Impact of window blinds on daylight-linked dimming and automatic on/off lighting controls

This paper presents the field-measured performance of two commercial photocontrolled lighting systems, continuous dimming and automatic on/off, as a function of various configurations of manual and photocontrolled automatic venetian blinds. The performance indicators considered were the space illumination and the electric lighting consumption as a function of blind slat angle and retraction area. The results showed that under clear sky and without blinds both lighting control systems reduced the lighting energy consumption on average by 50–60% when compared to lights fully on from 6 AM to 6 PM. These savings, however, dropped by 5–45% for the dimming system, and by 5–80% for the automatic on/off system with the introduction of various static window blind configurations. The savings in lighting energy were more significant when the lighting control systems were used with photocontrolled blinds. This was due to the capability of the blinds to adjust their position automatically in direct response to the variable daylight levels.     

Optimization of the performance of double-façades with integrated photovoltaic panels and motorized blinds

Double-façades with integrated photovoltaic panels may be employed to generate electricity, thermal energy and for daylighting. A theoretical study of double-façades with integrated photovoltaics (PV) and motorized blinds is presented, which investigates the effect of various design parameters in order to maximize the conversion of solar radiation to useful energy. Two configurations of the façade with a lower section with integrated PV and an upper Vision (viewing) section with motorized blinds, are examined. A one-dimensional finite-difference thermal model is developed, with an algorithm that iteratively determines which convective heat transfer coefficient correlation to use for each surface inside the cavity using expressions that consider system characteristics and temperature distribution. When PV modules are installed in the middle of the cavity, air flows on both sides, increasing PV section overall (thermal-electric) efficiency by about 25%, but lowers electricity generation by 21%. Integrating 0.015 m long, 0.002 m wide fins to the PV back plate leads to a similar increase in efficiency without compromising electricity generation. Placing the blind in the middle of the cavity increases the Vision section efficiency by 5%. Using this approach to optimize performance can lead to combined thermal-electric efficiencies of over 60%.     

Performance and economic analysis of air flow windows in a tropical climate

An experimental study was conducted in Thailand to determine the thermal performance of twin glazed windows with dynamic insulation. The effects of blinds situated either between or outside the glazing were analysed. With an external blind, the heat transfer coefficient was 1–25 W/m²°C with natural convection and 0–6 W/m²°C for a flow of 20m³/h (glass area = 2–16m²). The solar flux transmitted was evaluated analytically and experimentally depending on the blind's position. An economic study was performed on a six-sotrey air-conditioned building in Thailand. It showed in tropical countries that it may be more economical to use air flow windows than to have tinted single or double glass windows.     

A hybrid ray-tracing and radiosity method for calculating radiation transport and illuminance distribution in spaces with venetian blinds

This paper presents a hybrid ray-tracing and radiosity method for processing luminous flux in spaces equipped with horizontal venetian blinds. The method considers both diffuse and specular characteristics of the blinds and aims to establish a balance between computational speed and accuracy. Direct components are treated with ray-tracing techniques employing a shining factor for the blinds to split between specularly and diffusely reflected components. The specular components are traced inside the blind cavity and inside the room while the direct-diffuse components inside the blind cavity are processed in a two-dimensional radiosity calculation until the final diffuse flux departing the cavity is determined. Diffuse-to-diffuse transmission is considered using a traditional radiosity method. Each room surface is divided into sub-surfaces and given an initial luminous exitance, after accounting for directly traced portions. Then a three-dimensional radiosity method is employed for the entire room to compute illuminance distributions on each sub-surface and on the work plane. Comparison between the current model and results obtained with full radiosity showed that significant errors can be introduced by improper modeling of blind specular components for almost all profile angles and slat angles.An in-depth analysis of the transmission process with different profile angles and shining factors showed the potential of blinds with diffuse characteristics to transmit more light than blinds with highly specular surfaces for certain angles. Further analysis for profile angle close to 45°, showed that for certain commonly used slat angles, a second reflection occurs at the bottom side of the upper slat, redirecting direct light towards the work plane, with serious potential glare consequences. The model contributes to rapid and accurate assessment of illuminance/solar radiation distribution in spaces with venetian blinds and related potential lighting energy savings when electric lighting controls are utilized. Analysis of the number of inter-reflections as a function of profile and slat angles with simultaneous consideration of different reflectances and shining factors is particularly important for providing guidelines and recommendations for venetian blinds optimized design and control.     

