The Role of Adiabatic Humidification in MEP Design
Introduction to Humidity Control
Humidity control is a key factor within the MEP industry that can heavily dictate which heating and cooling systems are implemented within a building. The majority of variable air volume (VAV) systems are required to remove moisture from the supply airstream in the air handling unit. This is done through the cooling coil, which cools the air and wrings out moisture into the condensate drain. A reheat coil will raise the temperature back to the desired setpoint, where the resultant indoor space relative humidity falls within a typical range of 45-60%.
Certain projects require moisture and humidity control year-round, due to factors such as geographical location or program type. During the winter, when outdoor air humidity is generally low, critical building spaces such as museums or libraries will need additional moisture in the airstream to maintain a constant relative humidity setpoint.
What is Adiabatic Humidification?
To humidify a space, moisture needs to enter the airstream in a gaseous state. Utilizing steam is a common method of humidification, which is an isothermal process. Boilers or heat exchangers are required to generate steam that will be mixed into the system at the air handling unit. In order to create that vapor form from a liquid, 1,000 BTUs per pound of water are required.
While 1,000 BTUs per pound of water are still needed, adiabatic humidification is an alternative process that does not require any creation of heat. Energy is drawn from the surrounding atmosphere, turning water into vapor and humidifying the air. Atomized water is introduced into
the air through several high-pressure spray nozzles. These nozzles are arranged perpendicular to the flow of air, spraying water into the media. Hot air travels into the adiabatic section, then cool water is
cleaner method of generating humidity. Adiabatic systems can also contribute to a project’s overall goal to provide an allelectric humidification option, reduce carbon emissions, and provide an energy
sprayed and evaporated into the system. While this process increases relative humidity in the airstream, it cools down the air at the discharge once the energy has been used to evaporate the water.
Pros: Energy Efficiency, Reduced Carbon Emissions, Ease of Maintenance, and Cost Savings
If an owner or engineer is implementing a central humidification system into their building, she might consider adiabatic humidification for the simple reason that steam is not readily available. If there is no central plant to produce steam, or it becomes too costly to install a steam boiler, then utilizing adiabatic humidification is a reasonable alternative.
Steam boilers that use natural gas and/ or oil will not only waste fossil fuels but create greenhouse gas emissions and contribute to ozone depletion. Nozzle spray humidification naturally absorbs moisture from the atmosphere without having to generate additional humidity. The energy savings accrued from this process will save owners money over time, while also ushering in a
efficient solution in terms of operating cost and lower input kW per humidification capacity.
The high-pressure spray system is relatively easy to install, comprised of only a grid of nozzles that are fixed into the air handling unit. High-pressure pump skids transfer treated water from the reverse osmosis (RO) filter and water treatment system to the manifold in the air handling units; inlet water is connected to the main domestic cold-water line. The system requires semiannual and annual maintenance, including salt maintenance, nozzle cleaning, and maintenance of the water treatment system. Adiabatic systems require minimal
“ The Role of Adiabatic Humidification…” continued from page 1
maintenance compared to the service that is needed for steam boilers.
Cons: Potentially Expensive Water Purification, Larger Space Requirement, and Necessity for Reheat Coils
Reverse osmosis (RO) is a water purification process that is necessary for all adiabatic systems. The water that is sprayed into the supply airstream must be deemed treated before it enters an occupied space. An RO system filters out harmful toxins and minerals while allowing healthy water to enter the atomizer. One of these skids can become costly on larger scale projects, where the equipment is likely to be remote and require additional mechanical room space and piping.
The distance necessary to absorb the water sprayed into the air stream is typically much longer than a traditional steam humidification system needs. A spray nozzle within the air handling unit requires a section length of approximately five feet but can be as long as six feet. Mechanical rooms short on space or with obscure floor areas may not be able to accommodate a larger air handling unit. Additional room is also required for high-pressure water pump modules and integrated, packaged reverse osmosis water treatment.
The absorption of water using the heat in the air will in turn cool the air stream. To rectify this, both preheat and reheat coils must be accounted for in the unit and
ASHRAE 241 – Control of Infectious Aerosols
A New Standard Is Introduced
In July of 2023, ASHRAE published Standard 241 – Control of Infectious Aerosols (Standard). The Standard was developed in response to a White House request to study the impact of indoor air quality and the transmission of diseases. It stands to reason that the COVID-19 pandemic had a significant impact on its development. With the introduction of this new standard, building owners now have a guideline to help combat airborne diseases and promote the wellbeing of building occupants.
MEP Impacts and Intent
ASHRAE Standard 241 outlines requirements for a building to implement an Infectious Risk Management Mode (IRMM) for its HVAC systems. While the Standard does not specify when a building should enter this mode, the thought process is that a building owner would decide if/when the risk is too high for that specific building and would implement an appropriate response. In the future, once more buildings are compliant with the Standard, local AHJs could determine when buildings should enter the IRMM.
