How do you calculate friction loss in a duct?

Asked By: Niccolo Atta | Last Updated: 18th May, 2020
Category: home and garden indoor environmental quality
4.1/5 (266 Views . 44 Votes)
The difference in the character of the flow from the case of water in a pipe stems from the differing Reynolds number Re and the roughness of the duct. The friction loss is customarily given as pressure loss for a given duct length, Δp / L, in units of (US) inches of water for 100 feet or (SI) kg / m2 / s2.

Click to see full answer


Subsequently, one may also ask, what is friction rate of duct?

Friction rate (FR) is the pressure drop between two points in a duct system that are separated by a specific distance. Duct calculators use 100′ as a reference distance. So, if you were to set the friction rate at .

Similarly, how do you calculate static duct pressure loss? Add total elbow equivalents to the length of straight duct to arrive at the total system duct length. Multiply the static pressure for 100 feet of duct by the percentage of 100 feet that you have. This will be the static pressure caused by the ductwork.

Similarly, you may ask, how do you calculate the airflow of a duct?

Traverse the Airflow in the Exhaust Duct An anemometer, a test instrument that measures air velocity is used to determine the average air speed in the duct. Then the average feet per minute is multiplied by the area of the duct in square feet to determine the airflow moving through the duct.

How do I calculate friction?

How to find force of friction

  1. Choose the normal force acting between the object and the ground. Let's assume a normal force of 250 N.
  2. Determine the friction coefficient.
  3. Multiply these values by each other: 250 N * 0.13 = 32.5 N .
  4. You just found the force of friction!

26 Related Question Answers Found

What is friction loss in HVAC?

Friction loss. From Wikipedia, the free encyclopedia. In fluid flow, friction loss (or skin friction) is the loss of pressure or “head” that occurs in pipe or duct flow due to the effect of the fluid's viscosity near the surface of the pipe or duct.

What is the formula for static pressure?

There are two common ways to measure this pressure. The first and most common is to use the force exerted by the fluid divided by unit area. Another way to calculate static pressure is to determine the fluid's pressure head, or how far the fluid will rise when it's no longer constrained.

What is duct Tel?

The total effective length (TEL) is the sum of all those fitting effective lengths plus the lengths of straight duct. The lengths of straight sections of duct add up to 36 feet for the supply side and 13 feet for the return side.

How do you measure duct size?

How to Determine Duct Size Per Room
  1. Look at the plate on your furnace to figure out how many BTUs it produces.
  2. Multiply that number by the amount of cubic feet of airflow per minute (CFM) your type of furnace produces.
  3. Divide your number by 10.
  4. Calculate the size of your ducts vents by multiplying the length by the width.

How much CFM do I need calculator?


How to Calculate the CFM of a Room
  1. Measure the room's width and length.
  2. Multiply the three measurements from step 1 to determine the cubic footage of the room.
  3. Multiply the cubic volume of the room by the number of times you want the air to turn over or exchange in an hour.
  4. Divide your answer from step 3 by 60 to calculate CFM.

What are standard duct sizes?

Rectangular or square ducting comes in standard sizes ranging from 3-by-7 inches to 35-by-40 inches. Sizing is based on airflow needs per cubic foot per minute, as well as velocity.

What is the formula of CFM?

CFM = FPM x Duct Cross Sectional Area
Finding the Flow Velocity, typically expressed in feet per minute (FPM), is the first step in filling in our equation variables. To find the Flow Velocity, we use the equation: FPM = 4005 x √ΔP (The square root of the Velocity Pressure).

What does CFM mean?

Cubic Feet per Minute

What is airflow rate?

In engineering, airflow is a measurement of the amount of air per unit of time that flows through a particular device.

How many CFM do I need for 1000 square feet?

Heat and energy recovery ventilators
Total area of home (square feet) Continuous ventilation rate
1,000 square feet 50 CFM
2,000 square feet 100 CFM
3,000 square feet 150 CFM

How do you measure air flow?

Step 2: Optics Setup
  1. Place your point light source on a stable surface on one side of a room.
  2. Place your mirror on another very stable surface on the opposite side of the room, facing your point light source.
  3. Vertically position a white piece of paper or posterboard near your point light source.

How do you measure volume of air?

Air volume is measured with anemone meter put in the duct. By anemone meter velocity is measured. Multiply cross section area of duct by velocity, gives you volume. Determining air flow is a matter of multiplying the cross sectional area of a duct by the air velocity.

What is duct calculator?

Duct Size Calculator. Ductulator is an engineering tool to calculate air duct dimensions based on given inputs including air-flow, duct material roughness and either air pressure static loss (friction method) or air velocity (velocity method).

What is a normal static pressure in ductwork?


Static pressure is one of the most important factors in HVAC design. Simply put, static pressure refers to the resistance to airflow in a heating and cooling system's components and duct work. The push of the air must be greater than the resistance to the flow or no air will circulate through the ducts.

How do you read static pressure?

Insert the static pressure tip into the test port on the return side with the tip facing the airflow. Read and record the negative static pressure. Don't forget to insert port plugs into the test ports when you're done testing. STEP 6: Calculate the system's Total External Static Pressure by adding the two values.

How do you find velocity with pressure?

Velocity pressure is calculated by taking the difference of the total pressure and static pressure. To measure the velocity pressure, connect a Pitot or averaging tube to a velocity sensor and place the tube into the air flow of the duct.