Air-handling unit

Air changes per hour

How many times the air in a building is changed on an hourly basis

Airflow proving switches
Airflow sensing device to prevent humidification during insufficient airflow

Alternate water seal
Nonstandard P-trap configuration installed before the drain valve on a steam generator

Amps / Current (I)
Measure of the flow of electricity; current is measured in Amps

Controller language

British standard pipe thread

Building volume
Interior building volume (i.e., ft3 or m3)

Condensate pump
Pump used to push condensate to a more desirable location

Control cabinet with time delay
Control cabinet includes the component that can delay the opening and closing of a valve or relay based on demand

Desired conditions
The desired final relative humidity and dry bulb temperature of a space

Dew point temperature
The saturation temperature corresponding to the humidity ratio and pressure of a given moist-air state

Dew point transmitter
Sensing device based on dew-point used to control demand for a humidifier

Direct steam
Live or pressurized steam as from a boiler

Dispersion product
Steam distributor

Dispersion tube insulation
Insulation applied to dispersion tubes to limit air heat gain and associated condensate losses

(Diameter Nominal) Nominal piping measurement in millimeters

Drip-tee kit
Includes an inline tee connector, two hose cuffs, and four hose clamps

Dry bulb temperature
The temperature of the air indicated by any type of thermometer or thermocouple that has not been affected by evaporation or radiation

A channel or tube for conveying air

End-of-season drain
Opening a drain valve automatically after a period of non-use

F&T trap
Float and Thermostatic trap

Face height
Height of a dispersion assembly area where humidification steam is dispersed

Face width
Width of a dispersion assembly area where humidification steam is dispersed

A bolt-together fitting

Flange, screw-on
Flange that is screwed to a threaded nipple

Generation product

Atmospheric steam generator

Grains of moisture
Mass of water in grains per mass of dry air (i.e., grains/lb dry air or grains/kg dry air)

Hand direction
Right handed or left handed orientation of steam dispersion tube. Facing into the airstream, where separator is located is the hand direction (left or right).

Hard pipe kit
Includes two hose cuffs and four hose clamps

Header, dispersion assembly
Central steam distribution pipe of a dispersion assembly

Headers inside

Central steam distribution pipe of a dispersion assembly is installed inside a duct or air handling unit

Headers outside
Central distribution pipe of a dispersion assembly is installed outside a duct or air handling unit

Heat gain from assembly
Heat transferred to the air from a dispersion assembly, which can be reduced with insulation

Heat gain from steam
Irreducible heat gain when steam is dispersed into air

High-limit humidistats
Humidity sensing device used to reduce or stop steam generation if airstream is close to saturation

Infiltration volume
Air volume entering a ventilation system through exterior openings (i.e., windows, doors, or leakage)

Input signal
Control signal

Insulation, dispersion tube (nonpressurized steam)
PVDF insulation applied to a dispersion tube

Insulation, dispersion tube jacketed (pressurized steam)
Sheet steel wrapper with insulation between the dispersion tube and wrapper

Insulation, tank
Insulation placed on a humidifier to prevent hot surfaces

Interconnecting piping
The pipe between a steam generator and dispersion assembly

Operability between humidifier and building management system, using a language such as LonTalk, BACnet, or Modbus

IP 66 cabinet
Control cabinet with dust and drip-proof rating

I-P units
Inch/pound measurement

Communication jack

Kilograms per hour


Pounds per hour

Quantity of moisture required to meet relative humidity (RH) requirements (i.e., lbs/hr or kg/h)

Load plus loss
Total moisture required to meet the relative humidity plus offset steam lost as condensate formed in steam piping, measured in lbs/hr or kg/h

Control language used to communicate

Low-water float switch
Low water cutoff

Makeup-air ventilation system
Ventilation system with only outside air

Mixed-air ventilation system
Ventilation system with both return air and outside air

Control language used to communicate

Modulating humidistat
Humidistat that produces a modulating control signal

Term similar to a dozen except that the number of things in a dozen is 12, and the number of things in a mole is 6.023 x 1023. Avagadro figured out that this is the number of atoms (or molecules) in the atomic (molecular) weight of that substance expressed in grams. For example, the molecular weight of water is 18 so, a mole of water molecules has a weight of 18 grams (18 g/mole).

At least two atoms held together by covalent bonds. Molecules are neutral
because they do not have a net charge like ions. Water (H2O) is a molecule.

