COOLERS AND CONDENSERS t emperatures. However, the water based
corrosion, maintenance and health problems such as Legionella disease moved the industry towards dry bulb heat rejection systems such as air-cooled condensers and dry coolers.
The wet bulb efficiency advantage is applicable m ainly during peak periods such as high ambient operation but wet systems are designed to operate all year round and they have to be maintained even during low ambient periods, hence, the cost of water maintenance increases u nnecessarily.
T hese disadvantages can be overcome by e liminating the need for all year round wet operation by means of introducing wet bulb temperature during only peak periods i.e. high ambient conditions. This operation can be
initiated either via ambient sensor or alternatively via refrigeration head pressure i.e. condensing p ressure limit. As soon as the ambient dry bulb or alternatively the condensing pressure or the combination of both exceed a pre-set level if an adiabatic air cooling by water evaporation process is initiated, incoming air on temperatures can be reduced before heat rejection coils.
Adiabatic cooling process introduces water into i ncoming air stream which rapidly evaporates
the water and the hidden energy of water (in t he region of 2500kJ/kg (1,075 Btu/lb) for an average ambient air operation) provides a cooler d own stream air as much as 10°C (20°F) ~ 25°C (30°F) lower than the incoming air. Furthermore, the additional refrigerant side liquid sub-cooling provides further energy savings and reliable operation.
T o this effect conventional plastic drift
e liminators, rigid/paper mats, direct water spray o n to the coils and various forms of fogging systems as illustrated are applied in front of the heat rejection equipment for the purpose of providing a cooling for the incoming air.
Adiabatic cooling technologies
A lthough all of the above systems are applied around the world, it is vital to evaluate the application and choose an appropriate systems to suit the site and unit requirements.
As excessive fogging may scale up the coil if it used for extensive periods and/or for a windy l ocations and as the water reservoir still contains permanent water which can considered not only a health hazard but high maintenance requirement. Furthermore, some of these units p roducts suc h a s pads may cause considerable pressure drop and
p rone to clogging especially dusty environments. Also, the constant water atomisation using a high-pressure pump may result in not only very high water consumption but also adds additional maintenance requirement and most importantly of all may consume considerable energy.
Mesh concept is based on using non-metallic w ired mesh panels to cool the air stream without any by-pass for the air to go through. Adiabatic cooling effect is provided via intermittent water spray over a mesh surface, which reduces the airside pressure drop significantly as well as water rapidly and efficiently evaporates on a large mesh surface. By using (2~3 Barg (30~45 psig) mains w ater supply directly from the city mains water without any pump, recirculation system and any water reservoir, the health risk associated with a still water as well as the water losses due to free water evaporation form the surface of the water tank can be eliminated.
T hese meshes can be applied either horizontal or vertical or any inclined position in front of a heat rejection surface to suit ay make/ model independent of any manufacturer’s units. A software driven controller initiates the intermittent water spray operation based on a mbient conditions or alternatively, a condensing
Greenmill
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