Transparent Insulation Systems Research Articles

Optimal Control Strategies for Switchable Transparent Insulation Systems Applied to Smart Windows for US Residential Buildings

This paper evaluates the potential energy use and peak demand savings associated with optimal controls of switchable transparent insulation systems (STIS) applied to smart windows for US residential buildings. The optimal controls are developed based on Genetic Algorithm (GA) to identify the automatic settings of the dynamic shades. First, switchable insulation systems and their operation mechanisms are briefly described when combined with smart windows. Then, the GA-based optimization approach is outlined to operate switchable insulation systems applied to windows for a prototypical US residential building. The optimized controls are implemented to reduce heating and cooling energy end-uses for a house located four US locations, during three representative days of swing, summer, and winter seasons. The performance of optimal controller is compared to that obtained using simplified rule-based control sets to operate the dynamic insulation systems. The analysis results indicate that optimized controls of STISs can save up to 81.8% in daily thermal loads compared to the simplified rule-set especially when dwellings are located in hot climates such as that of Phoenix, AZ. Moreover, optimally controlled STISs can reduce electrical peak demand by up to 49.8% compared to the simplified rule-set, indicating significant energy efficiency and demand response potentials of the SIS technology when applied to US residential buildings.

Transparent insulation materials market in Europe

This paper presents the European market of transparent insulation materials as viewed by manufacturers. The objective of the study was to analyse the application of transparent insulation materials in the construction sector across Europe, determine the popularity of various technologies and materials used to manufacture them, the competition among transparent insulation manufacturers, investment in the development of new transparent insulation technologies, and trends in demand for transparent insulation in Europe. The analysis was performed on the basis of a survey of manufacturers. The use of transparent insulation is associated with high cost, yet the potential return on investment in the form of savings over the course of a building’s life-cycle convinces many potential developers to apply these materials. Based on the results of the survey, it can be concluded that European companies follow the increase in energy-efficiency and the transparent insulation market is prosperous, yet differs from country to country. It was observed that the positive perception of indirect heat gain transparent insulation systems was the most prevalent in Germany. The paper also explores the situation on the author’s domestic market – the Polish transparent thermal insulation market.

Coupled transparent insulation system with low emissivity solar absorber: An experimentally validated building energy simulation study

A conversion of shortwave to longwave radiation heat transfer in building envelope system represents an substantial part in low-energy design campaing. For that reason, an experimental test sample of a novel solar façade element based on a Transparent Insulation Material (TIM) with a selective and a nonselective absorber was developed. The investigated element is a part of an opaque lightweight structure of a building envelope. The capability of one widely used Building Energy Simulation (BES) tool is analyzed in terms of its ability to model the performance of the TIM façade element. The good consistency between the simulation results and the experimental data obtained specifically via cooling period indicates that the reference simulation model based on high emisivity of solar absorber was reliable when predicting the energy performance of TIM based façade models. However, the low emissivity of solar absorbers in the façade cavity gives rise significant limitations. They were identified concerning the BES calculation methods and modeling principles. The computational results are significantly underestimated in case of low emissivity internal surface. The methodology developed in this study is expected to provide a reference for simulating the thermal and energy performance of TIM-based building elements with different solar absorbers.

The effect of changing surface emissivity on the natural ventilation rate of a narrow air cavity integrated in a transparent insulation façade

A transparent insulation material (TIM) can be incorporated in a building element in order to improve its thermal performance, including solar heat gain. However, some overheating protection needs to be implemented. The provision of natural ventilation in a façade cavity to avoid overheating, along with other potential techniques, could require a completely different approach to TIM integration in solar façade concepts. This paper concerns an analysis of the effect of different absorber emissivity behind a transparent insulation system. The emissivity changes are primarily studied in order to determine their effects on the overall radiation - natural convection heat transfer through a narrow façade air cavity. A comparative investigation was conducted using experimental full-scale dynamic outdoor tests and the building energy simulation (BES) approach. The thermodynamic response affected by the radiation - natural convection transfer is identified, specifically during the summer peak period, that corresponds to overheating. Depending on the ventilation regime, a low emissivity solar absorber inside a narrow air façade cavity may increase the cooling energy load and temperature response of a façade by 25 and 36%, respectively, in comparison with a high emissivity absorber. When the emissivity of the zone inside the cavity was changed, significant limitations were identified in the BES calculation methods for both vented and unvented cases.