An open-loop venetian blind control to avoid direct sunlight and enhance daylight utilization

Shading devices, such as venetian blinds, are widely used to eliminate glare and maintain a comfortable working environment for occupants. This paper proposes an open-loop control of blind height and slat angle based on an analytic model of solar position, and geometry of venetian blinds and the windows. The algorithm enables completely blocking direct sunlight from entering the room beyond a certain user specified interior distance from the window while enhancing daylight utilization. We derive closed-form solutions for blind height and angle which are easily implemented in practice. Moreover, the proposed blind control algorithm is simulated with favorable performance. The algorithm has also been implemented and verified in real-time test-beds.     

Lightswitch-2002: a model for manual and automated control of electric lighting and blinds

A simulation algorithm is proposed that predicts the lighting energy performance of manually and automatically controlled electric lighting and blind systems in private and two-person offices. Algorithm inputs are annual profiles of user occupancy and work plane illuminances. These two inputs are combined with probabilistic switching patterns, which have been derived from field data, in order to predict the status of the electric lighting and blinds throughout the year. The model features four different user types to mimic variation in control behavior between different occupants.An example application in a private office with a southern facade yields that––depending on the user type––the electric lighting energy demand for a manually controlled electric lighting and blind system ranges from 10 to 39 kW h/m² yr. The predicted mean energy savings of a switch-off occupancy sensor in the example office are 20%. Depending on how reliably occupants switch off a dimmed lighting system, mean electric lighting energy savings due to a daylight-linked photocell control range from 60% to zero.     

Free convection frost growth in a narrow vertical channel

Processes involving heat transfer from a humid air stream to a cold plate, with simultaneous deposition of frost, are of great importance in a variety of refrigeration equipment. In this work, frost growth on a vertical plate in free convection has been experimentally investigated. The cold plate (0.095 m high, 0.282 m wide) was placed in a narrow (2.395 m high, 0.01 m deep) vertical channel open at the top and bottom in order to permit the natural circulation of ambient air. The cold plate temperature and the air relative humidity were varied in the −40 to −4 °C and 31–85% range, respectively, with the air temperature held fixed at 27 °C (±1 °C). The main quantities (thickness, temperature and mass of frost, heat flux at the cold plate), measured during the time evolution of the process, are presented as functions of the input parameters (relative humidity and cold plate temperature); in particular, the role exerted by the plate confinement on the frost growth is discussed. Data are recast in order to identify compact parameters able to correlate with good accuracy frost thickness, mass and density data.     

Numerical study of thermal characteristics of double skin facade system with middle shade

Architectural shade is an effective method for improving building energy efficiency. A new shade combined with the double skin façade (DSF) system, called middle shade (MS), was introduced and developed for buildings. In this paper, a 3D dynamic simulation was conducted to analyze the influence of MS combined with DSF on the indoor thermal characteristics. The research on MS for DSF involves the temperature, the ventilation rate, the velocity distribution of the air flow duct, and the indoor temperature. The results show that the angle and position of the shade in the three seasons are different, and different conditions effectively enhance the indoor thermal characteristics. In summer, the appearance of MS in DSF makes the indoor temperature significantly lower. The indoor temperature is obviously lower than that of the air flow duct, and the temperature of the air flow duct is less affected by MS. The influence of the position of blinds on indoor temperature and ventilation rate is greater than the influence of the angle of blinds. According to the climate characteristics of winter and transition season, in winter, early spring, and late autumn, the indoor temperature decreases with the increase of the position of blinds at daytime, but the opposite is true at night. The results found in this paper can provide reference for the design and use of MS combined with DSF in hot summer and cold winter zone.     

Bi-directional transmission properties of Venetian blinds: experimental assessment compared to ray-tracing calculations

An accurate evaluation of daylight distribution through advanced fenestration systems (complex glazing, solar shading systems) requires the knowledge of their Bidirectional light Transmission (Reflection) Distribution Function BT(R)DF. An innovative equipment for the experimental assessment of these bi-directional functions has been developed, based on a digital imaging detection system. An extensive set of BTDF measurements was performed with this goniophotometer on Venetian blinds presenting curved slats with a mirror coating on the upper side.In this paper, the measured data are compared with ray-tracing results achieved with a virtual copy of the device, that was constructed with a commercial ray-tracing software. The model of the blind was created by implementing the measured reflection properties of the slats coatings in the ray-tracing calculations. These comparisons represent an original and objective validation methodology for detailed bi-directional properties for a complex system; the good agreement between the two methods, yet presenting very different parameters and assessment methodologies, places reliance both on the digital-imaging detection system and calibration, and on the potentiality of a flexible calculation method combining ray-tracing simulations with simple components measurements.     

