Integrated Eco-Friendly Outdoor Cooling System – Case Study of Hot-Humid Climate Countries

This research proposed an integrated eco-system for conditioning an outdoor public area (park or sport) in a hothumid environment. It is accomplished by the use of a dehumidifier control machine driven by renewable solar power; after which air is distributed throughout a ducting system. The system will harvest moisture from the air, utilize it for drinking water production and plants irrigation as well as deliver low temperature, low humidity ratio air for controlling the outdoor air, which results in a comfortable outdoor relative humidity and temperature (24 °C, 50% RH). The Integrated Eco-Friendly Cooling System (IEFCS) is a sustainable self-dependent in energy and water sources. It provides a positive impact on the microclimate of the site, assists in night illumination, supplies water for drinking, plant irrigation, and allows people to enjoy a thermally comfortable atmosphere. The advantages include low maintaining cost as well as the possibility to be scaled and implemented anywhere according to the selected location.


INTRODUCTION
Outdoor cooling is a hard task, as no boundaries are predetermined. Most of the outdoor cooling techniques have a passive nature [Kaboré et al. 2018, Santamouris et al. 2017]; vegetation and planting are frequently used to control the microclimate of a semi-open space. Cooling microclimate using passive cooling elements (PCEs) in the semi-outdoor space of a passive house located in one of the Japan's hottest cities was performed [Del Rio et al. 2020]. Controlling the outdoor air temperature relative humidity and purity is a challenging task for engineers. Hot dry climates are usually controlled by passive cooling or radiative cooling techniques, evaporative cooling also can be used, such as using water pools or spry cooling. Evaporative cooling will always be a favorable solution when the outside humidity is low [Kim & Jeong 2013, Kim et al. 2014; however, where space is close to sea, this technique should be avoided. Hot humid climates are of special interest; radiative and evaporative cooling may increase the relative humidity and thus prevent achieving comfort conditions. The area of interest in this work involves the Arabian Gulf Countries (AGC), which are characterized by a hot-humid climate (HHC). Even though mist spray cooling [Ulpiani 2019] is used in Macca during the Pilgrimage season as an effective Integrated Eco-Friendly Outdoor Cooling System -Case Study of Hot-Humid Climate Countries cooling technique, the area is quite large and the number of people in active simultaneous motion reaches millions. Limited hot humid areas for sports or recreation activities may have a better solution that cools the space and reduce its relative humidity. Passive-evaporative cooling will make the case worse because of the high relative humidity in humid areas [Hui & Cheung 2009, Doulos et al. 2004, Vangtook & Chirarattananon 2007. Many researchers noted that humidity is not the only factor aff ecting the outdoor microclimate control, since the energy saving and type of energy used are also relevant [Hong Yuping et al. 2008, Chàfer et al. 2020. Recently, the outdoor air conditioning received a huge interest as the world cup organizing activity was assigned to one of the Gulf countries, i.e. Qatar. Qatar is a country with hot-humid climate that will host the world cup in 2022. Qatar suff ered a lot from extreme climate and worked to solve this problem using huge air conditioning devices that blow air from hundreds of openings in the space [Matzarakis & Fröhlich 2014, Budaiwi & Abdou 2000]. Such a technique consumes huge amounts of energy and costs a lot of money. As Qatar is an oil-producing, rich country, this technique was applicable, but of course it is not a worldwide applicable solution. In hot-humid climates planting trees will reduce the air temperature as well as increase the relative humidity, which is not adequate. There is a need to cool air and reduce its relative humidity to provide comfortable conditions for people. The idea of this project is based on using renewable solar energy umbrellas to collect the energy required to drive a (WGA) machine which in turn produces the air with a low temperature low humidity ratio. This selfdependent system will remove moisture from air as well as supply fresh water for drinking and plant irrigation. In addition, it will supply the air characterized by low temperature and low humidity ratio that will exchange heat with the air entering the machine, which will then be mixed with the outdoor air to achieve the suitable relative humidity and temperature (24 °C, 50% RH).

METHODOLOGY Site Characteristics
The investigated site is a desert landscape characterized by hot-humid air conditions and high solar intensity. Thus, the sand temperature is very high, reaching about 60°C, and air temperature may reach 47°C with up to 70-80% relative humidity. Such climate is common in the Arab Gulf sea side cities, including Abu Dhabi, Dubai, Jeddah, Bahrain, Aqaba and Kuwait [American Society of Heating, Refrigerating and Air-Conditioning Engineers, 2017]. Figure 1 shows a typical site used in the project implementation. The site has been randomly selected from Jeddah city Saudi Arabia through Google Earth.  Figure 1 depicts a location where high temperatures and high relative humidity restrict individuals from engaging in daytime activities such as sports or relaxation. It is well-known that departments of municipalities in each city are striving to provide people with recreation parks in each sub-area of the city. The high temperature and high relative humidity make such option impossible except in closed areas. The use of closed area all the time may create health and psychological problems. In order to overcome such a problem, an integrated eco-friendly outdoor cooling system is proposed to make the desert land with hot-humid weather a comfortable area for sports or recreation during day and night time.

