By Chad Edmondson (JMP) and Norman Hall (RLD)
Last week, we reviewed different types of steam humidifier distribution methods, which are inexpensive but have longer absorption distances. Many HVAC installations require very short or non-wetting absorption distances. Humidifier distribution panels provide solutions to this requirement. This week we'll review the options for these dispersion methods.
Panel Style Dispersion Choices for Steam Humidifiers
There are a variety of panel-style distribution options to add humidification steam into ducts. DriSteem offers several within their Ultrasorb line. Each is somewhat distinct and it is important to understand the differences before settling on a specific model for a given application.
Once in a while the job conditions require the dispersion tubes in a vertical duct. The air flow direction moves straight down from an AHU through the duct. In this case, you would need a dispersion panel with the horizontal tubes, e.g. an Ultrasorb LH. This application is only available with non-pressurized humidifiers such as the electric gas or steam-to-steam units.
If the air flow is horizontal, whether in the AHU or in the ductwork, there are a number of panel style choices, based on capacities and cost.
The Ultrasorb MP provides capacities up to 2720 PPH and is the lowest installed cost choice for the engineer to specify. The panel, unless very large, is normally shipped assembled and includes the headers. The steam supply and condensate return are accomplished in a single fabricated header located at the bottom of the assembly. These benefits reduce the installed cost. This lower installed cost panel is also available with high efficiency tubes as an option.
Both the LH and LV panels (see below) offer capacities up to 4000 PPH. The choice of horizontal or vertical tubes depends on the steam supply means (generator or pressurized steam) and the air flow direction (vertical or horizontal). Your sales representative can assist you in the selection. This middle-of-the-road first-cost panel is also available with high-efficiency tubes as an option.
Another model, the Ultrasorb XV, carries a higher cost, but it's loaded with value. The humidifier is shipped assembled unless dimensions exceed 98” or as requested. This panel comes standard with high-efficiency tubes, which reduce the number of tubes required and the heat gain to the air. The XV has an internal heat exchanger to allow low-pressure condensate to be returned to the boiler without the need of a condensate pump. The condensate can be lifted, subject to steam pressure, with a steam trap and check valve up to a condensate return main. This unique panel has two steam inlet connections and is ideal for use with pressurized steam or steam-to-steam humidifiers.
Why Specify High-Efficiency Tubes?
Steam humidifiers are used most often in institutional and larger commercial buildings. One key drawback is the heat gain to the air in the duct. Most manufacturers of panel-style humidifiers provide insulation on the tubes as an option.
What's the difference between standard insulation and high-efficiency insulation? Standard insulation on humidifier tubes may be ceramic-coated with a thermal insulated coating known as TIC, or stainless steel shielded with an air gap. The high-efficiency PVDF insulation option has an “R” value over three times that of these other standard tubes. This reduces wasted energy and condensate up to 85%.
You can read more about insulation and the effect on operating costs. (This chart was taken from that article.)
Next week we'll conclude the humidification series with a discussion about condensate handling.