COOLING CONDENSATION TYPE ATMOSPHERIC WATER GENERATOR

A cooling condensation type AWG is one that uses refrigeration technology to condense water vapour and produce water. The cooling condensation type AWG is currently the most commonly available AWG designs on the market (Bruce, et al., 2008; Niewenhuis, et al., 2012; Global Market Insights, 2016). According to Niewenhuis et al. (2012), virtually all commercially available AWGs utilise this approach for condensation. The cooling condensation type AWG uses the vapour compression cycle to cool the humid air to below its dew point temperature. The process steps of a cooling condensation type AWG are as follows:

1. The compressor pumps refrigerant gas through heat exchanger coils. As the refrigerant pressure increases the temperature of the refrigerant increases proportionally. The refrigerant is discharged from the compressor as a highly super-heated vapour (Bruce, et al., 2008).
2. The high pressure and high temperature refrigerant vapour release heat to the surrounding components. As the refrigerant vapour loses heat it condenses and becomes a sub-cooled high pressure liquid (Bruce, et al., 2008). The component in which the refrigerant vapour condenses to a sub-cooled high pressure liquid is known as the condenser (Niewenhuis, et al., 2012).
3. The sub-cooled high pressure liquid refrigerant then passes through an expansion valve which reduces the pressure of the refrigerant (da Cunha, 2010). Due to the pressure drop the refrigerant experiences a temperature drop. The refrigerant flashes to a low pressure liquid-vapour mixture after the expansion valve (da Cunha, 2010).
4. The low temperature liquid-vapour refrigerant then goes through the evaporator and absorbs heat from the surroundings; in the case of an AWG the heat absorbed is mainly from the humid air (Bruce, et al., 2008). The absorption of heat leads to the evaporation of the liquid refrigerant to a low pressure superheated vapour (da Cunha, 2010; Niewenhuis, et al., 2012). The low pressure vapour flows to the suction of the compressor and the cycle are repeated (Bruce, et al., 2008; da Cunha, 2010). During this process, the humid air is cooled down to below its dew point temperature at which the water vapour condenses and is collected in a reservoir.
5. The water collected in the reservoir undergoes treatment steps in order for it to meet drinking water regulation standards.

WATER TREATMENT PROCESSES

Air is contaminated due to toxic emissions being released into the environment as well as airborne diseases, dust particles and bacteria. The water vapour obtained from condensing humid air can carry these contaminants and thus water treatment is required to ensure that the quality of the water is within acceptable standards. Commercially available AWGs are equipped with a treatment system which the condensed water vapour is circulated through before it is released to the reservoir for usage.

The water treatment process of commercially available AWGs is as follows, see Figure below for a schematic illustration of the water treatment process:

1. Air is pulled into the unit using an extraction fan. The air is pulled through an air filter to prevent air born micro particles and dust particles from getting into the unit (Dew Point Manufacturing, 2015). In the case of the Free Cool Systems AWG design the air filter used is an electrostatic filter which can remove up to 93% of all airborne particles (Free Cool Systems, 2015).
2. The clean humid air is blown across the evaporator unit of the AWG system and water vapour in the air is condensed.
3. The water produced is then collected in a reservoir. The collected water goes through a number of treatment processes to ensure that the water reaches drinking quality standards.
4. The first treatment stage uses an ultraviolet (UV) light in the case of the Free Cool Systems design (Free Cool Systems, 2015). The water stays in contact with the UV light for approximately 30 minutes to kill off up to 90% of the germs and bacteria in the water (Free Cool Systems, 2015). In the case of the Dew Point Manufacturing design, the first treatment step is a sediment filter which removes any remaining foreign particles in the water (Dew Point Manufacturing, 2015). The Dew Point Manufacturing design uses a less effective air filter before condensation and therefore needs an additional filter to ensure that foreign solids are effectively removed (Dew Point Manufacturing, 2015).
5. The next process treatment step in the Free Cool Systems design is activated carbon filtration and ultra-filtration (Free Cool Systems, 2015). The water is pumped through two activated carbon filters, to remove up to 90% of any volatile organic chemicals which is followed by a single ultrafiltration membrane, with a pore size of 0.15mm, to filter any remaining bacteria and viruses (Free Cool Systems, 2015). The Dew Point design starts its treatment process with a pre-carbon filter to remove odour and bad taste (Dew Point Manufacturing, 2015).

ADVANTAGES OF A.W.G. TECHNOLOGY

There are a number of major advantages for AWG systems which make them an attractive solution for water crisis relief. Firstly, the system requires no operator intervention when it is running. In addition, the solution produces water through condensation which is a natural phenomenon and an integral part of the naturally occurring water cycle.

The major disadvantage of competing water recovery solutions such as acid mine drainage and seawater desalination is the highly concentrated sludge and brine solutions produced which are harmful to the environment when disposed of.

AWG technology on the other hand produces zero sludge or waste products. The dehumidification process has no known negative environmental effects and using AWG technology can help to preserve our natural water resources which are home to many aquatic species.

This technology is typically supplied as a turnkey solution which only requires feed power and a warm
humid environment to function adequately. For the design developed in this study, an additional interface is required between the household and the condenser unit to allow the condenser fan to draw cool air from the household during warm days which significantly improves the system’s efficiency.

The improvement of the technology over the years, now also allows it to run from other alternative energy sources like solar power.

OTHER AWG KEY BENEFITS

Positive Social Impact

• Contribution to constitutional right for all citizens to have access to safe, clean drinking water
• Meeting WHO standards for drinking water: No risk of water-borne diseases, No chemicals & toxins, No chlorine and No cancer-causing hormones.
• Direct Jobs created- installation & maintenance.
• Large quantities enable localisation

Sustainable and environmentally friendly

• Servicing an ever growing demand with low carbon emissions.
• No waste products
• Chemical free: sourced from high quality water held in the air.
• Does not deplete diminishing ground water reserves