Introduction to HVAC Heating Ventilation Air Conditioning Content

Introduction to HVAC Heating, Ventilation, & Air Conditioning

Content covered: u Terminology, principles & properties of air relevant to IAQ. u Primary HVAC system functions and their impact on IAQ. u Major HVAC system components & configurations used to perform these functions.

Part I - Air u Terminology u Principles u Properties

Dry Air Approximate Composition (by volume): 78. 0 % 20. 9 % 1. 0 % 0. 1 % Nitrogen Oxygen Argon Other Gases

Wet Air = Dry Air + Water Vapor

Wet Air Composition Approximate Composition: 78. 0 % 20. 9 % 1 -2% 1% 0. 1 % Nitrogen Oxygen Water Vapor Argon Other Gases

Answer: “Billions and Billions. . . ” Question: How many molecules of air are in this room?

Answer: Really fast! Question: How fast do air molecules typically move?

Pressure = Force / Area u The total force exerted upon a given surface at any instant divided by the area of that surface u Expressed in “pounds per square inch” (psi)

Barometric Pressure u The total force of all air molecules impacting a given surface at a given instant in time divided by the area u AKA: “Atmospheric Pressure” u Measured using a barometer and stated in “inches of mercury”

Trick Question #1 u Which weighs more: 1 cubic ft. of dry air or 1 cubic ft. of humid air?

Air Density u Mass u At of air per unit volume 70 ° F. , the density of dry air is 75 lbs. per 1000 cubic ft.

Why Does Warm Air Rise? As the temperature increases, Causing its density to DECREASE

Vapor A gas which may condense to a liquid at normal temperatures Water Vapor is actually H 2 O gas occurring in a mixture with dry air.

Relative Humidity (RH) Ratio of the amount of moisture present in the air to the maximum amount which it can hold at saturation at a given temperature

Human Thermal Comfort u Defined in terms of both temperature AND relative humidity u ASHRAE Standard 55 -1992 contains a chart for determining human thermal comfort

Trick Question #2 u Which can hold more water vapor: WARM air or COOL air?

Sensible Heat The amount of heat which when added to air causes a change in temperature with NO CHANGE in the amount of water vapor present

Latent Heat The heat content of the water vapor present in the air

Total Heat = Sensible Heat + Latent Heat

Part II u HVAC System Functions u Impact on Indoor Air Quality

The Basics Heating Ventilation Air Conditioning

HVAC System Functions u Heating u Cooling u Ventilation u Filtration u Dehumidification u Humidification u Distribution

Impact on IAQ Over 50% of all IAQ problems are due to Inadequate Ventilation!