Field investigation of night radiation cooling under tropical climate

This paper discusses the feasibility of cooling by using night radiation under Thailand’s hot and humid climate. Four types of roof radiators were made by using common construction materials. They were examined under three sky conditions: clear, cloudy and rainy, respectively. Investigation was done, mainly, based on the temperature of different surfaces of a roof radiator. The experimental results showed that the depression of different surface temperatures is in the range of 1–6°C below ambient temperature under clear and cloudy skies. Under rainy skies, the temperature of different surfaces of roof radiators and ambient air was fairly close. Apart from sky conditions, the factors which affect the night radiation cooling are the thermal emissivity of materials and water condensation on the radiator surface area. Finally, this first study indicated that cooling by using night radiation is feasible mainly during tropical winter season.     

A solar cooling project for hot and humid climates

This paper presents a solar house built in a southern city of China where the summer is long, hot and humid. The house was designed appropriately for the climate and was constructed with local building materials where possible. A multifunctional solar system was used and a method for indoor ventilation was proposed. The design included double walls and a triple roof in order to remove heat by ventilation of the building envelope. The external walls were clad with unglazed bricks to allow evaporative cooling. The house has been monitored since completion and more than one year of data is available. Analysis of the monitored data shows that the solar techniques proposed in this design are effective in a hot and humid climate. Effective ventilation strategies for the improvement of thermal comfort are also discussed.     

Thermal performance of an evaporatively cooled building: Parametric studies

A single-storey office building in a hot and dry climate is modelled for evaporative cooling. The counterflow cooling tower is modified to precool the tower inlet air by the tower exit air in a heat exchanger. Centralized evaporative air cooling, using the modified cooling tower, and roof evaporative cooling are considered to provide comfortable living conditions in the space. The thermal performance of such a building is analysed for various operating parameters. The study indicates that centralized evaporative air cooling is feasible, to maintain near-perfect comfort conditions in hot and dry climates. Modified cooling tower and roof evaporative cooling further enhance the scope of evaporative cooling for comfort applications.     

Thermal mass and night ventilation as passive cooling design strategy

We calculated the influence of thermal mass and night ventilation on the maximum indoor temperature in summer. The results for different locations in the hot humid climate of Israel are presented and analyzed. The maximum indoor temperature depends linearly on the temperature difference between day and night at the site. The fit can be applied as a tool to predict from the temperature swing of the location the maximum indoor temperature decrease due to the thermal mass and night ventilation. Consequently, the fit can be implemented as a simple design tool to present the reduction in indoor temperature due to the amount of the thermal mass and the rate of night ventilation, without using an hourly simulation model. Moreover, this design tool is able to provide for the designer in the early design stages the conditions when night ventilation and thermal mass are effective as passive cooling design strategy.     

Solar hybrid cooling system for high-tech offices in subtropical climate – Radiant cooling by absorption refrigeration and desiccant dehumidification

A solar hybrid cooling design is proposed for high cooling load demand in hot and humid climate. For the typical building cooling load, the system can handle the zone cooling load (mainly sensible) by radiant cooling with the chilled water from absorption refrigeration, while the ventilation load (largely latent) by desiccant dehumidification. This hybrid system utilizes solar energy for driving the absorption chiller and regenerating the desiccant wheel. Since a high chilled water temperature generated from the absorption chiller is not effective to handle the required latent load, desiccant dehumidification is therefore involved. It is an integration of radiant cooling, absorption refrigeration and desiccant dehumidification, which are powered up by solar energy. In this study, the application potential of the solar hybrid cooling system was evaluated for the high-tech offices in the subtropical climate through dynamic simulation. The high-tech offices are featured with relatively high internal sensible heat gains due to the intensive office electric equipment. The key performance indicators included the solar fraction and the primary energy consumption. Comparative study was also carried out for the solar hybrid cooling system using two common types of chilled ceilings, the passive chilled beams and active chilled beams. It was found that the solar hybrid cooling system was technically feasible for the applications of relatively higher cooling load demand. The annual primary energy consumption of the solar hybrid cooling system was lower than that of the conventional vapour compression refrigeration system up to 36.5%. Between the two options of chilled ceilings, the passive chilled beams were more energy-efficient to work with the solar hybrid cooling system in the hot and humid climate. Harnessing solar energy for driving air-conditioning would help in reducing the carbon emission, hence alleviating the climate change.     

