Development and Testing of Solar Powered Evaporative Air-Cooling System with an Improved Performance

Abstract

This study proposes a new active direct evaporative cooling system that uses a bundle of cotton fibers as an evaporating surface and activated carbon as a moisture adsorbent. A two-stage evaporative cooling experimental setup consisting of an activated carbon adsorbent in between the cooling pad was designed, fabricated, and tested at Bahir Dar, Ethiopia. The fiber bundle (pad 1) was wetted with water and ambient air was forced through it using a fan then the air that exiting from pad 1 was forced through a bulk of activated carbon (moisture adsorbent), and then the air from the adsorbent passed through the second wetted fiber bundle (pad 2). The energy source for the fan and pump was the solar photovoltaic energy system. The average temperature drop of the cooler without the moisture adsorber was 9.33°C and with the inclusion of the moisture, the adsorber gave an additional temperature drop of 1.5°C to 4.95°C. During the hot dry season, the average relative humidity of the ambient air, pad 1 outlet, adsorbent outlet, and pad 2 outlets were 28.26%, 76.12%, 55%, and 88.2% respectively. The cooler with moisture adsorbent had a cooling capacity of 3653 W, an effectiveness of 94.25%, and a COP of 52.2. The developed solar evaporative cooling system can provide energy-efficient, sustainable, affordable cold air for different applications. The cooler could be used by small-scale farmers, wholesalers, and retailers for the cooling and storage of horticultural products to reduce the postharvest loss in fresh produces.

Keywords:

• Evaporative Cooler
• Air Cooling
• Cooling Capacity
• Solar Energy
• Cold Storage
• COP

PUBLIC INTEREST STATEMENT

These work is focused on designing, developing and testing of solar-powered evaporative cooling systems. The developed evaporative cooler is environmentally friendly, has green technology, and is affordable for small-scale farmers. It uses water as a refrigerant, solar energy as the energy source, and uses local materials. It was developed with new materials, using locally grown cotton as a raw material which increases the air-cooling performance of the cooler. The result revealed that the cooler has an improved cooling performance. The cooler could be used by small-scale and cooperative farmers, wholesalers, and retailers for the cooling and storage of horticultural products such as tomatoes to reduce the postharvest loss.

Nomenclature

Cp specific heat capacity of air, kJ/kg k

T dry bulb temperature of the air, °C

RH relative humidity of air, %

Q cooling capacity, W

A cross-sectional area of the cooling pad, m²

V frontal air velocity, m/s

T_idinlet dry bulb temperature, °C

T_odoutlet dry bulb temperature, °C

T_wbwet-bulb temperature, °C

Abbreviations

S_w percentage of water absorbed, g/g

m_wfiber wet mass, g

m_dfiber dry mass, g

S_Esaturation efficiency, %

m_amass flow rate of air, kg],

COP coefficient of performance

Wf power consumption of air fan, W

W_ppower consumption of water pump, W

Greek symbols

${\rho }_{\alpha }$ the density of air, kg/m³

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author Contribution Statement

Tadelle N. Mekonen: Conceived and designs the experimental set-up; performed the experimental testing; Analyzed and interpreted the result; Wrote draft the paper.

Mulugeta A. Delele: Conceived and designs the experimental set-up; Supervised the research; Revised the draft paper.

Sisay W. Molla: performed the experimental testing; Revised the draft paper.

Additional information

Funding

The authors received no direct funding for this research.

Notes on contributors

Tadelle N. Mekonen

Tadelle N. Mekonen, Email: [email protected]

Mulugeta A. Delele

Mulugeta A. Delele, [email protected]