IRMM can look different for each specific type of building (office, school, etc.).
The objective of the IRMM is to deliver a minimum Equivalent Clean Airflow Rate (ECA) to each space in the building. Clean airflow is defined as “the flow rate of pathogen-free air that, if distributed uniformly within the breathing zone, would have the same effect on infectious aerosol concentration as the sum of actual outdoor airflow, filtered airflow, and inactivation of infectious aerosols.” From an HVAC standpoint, this could be
MEP 2040 Challenge
system design. The preheat coil ensures that the supply air is warm enough to absorb the water. Now that the heat in the air has been lost to evaporation, the supply air must utilize reheat to bring the temperature back to setpoint. While most air handling units already include reheat coils, the addition of a preheat coil will increase unit length and cost. The adiabatic system controls strategy is typically more robust than is the case with a standard steam humidification system. Integration between the controls system, air handling unit, and humidification system requires a higher level of coordination to ensure that the air dewpoint control at the air handling unit discharge is maintained.
accomplished by several methods. One would be to increase the outdoor airflow rate to meet the minimum ECA. This value would be significantly larger than code minimum ventilation rates. To save energy and equipment costs, air cleaning technology could be implemented instead. The use of Ultraviolet C lights in supply air streams, bipolar ionization, and use of High Efficiency Particulate Air Filters (HEPA) all could be used to “clean” the air.
“ASHRAE 241…” continued on page 3
Kohler Ronan is pleased to join a growing number of MEP/FP industry leaders in accepting the MEP 2040 Challenge posed by the Carbon Leadership Forum (CLF). As signatories, we are committed to “advocate for and achieve” net-zero operational and embodied carbon by 2030 and 2040 respectively, across all our projects.
Approved Technical Consultant in NY & CT –Incentive and Rebate Assistance
Kohler Ronan is an approved Technical Consultant providing valuable assistance to clients interested in accessing incentives in both New York and Connecticut. In New York, we are approved under NYSERDA’s Commercial New Construction Program and also serve as an Independent FlexTech Consultant. As part of the Energize Connecticut initiative, Kohler Ronan is approved for projects within Eversource and United Illuminating territory. Under each of these programs, our professionals provide technical support in the form of energy modeling and controls commissioning to assess and identify appropriate energy efficiency opportunities for new construction and substantial renovation projects. For details, please email Madhav Munshi at mmunshi@kohlerronan.com.
As an example, I looked at Kohler Ronan’s NYC office space. The office can accommodate a maximum of 66 people (counting all desks, conference rooms, and pantry area). The space is served by a dedicated air handling unit delivering 6,000 CFM of supply air. During normal operation, 1,200 CFM of that supply air is fresh outdoor air. Per the Standard, office spaces are required to supply 30 CFM of clean air per person to the space. So, for Kohler Ronan’s office, 1,980 CFM of clean air is necessary in IRMM to be in compliance. During peak occupancy, we would not be in compliance with the Standard; we would need to provide an additional 780 CFM of clean air. During COVID, a standalone air filter with a capacity of 950 CFM was placed in the open seating area to put the firm above the threshold.
As an alternative, if the standalone unit had not been installed, the office could have reduced capacity to limit the space to only 40 people. Other options would have been to increase the amount of outdoor air or install UV lighting in the ductwork to clean the entire airstream.
housed in mechanical equipment rooms (MERs), but these rooms would need to be larger than a typical MER. If not provided for in the MER, the air could be cleaned locally within each space via HEPA filters and recirculation units. These units could be located on the floor in each room; however, this might pose additional architectural challenges. Alternatively, the equipment could be placed above the ceiling, with ductwork connected to grilles and diffusers. This equipment would be in addition to the main HVAC system, so the design team would need to accommodate additional equipment and diffusers within an already crowded reflected ceiling plan (RCP).
Owner Impacts
For the owner, this Standard could be an excellent tool to keep building occupants healthy and well. Studies have highlighted the positive impact on indoor air quality and occupant health and productivity. Improving the indoor air quality is a worthwhile investment not only during a pandemic response, but every day of the year.
first cost to the job, while the equipment itself would likely take valuable square footage either on the roof or within mechanical rooms of the spaces they are serving. Additionally, the operation of aircleaning equipment would also increase energy usage and ongoing operating and maintenance expenses. A large part of the compliance would fall on the end user charged with running and properly maintaining the equipment after design and construction. Finding the right balance between occupant wellbeing and costs will be the key to the Standard’s implementation.
REVIT® CORNER
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Arc hitectural Impacts
For the architect, the Standard warrants additional space for the added equipment. In some cases, all the equipment may be
Lest we think it a simple task, be advised that there are obstacles to overcome when implementing ASHRAE 241. Installing the air cleaning equipment would increase the
If you haven’t already done so, you may wish to test this software with your team.