Performance of solar-desiccant cooling system with Silica-Gel (SiO2) and Titanium Dioxide (TiO2) desiccant wheel applied in East Asian climates

This paper shows the numerical investigation of the developed solar-desiccant cooling system applied in the East Asian climatic conditions with two different desiccant wheel coating materials – the Silica-Gel (SiO₂) and the Titanium Dioxide (TiO₂). The developed and validated numerical model of the system is currently used in the present study incorporating the two new materials in the desiccant wheel. The system was applied in temperate climate (Beijing and Tokyo), subtropical climate (Taipei and Hong Kong) and tropical climate (Manila and Singapore). The study showed that the specification of the solar-desiccant cooling system varies depending on the climatic conditions. It showed that the required flat plate collector area was getting larger from the temperate climate to the tropical climate. The storage tank requirement was getting bigger in the tropical climate compared to the subtropical and temperate climate. The volumetric flow rate of air was getting higher from temperate climate to tropical climate. In the comparison of the two materials, it was found that the Titanium Dioxide (TiO₂) can support lower indoor temperature and humidity ratio than the Silica-Gel (SiO₂) with the same specification of the solar thermal system and desiccant cooling system. In general, the solar-desiccant cooling system can provide the required indoor temperature and humidity ratio. However, for the hot and humid climate such as in tropical, large size of the solar thermal system is needed. In addition, higher volumetric flow of air to support the high cooling load is required. With regard to the new material, Titanium Dioxide, it is proven to be a good alternative material since it can provide lower indoor temperature and humidity ratio with higher cooling performance than the Silica-Gel.     

Performance analysis and improvement of the use of wind tower in hot dry climate

Wind towers for passive evaporative cooling offer real opportunity for improving the ambient comfort conditions in building whilst reducing the energy consumption of air-conditioning systems.This study aims at assessing the thermal performance of a bioclimatic housing using wind towers realized in a hot dry region of Algeria. Performance monitoring and site measurement of the system provide data which assist model validation. The analysis and site measurement are encouraging, and they confirm the advantage of the application of this passive cooling strategies in hot dry climate.A mathematical model is developed using heat and mass transfer balances. For a more effective evaporative cooling, a number of improvements on wind tower configurations are proposed.     

Vernacular technologies applied to modern architecture

Various technologies as can be seen in vernacular architecture especially in Japanese traditional buildings are reviewed and the ways and means to have those technologies applied to the design of modern architecture are discussed with some examples. It is stressed that the vernacular technologies have been devised uniquely to the region where people lived to cope with the severe climate by inventing various devices without resorting to fossil fuels, thus the form of vernacular architecture representing regionalism of their own. For example earth sheltered buildings corresponds to thatched roof houses where evaporation from the wet surface gives rise to cooling effects in hot and humid climate. The optimum shape of sun shades is devised to a given orientation so that it allows the air to flow through for making ventilative cooling effective. Direct solar heat gain as representing a passive solar system is no less than fundamental for both vernacular and modern architecture with most appropriate design of geometry associated with wall orientation. Various suggestions are given for architects to consider how to apply vernacular technologies to the design of modern architecture.     

Solar passive building in Delhi: Numerical simulation and validation

A two floor hostel for married research scholars consisting of 12 apartments was designed and constructed for the composite climate of Delhi; the design incorporates many passive features. Using modified admittance procedure and Fourier analysis of the periodic parameters, the building was numerically simulated to obtain its thermal performance on an hourly basis. Two apartments of the building (one on the ground floor and one on the first floor have been experimentally monitored by a microprocessor aided data acquisition system. The observations validate the numerical model.     

