Brochure

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Particulate: Small liquid or solid particles found in
air or emissions. Airborne particles can be gener-
ated as a result of a mechanical break up of solid
matter (“coarse particles”) or through chemical
reactions or condensing gases (“fine particles”).
Typically measured in micrometers, particle sizes
vary greatly in size and therefore behavior.
Particles greater than 1 micron tend to settle out
of the atmosphere but remain suspended given
sufficient air currents. Particles ranging from
0.1 to 1 micron tend to stay airborne with the
slightest air movement, and smaller than 0.1 will
typically remain suspended indefinitely.
PELs: Permissible Exposure Limits (standards set
by the Occupational, Safety and Health Adminis-
tration, OSHA).
Pickup: Additional heat needed to warm the water
in a hydronic heating system after a period of off-
time such as overnight.
Plenum: Air compartment connected to a duct
or ducts.
Pollutant pathways: Avenues for distribution of
pollutants in a building. HVAC systems are the
primary pathways in most buildings; however all
building components interact to affect how air
movement distributes pollutants.
Positive pressure: Condition that exists when
more air is supplied to a space than is exhausted,
so the air pressure within that space is greater
than that in surrounding areas. Under this
condition, if an opening exists, air will flow from
the positively pressurized space into surrounding
areas.
Pressure drop: Decrease in water pressure caused
by friction between water and the inside surface
of a pipe as the water moves through the pipe.
Static pressure: In flowing air, the total pressure
minus velocity pressure. The portion of the pres-
sure that pushes equally in all directions.
Total pressure: In flowing air, the sum of the static
pressure and the velocity pressure.
Velocity pressure: In flowing air, the pressure due
to the velocity, and density of the air.
Radiant heat transfer: Radiant heat transfer
occurs when there is a large difference between
the temperatures of two surfaces that are exposed
to each other, but are not touching.
Register: Device that covers the opening of
the supply ductwork.
Reheat: Heat supplied at the point of use while
a ventilated air supply comes from a central
location.
Relative humidity (rh): Amount of moisture in the
air compared to the amount of moisture the air
would hold if it were saturated.
RELs: Recommended Exposure Limits (recom-
mendations made by the National Institute for
Occupational Safety and Health (NIOSH)).
Respirable particles: Airborne particles that are of
a size that can penetrate into the lower respira-
tory tract. Such particles are often labeled “PM
10
”
particles, which include particulate matter with a
diameter of 10 micrometers or less.
Return air: The air that is removed from a space
and recirculated or exhausted to the outside.
RMS: “root mean square.” It comes from a math-
ematical formula that calculates the “effective”
value (or heating value) of any ac wave shape.
“True-rms” calculates the heating value based
upon the rms formula, providing an accurate value
regardless of the wave shape.
Saturated air: Air which cannot hold more mois-
ture, where the addition of moisture will result in
condensation.
SEER: The Seasonal Energy Efficiency Ratio is a
measure of the cooling efficiency of an air con-
ditioner or heat pump. The ratio is defined as the
total output provided by the unit over a typical
usage period divided by the total energy input
over the same period of time. The higher the
SEER number, the more efficient the system is at
converting electricity into cooling power.
Sensible heat: Heat that does not involve a change
of state measured with a thermometer or sensed
by a person.
Setpoint temperature: 1. In a forced-air heating
system, the temperature at which the switch in
a thermostat opens and closes. 2. In a hydronic
heating system, the temperature at which the
boiler water is maintained.
Sick building syndrome (SBS): Term that refers
to a set of symptoms that affect some number of
building occupants during the time they spend in
the building and diminish or go away during peri-
ods when they leave the building. Cannot be traced
to specific pollutants or sources within the building.
(Contrast with “Building related illness”).
Sources: Sources of indoor air pollutants. Indoor
air pollutants can originate within the building
or be drawn in from outdoors. Common sources
include people, room furnishings such as carpet-
ing, photocopiers, art supplies, etc.
Specific heat: Ability of a material to hold heat.
Expressed as the ratio of the quantity of heat
required to raise the temperature of a substance
1 °F to that required to raise the temperature of an
equal mass of water 1 °F
Stack effect: The overall upward movement of
air inside a building that results from heated
air rising and escaping through openings in the
building super structure, thus causing an indoor
pressure level lower than that in the soil gas
beneath or surrounding the building foundation.
A detailed list of heating,
air conditioning, and HVAC terms
Glossary