Proposed site solution
Changing the country's environment, of course, is not an option. Engineers can only manipulate the microclimate of the site, which may be accomplished by lowering both the temperature and relative humidity of the site using an integrated ecofriendly cooling system, as illustrated in Figure 2. The following are the major system components: a) Smart Solar Umbrellas that monitor the sun Photovoltaic (PV) devices in the shape of a rose offer both shade and DC electricity to an inverter, which generates AC power. Batteries are used to store extra power for nighttime lights. b) Machine extracting water from the air: is a vapor compression machine that employs a refrigeration cycle to cool the evaporator, which extracts water vapor from the air, resulting in a low temperature-low humidity ratio in the released air. To raise the temperature of the machine, the expelled air exchanges heat with the air entering it (heat recovery). c) Air mixing and distribution system: controlled mixing of medium temperature-low relative humidity air with outdoor high relative humidity-high temperature air to achieve air within the human comfort zone. To keep the site temperature within the desired range, this comfortable air is circulated by ducts and diff users from decorative locations. d) Trees and plants: according to the site objectives, the trees and plants are planted to provide extra shading and an attractive view.
The operating premise of IEFCS begins with the use of abundant high-intensity solar energy in these nations as a source of energy, which is gathered using Smart Solar Umbrellas (SSU). SSU converts solar energy into electrical energy and provides shade to the designated place. The electrical energy generated by SSU is utilized by the Water Generation Machine (WGM) to condense Figure 2. The integrated eco-friendly cooling system water vapor from the air, lowering its humidity ratio. WGM produces low-temperature, low-humidity air. This air is then mixed with outside air to make the air that is within the human comfort zone. Trees and plants growing well in hot, humid regions are adopted.

SYSTEM COMPONENTS Smart solar umbrella
SSU is a sun-tracking solar PV system (smart fl ower) made up of twelve solar cells stacked on individual "petals". Figure 3a depicts a solar fl ower (SF) that blooms like a fl ower at the start of each day and closes at nightfall. In addition to solar cells, the SF system has a dual-axis tracker, which allows its petals to track the Sun across the sky throughout the day. The 12-petal, 18-m 2 structure generates 2.5 kW of electricity.
SFs are considered to be the main source of energy for this system. The specifi cations of SSU or SF are given in Table 1.
This system should be sized to drive the water generation from air machine (WGM) -displayed in Figure 3b.

Water generation from air machine
The produced electrical power from the SF system will supply a regulator to control the voltage before entering the storage battery. An inverter will be used to invert the DC power from battery to AC power as shown in Figure 2. This AC power will drive WGM.
Many approaches, including adsorption, absorption, and vapor compression refrigeration . WGM is a system that uses refrigeration cycle to lower the temperature of air fl owing over a specially designed evaporator of the refrigeration cycle. It allows higher contact between air and evaporator surfaces; air reaches the dew point temperature and condenses on the evaporator surfaces. The machine results in liquid water and low-temperature/low-humidity air which will be used to cool the outdoor space. The selected WGM for this study is shown in Figure 3b. The technical specifi cations are given in Table 2. Figure 3b shows a WGM that produces pure drinking water from the humidity in the air. The machine is energy-effi cient and economically feasible. WGM requires only electricity to function; there is no need for plumbing or infrastructure. With electrical supply, WGM produces up to 800 liters of clean, safe drinking water per day.

Air mixing and distribution system
The system shown in Figure 4 is a sketch for the air mixing-distribution system, used to distribute air all over the outdoor area for microclimate control. This air distribution system (ADS) depends largely upon the outdoor land usage. In the case of a park, diff users may be placed below   the umbrellas and beneath the seats throughout the park area, if a sport region is considered, air may be distributed around the area of the playground. Nevertheless, the air distribution system is highly sensitive to the case studied, it depends on the shape, purpose and ambient conditions of the site.

Trees and plants
Trees and plants play a great role in landscaping; they are the foundation of most landscape plantings. Several factors infl uence the choice of plants, including function required, weather conditions and human relaxation. Generally, landscape must be designed to be attractive and benefi cial, with fairly low-maintenance. The bellshaped fl owers in Figure 5a are rose to purple in color, highly adoptable to hot-humid climates, bearing fruits which are round in structure. The plant was chosen for its growth up to a height of 8-9 meters, climbers, extenders and suitability to hot humid climates. It is to be located on walls and fences, blocking unwanted views in the park.
Vernonia Elaeagnifolia is commonly known as curtain creeper and is a climber. Vernonia climbs up and then falls down beautifully over a wall or railing. It is a foliage plant, grown primarily for its habit of forming a green curtain. The plant was selected for its abilities to survive in hot humid climates. Royal Palm Figure 5b was selected to be located in diff erent positions of the landscape. Palm tree is one of the most sought-after landscape palms for their eventual large size.