Investigation on the thermal performance of different lightweight roofing structures and its effect on space cooling load

The lightweight aluminum standing seam roofing system (LASRS) has been widely used as a building element in the construction of either commercial or governmental buildings, and has been proven to be an economic roofing system. However, little research has been conducted into its thermal performance and the effect of the absorptivity (colour) of its external surface on space cooling load in the hot humid area. This paper aims to investigate the thermal performance of the LASRS. A dynamic model is introduced for analyzing the transient heat transfer through the roofs, which was solved by the control volume finite-difference method employing an explicit scheme and validated by measured data. The simulation results show that the heat flux through the roofing system with a polyurethane insulation layer is smaller than that through the lightweight roof with glasswool insulation R1. The space cooling load reduction ratio for light painted envelop could reach about 9.3% compared with black painted one. The cooling load reduction ratio ranges from 1.3% to 9.3% for the roof structure R1 with various surface colour. Therefore, the space cooling load for air conditioning of the building can be considerably reduced (up to 20%) by employing a lightweight roof using polyurethane insulation with white painted surface colour.     

Cooling load reduction of buildings using passive roof options

A model is presented to predict the thermal performance of a building with shading and roof ponds. A computer program is written to calculate hourly cooling load requirements by the numerical solution of the energy balance equation for the building. This simulation is validated for a bare roof by comparison with field data taken from an actual house in Shiraz, Iran. The effectiveness of the different roof options for passive cooling have been examined. Results indicate that for the house under study (of popular size and building material for Shiraz) cooling load demand reductions of 79.0%, 58.1% and 43.6% may be obtained by using shaded-pond, pond, and shaded roofs respectively.     

A ventilated courtyard as a passive cooling strategy in the warm humid tropics

The paper investigates the potential of a courtyard for passive cooling in a single storey high mass building in a warm humid climate. The inclusion of an internal courtyard in building design is attributed to the optimization of natural ventilation in order to minimize indoor overheating conditions. However, the efficiency of this strategy greatly depends on the design details of the building composition in providing appropriate airflow pattern to the courtyard. From the results of thermal measurements, a significant correlation between wall surface temperatures and indoor air temperatures is evident. A reduction of indoor air temperature below the levels of ambient is seen as a function of heat exchange between the indoor air and high thermal mass of the building fabric. However, this behavior is affected by indoor airflow patterns, which are controlled through the composition between envelope openings and the courtyard of the building.From a computational analysis, several airflow patterns are identified. A relatively better indoor thermal modification is seen when the courtyard acts as an air funnel discharging indoor air into the sky, than the courtyard acts as a suction zone inducing air from its sky opening. The earlier pattern is promoted when the courtyard is ventilated through openings found in the building envelope. The computational simulation utilizing the standard k-ε turbulent model with isothermal condition agrees closely with the measurements taken from the field investigation.     

Thermal behavior of buildings with curved roofs as compared with flat roofs

In this paper, a detailed finite element model dealing with heat transfer through a domed or vaulted roof is suggested based on a three-dimensional heat transfer equation and solar geometry. This model allows a comparison of the thermal behavior of curved and flat roofs in terms of heat flux and daily heat flow through them into an air-conditioned building under different climatic conditions. The results of numerical calculations show that the ratio of daily heat flow through curved roofs to that through flat ones is not affected by the curve radius, thickness and construction material of the roof, but is significantly influenced by the half rim angle θ₀ of the roofs and the ambient temperature. Compared to a flat roof, under typical hot dry climatic conditions, the daily heat flow through a domed roof of θ₀=90° is about 40% higher, whereas the daily heat flow through a south–north oriented and an east–west oriented vault of θ₀=90° is about 20 and 27% higher, respectively. The reason for this is mainly attributed to the convective heat transfer between the enlarged curved roof and ambient air. However, when θ₀<50°, heat flux and daily heat flow through a curved roof is close to that through a flat roof. The results also confirm that curved roofs are not suitable for areas with higher air temperature and intense sky diffuse radiation typical of hot humid areas.     

