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Systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more

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Air - Density and Specific Volume vs. Altitude

Density and specific volume of air varies with elevation above sea level.

Air Change Rate

Calculate air change rates - equations in imperial and SI units

Air Change Rates in typical Rooms and Buildings

Fresh air - or make up air - requirements - recommended air change rates - ACH - for typical rooms and buildings - auditoriums, kitchens, churches and more

Air Curtains and Air Screens

Air curtains or air screens in open doorways are used to keep acceptable indoor comfort in buildings

Air Duct Components and Minor Dynamic Loss Coefficients

Minor loss - pressure or head loss - coefficients for air duct distribution systems components

Air Ducts - Friction Loss Diagram

A major loss diagram for air ducts - Imperial units ranging 10 - 100 000 cfm

Air Ducts - Friction Loss Diagram

Major loss diagram for air ducts - in imperial units ranging 10 000 - 400 000 cfm

Air Ducts - Friction Loss Diagram

Major loss diagram for air ducts - SI units

Air Ducts - Sizing

Air flow and required duct area

Air Ducts - Temperature, Pressure and Friction Loss

Temperature and air pressure influence on air ducts friction loss

Air Ducts - Velocity Diagram

Air flow volume, duct size, velocity and dynamic pressure

Air Ducts Minor Loss Coefficient Diagrams

Minor loss coefficient diagrams for air ductwork, bends, expansions, inlets and outletsĀ  - SI units

Air Filter Arrestance and Efficiency

Air filters efficiency and arrestance

Air Flow Velocity due to Natural Draft

Air flow - volume and velocity - due to stack or flue effect caused by indoor hot and outdoor cold temperature difference

Air Heating Systems

Using air to heat buildings - temperature rise diagram

Air Intakes and Outlets

Ventilation systems - air intakes and outlets - rules of thumbs

Air Return Intakes - Sizes and Capacities

Size and capacity of air return intake

ASHRAE - American Society of Heating, Refrigerating and Air-Conditioning Engineers

ASHRAE Standards

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Belt driven Fans - Motor and Fan Speed

Speed of Fan versus Speed of Motor

Belt Transmissions - Length and Speed of Belt

Length and speed of belt and belt gearing

Carbon Dioxide Concentration in Rooms with People

The carbon dioxide concentration in a room can indicate air quality and ventilation system efficiency

Carbon Monoxide and Health Effects

Exposure to Carbon Monoxide - CO and the health effects

Circular Ducts - Dimensions

Sizes of circular ventilation air ducts

Classification of Ventilation Dampers

Dampers in ventilation systems may be classified through function, construction or leakage class

Classification of Ventilation Systems

Ventilation systems can be classified by functions, distribution strategies or by ventilation principles

Clean Rooms - Federal Standard 209

Clean rooms are maintained virtually free of contaminants like dust or bacteria

Clean Rooms - ISO Standard 14644

The clean room class limits according ISO Standard 14644-1

Colebrook Equation

Calculate friction loss coefficients in pipes, tubes and ducts

Design of Ventilation Systems

Design procedure for ventilation systems - air flow rates, heat and cooling loads, air shifts according occupants, air supply principles

Duct Sizing - Equal Friction Method

The equal friction method for sizing air ducts is easy and straightforward to use

Duct Velocity

Calculate velocities in circular and rectangular ducts - imperial and SI-units - online calculator

Ducts - Diameter and Cross-Sectional Area

Circular ducts and cross-sectional areas

Ducts - Sheet Metal Gauges

Sheet metal gauges used in ductwork

Ducts Sizing - Velocity Reduction Method

The velocity reduction method can be used for sizing air ducts

Ductwork Seal Classes

Ductwork prone to air leakages

Ductwork Support

Ductwork support and recommended distance between hangers

Energy Equation - Pressure Head Loss in Ducts, Tubes and Pipes

Pressure and head loss in ducts, pipes and tubes

Equivalent Diameter

Convert rectangular and oval duct geometry to a equivalent circular diameter - online calculator with imperial and SI-units

Equivalent Diameter - Rectangular and Circular HVAC Ducts

Equivalent diameter for rectangular and circular ducts - air flows between 100 - 50000 cfm

Evacuation of Air - minimum Capture Velocities to avoid Pollution products transferred to the Room

Capture velocity to avoid pollution products from galvanic baths, spray painting boxes and more contaminating the surrounding room and environment

Exhaust Hoods

Sizing exhaust hoods - air volume flow and capture velocities - online exhaust hood calculator

Exhaust Outlets - Capturing Air Velocities

Capturing air velocity in front of an exhaust outlet - online exhaust outlet velocitycalculator

Fan Affinity Laws

Affinity laws can be used to calculate volume capacity, head or power consumption when speed and wheel diameters are changed

Fan Capacity Diagrams

Pressure, head, air flow volume and fan capacity diagrams

Fan Classification - AMCA

Fan classification established by AMCA

Fan Inlet - Suction Pressure and Air Density

High suction pressure at a fan inlet decreases the density of air - and should be corrected for proper selection of the fan

Fan Motors - Starting Torques

A fan motor must be capable of accelerating the fan wheel to operating speed

Fan Troubleshooting

Guide to troubleshooting fan problems

Fans - Air Temperature and Volume Flow, Pressure Head and Power Consumption

The temperature and density of the air influences on the volume flow, pressure head and power consumption in a fan

