Feature
Humidair at Frigair 2022 . -
© RACA Journal | Benjamin Brits
EQUIPMENT FUNCTION AND DIFFERENTIATING METHODS Humidity control either adds or removes moisture from the air which can be achieved in a variety of methods using sensors . Humidification and de-humidification are separate functions with separate equipment . A full design should be completed and is always recommended .
One type of humidifier boils water to create dry steam which could be supplied in air handling units . Dehumidification can be affected by a cooling coil followed by a reheating coil or resistance heater . Alternatively , desiccant dryers can be used if low relative humidity is necessary for the particular application . Custom solutions are possible through incorporation of these functions into bulk air supply or by direct in-space inclusion .
Pieter Aldred , managing member of Humidair , says : “ For humidification , it is preferred to use a ducted air distribution system to introduce the required humidification . This is not always possible though when the required design RH is higher than the evaporator dew point temperature of the air in the AHU 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 .”
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 , rear wall mount , or ceiling mounted .
“ If you want to raise RH , designers can focus on units that use adiabatic or ultrasonic techniques ,” says Aldred . “ Simply , these use a process of either evaporative media , misting or fogging to push water into the air . Adiabatic techniques generally require little energy . 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 .”
He continues , “ In a de-humidification process , techniques include ; the condensation method – that is only highly effective in warm climates ; a heater that dries the air out ; a heat pump is essentially a reversed air-conditioner ; and then desiccant dehumidification which is required mostly in specialised processes of 20 % RH or less . 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 which creates condensation and needs to be removed . Other production types may require negative degree dew points too .”
Christiaan Schalekamp , technical sales director at Humidair , 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 as to which option is more ideal 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
“ Location , location , location ! The most convenient place to put a steam humidifier is not always the best .”
28
RACA Journal I March 2023 www . refrigerationandaircon . co . za