Outdoor airflow analysis and potential for passive cooling in the traditional urban context of Dubai

The main aim of the study is to investigate passive cooling performance in traditional urban contexts in the hot humid climate of the city of Dubai. Three cases were simulated for Al-Ras area with laminar and turbulent wind flow depending on Computational Fluid Dynamics (CFD) methodology. The laminar case was firstly run to study the general wind behavior around buildings and at the pedestrian level. The other two cases were turbulence modeling in both winter and summer seasons. The results were merely discussed and analyzed in terms of passive cooling via natural ventilation and its impact on human comfort. Narrow street canyons (4 m and less) can accelerate wind speed passing through it, resulting in a better passive cooling performance but sometimes in creating eddies if there are lots of bending angles. When the wind speed is higher (5 m/s), wind can reach deeper inside the traditional narrow streets providing better potential for thermal comfort. Most locations (49–57% of the studied area) inside the traditional urban context (street canyons aspect ratio, AR = 2–0.67) have wind speeds that range from light breeze to gentle breeze (according to Beaufort scale); which has the potential to provide natural cooling with around 5–8.5 °C lower temperature comfort sensation with basic assumption of 1.3 metabolic rate (MET) and 0.4 insulating value of summer clothing (CLO).     

Ditigal simulation of indoor temperatures of buildings with roof ponds

A theoretical model is presented to predict the thermal performance of a building with roof ponds. Equations have been derived for the estimation of steady periodic heat fluxes through the roof slab and the outer walls. Energy storage and release by the partition walls and the floor has been considered. The other cooling loads have been estimated using the methods recommended in the ASHRAE Guide and Data Book. Hourly indoor temperatures are obtained by the numerical solution of the energy balance equation for the building. The algorithm that has been developed for digital simulation of the indoor temperatures is presented. The effectiveness of different kinds of roof-pond systems, i.e. shaded ponds, “Sky-therm”, etc. for passive coolings have been examined. The studies indicate that the indoor temperatures of a building located in Delhi can be maintained below 30°C in summer while the maximum dry-bulb temperatures are above 40°C.     

Thermal performance and embodied energy analysis of a passive house – Case study of vault roof mud-house in India

This paper investigates thermal performance of an existing eco-friendly and low embodied energy vault roof passive house (or mud-house) located at Solar Energy Park of IIT Delhi, New Delhi (India). Based on embodied energy analysis, the energy payback time for the mud-house was determined as 18 years. The embodied energy per unit floor area of R.C.C. building (3702.3 MJ/m²) is quiet high as compared to the mud-house (2298.8 MJ/m²). The mud-house has three rooms with inverted U-shape roof and remaining three rooms with dome shape roof. A thermal model of the house consisting of six interconnected rooms was developed based on energy balance equations which were solved by using fourth order Runge Kutta numerical method. The predicted six room air temperatures were found in good agreement with the experimental observed data on hourly basis in each month for one year. The annual heating and cooling energy saving potential of the mud-house was determined as 1481 kW h/year and 1813 kW h/year respectively for New Delhi composite climate. The total mitigation of CO₂ emissions due to both heating and cooling energy saving potential was determined as 5.2 metric tons/year. The annual carbon credit potential of mud-house was determined as € 52/year. Similar results were obtained for the different climatic locations in India.     

