Effect of solar absorptivity and emissivity of exterior surfaces on the thermal performance of a building

The effects of the solar absorptivity and the thermal emissivity of exterior building surfaces on the indoor air temperature of a one room building are evaluated in terms of the discomfort index. The thermal performance of the building has been investigated for four different climates prevalent in India, namely, composite (New Delhi), hot and dry (Jodhpur), cold and humid (Srinagar), and cold and dry (Leh). The results confirm the common-sense view that the building surface should have low solar absorptivity and high thermal emissivity in hot climates and high solar absorptivity and low thermal emissivity in cold climates for indoor thermal comfort conditions.     

Recent research on an indirect evaporative cooler (IEC) Part 2: thermal performance of a non-conditioned building coupled with an IEC

The thermal performance of a non-conditioned building fitted with an indirect evaporative cooler (IEC) has been investigated in terms of hourly, monthly and seasonal discomfort index. The effect of various design parameters of the IEC on the discomfort index has been investigated for three different climatic areas of India, i.e. hot–dry, warm, humid and composite. The analysis has shown that the IEC is effective for creating thermal comfort conditions in buildings in dry–hot and composite climates. © 1997 by John Wiley & Sons, Ltd.     

Recent researches in indirect evaporative cooler V: relative thermal performance of buildings coupled to direct and indirect evaporative cooler

A mathematical model has been developed to evaluate the relative thermal performance of a building coupled with an indirect or direct evaporative cooler. Using periodic analysis for taking into account thermal storage of building envelope, explicit expressions have been obtained for room air temperature and room air humidity. For comparing their performance under different climatic conditions, numerical calculations have been made taking meteorological parameters for a typical day for Delhi (composite climate), Jodhpur (hot-dry climate) and Madras (hot-humid climate). It is found that the indirect evaporative cooler is a more effective and energy efficient system than the air-conditioner; it can hence be commercially used for computer and electronic exchange applications as well as for human comfort in a variety of climatic conditions, whereas direct evaporative cooler has limited use (only in hot-dry and composite climates). © 1997 by John Wiley & Sons, Ltd.     

Effect of orientation on thermal performance of a building

The effect of aspect ratio and orientation of a non-airconditioned building on its thermal performance has been analysed in terms of discomfort index for hot-dry and composite climates. It is shown that the discomfort index for east-west orientation is smaller than that for north-south orientation but the difference even for the largest aspect ratio considered is not more than 10%.     

Thermal performance of a building coupled to an evaporative cooling tower

The thermal performance of a building fitted with an evaporative cooling tower has been evaluated in terms of discomfort index for two climates, namely, composite and hot-dry, typified by New Delhi and Jodhpur, respectively. The effects of various evaporative cooling parameters (height and cross-sectional area of the tower, packing factor, area of the pads, resistance offered to the air flow and local wind conditions) on the performance of the building have been analysed. It was found that, for given parameters of the tower and wind conditions, there is an optimum height of the tower for which the thermal discomfort condition in the building is minimum. The optimum values of the tower height for comfort conditions in the building for various other tower parameters have been obtained for each climate.     

Effect of under-floor water storage on the thermal performance of a room

The thermal performance of a room coupled to an evaporatively cooled water storage tank below its floor has been evaluated in terms of the discomfort index for the hot-dry climate of Jodhpur. For a given depth of the storage tank, the effect on the room air temperature of the flow rate with which water is cooled evaporatively has been analysed. It is seen that the storage coupling reduces the mean room temperature but does not affect the swing in the room temperature.     

Effect of different surface treatments of the surrounding earth on thermal performance of earth-integrated buildings

The thermal performance of earth-integrated buildings can be suitably modified by appropriate treatment of the surrounding earth's surface (namely shading, wetting, blackening and glazing with cheap plastic sheets). The effect of these surface treatments on the thermal performance of a partially sunken room has been investigated for three different climates: hot and dry, hot and wet and cold and dry, typified by Delhi, Madras and Leh, respectivly.     

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.     

Variation of discomfort with south window area and insulation on walls/roof

Dependence of the discomfort index on the south window area and the cost of optimally distributed insulation over the walls and roof (corresponding to different available investments) of a non-air-conditioned one room building is investigated. It is assumed that, in the winter, the wooden shutters provided in the window are opened during the day and are closed during the night, and that, in the summer, the shutters are closed during the day and are opened during the night. It is seen that the discomfort decreases with increasing window area and an increasing amount of insulation.     

