Transparent Insulation Research Articles

Computer simulation of transparently insulated buildings for energy evaluation

SYNOPSIS A dynamic computer simulation model has been developed to evaluate the energy performance of buildings cladded with Transparent Honeycomb Insulation (THI). The U-value of THI is dependent upon the honeycomb cell dimensions, thermal characteristics of the material and temperatures encountered across the honeycomb insulation. Solar transmittance of THI is also angle-dependent. Two new modules for TRNSYS have been developed to incorporate these two special characteristics of honeycomb insulation in the simulation model. The simulation model not only confirms convection suppression capability of the insulation but also facilitates the change in the design and material of THI during simulation. As an example a room with a transparently insulated thermal storage wall has been simulated and results show minimising the heat loss and maximising the solar gain potential of THI.

Transparent thermal insulation materials and systems: state of the art and potential for the future

Transparent or translucent insulation materials (TIM) represent a class of materials with a high potential for increasing the efficiency of solar thermal systems. A large number of materials and material combinations have been subjected to theoretical and experimental investigation. An overview of generic types, characterisation methods, simulation models, commercial materials, and actual systems is given, and the future potential of transparent insulation is shown as well as current market penetration. Results of selected demonstration projects with active and passive systems are presented. The most prominent application of transparent insulation was in the self-sufficient solar house in Freiburg. A detailed energy balance of this house is given. In addition the use of TIM in retrofitting as well as in low energy apartment blocks is discussed.

00/00352 Comparative study of transparent insulation materials cover systems for integrated-collector-storage solar water heaters

00/00352 Comparative study of transparent insulation materials cover systems for integrated-collector-storage solar water heaters

00/00365 Finite time thermal analysis of ground integrated-collector-storage solar water heater with transparent insulation cover

This paper describes the design and performance of a convex type of solar water heater. The main purpose of a convex solar collector is to accomplish static tracking for the sun radiation without additional cost, that is, to collect energy efficiently in the early and later times of the day due to the low angle of incidence with a high percentage of solar radiation perpendicular to the collector plate.Two adjacent types of collectors, flat plate and convex type with the same projected area, were constructed and tested under the same conditions. Comparisons were made of the lumped efficiency and useful energy under different conditions. The efficiency and the useful energy were considerably greater for the convex type collector than for the flat plate collector under the same environmental and insolation conditions. An additional 45% energy gain was achieved from the convex type compared to the flat plate collector.

Finite time thermal analysis of ground integrated‐collector‐storage solar water heater with transparent insulation cover

A transparent honeycomb insulated ground integrated-collector-storage system has been investigated for the engineering design and solar thermal performance. The system consists of a network of pipes embedded in a concrete slab whose surface is blackened and covered with transparent insulation materials (TIM) and the bottom is insulated by the ground. Heat may be retrieved by the flow of fluid through the pipe. A simulation model has been developed; it involves the solution of the two-dimensional transient heat conduction equation using an explicit finite-difference scheme. Computational results have been used to determine the effect of such governing parameters as depth as well as pitch of the pipe network and collector material on the thermal performance of the system. The pipe network depth of 10 cm and the TIM cover made of 5 cm compounded honeycomb seem suitable for the proposed system. Solar gain (solar collection efficiency of 30–50% corresponding to collection temperature of 40–60°C) and the diurnal heat storage characteristics of the system are found to be of the right order of magnitude for solar water heating applications. Copyright © 1999 John Wiley & Sons, Ltd.

Finite time thermal analysis of ground integrated-collector-storage solar water heater with transparent insulation cover

A transparent honeycomb insulated ground integrated-collector-storage system has been investigated for the engineering design and solar thermal performance. The system consists of a network of pipes embedded in a concrete slab whose surface is blackened and covered with transparent insulation materials (TIM) and the bottom is insulated by the ground. Heat may be retrieved by the flow of fluid through the pipe. A simulation model has been developed; it involves the solution of the two-dimensional transient heat conduction equation using an explicit finite-difference scheme. Computational results have been used to determine the effect of such governing parameters as depth as well as pitch of the pipe network and collector material on the thermal performance of the system. The pipe network depth of 10 cm and the TIM cover made of 5 cm compounded honeycomb seem suitable for the proposed system. Solar gain (solar collection efficiency of 30–50% corresponding to collection temperature of 40–60°C) and the diurnal heat storage characteristics of the system are found to be of the right order of magnitude for solar water heating applications. Copyright © 1999 John Wiley & Sons, Ltd.

