Evyatar Erell

Urban Microclimate : Designing the Spaces Between Buildings

Preface Introduction 1. Scales of Climatic Study 2. The Urban Energy Balance 3. The Urban Heat Island 4. Urban Airflow 5. The Energy Balance of a Human Being in an Urban Space 6. Thermal Preferences 7. Application of Climatology in Urban Planning and Design 8. Microclimate Design Strategies in Urban Space 9. Vegetation 10. Linear Space 11. Modelling the Urban Microclimate Case Study 1: Neve Zin Case Study 2: Clarke Quay Glossary

Experimental studies on a novel roof pond configuration for the cooling of buildings

A new evaporation based passive cooling technology was tested. The technology is based on the exposure of “floating” wetted cloth to the ambient air. It was compared to various other passive cooling techniques, with very favorable results. Two identical shallow ponds were constructed. One of them was covered with white cotton towels stretched on a densely perforated PVC panel supported by pieces of waterproof polystyrene keeping it just floating on the water surface. Five comparable experiments of different cooling techniques have been carried out. The results indicate that the new cooling technique performed slightly better than the pond with movable insulation, which is widely considered as one of the best roof cooling techniques based on evaporation. It seems that the higher efficiency of the tested technique is due to the thermal stratification created in the water inside the pond, which more effectively resists the transfer of heat gains from the sun and ambient air into the deep water of the pond. In turn, the water temperature near the floor of the pond is lower, thus heat flow from the building to the pond is increased. During the experiment, all the ponds which were compared were ranked according to performance (from best to worse): shaded pond with towels floated on it, pond with towels floated on it and pond with movable insulation, shaded open pond, open pond, covered pond.

Radiative cooling of buildings with flat-plate solar collectors

Abstract Roof ponds cooled by nocturnal long wave radiation have often been proposed as a cheap and effective means of providing thermal comfort in buildings in hot-arid locations. Many of the schemes incorporate flat-plate radiators through which the water is circulated at night to be cooled. An analytical model originally developed for heating applications was adapted to the description of such a nocturnal, long wave radiative cooling apparatus. The accuracy of the model was verified on the basis of experimental data from three types of radiators tested at the experimental facilities of the Center for Desert Architecture and Urban Planning at Sede-Boqer, Israel, under a variety of operating regimes. The model allows accurate prediction of outlet temperatures, taking into account the design characteristics of the specific radiator, the environmental conditions and the pattern of operation of the system. Analysis of flat-plate solar collectors converted to radiative cooling of buildings suggests that under typical environmental conditions, they may be less efficient for this type of application than radiators having no fins.

Refining the use of evaporation in an experimental down-draft cool tower

Direct evaporative cooling has long been recognized as an energy-efficient and cost-effective means for space conditioning in hot dry areas. In order to extend the use of evaporative cooling to include exterior or semi-enclosed spaces, a down-draft evaporative ‘cool tower’ was integrated in the project of a 500 m2 glazed courtyard located at the heart of a building complex in the arid Negev Highlands of southern Israel, designed by the authors. The present article describes the development of the cooling tower system, undertaken in three phases: (i) Prototype analysis. Performance of a small-scale tower was monitored, and comparisons were drawn between varying rates and mechanisms of water and air supply. The results indicated a potential for substantial temperature reduction in the order of 10 °C under summer daytime conditions, but a meager cooling output when using a natural draft system. Mechanical-forced air flow was thus utilized in the actual tower. (ii) Field monitoring. The cool tower, approximately 10 m in height and 10 m2 in cross-sectional area, was operated and monitored during a summer season; its performance was analyzed using a series of water supply mechanisms and operating modes. The system produced a peak cooling output of just over 100 kW, with a wet bulb temperature depression of close to 85–95% during all hours of operation, and a water consumption rate of approximately 1–2 m3/day. (iii) Refinement. Potential improvement in the systems operation was investigated through the development of a wind capture mechanism for increasing inlet pressure and air flow to the space. Both fixed and dynamic capture units were investigated, with wind speed and direction as well as internal air speeds measured in the small-scale prototype tower. The wind capture unit with the simplest configuration and best performance is recommended for future integration in the full-scale tower.