A method for calculating the solar transmittance, absorptance and reflectance of a transparent insulation system

Transparent insulation materials (TIMs) can combine the advantages of opaque insulation with solar collection when applied to building facades. Mathematical models developed to calculate the optical performance of a transparent insulated (TI) system are presented. The TI-system modelled consisted of a 6mm outer glass pane, a 22mm wide polymethylmethacrylate (PMMA) capillary cell section and an 8mm inner glass pane. When solar beam radiation passed through the TI-system, the solar transmittance, absorptance and reflectance that occurred in the system were calculated. Optical interactions at each layer in the TI-system were numerically modelled for five incidence angles. A direct to diffuse transmittance was calculated for solar radiation passing through the PMMA capillary cells with an incidence angle, θi, in excess of 0°. The calculated transmittance for the PMMA capillary cells at 0° incidence angle was 0.8264 with overall solar transmittance of up to 0.66 calculated for the whole TI-system, a value which is consistent with that found in previous research. This paper presents a method for calculating the optical properties for multiple PMMA capillary cells, encapsulated between two glass panes for different solar incidence angles, with input of relevant data from other sources. This method can also be adapted for other types of glazing systems.

Goal directed life cycle costing as a method to evaluate the economic feasibility of office buildings with conventional and TI‐façades

Transparent insulation systems (TI‐systems) of less than 20cm thick have been developed as an alternative to opaque wall insulation and windows, which provide a financial return to building occupants when applied to building façades. Lack of detailed cost analysis of TI‐systems is a major constraint to the application of TI‐wall and TI‐glazing in buildings. A goal directed life cycle costing (LCC) technique and sensitivity analysis used to evaluate the economic feasibility of TI‐applications in office buildings form the basis of this research. It was undertaken as part of research to determine optimum energy and cost performance of TI‐systems for external cladding of high‐rise and low‐rise office buildings in temperate and tropical climates. The LCC of the buildings with conventional façades were compared with those with TI‐façades. The results show that LCC can be used to evaluate the economic feasibility of low carbon technologies such as TI‐systems effectively. A detailed account is provided of how different sources of cost data can be captured, collected and integrated to perform selective goal directed LCC analysis in the absence of detailed historical LCC data. The use of the goal directed LCC method and cost influence diagram presented in this research can be adopted as a standard method for assessing the economic feasibility of applying low carbon technologies to buildings.

Facade systems with variable solar control using thermotropic polymer blends

Thermotropic layers integrated into glazing or transparent insulation systems reversibly reduce the total solar energy transmittance by becoming opaque when heated. Characteristics of both systems have been measured as a function of temperature and incidence angle, including the total solar energy transmittance for a thermotropic heat-mirror insulating glazing unit (IGU). Properties of complex thermotropic glazing systems have been simulated, starting from data characterising the thermotropic layer. The results show good agreement with measured data. A prototype system sample of a thermotropic heat-mirror IGU was integrated into an outdoor test facility and a thermotropic TEIF (transparent exterior insulation and finish) prototype system was installed into the facade of a demonstration house. Both systems have been monitored and showed the expected switching properties, resulting in the desired overheating protection. Computer simulations of the building integration of the thermotropic TEIF system have been performed, showing a strong dependence of the optimum switching temperature on the total solar and internal gains of the building.

Transparently insulated hybrid wall

The overheating protection of walls equipped with transparent insulation (TI) usually requires cost intensive, often unreliable mechanical shading devices. An effective way to avoid overheating and simultaneously increase the solar gains is the direct cooling of the outer wall surface (absorber). For this purpose, water is pumped through a system of pipes that is attached to the outer wall surface. The heat transferred to the fluid can be used for hot-water production and/or space heating. Thus, the passive solar TI system is extended to an active/passive solar system, called the transparently insulated hybrid wall (TIHW). In this paper the results of experimental investigations of a laboratory model (aperture 1 m 2) are presented: more than 75% of the absorbed heat could be removed by the fluid. The surface temperature at the inner wall remains moderate even after a long period of high irradiance. Already with small flow rates an effective cooling is achieved. Finally the fast reaction of the system after turning on the fluid pump enhances the control of the TI system in order to avoid overheating in adjacent rooms.

Transparent Insulation System for Passive Solar Energy Utilization in Buildings

Transparent Insulation System for Passive Solar Energy Utilization in Buildings