Comparative study of transparent insulation materials cover systems for integrated-collector-storage solar water heaters

The thermal performance of transparently insulated integrated-collector-storage solar water heaters is investigated theoretically as well as experimentally for a comparative study of cover systems having transparent insulation materials devices placed between the top glazing and the absorber. The data on solar transmittance, heat loss reduction characteristics and solar collector-storage efficiencies of various configurations is generated for the system performance comparisons. These hot water systems exhibit average (diurnal basis) solar collection and storage efficiencies in the range of 20–40% at a collection temperature of 40–50°C. The performance of water heaters with cover system having absorber-perpendicular configuration of TIM excel over absorber-parallel TIM covers. The effect of variation in the temperature of heat collected and cost of cover systems on the performance comparisons is also discussed.

Numerical model of a building with transparent insulation

An explicit finite difference simulation model is developed to study the thermal performance of an outdoor test-room with one transparently insulated (TI) wall. The thermal behavior of the room is examined under different control strategies for the shading device and for air flow through the TI wall to the room. Simulation results indicate significant energy savings with practically no auxiliary heating required on cold sunny days in Montreal. However, appropriate control strategies are required to prevent overheating of the room and discomfort. Air flow through the TI wall and then into the room succeeds in lowering its room surface temperature to less than 31°C and reducing to zero the auxiliary heating required on any clear day. Blind control is based on several criteria, including outside temperature, room-facing surface temperature of TI wall (not to exceed 29°C) and room air temperature not to exceed a certain maximum.

A NOVEL ALGORITHM TO INVESTIGATE CONJUGATE HEAT TRANSFER IN TRANSPARENT INSULATION: APPLICATION TO SOLAR COLLECTORS

A theoretical method and novel computational algorithm are presented for the analysis of radiation heat transfer in transparent insulation (TI) structures. The radiation spectrum is separated into short- and long-wave components. The former problem is solved by a one-dimensional ray tracing method, and the latter is treated by a three-dimensional discrete transfer method, extended to the case of anisotropic reflection (and transmission) on the lateral channel walls. In existing models, using multidimensional accurate computational methods, these boundaries are usually assumed to be diffuse in the infrared spectrum. This assumption is relaxed here, which is a main innovative feature of the algorithm. The method is applied to simulate solar flat-plate collectors with a TI made of honeycomb or glass capillaries. The heat transfer analysis also includes convection in the air gap between the TI and the absorber plate and conduction. An iterative numerical procedure was developed to solve the nonlinear conservation equations for obtaining the temperature field within the TI structure channel and the temperatures and heat fluxes on the top glass cover and on the absorber plate. A comparison with the case of isotropic (diffuse) reflection shows a drastic difference in collector performance results: for 100 mm TI depth, the calculated maximal plate temperature in the anisotropic model is about 140 C below that of the isotropic model. The ratio of the heat flux on the latter to the incident insolation on the collector is considered as an efficiency of the collector. The effects of optical properties, geometry, and operating conditions on the performance of the solar collector (efficiency and maximal stagnation temperature of the absorber plate) are discussed and compared with results for the case without TI and with published experimental data. The results indicate the expedience of collectors with TI channels of rather large thickness hc. For the collector studied here, the efficiency increases asymptotically with hc up to 150 - 160 mm (corresponding to aspect ratios of 30 - 32).