Numerical study on convective flow in a three-dimensional enclosure with hot solid body and discrete cooling

The aim of the present numerical study is to analyze the effect of cooler location and aspect ratio and position of the hot solid body inside the enclosure on three-dimensional natural convection flow in a cubical enclosure. The cooler and heater positions and aspect ratio of the heater in a cavity are examined under different combinations of partially cooling vertical sidewalls and, hot solid body in the cubical cavity. That is, (i) different cooler locations with a fixed size of the hot solid body, and, (ii) centrally located hot solid body with different aspect ratio. The three-dimensional convective flow and thermal arrangements in the enclosure are analyzed using the distribution of streamlines, isosurfaces, and Nusselt number. It is found that the cooler location and aspect ratio of hot solid body play a key role on convective cooling and energy transport inside the enclosure. The unit aspect ratio of hot solid body provides higher energy transport inside the enclosure for all cooler positions.     

Recent researches in indirect evaporative cooler III: optimization of the cooling potential of a room–coupled indirect evaporative cooler

A mathematical model based on heat transfer principles, for characterizing the cooling performance of a room coupled indirect evaporative cooler (tube type) has been developed. Two dimensionless parameters, i.e. environment factor, ϕ and cooling factor, CF have been defined to characterize the performance of IEC coupled with a room. The optimum values of these parameters have been obtained for different environmental and thermal load conditions. In addition to this, a linear relationship has been obtained for the optimum size of a cooler to remove maximum heat from a room of given size. © 1998 John Wiley & Sons, Ltd.     

Adaptation of an adsorptive solar refrigerator to Moroccan climates

In this paper, we introduce a model taking account of the real operation of an adsorptive solar refrigerator using activated carbon-methanol pairs, as a function of the climatic conditions: ambient temperature and insolation. The model is used to simulate the operation of the refrigerator in two Moroccan climates: Rabat, temperate and humid, and Marrakech, dry and hot. The numerical simulation shows that the behaviour of the refrigerator is different from one climate to the other. In Rabat, which has a Mediterranean climate, the cold room temperature can be maintained at a value practically always less than 5°C; whereas in Marrakech, which has a pre-Saharan climate, an overheating problem can arise in the summer season and temperatures in the cold room can reach 17°C. Results also show that in both climates we are confronted with the problem of freezing because the cold room temperatures can be less than 0°C and reach − 15°C in the winter.     

Long-term trends of heat stress and energy use implications in subtropical climates

Past and future trends of human comfort in terms of heat and cold stresses under the local subtropical climates using measured meteorological data as well as predictions from general climate models were investigated. Summer discomfort showed an increasing trend (and winter discomfort a decreasing trend) over the past 41 years from 1968 to 2008. Monthly mean minimum and maximum temperatures and moisture content predictions from a general climate model (MIROC3.2-H) were used to determine summer and winter discomfort for future years (2009–2100) based on two emissions scenarios B1 and A1B (low and medium forcing). The 92-year (2009–2100) mean cold stress would be reduced from the 41-year (1968–2008) mean value of 8.7 to about three for both emissions scenarios. The 92-year mean heat stress would be 115.9 and 120.6 for B1 and A1B, respectively, representing 31.6% and 36.9% increase over the 1968–2008 long-term average of 88.1. These suggest that the already small winter heating requirement in subtropical Hong Kong would become even more insignificant in future years, whereas the increasing trend of summer discomfort would result in more cooling demand in the built environment.     

A study on a ventilation stack integrated with a light pipe

A theoretical and experimental study has been conducted on the performance of a vertical light pipe that also functions as an air flow stack for night ventilation. The rectangular light pipe of height 3 m and cross-section area 0.0625 m² surrounded by an air duct of total cross-section area 0.23 m² is situated above a room of height 3.8 m and floor area 9 m². Heat transfer from the hot water in the wraparound hot water jacket to the air in the duct is assisted by stainless steel fins. The ventilation of the room, due partly to the buoyancy of the air in the duct and partly to the wind effect, amounted to nearly 10 air changes per hour which is sufficient for passive cooling during cooler night periods. The light pipe has specular reflecting walls. It was found that the transmission of daylight through the light pipe in the middle of a partly cloudy day was sufficient for illuminating the room to general illumination level.     