Study of free convective heat transfer from horizontal conic

Theoretical and experimental considerations of free convective heat transfer from horizontal isothermal conic in unlimited space are presented. In the theoretical part of the paper we introduced the curvilinear coordinate system compatible with conical surface and gravity field. The equations of Navier-Stokes and Fourier-Kirchhoff were simplified in this local orthogonal system. The resulting equation have been solved by asymptotic series in the vicinity of horizontal element of the cone. The final Nusselt-Rayleigh relation as a function of the conic base angle was verified experimentally. The experimental study was performed in water and air for conics with the angles equal to α=0 (vertical round plate), 30°, 45° and 60° and diameter of the base D=0.1 m. The experimental results are in a good accordance (maximum within +8.7%) with the theory.     

The impact of venetian blind geometry and tilt angle on view,direct light transmission and interior illuminance

Venetian blinds are a common type of shading. They can reflect and transmit light efficiently into buildings by adjusting the louver angle and at the same time allow some view to the outdoors. This paper presents a systematic method for calculating projected view (or shaded) fractions for venetian blinds of any shape (flat and curved) as a function of rotation angle, taking into account edge effects and slat thickness. General analytical direct transmittance equations and charts – derived from pure geometrical characteristics – were also developed for flat slats (including thickness and edge effects) and curved slats (circle arcs) as a function of blind tilt angle and profile angle. The last part of the paper investigates the impact of slat shape and reflectance on window-blind system effective reflectance and the associated contribution to the inter-reflected component for different window areas.     

Performance of unglazed solar ventilation air pre-heaters for broiler barns

Solar radiation is an interesting heat source for applications requiring a limited amount of energy, such as pre-heating cold fresh air used in venting livestock barns. The objective of this study was to evaluate the energy recovery efficiency of a solar air pre-heater consisting of an unglazed perforated black corrugated siding where the incoming fresh ventilation air picks up heat from its face and back. Installed on the southeast wall of two broiler barns located 40 km east of Montreal, Canada, the performance of solar air pre-heaters was monitored over 2 years. Sensors inside the barns monitored the temperature of the ambient air, that pre-heated by the solar collector and that exhausted by one of the three operating fans. An on-site weather station measured ambient air temperature, wind direction and velocity and radiation energy absorbed on a vertical plane parallel to the unglazed solar air pre-heaters. The measured vertical solar radiation value was used to evaluate the heat recovery efficiency of the unglazed solar air pre-heaters. Using data from the Varennes Environment Canada weather station located 30 km northwest, the solar sensors were found to measure the absorbed solar radiation with a maximum error of 7%, including differences in exterior air moisture. Unglazed, the efficiency of the solar air pre-heaters reached 65% for wind velocities under 2 m/s, but dropped below 25% for wind velocities exceeding 7 m/s. Nevertheless, the unglazed solar air pre-heaters were able to reduce the heating load especially in March of both years. Over a period starting in November and ending in March, the solar air heaters recovered an energy value equivalent to an annual return on investment of 4.7%.     

Experimental study of the transient adsorption/desorption characteristics of silica gel particles in fluidized bed

Transient adsorption/desorption characteristics of spherical particles of silica gel (about 3 mm in diameter) in a fluidized bed have been studied experimentally. To control the humidity of inlet air, a humidifier is designed and fitted in a proper location in the system. The system is well instrumented to measure the inlet and outlet air parameters as well as bed temperatures during the experiments.     

The optical characteristics of black chrome solar selective films coated by the pulse current electrolysis method

The application of the pulse current method for black chrome electrocrystallization has been investigated. Plating parameters to optimize the optical properties of the solar selective film included the bath composition, current density, plating time, duty cycle and substrate. The bath composition was 250–300 g/ℓ of chromic acid, 10–15 g/ℓ of propionic acid and 0.5 g/ℓ of a proprietary additive. It has been observed that the black chrome coatings exhibited reasonable optical properties for commercialization when the plating parameters were properly controlled; absorptance (α) was 0.944 and 0.94, and emittance () was 0.084 and 0.15 for nickel and cooper substrates, respectively. Thermal stability of the black chrome coatings was also studied by aging at 300°C and 450°C in air for 24 h. This study implies that the pulse current electrolysis method could enhance the optical properties of black chrome solar selective coatings for practical solar applications.     

