How a Marlo Stratomizer Works

February 27, 2023


The Marlo Stratomizer® Dampered Face and Bypass Coil – also known as an Integral Face and Bypass Coil (IFB) – provides the most reliable method of preheating and tempering fresh outside air. The coil sections maintain full steam pressure or constant hot water flow to the coil at all times to virtually eliminate freezing.

The Stratomizer can provide significant benefits in a wide range of applications, particularly in climates where temperatures can fall below or near freezing. The main advantages include protection against freezing, constant airflow and more accurate temperature control. Stratomizers can be added to air handling units (AHUs) to pre-heat the air entering the unit, or be used to heat make-up air entering the building.

Challenges without a Stratomizer

The need for the Stratomizer was born out of the fact that standard steam and hot water coils are not consistent at warming cold air entering a building. In traditional systems, steam (in steam coils) or water temperature (in hot water coils) is modulated in an attempt to control the temperature of incoming air. But this can often result in condensate building up and freezing inside the coils, which can cause the tubes within the coil to burst. Also, with this method, accurately controlling exiting air temperature can be very difficult.

One solution to overcome these problems would be to use a separate heating coil to heat incoming air. However, this drastically increases costs – including the original coil purchase price, as well as installation and maintenance costs. Another option would be to use a more traditional face and bypass configuration, which includes a face and bypass damper. This can help mix the incoming cold air with heated air, but not nearly as effectively or efficiently as the multiple dampers inside a Stratomizer. In addition, the Stratomizer does a better job of mixing the air in a much shorter distance downstream of the unit, creating a more uniform temperature. 

How the Stratomizer offers the perfect solution

The Marlo Stratomizer consists of multiple heating coils, each featuring specially designed damper blades (also referred to as vanes) which open and close in virtually limitless positions to precisely mix the cold bypass air with the air heated by the coils. Multiple smaller bypass and heated airstreams, which are intermixed, not only provide better mixing, but also do it closer to the coils – not far downstream as in older face and bypass systems. The result is much more accurate downstream temperature control.

The positioning of the damper blades is controlled by temperature sensors in the downstream air. The blades open and close to correctly proportion the heated and bypass air to maintain the designated discharge air temperature. Therefore, the preset discharge air temperature is maintained, despite any and all variations in the inlet air temperature.

Maximum coil freeze protection

With the Stratomizer, the steam pressure or hot water flow to the coils is never modulated, as in legacy systems. To the contrary, the coils operate with full stream pressure or maximum water flow at all times, generating constant heat. Again, it is the proportioning of the incoming and heated air, via the continual repositioning of the damper blades, that achieves accurate exiting air temperature. As a result, the full steam pressure or constant water flow eliminates the possibility of the coils freezing.

Customized to meet specific needs

While the basic function and advantages remain the same, each Stratomizer is customized to meet the individual needs of the application. You can select the Stratomizer using our MarloMetrics® configurator software to meet your requirements for airflow and downstream air temperature, depending on your specific system and climate conditions.

We can add special features, such as 1” tubes (rather than our standard 5/8” tubes), your choice of heavy-duty copper, steel or stainless steel headers, and any number of other options. All Stratomizers feature extruded, anodized aluminum damper blades with neoprene blade seals. These heavy-duty blades won’t rust and don’t flex, which minimizes air leakage, resulting in tighter temperature control and more precise downstream temperatures. In addition, unlike other face and bypass coils, all of the Stratomizer’s linkages are made of non-ferrous metal and are positioned outside the air stream, so they are not subjected to dirt and debris that can impact performance.

The Stratomizer is more important today than ever before

After the Covid-19 pandemic, both ASHRAE and the CDC continue to recommend that building HVAC systems bring in more outside air – up to 100% if possible. In colder climates, a Marlo Stratomizer dampered face and bypass coil can make this easier and much more efficient. By preheating cold incoming air, the Stratomizer can lessen the load on your HVAC system and minimize energy usage and costs – while also offering reliable freeze protection.

Learn more about the Stratomizer, and contact your Marlo Independent Manufacturer’s Representative (IMR) if you have any question or want to discuss your individual needs. Or you can always send us an email at [email protected].

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