Molecular weight
Molecular weight is determined by adding the atomic weights of each element in a molecule. The atomic weight for hydrogen is 1 (its nucleus contains only 1 proton), and oxygen’s atomic weight is 16 (its nucleus contains 8 protons and 8 neutrons for a total of 16). So, H2O has a molecular weight of 18. PH pH is a measure of the acid or base levels of the water. H+ is acidic and OH- is basic. The pH range is 0 to 14. The number is technically the negative log10 of the H+ ion concentration. 7 is neutral (hydrogen ions and hydroxyl ions are equal). > 7 is basic (hydroxyl ions are greater than hydrogen ions). < 7 is acidic (hydrogen ions are greater than the hydroxyl ions).

Multiple-tank control
Single-point control of multiple humidifiers

Natural ventilation system
Ventilation system without the use of a mechanical device

NEMA-1 safety switch
External disconnect for electric humidifier

NEMA-12 cabinet
Control cabinet with dust proof rating

NEMA-4 cabinet
Control cabinet with dust and drip proof rating

Nonpressurized steam dispersion
Dispersion systems designed to accept steam from DriSteem steam generators

National pipe thread

Open space
Area with no ductwork

Outside air intake rate
Rate at which outside air enters a ventilation system

Outside air volume
Air volume entering a ventilation system from outside

Outside conditions
The outside dry bulb temperature and relative humidity

Pilot positioner
Positioning a valve using a pilot air control signal

Polyvalent ion
An ion that has a charge greater than one.

Potable water

Tap (or drinking) water

Pressurized steam dispersion
Direct or live steam dispersion product

Project, DriCalc
Job name or reference number

Redundant tank
Backup system or tank

Relative humidity (RH)
The wetness or dryness of air at a given temperature and pressure

Remote temperature sensor
Prevents condensation on structural members

The minimum nonwetting height above the steam outlet

RO/DI water
Reverse-Osmosis filtered, or DeIonized water

Same-side piping
Steam supply and condensate connection are on same side of the steam dispersion assembly

Sealed combustion
Air for combustion is ducted directly to a humidifier

Seismic certified
Humidification equipment that has gone through third party shake testing to validate operation after a seismic event. May have additional or different support methods or structural enhancements

Steam and condensate separating device

Separator orientation
Separator may be in the upright or horizontal position

SI units
System International metric unit system

Softened water
Water where calcium and magnesium ions have been replaced with sodium ions

Solenoid valve
Electromagnetic valve

The minimum nonwetting width from the steam outlet

SSR sequencing modulation
One heater stage is controlled by a Solid-State Relay while others are controlled contactors

SSR, 100%, modulation
All heater stages are controlled by a Solid-State Relay

Steam dispersion enclosure
Box that contains the header

Steam dispersion panel
Dispersion system with a frame or case

Steam hose
Hose that connects a steam generator to a dispersion assembly and designed to withstand high temperatures

Steam trap
Device that prevents steam flow but allows condensate to flow through

Steam valve Cv/Kv
Flow coefficient of a valve

Steam valve size
Inlet and outlet size of the steam valve body

Generating nonpressurized steam via direct steam and a heat exchanger

Steam filter upstream of the steam valve to remove debris

System (DriCalc)
Humidification system for a space

Tag name
Individual humidifier identification

Temperature switch
Temperature activated switch prevents the operation of a control valve

The minimum nonwetting horizontal distance from the steam outlet

Total air volume
Total volume of air in a ventilation system

Total dissolved solids (TDS)
All substances that are dissolved in the water. Principal TDS contributors: calcium and magnesium carbonates and bicarbonates (principal scale forming substances) among others.

TP modulation
Time-proportioned modulation

Hanging support system for a humidifier

Tube spacing on-center
Spacing between dispersion tubes, measured from the tube center line

Thin walled pipe designed to withstand high temperatures

Tubing, insulated
Thin walled pipe with insulating cover

Volts alternating current

Valve control, electric
Electric control signal for steam valve(s)

Valve control, pneumatic
Pneumatic control signal for steam valve(s)

Venting, horizontal
Side wall venting

Weather cover
Enclosure that prevents rain from wetting humidifier components

Wet bulb temperature

An expression of the temperature of the air when a wick or sock, wetted with water, encases the sensing element of a dry bulb thermometer and air is passed over it at a velocity of 700 feet per minute or more

Y connector kit
Includes a Y connector, three hose cuffs, and six hose clamps