Passive cooling for buildings in hot and dry climate Goutham Varaprasad 1120100334
Abstract—cooling an indoor space of a building is one of the major interests in hot climatic regions. The thermal discomfort in indoor spaces of buildings in these regions caused is removed by air conditioning or conventional cooling methods. Heating, ventilation and air conditioning are the major energy consumptions in a building. There is a huge practice of using air conditioning for cooling or heating a building. The conventional cooling or heating methods have impact on energy supply which cannot meet to its energy demand. This demands the need of an alternate and sustainable method for cooling and heating a building. Integrating passive methods of cooling into a building will reduce energy usage. The aim of the study is to understand thermal characteristics of indoor spaces in a building with the use of passive cooling techniques. Passive cooling techniques such as radiant cooling, evaporative cooling, night ventilation, trombe wall can reduce the thermal discomfort which directly reduces the need of active cooling system. The demand for energy to cool or heat a building is reduced due to the passive techniques integrated in the building. Thus making it an energy efficient building. Keywords—Passive Cooling, Passive Techniques, Energy Efficiency, Air Conditioning. I. INTRODUCTION India being one of the nations with largest population in the world. It is expected to have 17.6% of total world’s population by 2020. Energy consumption rate is increased by 7.5% in 2014 which is the highest growth rate among other developing nations in the world. And is expected to have a surge in consumption of energy. India is categorized into main different sectors in energy usage such as industry, transportation and others. A large amount energy is being consumed by building sector. Buildings share 50% of total energy usage worldwide. The percentage of energy usage is expected to increase because of the growth in population, infrastructural development and development in life style of the building occupants. Most of the energy which is supplied is produced through the fossil fuel which will be depleting in few decades. So as to avoid the energy crisis, interest is shown by researchers to preserve the energy sources. The Global buildings performance network (GBPN) says Goutham Varaprasad is with the School of Planning and Architecture, Vijayawada, Andhra Pradesh, India 520008. (Phone: 9441301901; e-mail: gouthamnaik2cu@gmail.com).
that with existing using conditions of buildings in India, it could reach to 700% of GHG emissions by 2050[1]. To decrease the global usage of energy resources, passive cooling or heating techniques are introduced into buildings which can reduce the energy demand for cooling a space. This study investigates the ways to reduce cooling loads in a buildings using passively methods and make the building net zero energy/emission. II. BACKGROUND In the present day of need and interest towards a sustainable development. The requirement of passive strategies for cooling has become necessity for bringing down the energy consumption and reduce the GHG emissions. III.PROBLEM Consumption of nonrenewable energy sources for cooling a building by using active cooling systems IV. OBJECTIVE To reduce the thermal discomfort in indoor spaces with the use of passive cooling strategies. Understanding the basic concepts of energy efficiency. To understand the Impacts of passive cooling strategies on indoor spaces of a building and to study the comfort conditions of naturally ventilated spaces. V. SCOPE AND LIMITATIONS The scope of the research is to the extent till various attributes of passive techniques are known. The research is limited to the strategies for passive cooling of a building in hot and dry climate cities. VI. METHODOLOGY Various passive techniques for heat dissipation were discussed for their contribution of cooling. The discussed techniques then are implemented in a building to analyze the achieved cooling rate. Analysis is done to find out the zones where the requirement to cool and the energy usage is high. Parameters affecting energy demand in building: 1. Environmental parameters 2. Structural parameters a. Building geometry b. Building orientation c. Space arrangement d. Building materials
The mentioned passive cooling technologies, this paper presents the major role of evaporative cooling, nocturnal radiative cooling, PCM based free cooling of buildings and corresponding hybrid technologies from the available literature with the objective of selecting a suitable technology based on the geographical and climatic conditions. VII. LITERATURE REVIEW Passive cooling: It is a building design approach focusing on heat gain control and heat dissipation in building in order to improve indoor thermal comfort with low or no energy consumption. Maintaining a comfortable environment within a building in a hot climate depends on reducing the heat gains into building and removing the heat from building. This method works either by preventing heat from entering inside or by removing heat from the building. Natural cooling utilizes onsite energy from the natural environment, combined with design of building components to remove heat.
Chilled slabs Radiant cooling through slab can be provided from floor or ceiling. But the heat is transferred towards the slab due to its natural properties so, radiant cooling is done through ceiling in most of the time. Cooled water is circulated through the ceiling which has many advantages also. It is easy to work on ceilings which can be left exposed for the work than floors. Heated air always goes upwards, which can be cooled through the chilled slab. It cost less per unit of surface area and become integrated with building structure
Techniques which involve in passive cooling: Radiant cooling Evaporative cooling Night ventilation Earth coupling
Radiant cooling-It is a system using surface controlled with temperature that cools inside temperatures by removing the heat. Heat is transferred from objects, occupants, equipment's and lights in a room to a cooled surface. Radiant cooling Systems Chilled slabs: chilled water is sent through the slabs Ceiling panels: radiant cooling panels are attached to ceilings but can be attached to walls also.
Ceiling panels Radiant cooling panels have similar working procedure of chilled slabs but are in the form of panels. These panels are attached to ceilings and can also be attached to walls also. They are suspended from ceilings and can be a continuous drop ceiling. Chilled panels are better in buildings which have variation in cooling loads. These panels provide acoustic characteristics than slabs. As they can be simply attached to any ceiling they make a better option in retro fitting buildings. These panels can be integrated to the ventilated system through the ceiling.