Synthesis and properties of some monolithic silica carbogels produced from polyethoxydisiloxanes dissolved in ethylacetoacetate (etac) and acid catalysis

The aim of the present work described in this paper was to synthesize transparent and superinsulating monolithic carbogels in order to use them as transparent double window insulation spacers at the laboratory scale. The monolithic silica carbogels were made by sol–gel technique using mixtures of a new family of precursors noted PEDS-Px (or polyethoxydisiloxanes which are prepolymers of silica differing by their substoichiometric hydrolysis degrees) [G.M. Pajonk et al., J. Non-Cryst. Solids 186 (1995) 1] with organic solvents in the presence of hydrofluoric acid with no excess of water added, and subsequent drying in the supercritical conditions with respect to CO 2 [P.H. Tewari et al., in: L.L. Hench, D.R. Ulrich (Ed.), Science of Ceramic Chemical Processing, Wiley, New York, 1986, p. 123]. Our research was focused at finding the best conditions of preparation of the monolithic silica carbogels in terms of optical and thermal insulation properties. A new solvent ethylacetoacetate (etac) was found to be much more soluble in liquid CO 2 than common alcohols and acetone, and the so obtained carbogels, with etac, present very interesting optical visible transmission and thermal properties respectively. The best samples were prepared from mixtures composed of 60% of a prepolymer prepared with 1.8 moles of water per TEOS mole (noted P 900) and 40% of etac (on a volumetric basis), and presented very good transparency close to the one shown by a flat glass pane together with a very small thermal conductivity (unequalled, to the best of our knowledge, by any other solid material at the present time).

A MONTE CARLO METHOD FOR THE SIMULATION OF TRANSIENT RADIATION HEAT TRANSFER: APPLICATION TO COMPOUND HONEYCOMB TRANSPARENT INSULATION

A new Monte Carlo algorithm for the calculation of radiant heat exchange in combination with heat conduction in three-dimensional enclosures is presented. Transient phenomena can be treated with a small number of photon bundles. The code automatically minimizes the statistical error for transient and steady-state phenomena. Different methods are discussed for the estimation of the statistical error. A simple method for the continuous testing of accuracy during run time is proposed. The influence of the numerical parameters such as number of photon bundles and time step on the accuracy of the results is studied in detail. The algorithm is tested and validated for the combined conduction and radiation heat transfer in honeycomb-type transparent insulation materials. Good agreement between numerical and experimental results is obtained.

Pearl luster pigments as overheating protection in transparently insulated solar façades

Transparently insulated (TI) walls are an efficient means to reduce the heating demand of buildings. However, large scale use of TI is still not realized, basically due to overheating problems. Mechanical shading devices are expensive and may malfunction. Furthermore, the lack of acceptance from architects because of the missing color-designability remains an unsolved problem. A promising solution for both mentioned points is a coating of pearl luster pigments on the TI wall. These pigments show an angle-dependent transmittance and reflectance and their color is variable. The pigments are structured similarly to natural pearls, where the color is caused by an interference effect of multiple layers with alternating refractive indices. A model for radiation transfer in the pigments has been derived and verified experimentally. The model can be used to design pigments with tailor-made properties. Based on insolation data from the test reference year for Wuerzburg, Germany (TRY05), the ideal cut-off angle which depends on the latitude has been calculated for a middle-European location, considering direct and diffuse solar radiation. This allows to derive the energy savings potential of TI walls covered with optimized pearl luster pigments. Finally, a 1.6×2.4 m 2 glass cover, equipped with selected pigments, was installed at the ZAE test facility in Wuerzburg. These experiments show that the heat flux into the room in summer is reduced drastically and overheating can be prevented.

SPECTRAL TRANSMISSION AND REFLECTION OF THE DOPING SEMICONDUCTOR/METAL FILMS SYSTEMS

The paper presents that the plasma frequency ωp of semiconductor films are regulated by the way of changing its doping concentration,which lead to high transmission.Zone of the film shift visible spectral rang Vω,the semiconductor film is combined with the metal which thinness induced transmission frequency ωg locate in the edge of ultra violet range to compose the excellent D/M spectral transmission and reflection film systems.Besides,it is also necessary to select the most suitable combination of the thickness between the semiconductor and the metal films for forming the excellent transparent heat insulation film.

Solar gain characteristics of absorber-parallel transparent insulation materials

The solar gain characteristics of an absorber parallel slab of Transparent Insulation Material placed between the absorber plane and the glass cover of a solar collector/storage system are investigated. The transmittance of the cover system to solar beam radiation is determined by taking into account the absorption and reflection by the slab. The sky and ground diffuse radiation transmittances are computed by a numerical technique. Steady state one dimensional conduction with internal heat generation in the Methyl Methacrylate (MMA) slab is considered to compute the solar gain. The results are compared with such transparent insulation materials as honeycombs, double glazing and single glazing. The honeycomb cover system shows the best performance, characterized by about 12% higher solar gain than the MMA slab.

