Investigation of Water Footprint and Ecological Footprint of Passive Hybrid Cooling System

Document Type : Research Paper


1 Department of Architecture, Kermanshah Branch, Islamic Azad University, Kermanshah, Iran

2 Department of Architecture, Faculty of Engineering, Razi University, Kermanshah, Iran


The rapid growth of global population has placed an immense stress on the demand of natural resources and contributes to the destruction of the natural environment. As the planet is now consuming natural resources in the production of goods and services faster than the environment can regenerate, strategies are urgently required to manage the ecological assets in a more effective way. The planet has biophysical limits on natural resources production and waste absorption.Buildings are one of the main factors in energy consumption and greenhouse gas emissions.Buildings consume about 40% of global energy consumption. All building services such as heating, ventilation, and air conditioning (HVAC) systems consume more than 60% energy in buildings, which is mainly supplied by fossil resources. Today, because of the need for an effective method to achieve efficient energy and biocompatible architecture, the use of natural ventilation systems in buildings has become more significant. One of the methods to create comfortable conditions in the interior is a use of evaporative cooling in the cooling systems. Unlike air conditioners, evaporative cooling can be considered as an acceptable solution for sustainable construction, which reduces energy consumption and greenhouse gases.Evaporative cooling is widely used as a passive cooling method in the built environment. In the system, the movement of air on a wet surface causes the water evaporation through the air energy absorption, thereby reducing the temperature and increasing the amount of vapor contained in the air.We need indicators to demonstrate the current carrying capacity of the Earth so that decision makers are better informed to set goals, establish options for actions, and monitor progress regarding stated goals. Footprint is a quantitative measurement of natural resources and it is used to assess the extent of human activities impact on global sustainability. Ecological footprint was initially developed by Wackernagel and Rees in 1992 , and is now widely used as an indicator for environmental sustainability. The international average water footprint is 7452(〖Gm〗^3⁄year) and this amount is reported to be 102/65(〖Gm〗^3⁄year) for Iran .
The aim of this study is to design a Passive cooling system to provide comfortable conditions in residential Buildings. Also, with minimal water and electricity consumption, it will reduce ecological footprints and water footprints and also reduce the amount of electricity consumption in the building. This research was done experimentally-analytically. In order to calculate the efficiency of the proposed system, on August 4th to 7th, the temperature, humidity, and wind speed of the interior room were measured by considering the system. The Hybrid Passive Cooling System (HPCS) consisted of two distinctive systems: the Solar Chimney (SC) and Evaporative Cooling Cavity (ECC). The ECC system was connected to the northern view of the room and SC system was installed to the southern view of the room. The air entered the tower via the openings of the head tower in all directions and passed through the clay cylinders. In this section, the air is cooled and diverted downward. The SC system creates sufficient temperature difference between the interior and exterior by maximizing the solar energy gain and performed air ventilation in the SC and ECC systems. The proposed hybrid system was built in the campus of Azad University, Kermanshah branch in August and was tested from August 4th to 7th. In order to calculate the efficiency of the proposed system, on August 4th to 7th, the temperature, humidity, and wind speed of the interior room were measured by considering the HPCS. To evaluate the water consumption of the HPCS, two scenarios were considered and their results were compared with each other. Scenario (1):on August 4th-7th, the amount of water reduction inside the clay cylinders was measured from 9:00 AM to 3:00 PM. Scenario (2): On August 18, the room temperature and humidity were measured from 9:00 AM to 3:00 PM.Based on the results,Cool performance of HPCS: the lowest temperature was recorded 21.1 ° C at 9:00 AM on the 5th of August. The lowest temperature is noon on 22.9℃ and on the 6th of August. At 3 PM, the lowest air temperature of 23.72 was reached on the 5th of August. The highest difference between the temperature of the inlet windcatcher and the outside environment is 16.3℃, which is on the 7th of August and at 3:00 PM. the ECC system can increase the RH of air by an average of 34 %. the highest outlet air velocity of the tower is 0.72 m⁄s, at 3:00 PM on the 5th of August. The lowest air velocity is 0.5 m⁄s at 9:00 AM on the 6th of August. Water and electricity consumption of evaporative cooler in scenario 2: To investigate scenario 2, on August 18, the temperature and humidity inside the room and the outside environment were measured from 9:00 AM to 3:00 PM. The lowest and highest levels of indoor humidity are 16% at 3 PM and 27% at Noon, respectively, while the outdoor humidity is 13% at 3 PM and 19% at 12 Noon. The evaporative cooler lowers the indoor ambient temperature by an average of 5% and increases the ambient humidity by an average of 7%.Comparison of electricity and water used in scenarios 1 and 2: The amount of electricity consumed in Scenario 1 is zero, but in Scenario 2, this value is 12112.9 kJ per day. The environmental footprint of electricity consumed in Scenario 1 is zero, but in Scenario 2, it is 1.05 Gigabits per year. The water used in Scenario 2 is 0.04 m^3more than Scenario 1.The results showed that the chamber can provide comfort conditions with zero energy consumption by using a hybrid system during the hottest days of the year from 9:00 AM to 3:00 PM. The power consumption of the evaporative cooler in the 3 months of summer is 1.13 GJ, while the power consumption of the designed hybrid system is zero. The ecological footprint of the power consumption of this system is zero, while the ecological footprint of the evaporative cooler is 1.05(Gj⁄year). From the data obtained, we conclude that the passive hybrid cooling system has the lowest ecological footprint of water and electricity compared to evaporative coolers. The system is also able to provide indoor comfort on the hottest days of the year.


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