A

AFUE

(Annual Fuel Utilization Efficiency) A rating that denotes the efficiency of gas heating equipment. It is the amount of heating your equipment delivers for every dollar spent on fuel. A higher rating indicates more efficient equipment. This rating is calculated in accordance with the Department of Energy test procedures.

Air Change

Replacing the volume of a space in one hour; space volume in cubic feet divided by 60 yields 1.0 Air Change in CFM.

Air densities

The density of dry air at sea level is 0.0745 lb/ft2 at 70F or about 1/800th the density of water. But as altitude and temperature (or both) increases, the density drops dramatically. This is because the density of air is proportional to the pressure and inversely proportional to temperature. And the higher you go into the atmosphere, the lower the pressure gets. Pressure is approximately halved for each additional increase of 56 km in altitude.

Air Handler

A steel cabinet containing a blower with cooling and/or heating coils onnected to it.

Air Transported Moisture

Moisture movement associated with the movement of air from one place to another
by means of a pressure differential.

ASHRAE 62.2

(American Society of Heating, Refrigeration, and Air‐Conditioning Engineers) Published standards for introducing Outside Air for occupant health and comfort; 62.1 for commercial, 62.2 for residential; now adopted into law as part of most building codes. The residential requirement, “Ventilation and Acceptable Air Quality in Low‐Rise Residential Buildings” has been in existence since 2003. The standard describes three primary sets of requirements for acceptable indoor air qualitycontrol in homes; they are whole house ventilation, local exhaust and pollutant. The most common elements are the following:

• Whole house mechanical ventilation using the formula ; Ventilation Rate=7.5cfm
  (number of bedrooms + 1) x (0.01 x Conditioned floor area or home)
• Bathroom exhaust specified at low sone, 50 cfm intermittent or 20cfm continuous
• Kithchens vented to the exterior at 100 cfm intermittent or equivalent to 5 air
  changes per hour if continuous.
• Clothes dryers vented to the outdoors
• Minimum filtration of ducted supply air systems of MERV 6

B

Backdrafting

Reverse flow of combustion gases down the chimney of a vented combustion appliance, which is often caused by depressurization of the room where the appliance is located

Balancing

Process of adjusting the flow of air in duct systems, or water flow in hot-water heating systems

Blower Door

A blower door is a calibrated fan (or blower) in a portable expanding frame, typically installed in an exterior door opening. Blower doors are used to determine the leakiness of a building envelope. A blower door measures the total air flow rate through all of the openings in a house by extracting air from (or blowing it into) the house and measuring the air pressure drop across the house. From this information, the area of all the house cracks and openings can be calculated.

BTU

Amount of energy required to heat one pound of water one Fahrenheit degree.

BTU/hr

British thermal units per hour. A BTU is the quantity of heat required to raise 1 pound of water
by 1 degree Fahrenheit.

Building Science

The relationship of building materials and the building enclosure o heat, air, radiation, and moisture; controlling damage caused by these elements.

C

Capillary action

The ability of water to move through materials, even upward against gravity, through small tubes or spaces.

CFM-cubic foot per minute

Cubic foot/feet per Minute; measure of Airflow.

CFM₅₀

The number of cubic feet per minute of air flowing through the fan housing of a blower door when the house pressure is 50 pascals (0.2 inches of water). This figure is the most common and accurate way of comparing the air tightness of buildings that are tested using a blower door.

Coefficient of Performance (COP):

A ratio calculated by dividing the total heating capacity provided by the heat pump, including circulating fan heat but excluding supplementary resistance heat (Btu's per hour), by the total electrical input (watts) x3.412. (See Heating Seasonal Performance Factor, below.)

Coil

A snakelike piece of copper tubing surrounded by rows of aluminum fin that clamp tightly to the tubing in order to aid in heat transfer.

Condensation

Water changing from vapor to back into liquid; the resulting liquid water.

Conduction

Transfer of heat, but not mass, from warmer to colder regions of a substance, or
adjacent substances in contact.

Convection

Circulation caused by the buoyancy of heated or cooled fluids; more likely a reference to air than to water in HVAC.

Cooling Degree Day

The number of degrees that a day's average temperature is above 65 Fahrenheit,
the temperature at which people will start to use air conditioning to cool their buildings.

D

Data logger

An electronic device that records data over time or in relation to location either with a built in or external instrument or sensors. In home energy auditing, they may be used to monitor various data points, such as temperature, water, humidity, gas flow, power, solar radiation, and wind.

Dehumidification

Removing water vapor from air.