Controlling the transmission of radiant energy through windows: a novel ventilated reversible glazing system

State-of-the-art glazing systems can provide very good solutions for cold climate conditions, and fairly effective ones for warm climates. However, there is still no window system on the market that can offer the flexibility required to provide a comfortable visual environment and an efficient energy response in climates where heating is required in winter, and cooling is required in summer. This paper describes an experimental investigation of a novel glazing system, designed to overcome glare and radiation damage to interior furnishings, yet which causes no reduction in the energy efficiency of the glazed opening compared with a conventional window used in direct gain systems. The proposed glazing system (patent pending) incorporates a rotatable frame holding two glazing components: transparent glazing providing a weatherproof seal, and absorptive glazing with a low shading coefficient1. The absorptive glazing is fixed at a small distance from the clear glazing, forming an airspace between them which is sealed at the sides but open at the bottom and top, so that air flows freely through it. In summer, the absorptive glass faces the exterior of the building, absorbing excessive solar radiation and dissipating the heat to the ambient air. In winter, the glazing assembly is rotated so that the absorbing glass faces the interior, reducing glare but allowing effective convective and radiative heating of the adjacent space.

Adaptive architecture: integrating low-energy technologies for climate control in the desert

Abstract The article describes a ‘climatically adaptive’ approach to intelligent building in which a variety of technologies are integrated in the architectural design to provide thermal comfort with a minimal expenditure of energy. This concept is illustrated by the design of the Blaustein International Center for Desert Studies, a multi-use complex completed recently at the Sede-Boker Campus of Ben-Gurion University of the Negev. In response to the local climate of this desert region, a number of strategies were developed by the authors to exploit natural energy for heating and cooling: earth berming of major parts of the building, ‘selective glazing’ for seasonal shading and energy collection, a down-draft ‘cool-tower’ for evaporative cooling and a hybrid mechanism for hot-air supply are several of the unique systems whose performance and feasibility are analyzed within the context of the overall building design.

Heating experiments with a radiative cooling system

A hybrid space-cooling system for hot arid zones previously investigated by the authors was based on the nocturnal radiative cooling of water circulated through flat plate radiators. Preliminary investigations also indicated that the same system, with no modifications to the physical set-up, could provide a significant proportion of the winter heating requirements of buildings exposed to these climatic conditions, where summers are hot yet winters are frequently cold enough to justify the installation of heating systems. The heat output of the system averaged 370 W/m2 of collector under the sunny but cool conditions typical of Sde-Boker winters. However, on windy and overcast days the thermostat control prevented water circulation and the system was inoperative. The primary factors determining the heat output were the intensity of global solar radiation incident on the collectors, wind speed and the temperature difference between the water in the roof pond and the ambient air. An expression was derived linking these parameters, which may be used to predict the heat output of the specific system with a high degree of accuracy, and thus define the climatic conditions where such a system may be of value.

Bricks made of coal fly-ash and slag, cured in the open air

Abstract Volume mass, compressive strength, water uptake and water absorption of pressed test samples made of a mixture of coal fly-ash, slag and sodium silicate solution (water-glass) were determined. It was found that such mixtures can solidify in the open air and form water-stable materials. The composition and structure of new formations for the binder and cured material itself were established using X-ray diffraction and a scanning electron microscope. The material has a high water uptake, which may be reduced using a number of different methods, the best of which is short-term impregnation with a hydrophobic material of the siloxane group. The water uptake and water absorption of compressed samples impregnated with such materials are similar to those of comparable building materials, such as lime-sand bricks, clay bricks or concrete blocks.

Analysis and experimental verification of an improved cooling radiator

Roof ponds cooled by nocturnal long wave radiation have often been proposed as a cheap and effective means of providing thermal comfort in buildings in hot-arid locations. Many of the schemes incorporate flat-plate radiators through which the water is circulated at night to be cooled. This paper analyzes the parameters affecting the performance of such a radiator, specifically designed for nocturnal radiative cooling. A cheap, simple and flexible design for a cooling radiator was suggested as a result of the analysis, and tested at the experimental facilities of the Center for Desert Architecture at Sede-Boqer, Israel. The mean nightly cooling output of the radiator - due to the combined effect of radiation and convection - was over 90 watts/m2 under typical desert meteorological conditions. The analytical model adapted for this application allows accurate calculation of the fluid temperature at the outlet of the radiator, as a function of the properties of the radiator, the meteorological conditions and the operating parameters of the cooling system.

The Application of Urban Climate Research in the Design of Cities

Abstract In spite of the growing body of research on urban climatology and the increasing demand for architects and urban planners to practise climate-conscious design, there is too little evidence of the application of urban climatology in practice. This chapter explores the relationship between climatologists and urban planners, seeking to establish some of the reasons for this state of affairs. It then sets out a methodological framework for the application of climatology in the planning process, outlining possible goals for such intervention, as well as its limitations. The chapter then attempts to establish the effects on the urban microclimate of a broad range of decisions taken routinely by architects and planners, based on an extensive survey of applied research in the field.