Evaporative cooling It is a cooling technique in which outside air is cooled by evaporating water before it is brought in to a building. Air is drawn over the wet plates of heat exchanger, the evaporated water is carried through the air and discharged to the outside of the building. Fresh air moving past the dry side of the plates. Direct evaporative cooling (DEC) and Indirect evaporative cooling (IEC) are two evaporative cooling types. Direct evaporative cooling (DEC) In this process, air is cooled by sending an air stream into water This increases humidity in process of cooling the air by adding moisture into it.
Earth tubes types 1. Vertical closed loop. In the vertical closed-loop ground heat exchanger, an air can circulated through preserved pipe loops covered in vertical bore holes. The bore holes are typically 45-60 meters deep. Heat is transferred, from the ground during the winter and to the ground during the summer. A vertical heat exchanger can be installed on smaller lots somewhat than the horizontal system.
Indirect evaporative cooling (IEC) This process is similar to DEC but the difference in this is, two air streams are separated by a heat exchanger wall. One side of wall is wet & other side is dry. Working air passes through wet side and cools the dry side indirectly because of which moisture is not added to the cool air.
Trombe wall: Trombe wall is a massive wall that covered by an exterior glazing with an air gap. In summer, damper A and upper vent are closed. The buoyancy forces generated by the solar heated air between the warm wall and glazing draws room air from the lower vent and the heated air is then flows out to the ambient through open damper B.
2. Horizontal closed- loop. In horizontal closed-loop ground heat exchanger, an air is circulated through sealed pipe loops buried horizontally, about 2 meters underground. During cold weather the pipe lops absorb heat from the earth and deliver it the house. In the summer the processes is reversed for air conditioning, and the system transfers the heat from the house to the ground. The outer piping system is able to be either an open system or closed-loop. - An open system takes advantage of the heat retained in an underground body of air. The air or water is drawn up through a well directly to the heat exchanger, where its heat is extracted. The air is discharged either to an above-ground body of air or water, such as a stream Passive evaporative cooling wall (PECW) A passive evaporative cooling wall (PECW) which was constructed of porous pipe-shaped ceramics with high water soaking-up ability. The air passing through the PECW unit was cooled and its temperature could be reduced by around 20C during summer daytime
temperature of the building. Building construction specifications
s This cooling effect from the PECW unit can be quantified in terms of the cooling efficiency. As limitations of this cooling system, it is not suitable for the extreme humid climate and locations with a shortage of water for evaporation. VIII. ANALYSIS
The passive cooling systems are applied to an energy-efficient villa design in kingdom of Saudi Arabia (KSA) that was developed based on an optimization analysis using KSA climate conditions. The optimum building envelope had the following energy efficiency measures R-15 wall insulation, R-25 roof insulation, 20 cm concrete wall, 70 cm overhang window shading, and double glazing windows. The thermal insulation is located in the outer layer of the exterior walls. The base case building model has uninsulated exterior walls and roof. The improved building envelope has resulted in a significant reduction in cooling energy end-use. The energy use intensity of the base case villa design is 228 kWh/m2 per year while it is 136 kWh/m2 for the energy efficient villa design. Since most of the electrical energy consumption is attributed to space cooling, the passive cooling strategies should have a significant impact on reducing the annual energy consumption of the residential buildings (villas) in Saudi Arabia’s hot climate. Thermal analysis is done to the building using passive cooling techniques. It shows the inside and outside
Several energy simulation packages that can be used to evaluate the energy performance of buildings to select optimal design specifications for energy-efficient buildings. ENERGYPLUS has been selected to perform the energy simulation analysis. A main advantage of simulation method is that it uses a heat balance method for heat transfer calculations. This method is known for its accuracy comparing to the other methods such as weighting factor approach especially when modelling advanced systems such as thermal mass, radiant panels, and chilled beams.
The total annual energy consumption of the energy efficient building with the PEC system is found to be 48,550 kWh while the total annual energy consumption of the same building with only optimized envelope systems is estimated to be 71,400 kWh. As a result, the total annual energy consumed by the villa can be reduced by about 32% when the PEC system is utilized. Moreover, the indoor thermal comfort within the villa is well maintained during the entire year with the PDEC system occasionally through assistance by the HVAC system.
Passive evaporative cooling system was found to increase the indoor relative humidity level, which ranges between 20 and 27%. During the day in summer, the maximum water usage is 0.007 m3 per hour. Total water required for the passive evaporative cooling system is about 0.35 m3 per day
electricity consumption more and peak cooling load could be reduced substantially with the proper use of optimal building with passive cooling methods.
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Hourly electrical energy use and outdoor temperature profiles for four design configurations for villa optimum building envelope design, optimum building envelope design with passive cooling systems. IX. CONCLUSION Buildings are durable and they have long-term consequences. Due to the poor housing design, minimal building regulations, an absence of building performance evaluation and various social and market factors lead to a high and growing adoption of air-conditioning and other techniques which mechanically control the indoor environment. Depending upon the local variations, design, and occupational behavior a lot of energy is used for indoor air conditioning (heating & cooling). The problem is the percentage of energy consumed in a building for heating and cooling. The building users use airconditioning and other mechanical strategies to control the indoor environment. The objective was to improve overall understanding of current passive cooling design implementation. Passive evaporative cooling is typically suitable for hot and dry climates. This passive cooling system is able to cool the indoor spaces with minimal use of energy. Evaporative cooling systems to be very cost-effective. It was found that
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