Dew Point Temperature

Water vapor at saturation; 100% RH; colloquial: temperature at which water begins
to condense out of air.

Diffuser

Device installed over openings in room surfaces created for Air-flow that aspirates room air, causing it to mix with the air stream; normally used in ceilings; always a Supply; damper or shutter for regulating Air-flow is described separately.

Diffusion

Is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion.

Dry bulb temperature

Ordinary air temperature; as opposed to wet bulb temperature.

Duct

Conduit through which air is transported; normally modified by state of air as in
Supply Duct, Return Duct, etc.

Duct Blaster

A blower-door-like device used for testing duct leakiness and air flow in a forced
air heating or cooling system.

E

Emissivity

The ability of a material to emit radiant energy from its surface. Also called emittance.

Energy

Energy is power used over a specified time (energy = power x time)
A 3 ton 13 SEER unit draws nearly 3,500 watts (power) while running on full capacity. If it runs for 3
hours a day at full capacity, how much energy does it consume in the 3 hours?
(Answer: 10.5 kWh)

ERV

Or Energy/Enthalpy‐Recovery Ventilator – a ventilator that recovers latent and sensible energy from the exhaust airstream and imparts it to the incoming airstream. The main difference between an ERV & HRV, is that in an ERV the heat exchanger transfers a certain amount of water vapor along with heat energy, while a HRV only transfers heat.

ESP

EXTERNAL STATIC PRESSURE – The sum of the static and velocity pressures of moving
air system at the point of measurement.

Evaporation

Water changing from liquid into vapor.

Evaporator

The heat transfer coil of an air conditioner or heat pump that cools the surrounding air as the refrigerant.

Exfiltration

Room air lost from a space through cracks due to positive pressure.

Exhaust Air

The air flow leaving the conditioned space and discharged to the outdoors.

F

Face velocity

Is the average velocity of air passing through the face of an outlet or return.

Flow hood

Diagnostic tool used to measure air flow through ducts, supply registers, and return grilles.

Flow Plate

Or TrueFlow Air Handler Meter is a device designed to provide a simple and accurate measurement
of air flow through residential air handlers. Flows can be measured between 400 cfm and 2,200 cfm.

G

Geothermal/
GeoExchange Equipment

Heat pumps that uses the ground to transfer heat to and from the refrigerant in the unit. The unit circulates water through a heat exchanger in to a closed loop buried in the ground or by pumping water from a well through the unit.

H

Heating Degree Day (HDD)

A form of degree-day used as an indication of fuel consumption; in United States usage, one heating degree-day is given for each degree that the daily mean temperature departs below the base of 65°F. The number of degrees that a day's average temperature is below 65Fahrenheit (18Celsius), the temperature below which buildings need to be heated.

Heat Transfer

The science of estimating the amount, rate, and direction of heat flow; an inexact
science bounded by the Laws of Thermodynamics.

HRV

This device brings fresh, outside air into a home while simultaneously exhausting stale indoor air outside. In the process of doing this, an HRV removes heat from the exhaust air and transfers it to the incoming air, pre-heating it.

Humidity

The water vapor component of moist air.

I

Infiltration

Outside air introduced naturally through cracks due to wind and/or negative pressure.

Infrared Camera

Also called a thermographic camera, an “IR” camera is a device that forms an image using infrared radiation, similar to a common camera which forms an image using visible light.

J

Jump duct

Colloquial; transfer air duct.

K

kWh

One kWh is equivalent to 1,000 watt power draw over a 60 minute interval.
One kWh is equal to 3600 kilojoules or 3412 BTUs.

L

Latent heat of air

Energy removed from air due to the condensation of moisture.

Liquid Flow

Typically the flow of liquid moisture via gravity or capillarity.

Low-e

Short for low emissivity, which means the characteristic of a metallic glass coating to resist
the flow of radiant heat.

M

Manometer

Measuring device for fluid pressures. A digital manometer measures the air pressure relationship between two spaces, providing the magnitude of the pressure difference (if one exists) rather than just the direction.

Moisture meter

A moisture meter is a device which can check for moisture content in drywall, insulation, wood,
concrete and plaster. It can also assist in tracing leaks and finding exterior moisture sources.

N

NACH

The natural air changes per hour in a building, as calculated by dividing by the LBL ACH₅₀ Factor.
The number of cubic feet of air flowing through a house from indoors to outdoors during typical, natural conditions. This figure can be roughly estimated using a blower door, and can also be denoted as (natural air changes/hour or NACH or ACHnat)

P

Pascal

A unit of measurement of air pressure.