Design and performance analysis of a small solar evaporative cooler

In this paper, the process of design, manufacturing, and performance analysis of a simple yet innovative solar evaporative cooler is illustrated. This investigation aims to evaluate the performance of a very small cooler with minimum energy consumption (10 W). A solar evaporative cooler was made out of various simple electrical and mechanical components. The cooler was tested in a specified room with the volume of 510?×?310?×?320 cm³. In order to evaluate the performance of the cooler, the air temperatures at different locations in the room was measured and compared during five consecutive days. The results showed that the performance of the cooler is relatively reasonable during the summer. However, its performance can be improved using high-performance cooling pads and solar panels. This simple evaporative cooler benefits from the ease of manufacturing process, cost effectiveness, and high portability.     

Technoeconomic optimization of solar natural convection hybrid hot water systems

In this paper a techno-economic model for a hybrid domestic hot water system operating under natural convection mode is presented. Three modes of auxiliary energy supply viz.

• A electric heater fitted in the solar hot water tank.
• B electric heater fitted in a small water tank in series with the solar hot water tank, and
• C an instant electric heater fitted in the tap

have been considered. Taking into account the life and the capital and maintenance costs of the solar and electrical equipments, the cost of useful energy (Rs/kWh) has been calculated for different values of the collector area and the tank capacity, and thereby the optimum collector area and tank capacity (for a given demand), corresponding to minimum cost of useful energy, has been determined. From numerical calculations made for the climate of Delhi, India (a representative composite climate) corresponding to the two cases of monthly hot water demand viz. (i) constant monthly demand, and (ii) variable monthly demand, it is seen that case (C) is the most economic design of the hybrid hot water system; numerical calculations have also been made for this case corresponding to the climates of Srinagar and Madras (representing cold and hot climates). The effect of government subsidy on the optimized values of collector area, tank capacity and cost of useful energy has also been investigated for the climate of Delhi.     

Solar desorption of absorbent solutions

In hot humid climates, like that of Madras, a coastal city, it is attractive to dehumidify room air using an absorbent solution and desorb the water from the solution by solar heating. If a desorption tower is used for transfer of water from the solution to the outdoor air, a blower is required to produce the air flow. It is found by analysis, however, that it is possible to achieve this desorption in the solar collector itself. Water is transfered to the ambient air which flows through the solar collector-cum-desorber by thermo-siphon action. The performance characteristics of the proposed collector-cum-desorber were found to be excellent by theoretical calculations. These have been confirmed by experiments.     

Problems encountered when using japanese package-unit air-conditioners under United Kingdom conditions

An analysis is given of problems encountered when using air-conditioners specified for warm and wet climates in cooler and dryer ones. Suggestions are made for remedying the defects.     

Experimental study on the heat exchange effectiveness of a dry coil indirect evaporation cooler under various operating conditions

In this study, a pilot Dry Coil IEC unit, an indirect evaporation cooler established by connecting a direct evaporation cooler and a sensible heat exchanger (SHE) in series, was made, and the effectiveness data of the pilot unit were acquired under various operation conditions in an environmental chamber realizing a wide-range of indoor and outdoor air conditions. The test result shows that over 40% effectiveness can be acquired even in hot and humid climates by using the Dry Coil IEC proposed in this paper. The Dry Coil IEC reduces the cooling coil size by pre-cooling the process air during the cooling season. It can also be used as an SHE reclaiming the sensible heat from the exhaust air during winter operation. The pilot unit recovered over 60% of sensible heat in the test. In addition, a simplified model of Dry Coil IEC returning the various operation conditions was developed based on existing models of an SHE and a direct evaporative cooler. A polynomial equation returning the effectiveness of the Dry Coil IEC was derived as a function of seven independent variables highly influencing the performance of the unit. The experimental data acquired by the pilot unit operation agree well with the effectiveness values of the Dry Coil IEC predicted by the proposed model. It was also identified that the proposed equation agrees well with the existing model of the Dry Coil IEC applied to the energy simulation program.     

The research and development of the key components for desiccant cooling system

An air conditioning option, that is, desiccant cooling system (DCS) in which alternative energy source, such as solar energy, nature gas and rejected heat, can play their part for the benefit of environment and saving energy is constructed by regenerative dehumidification component combined with heat exchanger (recuperator) and evaporative cooler.The mathematical model of an rotary desiccant wheel that can be used to calculate the performance of stationary or rotary bed and transient or steady state operation is founded by considering many terms. A computer program for this new model has been compiled and some results of computer simulation compared with experimental value, they are good in agreement.The performance of evaporator is estimated by computer. We developed some kinds of evaporator of which the COP is about 1015 to decrease the room temperature and clean the air in drier climates. Using a new kind of chemical refrigerant invented by Zu-She Liu, the air conditioner will be simple in construction and very efficient (COP > 30).