Dimensioning, thermal analysis and experimental heat loss coefficients of an adsorptive solar icemaker

The dimensioning, a thermal parameters analysis and the experimental heat loss coefficients of an adsorptive solar refrigerator prototype used for ice production are presented. The solar icemaker operates in an intermittent cycle, i.e. without recovering heat. It uses the activated carbon–methanol pair whose basic components are an adsorber coupled to a static solar collector, a condenser and an evaporator. Some innovations were considered, especially those brought about by French researchers, in which the adsorber was always box-shaped with extended surfaces, and air condensers were used. For the present system, the adsorber is bi-facially irradiated and covered with transparent insulation material (TIM), the geometric configuration of the main components is multi-tubular, and a water condenser is used. TIM polycarbonate covers are used on the top and bottom of the adsorber. The components of the prototype were dimensioned after the results from numerical simulations using meteorological data valid for the hottest six months in João Pessoa (7°8′S, 34°50′WG), whose climate is typically hot and humid. The machine was designed to produce up to 10 kg of ice/day per square meter of solar collection surface. Analyses of the thermal parameters influence on the ice production as well as parameters for dimensioning each component of the machine are presented. The overall heat loss coefficient by the top and the bottom of the adsorber–solar collector component are experimentally evaluated. The tests were performed using an incandescent lamp panel disposed on a 1 m² surface, totalizing a thermal power of 3600 W. The results show a good efficiency of the TIM covers, achieving overall heat loss coefficient values between 0.54 and 1.90 W m⁻² K⁻¹.     

Performance improvement of a gas turbine cycle by using a desiccant-based evaporative cooling system

This paper focuses on power augmentation of a typical gas turbine cycle by using a desiccant-based evaporative cooling system. This technique requires a desiccant-based dehumidifying process be used to direct the air through an evaporative cooler, which could be either media-based or spray type. This could assist the evaporative cooling cycle to make necessary adjustment for any possible installation defects in a hot and humid climate. We make a comparison between performance improvement achieved by this technique and those of other evaporative cooling systems in different climatic conditions. We will show that our proposed technique, at least for hot and humid climates, is more effective than other evaporative cooling techniques.     

Numerical simulation and performance assessment of a low capacity solar assisted absorption heat pump coupled with a sub-floor system

A prototype low capacity (10 kW) single stage Li–Br absorption heat pump (AHP), suitable for residential and small building applications has been developed as a collaborative result between various European research institutes and industries. The primary heat source for the AHP is supplied from flat plate solar collectors and the hot/chilled water from the unit is delivered to a floor heating/cooling system. In this paper we present the simulation results and an overview of the performance assessment of the complete system. The calculations were performed for two building types (high and low thermal mass), three climatic conditions, with different types of solar collectors and hot water storage tank sizes and different control systems for the operation of the installation. The simulations were performed using the thermal simulation code TRNSYS. The estimated energy savings against a conventional cooling system using a compression type heat pump was found to be in the range of 20–27%.     

Life cycle energy analysis of a residential building with different envelopes and climates in Indian context

In this paper life cycle energy (LCE) demand of a residential building of usable floor area about 85.5 m² located at Hyderabad (Andhra Pradesh), India is evaluated under different envelopes and climates in Indian context. The house is studied with conventional (fired clay) and alternative wall materials (hollow concrete, soil cement, fly ash and aerated concrete) under varying thickness of wall, and insulation (expanded polystyrene) on wall and roof. The house is modelled for five different climatic zones of India, i.e. hot and dry, warm and humid, composite, cold and moderate. Study suggests that alternative wall materials alone (without insulation) reduce LCE demand of the building by 1.5-5%. Aerated concrete (AC), as wall material, has better energy performance over other materials. LCE savings are significant when insulation is added to external wall and roof. It varies from 10% to 30% depending on the climatic conditions. Maximum LCE savings with insulation are observed for warm and humid climate and least for moderate climate. For same thickness of insulation, LCE savings are much more with roof insulation than wall insulation. But wall insulation is found to be preferable to a thicker wall. It is also observed that there is a limit for thickness of insulation that can be applied on external walls and roof from life cycle point of view. This limit is found to be about 10 cm for composite, hot and dry, warm and humid, and cold climates and 5 cm for moderate climate.