The relative humidity level in our built environments is critical to prevent occupant discomfort and/or damage to building materials. Choose to read the quick high level summary, or test your knowledge by following this interactive blog that delves deeper and deeper into the details of the steam that we inject into our air.
Why is humidification important?
Outdoor temperatures vary greatly between the summer and winter months, and humidity levels also fluctuate with changing weather conditions and proximity to lakes and oceans. Modern buildings rely on mechanical ventilation systems to maintain consistent indoor temperatures and humidity levels.
Hot and humid weather during summer months will cause the air to feel heavy and damp, requiring air conditioning to increase occupant comfort and decrease the risk of mold and mites in building materials.
During winter months, heating systems are put into service that tend to decrease the relative humidity (RH). If the RH value falls below 30%, the air will feel dry, and may lead to occupant discomfort and/or damage to building materials. Low RH values also increase the potential of static charge build-up, which may affect negatively impact sensitive electronics and machinery.
How are RH values maintained?
Large buildings rely on air handler units (AHUs) to temper the recirculating air and introduce a portion of fresh outside air. These AHUs are comprised of multiple sections with different functions including:
- Air Filtration
The humidification function is often accomplished using Direct Steam Injection, whereby pressurized steam is sprayed directly into the air stream. This method is most common in facilities where a centralized steam system is already in place due to other process requirements.
Is there more to steam than just water?
Yes. There is always something other than pure H2O in steam.
Steam carries gases and may also contain specially formulated water treatment compounds used to protect piping from corrosion.
The gases are primarily carbon dioxide (CO2) and oxygen (O2). The concentration of these gases is dependent on the composition of the water being fed to the boiler. It is desirable to minimize the presence of these gases in a steam system to minimize the risk of corrosion.
Carbon dioxide is particularly harmful to steel piping because it forms carbonic acid as the steam condenses into condensate.
Water treatment compounds, called amines, are added to boiler water to combat the effect of carbon dioxide. Amine compounds are designed to evaporate with the steam to neutralize the acidic properties of condensate. This maximizes the useful life of piping infrastructure.
Should I be concerned about steam purity?
The concentration of amines in your steam is primarily dependant on your incoming water quality and is typically low,
In the order of a few parts per million, or 10,000th of 1%
Air can hold a surprisingly large volume of water as humidity.
Consider a 600 square foot area with 8 foot ceilings. If the room is at 22.5 degrees Celsius and RH is increased from 20% to 40%, a total of 500ml of steam was used.
Your water treatment professional is responsible for ensuring the concentration of amines in the air meet two main concentration guidelines to ensure there are no complaints from occupants, especially from those with sensitivities:
- Permissible Exposure Limits (PELs)
- Odor Threshold Limits (OTL)
In situations where the incoming alkalinity levels are elevated, the concentration of amine required to neutralize the resulting elevated CO2 levels may exceed OTLs, or even PELs. Implementing pre-treatment alternatives can reduce the incoming alkalinity and thereby reduce amine requirements.
Humidifiers are a critical component of a properly operating HVAC system to ensure occupant comfort and prevent damage to building materials. The multi-levels of this blog discussed the design and operational considerations to ensure safe and effective humidification at your facility. Consult your water treatment professional to; confirm that your amine dosage rates are below recommended concentration guidelines, and discuss the implementation of pre-treatment equipment to reduce occupants’ exposure to amines and lower your water treatment costs.