Determination of optimum working conditions R22 and R404A refrigerant mixtures in heat-pumps using Taguchi method

In this study, refrigerants R22 and R404A five of their binary mixtures which contain about 0%, 25%, 50%, 75% and 100% mass fractions of R404A were tested. It is investigated experimentally the effects of gas mixture rate, evaporator air inlet temperature (from 24 to 32 °C), evaporator air mass flow rate (from 0.58 to 0.74 kg/s), condenser air inlet temperature (from 22 to 34 °C) and condenser air mass flow rate (from 0.57 to 0.73 kg/s) on the coefficient of performance (COP) and exergetic efficiency values of vapor compression heat-pump systems. To determine the effect of the chosen parameters on the system and optimum working conditions, an experimental design method suggested by Genichi Taguchi was used. In this study, it was observed that the most effective parameters are found to be the condenser air inlet temperature for COP and exergetic efficiency.     

SOLAR CONTROL RESEARCH ACTIVITIES UNDERTAKEN IN THE FRAMEWORK OF PASCOOL

The Solar Control Subtask group activities were aimed at defining and validating an innovative combined procedure to model and experimentally characterize external shading devices. The objectives were pursued throughout joined activities on detailed and simplified modelling, pilot experiments and testing

The modelling was developed with some important innovative features, like three-dimensional characterization, actual representation of solar radiation and solar-optical properties, coupling of thermal performance Environment/Shading device/Glazing, actual film coefficients. It was based on the outcomes from specific experiments conducted in laboratory (solar-optical properties), in PASLINK test cells (film coefficients on glazing and shading device) and in a two-axis tracking bench equipped with a solar transmittance measurement apparatus properly developed. This outdoor testing allows to measure the average value of diffuse and angular direct solar transmittance of the non-homogeneous shading assembly with an accuracy better than ± 5%

Finally, on the basis of the above results an innovative procedure based on a combined modelling/testing activity for the full characterization of the devices (parameters of shortwave radiation, long-wave radiation and convective exchanges) was set up and validated. The validation was successfully performed on five widespread shading components (retractable Venetian blind with metallic tilting slats, shulter with wooden tilting slats, fixed slats system, sunbreaker with movable vertical fins, roller blind). Furthermore, a preliminary procedure for daylighting performance evaluation of the shading device was defined and tested.     

Experimental estimation of the transient free convection heat transfer coefficient on a vertical flat plate in air

Transient heat convection on a vertical plate has been interpreted both theoretically and experimentally, in terms of a variable heat transfer coefficient, by several authors. Few results concern the case were air is the fluid. Joule heating of a very thin vertical graphite foil has been tested experimentally here. Two different methods of inversion have been studied for estimating the local or global transfer coefficient, starting from infrared camera measurements. The second method has been able to provide the convective contribution to the measured global transfer coefficient. Experimental results with different levels of heating show that the early transfer coefficient decrease proportionally (in time t) to t⁻¹, and not to t^−1/2 as the early times conduction theory would anticipate. Other effects than those already presented in the literature remain to be investigated, in order to explain the discrepancy of this theory for air.Relaxation experiments show that enhancement of the wall/air exchange by a mastering of the transient heating of the whole wall seems to be quite difficult to obtain     

Analysis of an air cooled ammonia–water vertical tubular absorber

This paper presents a detailed analysis of an ammonia–water vertical tubular absorber cooled by air. The absorption process takes place co-currently upward inside the tubes. The tubes are externally finned with continuous plate fins and the tube rows are arranged staggered in the direction of the air flow. The air is forced over the tube bank and circulates between the plain fins in cross flow with the ammonia–water mixture. The analysis has been carried out by means of a mathematical model developed on the basis of mass and energy balances and heat and mass transfer equations. The model takes into account separately the churn, slug and bubbly flow patterns experimentally forecasted in this type of absorption processes inside vertical tubes and considers the simultaneous heat and mass transfer processes in both liquid and vapour phases, as well as heat transfer to the cooling air. The model has been implemented in a computer program. Results based on a representative design and nominal operating conditions of an absorber for a small capacity ammonia–water absorption refrigeration system are shown. A parametric analysis was realised to investigate the influence of the design parameters and operating conditions on the absorber performance. The noteworthy results that have effect on practical design of the absorber are presented and commented.