triple vacuum glazing, the U-value is increased by 36%. The centre-of-glazing U-value for both sizes is increased by 134.6%. The simulation results indicate that when using three low-e coatings in the triple vacuum glazing, the vacuum gap with two low-e coatings should be set to the direction facing the hot side environment, while the vacuum gap with one coating should face the cold environment. When using two low-e coatings in the triple vacuum glazing, the U-value of the total triple vacuum glazing with one low-e coatings in each of the vacuum gaps is 10.3% less than that with two low-e coatings in the outdoor side vacuum gap and 3.47% less than that with two low-e coatings in the indoor side vacuum gap. One coating should be set in both vacuum gaps rather than both coatings in the same vacuum gap.

Experimental characterisation of an asymmetric compound parabolic photovoltaic concentrator designed for building integration in the UK

SYNOPSIS A novel non-imaging asymmetric compound parabolic photovoltaic concentrator (ACPPVC) has been designed, constructed and experimentally characterised at the University of Ulster, Northern Ireland (54°36′N, 5°37′W). Different numbers of PV strings connected in series were experimentally characterised under outdoor conditions both with and without concentrators. Transient I-V curves for each set of parameter data points were determined and the maximum power generation, fill factor and efficiency of the system calculated for each individual I-V curve. The experiments showed that the use of an ACPPVC increased the maximum power point by 62% (i.e. the power by a factor of 1.62) when compared with a similar non-concentrating PV panel of identical cell area.

A low temperature sealed vacuum glazing system, performance, analysis and predicted economic and environmental benefits

Publisher Summary Vacuum glazing has the potential to displace and replace existing glazing if its cost can be made competitive with current products. The main uses of vacuum glazings is for the replacement of existing systems and new glazing in domestic and commercial buildings and where high insulating transparent features are required. The innovative features of the vacuum glazing developed at the University of Ulster, include the ability to use soft low-emittance coatings and tempered glass thus allowing windows with very low U-values to be produced, significantly less than those currently available for high temperature fabricated vacuum glazing.

Development of an Efficient Low- and Medium-Temperature Vacuum Flat-Plate Solar Thermal Collector

Production of heat accounts for over half of our overall primary energy consumption in domestic and industrial applications. Despite the great scope for deployment of solar thermal collectors to provide low- and medium-temperature heat, there is relatively little uptake of this technology. The requirements for heat provision are studied, and the desired characteristics of potential solutions considered. Application areas are discussed in addition to the potential for system integration. An assessment is made of the shortcomings of solar thermal collectors and the requirements for new technologies suggested. This leads to a design approach for a collector that is effective across a range of applications and provides further supplementary benefit for system or building integration.

Characterisation of a Line-Axis Solar Thermal Collector for Building Façade Integration

The integration of concentrating solar thermal collectors into the structural envelope of buildings can significantly increase the cost effectiveness of solar thermal utilisation in the UK. The key, however, to their wide scale application is performance. Typically, most solar thermal collectors are mounted on inclined roof structures, thus presenting an optimal surface area for solar gain. Vertical building facades offer an alternative mounting surface and whilst they may have an overall lower level of incident solar radiation, the collector receives a more uniform annual distribution of solar radiation, reducing potential summer over heating problems. Furthermore, facade integration is beneficial to the building performance as the collector unit results in a higher U-value realising higher building heat retention.

Thermal performance of vacuum glazing with tempered glass panes

The thermal performance (U-value) of 0.4 × 0.4 m and 1 × 1 m double vacuum glazing (DVG) and triple vacuum glazing (TVG) using annealed and tempered glass panes with pillar separations of 25 and 50 mm respectively was simulated. It was found that (1) for both dimensions of DVG with 0.03 emittance low-emittance (low-e) coatings, the U-values at the centre of the glazing area of the DVG made of annealed and tempered glass panes were 0.57 and 0.30 Wm−2 K−1, a reduction of 47.4 %; (2) for both dimensions of TVG with 0.03 emittance low-e coating, the U-values at the centre of glazing area of the TVG with annealed and tempered glass panes were 0.28 and 0.11 Wm−2 K−1, a reduction of 60.7 %. The reduction in U-values for both DVG and TVG results from the significant reduction in pillar number, leading to the large reduction in heat conduction through the pillar arrays. The reduction in U-values from using tempered glass panes instead of annealed glass panes for TVG is larger than that for DVG; this is because the radiative heat transfer of TVG with three glass panes is much lower than that in DVG with two glass panes; therefore, the heat conduction through the pillar array in TVG plays a larger role compared with that in DVG. The reduction in pillar number in TVG results in a larger reduction in U-value compared to DVG; thus, using tempered glass panes in TVG confers a greater advantage compared to DVG, given that DVG can also achieve a large reduction in U-value when switching from using annealed glass panes to tempered glass panes.

Simulated Thermal Performance of Triple Vacuum Glazing

The simulated triple vacuum glazing consists of three, 4 mm thick glass panes with two vacuum gaps with each internal glass surface coated with a low emittance coating. The two vacuum gaps are sealed by an indium based sealant and separated by a stainless steel pillar array with a height of 0.12 mm and a pillar diameter of 0.3 mm spaced at 25 mm. Both solder glass and indium based sealants have been successfully applied in vacuum glazing previously. The thermal performance of the triple vacuum glazing was simulated using a finite volume model. The simulation results show that although the thermal conductivity of solder glass (1 W.m−1 .K−1 ) and indium (83.7 W.m−1 .K−1 ) are very different, the increase in heat transmission of triple vacuum glazing with a 10mm frame rebate resulting from the use of an indium edge seal compared to a solder glass edge seal was 0.48%. Increasing both edge seal widths from 3 mm to 10 mm led to a 24.7% increase in heat transmission of the triple vacuum glazing without a frame and an 18.3% increase for a glazing with a 10 mm frame rebate depth. Increasing the rebate depth in a solid wood frame from 0 to 15 mm decreased the heat transmission of the triple vacuum glazing by 32.9%. The heat transmission of a simulated 0.5 m by 0.5 m triple vacuum glazing was 32.2% greater than that of 1 m by 1 m triple vacuum glazing.Copyright