Fans - Calculate Air and Brake Horsepower

AHP - Air Horse Power and BHP - Brake Horse Power

Fans - Efficiency and Power Consumption

Power consumption and typical efficiencies of fans

Fans and Capacity Control

Modulating fans and their capacities

Free Area Ventilation

Ventilation required for attic areas

Friction Head Loss in Air Ducts - Online Calculator

Head loss or major loss in air ducts - equations and online calculator for rectangular and circular ducts - Imperial and SI units

Garage Ventilation

Exhaust ventilation from garages and workshops

Gas Vent Termination - Clearance Tolerances

Clearance tolerance per roof slope for gas vent terminations - vent caps

Heat Recovery

Ventilation and heat-recovery calculations, sensible and latent heat -online calculators - imperial units

Heat Recovery Efficiences

Classification of heat recovery efficiencies - temperature efficiency, moisture efficiency and enthalpy efficiency - online heat exchanger efficiency calculator.

Heaters and Coolers in Ventilation Systems

The basic equations for heat transfer and the selecting criteria for heaters and coolers in ventilations systems


Sprayed coils, spinning discs and steam humidifiers

HVAC Dampers - Pressure Loss

Pressure head loss in HVAC damper

HVAC Diagram - Online Drawing Tool

Draw HVAC diagrams online with this Google Drive drawing tool.

HVAC Ducts - Air Velocities

Ductwork and recommended air velocities

Hydraulic Diameter

Hydraulic diameter of pipes and ducts

Indoor Design Climate Conditions for Industrial Product and Production Processes

Recommended indoor temperature and humidity for some common industrial products and production processes

Indoor Design Temperatures

Recommended indoor temperatures summer and winter

Industrial Environments - Selecting Ventilation System

A quick selection guide for ventilation systems and principles in industrial environments

Mechanical Energy and the Bernoulli Equation

The mechanical energy equation related to energy per unit mass, energy per unit volume and energy per unit weight involving head

Minor Loss Resistance in Ventilation Ducts

Air velocity, minor loss coefficient and minor loss in ventilation duct-works

Odor from Persons - Required Ventilation

Odor and smell - required air ventilation

Odor Intensity from Persons

Room volume, ventilation and odor intensity from persons

Online Air Duct Calculator

Online calculator to compute the friction loss in air ducts

Pollution Concentration in Rooms

Concentration of a pollution in a limited space as a room depends on the amount of polluted material spread in the room, supply of fresh air, outlets positions and construction, principles used for supply and outlet from the space

Pressure Classifications of Duct Systems

Duct systems are commonly divided into three pressure classifications

Pressure Loss in Ventilation Components

Pressure drops in common ventilation system components - like dampers, filters, heaters, coolers

Pumps, Compressors, Blowers and Fans

Comparing pumps, compressors, blowers and fans

Rates of Outdoor Supply Air

Recommended rates of outdoor make up air in some common types of rooms - banks, assembly halls, hotels and many more. Smoking and air supply rates

Rectangular Air Ducts - Velocity Diagram

Velocity diagram for rectangular air ducts - metric units

Rectangular Ducts - Commonly used Dimensions

Metric dimensions of commonly used rectangular air ducts in ventilation systems

Rectangular Ducts - Hydraulic Diameter

Hydraulic diameter for rectangular ducts - metric units

Relative Humidity in Production and Process Environments

Recommended relative humidity in production and process environments - like libraries, breweries, storages and more.

Required Air to Remove Moisture

Air flow required to remove vapor production in a room

Required Outdoor Makeup Air

Acceptable indoor air quality

Required Space for Ventilation and Air Conditioning Equipment

Sizes of ventilation and air conditioning rooms according DIN 1946

Room Area per Person

Recommended minimum area per person - common values for calculating indoor climate loads

Roughness & Surface Coefficients

Surface coefficients to calculate flow friction and major pressure loss - surfaces like concrete, galvanized steel, corroded steel and more

Scrubber Basics

In a wet scrubber process air is drawn through a mist of water made by spray nozzles, then through separators where water droplets with dust and particles are removed

Selecting Ventilation System in Comfort Environments

A quick selection guide of ventilation system in comfort environments

Sizing Circular Ducts

A rough guide to maximum air volume capacity of circular ducts in comfort, industrial and high speed ventilation systems

Spiral Duct Elbows - Weights

Ductwork - weights of galvanized round spiral elbows

Spiral Ducts - Dimensions

Standard dimensions of spiral ducts - Imperial units

Stack or Flue Effect

The stack or flue effect occurs when the outdoor temperature is lower than indoor temperature

STP - Standard Temperature and Pressure and NTP - Normal Temperature and Pressure

The definition of STP - Standard Temperature and Pressure and NTP - Normal Temperature and Pressure.

Types of Fans

Axial and propeller fans, centrifugal (radial) fans, mixed flow fans and cross flow fans

Types of Fans - Capacity Ranges

Centrifugal, axial and propeller fans and their capacity ranges

Typical Air Duct Velocities

Typical air duct velocities in applications like ventilation systems or compressed air systems

U-Tube Manometer

The inclined and vertical u-tube manometers are inexpensive and common in the differential pressure measurement with flow meters like pitot tubes, orifices and nozzles

Velocity Classification of Ventilation Ducts

Recommended air velocities in ventilation ducts

Ventilation Efficiency

The efficiency of a ventilation system may be related to temperature and/or pollution concentrations

Ventilation Filters

Classification of air filters used in ventilation systems

Ventilation Principles

Some commonly used ventilation principles - short cut, mixed air, displacement and piston principle

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