Perm

A measurement of how much water vapor a material will let pass through it per unit of time OR Semipermeable: speed at which water molecules pass through a material by diffusion (see diffusion).

Plenum

Relatively large chamber in an air duct or pathway experiencing low air velocity.

Pressure

A force encouraging flow by virtue of a difference in some condition between two areas.

Power

(units of energy): Electrical power is usually measured in watt (W), kilowatt megawatt (MW), etc. Power is energy transfer per unit of time.

Pressure drop

The decrease in pressure due to friction of a fluid or vapor as it passes through a tube or duct or/and lift.

Psychro-metrics

The science of the relationship between air, water vapor, and heat.

R

Radiation

Transfer of heat through space without the benefit of an intervening medium.

Retarder

Building enclosure element intended to slow penetration. Example: thermal insulation.

Return Air

Air drawn into a heating unit after having been circulated from the heater's output supply to a room.

R-Value

A measurement of thermal resistance to conductive heat flow through a material. R-value is primarily
for labeling insulation products. It is the inverse of the U-Value; R-value = 1/U-value

S

SEER

Cooling Efficiency. "SEER" is a measure of cooling efficiency for air conditioning products. SEER stands for Seasonal Energy Efficiency Ratio. The higher the SEER rating number, the more energy efficient the unit. The government's established minimum rating typical residential split air conditioning system is 13. SEER is calculated by the amount of heat removed, divided by the electrical input power.

Sensible heat

Energy removed from air due to cooling (as opposed to Latent eat). OR- Heat that can be measured or felt. Sensible heat always causes a temperature rise.

Smoke pencil

A smoke pencil is typically a hand-held device that emits a chemical smoke when squeezed. Smoke pencils can be used to quickly and accurately determine the air pressure relationship between two spaces - for example, between the indoors and outdoors or between a bedroom and the space inside the wall separating the bedroom from the hallway. If smoke gets sucked into a crack or opening, the smoke pencil is located in a region of positive air pressure with respect to the crack.

Solar Heat Gain Coefficient (SHGC)

The ratio of solar heat gain through a window to incident solar heat. Includes both
transmitted heat and absorbed and reradiated heat.

Sone

Measures the loudness of appliances like range hoods. One sone is about equal to a refrigerator running, while four is equivalent to normal conversation. This is a subjective unit of loudness, as perceived by a person with normal hearing, equal to the loudness of a pure tone having a frequency of 1,000 hertz at 40 decibels.

Solar reflectance

of an object is the extent to which if diffusely reflect light from the sun. It is therefore a more specific form of the term reflectivity. The percent of total solar energy reflected by a material. This is associated with many products today as an SRI on a scale of 0 to 1. (zero absorbing all visible light and 1 reflecting all)

Specific Heat

The amount of heat necessary to change the temperature of one pound of a substance 1 F.

Static pressure

The normal force per unit area at a small hole in the wall of a duct in respect to HVAC).

Supply

The ductwork that carries conditioned air from the air handler to the ooms in the house.

T

Temperature

A measurement of heat intensity.

Terminal Velocity

(fluid mechanics) The velocity with which a body moves relative to a fluid when the resultant force acting on it (due to friction, gravity, and so forth) is zero. In context of this class: Air begins to fall vertically when it slows to certain speed. (usually at a velocity 50-75 feet per minute)

Throw

Is the distance (measured in feet) that the air stream travels from the outlet to the point of terminal velocity. Throw is measured vertically from perimeter diffusers and horizontally from registers and ceiling diffusers.

Ton

Heat pumps and air conditioners are generally sized in tons. Typical sizes for single family residences are between two and five tons. Each ton equals 12,000 Btuh. It is important to note that actual capacity is not constant and will change based on outdoor or indoor temperatures. The published capacity rating of air conditioners and heat pumps is based on performance at the ARI standard temperature levels of 95 F outside, 80 F inside.

Total Heat

Total heat energy in a substance. The sum of both latant and sensible heat.

ΔT

T.D., Temperature Difference measured between 2 objects or environments.

U

Uvalue or UFactor

The amount of heat that will flow through a square foot of building cross‐section experiencing a temperature difference of 1° F.

V

Vapor

Any gas at a combination of temperature and pressure placing it very close to its dew point (saturation).

W

Wet bulb temperature

Temperature of wet wick slung through the air so that it cools by evaporation; surrogate for enthalpy; fortuitous phenomenon, has no scientific basis.