Humidity control


Below: Adiabatic evaporative humidifier proving humidity and cooling to a data centre


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Desiccant dehumidifier serving a car storage facility – complete with built-in heat recovery unit


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irstly, we would look at whether the application requires a humidifier, dehumidifier or both.


Secondly, does the application requires cooling?


If so, an adiabatic humidifier can assist in also providing low-energy cooling. Thirdly, what is the duty required? As some


systems are better suited to large outs than others.


Humidification Humidity can only be added to the air by either boiling the water to generate steam, spraying/ atomising water, or by evaporation. Steam humidifiers will unavoidably use a lot of


energy in the isothermal process of changing the physical state of the water from a liquid to a gas (steam). However, as a system this process may provide the most energy-efficient way of adding humidity – we will come back to this topic. Low-energy humidifiers are generally adiabatic


systems which include ultrasonic, high-pressure spray and evaporative humidifiers. Because no heat energy is required the power source is only to power oscillators in the case of the ultrasonics or small pumps in the case of the evaporative or spray system. Consequently, these use approximately 10% of the energy to run the humidifiers compared with steam generation. In addition, these cold-water humidifiers provide cooling to the air which can reduce the load on traditional air conditioning. Two energy savings in one system result in potentially lower running costs for the temperature/humidity control after adding the humidifier. The system design also needs to be considered to determine which method of cold-water humidification is best suited – induct or direct air and the duty all play a part. Large direct air systems are generally spray


systems. Small laboratories or test chambers are often suited to the ultrasonics.


10 January 2024


Energy efficiency in humidity control


Contractors and consultants often come to Humidity Solutions for advice about low energy humidity control. Simon Marshall of Humidity Solutions says the answer is often not straightforward, but equally, it is not complicated. By identifying a few key application criteria a sound recommendation can be made


Left: Simon Marshall, Humidity Solutions


Right: Induct low-energy high-pressure spray humidifier


Retrofit systems or new designs may require a Data centres and manufacturing process control


frequently favour evaporative systems. As mentioned earlier, despite using a lot of energy


themselves, steam humidifiers may in some cases be the low-energy option for the system. The reason for this is that adiabatic humidifiers, whilst using a small amount of energy themselves, do cool the air. This can be a great advantage in environments where excess heat is a by-product of the process, or in warmer climates. However, if the building or process requires heating, then this cooling effect may not be welcome and requires additional heat energy to be added to the air. This heat energy equates to the amount of energy difference between a similarly sized adiabatic system versus a steam humidifier – so no system energy saving.


larger heating coil to be added to provide this extra heat, larger burners, and bigger heat pumps, all of which come at a capital and running cost. Taking the energy source into account and the


cost per kW is also part of the calculation. It takes the same amount of energy to convert


water to steam whatever the technology. However, where the energy can be saved is in the way that the system prevents condensation, which when produced is throwing energy down the drain. So we can also make the steam humidifiers as efficient as possible – the normal steam humidifier has a drain cycle to remove dissolved solids from the steam cylinder to extend the maintenance period. However, by adding a reverse osmosis plant we can remove the minerals before entering the


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