GREEN GUIDE PART ONE
humidity and can reduce the load on the air conditioning or air movement so by installing a new piece of equipment you could be reducing the running costs of the plant. Truly green. Alternatively, in an air handling unit serving an office, the opposite may be true. You gain good humidity control, but you are cooling the air down which in this case probably requires you to run the heater battery for longer and harder than previously.
Surprisingly in this last application a steam humidifier could be the green solution. Good humidity control as before, but the steam entering the air handling unit does not affect the temperature. The heat energy in the steam is used to change state. The process goes straight up the dry bulb line on the psychometric chart. The correct humidity in an office, hospital or anywhere that we are working in creates thermal comfort. This is where the human body sweats to regulate its temperature – too hot and we sweat. If the air is dry, we sweat, and this moisture easily and quickly evaporates from the surface of our skin – like an evaporative cold-water humidifier it takes heat energy from a source to change state. In this case it is our body making us feel cooler.
If the air has a higher moisture content, 50%rh, then the evaporation process is less efficient and so we feel warmer. 23°C at 20%rh will feel the same as 20°C at 50%rh to the human body in the office. For
this reason, we can lower the heat setting if the humidity is correct - saving energy even over a steam humidifier generating the steam / humidity. In this case the steam humidifier is the low energy solution. Steam humidifiers vary, with four main options. Live steam - where you have a central steam boiler – common in hospitals as they also provide steam for sterilization and heating. If the boiler is used efficiently this is a very efficient way to produce humidity but becoming less popular due to the insurances required to run a pressurised boiler and the losses associated of running the steam supply some distance.
Gas is good for large humidifier loads but is not green at the point of use as you discharge the gases via a flue. Electrode and resistive humidifiers are the most frequently used and neither create any pollution at the point of use. This is where the electrical source is important and, if generated by an environmentally friendly method, limits damage to the environment.
The resistive humidifiers use less consumables but do require more time to empty the scale from the stainless-steel steam generating cylinder than replacing the consumable cylinder in the electrode boiler. The stainless-steel cylinder from some manufacturers has a lifetime guarantee, so is a very good option. However, the electrode boiler is a less expensive machine and therefore the cost of the consumables may be less than the
additional expense. Again, a humidity specialist will be able to cost this for your application, running hours and water quality.
The consumable steam generating cylinders should be recyclable, which is worth checking, and only one make of steam humidifier (resistive or electrode) is manufactured in the UK, also saving transport cost and pollution which again adds to the green assessment.
So, we can conclude. Replacement plastic steam cylinders if recyclable and Made in Britain may be a greener option than an ultrasonic low energy humidifier flown in from the Far East. Humidity control could allow you to turn your heating down with a net energy saving. Stable moisture levels in the air will reduce production waste and increase quality so saving energy, product, materials and time in many industrial applications.
Good humidity control will extend food product life and reduce freezing of cooling coils so reducing energy usage and wastage. Low energy humidifiers may not be the most energy efficient for the system as a whole and a 70kw steam humidifier may save you energy and costs.
Clearly humidity control can play a vital role in contributing to the ‘green’ argument – but specialist advice is strongly recommended to choose the best solution for each specific application.
www.acr-news.com
June 2020 33
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