RESULTS OF CALCULATIONS System sizing for the selected site
The size of the solar fl ower and accompanying water generating equipment from air must be sized according to the area of the site and its air conditions (T, RH). Jeddah in Saudi Arabia was taken as a sample city for our case study. The monthly average minimum and maximum temperatures are given in Figure 6A, whereas the monthly relative humidity data are presented in Figure 6B. WGM is explained in section 4.1.2, Figure 3b; its production rate is 550 L/ day, 5.6 kW power consumption and 350 Wh/L as energy effi ciency, the COP of the machine can be evaluated as follows: Hourly production rate = = = 550 24 = 22.91 /ℎ (1) Cooling Energy = = = 22.91 * 350 = 8020.8 (2) While Machine Consumed Electrical Power (MCEP) is 5.6 kW, as given in Table 2, then COP is, = = 8.0208 5.6 = 1.432 (3) The working mechanism of the proposed system combined with the air handling unit (AHU) is illustrated in Figure 7, where the WGM is integrated with the ADS, air enters the system at point 1, exchange of heat occurs in a closed HE lowering its temperature from 1 to 2 and raising the supply temperature from point 4 to 5. The heat exchanger is assumed to be adiabatic; all heat lost from the fi rst fl ow is transferred to the second fl ow. The heat exchanger eff ectiveness may be used to count for losses.
Air mass conservation ̇1 =̇2 =̇3 =̇4 =̇5 (4) Processes 1-2 and 4-5 in the heat exchanger, sensible heat transfeṙ 2 ℎ 1 −̇=̇1ℎ 2 (5) 4 ℎ 4 +̇=̇5ℎ 5 (6) where: ε is heat exchanger eff ectiveness defi ned as For mixing purposes after heat recovery, 1 ℎ 1 +̇2ℎ 2 =̇ℎ (11) Validating the used integrated system Each WGM consumes 5.6 kW of power, whereas each SF produces 2.5 kWp. This indicates that nearly three SFs are required to power one WGM, with a matching solar PV system size of 54 m 2 ( Table 1). The occupied zone for comfort control is 30×40×2.5 m, and the air volume covering the conditioned outside area is 30×40×2.5 m. As a result, the volume is 3000 m 3 . When this park is busy, the ventilation can range from 3-10 ACH. The lowest value will be considered in this study; however, greater values may be utilized if the design criteria require it. In this study, the air volume fl ow rate is assumed to be the ventilation fl ow rate (9000 m 3 /h) of three ACHs. Table 3, shows the monthly moist air properties in Jeddah.
Calculating the estimated exit enthalpy using the WGM with a 9000 m 3 /h air fl ow rate, 29 °C, and 60% RH, one machine will not be capable of extracting water, but it will be capable of reducing the temperature of the air to around 25-26 °C. The issue is characterized by a low sensible heat ratio (SHR), with space transfers of around 70 kW latent and 15 kW sensible to the outside air. To minimize the humidity ratio of the supplied air, a large cooling load will be  necessary. By performing system calculations, it was determined that each machine will need 0.065 kg/s of airfl ow rate, while a total of 0.83 kg/s is necessary to condition the region; this means that 13 WGMs and around 30 SFs should be employed. The total area required for such a system is around 500 m 2 , which accounts for 40% of the conditioned area. Such a system will be capable of lowering the outside air temperature and relative humidity from 42 °C and 80% RH to 10 °C and from 43 gw/kga to 7.5 gw/kga. The system will continually deliver 106 kg of water each hour. The conditioned air will be blown into the site and mixed with the site air; the new space temperature and relative humidity may then be measured and utilized as input values to the WGM.
On the psychrometric chart, Figure 8 depicts the processes for lowering the temperature and relative humidity of the location. More realistic data with accounting to heat losses and instantaneous mixing processes with heat recovery necessitate a simultaneous simulation of the given system, which will be the part of future extensive investigations of the suggested system.

CONCLUSIONS
The Integrated Eco-Friendly cooling system is a sustainable solution, self-dependent in terms of energy and water sources. It has a favorable infl uence on the site's microclimate, aids in night illumination, off ers water for drinking and plant irrigation, and allows people to enjoy thermally pleasant air in an open space. This project has the advantages of having a high CCF, low maintaining cost, producing plenty of clean water, and providing almost full shading. The system can accommodate any architecturally added designs, be deployed anywhere, and be scaled to fi t the allotted space.