RACA Journal September 2021 | Page 39

www . hvacronline . co . za RACA Journal I September 2021 37
Feature left behind through the evaporative function that forms salt dust which is not good for a system in terms of corrosion or scaling . This may require various pre-treatments such as chlorination or reverse osmosis . However , some electrode-type units , depend on minerals in the supply water to function .
“ For humidification , it is preferred to use a ducted air distribution system to introduce the required humidification as Willie has described . This is not always possible though when the required design RH is higher than the evaporator dew point temperature of the air in the air handling unit which limits results . It is always better to introduce the humidity in the return air duct or AHU . Supply air is often close to , or at dew point temperature , adding to risk of oversaturation . We suggest to only use supply air with over humidity protection in the form of a humidistat or high limit sensor down the line . Absorption lengths must also be calculated carefully . The alternative is to humidify within the space and both steam and most atomising humidifiers are suitable for indoor or industrial humidification requirements ,” notes Schalekamp .
Dehumidification equipment is generally installed serving the space directly . Process air is re-circulated in multiple passes . The unit can be free standing , wall mounted within , ducted outside , or ceiling mounted .
“ If you want to raise RH , designers can focus on units that use adiabatic or ultrasonic techniques . Simply , these use a process of either evaporative media , misting or fogging to push water into the air . Adiabatic techniques generally require very little energy too . These techniques reduce the temperature of the air and have added cooling benefit in summer months when temperatures are high , and humidity is low . Further , from a fresh air makeup perspective according to occupational health and safety standards , these techniques speak to using fresh air that is cooled and humidified for free or vice versa . Other techniques involve thermal functions as Wille alluded to . Heating water to the point of phase change is more expensive . Techniques here would include steam . Steam is appropriate where it is generally cold because you are adding heat as well . You can therefore also reduce wasting energy to increase your conditioning temperatures . This is not a cost-effective solution in hot environments though unless it ’ s a specific requirement ,” notes Andersen .
He continues , “ In a de-humidification process , techniques include the condensation method – that is only very effective in warm climates , a heater that dries the air out , a heat pump that most people only think about in terms of heating a geyser or pool but is essentially a reversed air-conditioner , and then desiccant dehumidification which is required mostly in specialised processes of 20 % RH or less at lower temperatures or for dewpoints less than zero degrees C . Desiccant techniques are also ideal for cold and wet climates , as well as certain process cooling such as cooling injection moulds where a combination of systems may be in operation that creates condensation and needs to be removed . Other production types may require negative degree dew points too .”
Schalekamp adds , “ The various principles of operation for both humidification and dehumidification would be the same , although refinement and quality could differ dramatically between brands . The decision of which option is ideally suited depends mostly on the output capacity , control accuracy and energy source availability . In general , when humidification is required , gas or electrical heated steam humidifiers are preferred . For humidification by means of evaporation or atomising ( adiabatic ) the energy consumption remains similar because preheating of air is required to counter adiabatic cooling and to allow efficient absorption . In our opinion , direct evaporative humidification is not suitable as a humidifier but rather for evaporative cooling and the benefit is free . Refinement such as wastewater management , water absorption efficiency , control accuracy , as well as economical maintenance requirements and product quality is evident in the different brands available . We regularly find the saying ‘ you get what you pay for ’ to be so true .”

www . hvacronline . co . za RACA Journal I September 2021 37