Numerical simulation of a building with one transparently insulated wall

A numerical simulation model is developed to study the thermal performance of an outdoor test-room with one Transparently Insulated (TI) wall. The thermal behavior of the room is examined under different control strategies for the shading device. Simulation results indicate significant energy savings. However, appropriate control strategies are required to prevent overheating of the room and discomfort.

Simulation of a new adsorptive solar ice maker using activated carbon-methanol pair

SYNOPSIS An analytical model of a new-conception of solid sorption solar cooling system and its numerical simulation are presented. This model combines instantaneous heat and mass transfers in each component of the machine, during a whole characteristic average day of each month. The innovation of the machine consists in the use of a polycarbonate honeycomb Transparent Insulation Material [TIM] cover for the solar collector and multitubular configurations for the reactor and the evaporator. The performance of the machine is evaluated utilising meteorological data for one region of Brazil close to the equator, for the hottest six months. The results are compared with those obtained by modeling the system with a single cover solar collector and those from an experimental study of a prototype with usual components realised in Tunisia. The average net solar Coefficient of Performance [COP] for the six months was 0.13 for the TIM cover system, corresponding to an ice production going from up to 7 to 10 kg per day per square metre of collector surface, respectively for March and December, with solar irradiations of 20 to 23 MJ/m2.

The research and development of the solar house in China

A brief recommendation about solar energy resources and the status of solar house research and development in China is introduced. The reasons for the slow development of an active solar house in the past is analysed. By combining with various research achievements, the passive solar house has had good advancement and applications. The demonstration transparent insulation material (TIM) solar house project in Shanghai is described as an example showing that with the development of solar material, absorbing and storage wall and air-conditioning measures, the passive and hybrid solar house has the potential to provide future wider applications in China.

A TRANSPARENT INSULATION MATERIAL FOR SOLAR COOKERS AND COLLECTORS

A Transparent Insulation Material (TIM) was manufactured from plastic film and shown to reduce the cover normalised heat loss coefficient, U/η0 by over 50% relative to a double-glazed cover system. Such a TIM could be made from polyester film to produce a stagnation-proof and cost-effective cooker which would have greater chance of adoption than less efficient cookers currently made. A cover produced in this fashion would have a normalised loss coefficient, U/η0, of approximately 3 W/m2K.

Solar sorption refrigerator

The performance of a solar sorption refrigerator is studied experimentally for three configurations of its collector cover: with single glazing, with double glazing and with single glazing plus transparent insulation. The collector consists of fifteen stainless steel tubes having a selective surface (with good thermal absorption coefficient) and contains granular activated carbon adsorbent with ammonia refrigerant. The collector surface area is approximately 1.43 m 2 and contains about 17 kg of carbon. The collector operates with good efficiency (36 to 47% depending on conditions) when in the single glazing configuration.

TIM–PCM external wall system for solar space heating and daylighting

An external wall system for solar space heating and daylighting composed of transparent insulation material (TIM) and translucent phase change material (PCM) is presented. This system enables selective optical transmittance of solar radiation. Visible light is mainly transmitted and invisible radiation is mainly absorbed and converted to heat, causing in particular phase change. The storage medium is also the absorber. The concept of the system is presented in detail together with the investigations carried out, including a brief outline of modeling, optical experiments on PCM samples and long-term experiments on a prototype wall as well as numerical simulations. The results indicate a promising thermal–optical behavior of the system. For instance in a Swiss lowland climate (Zurich-airport) a mean energy flux of 13 W m −2 (system efficiency 0.27) was calculated through a south facing TIM–PCM wall into the building during the month with the lowest irradiation (December). The parameters of the prototype wall with a mean melting temperature of the PCM of 26.5°C were assumed. When considering the percentage of time in which the building does not lose energy through the south facing TIM–PCM wall, a maximum can be reached with a mean melting temperature of approximately 20 to 21°C. In this case energy losses through the façade occur only during 1% of the time. With regard to the practical application of the system in buildings, aspects of reliability and durability have to be further investigated.