Nm3/Hr To M3/Hr FAD Calculations - LinkedIn

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A BRIEF ON CALCULATIONS AND UNDERSTANDING OF CONCEPT

Before proceeding ahead let us understand the concept of Free Air Delivery and its different measurement units

Free air delivery is the volume flow rate of gas compressed and delivered at the standard discharge point, referred to the atmospheric conditions of the site, not affected by the compressor. F.A.D. can be expressed in l/s, m3/min or cfm.

Most of the compressor manufacturers uses by ISO 1217 annex C (downstream of the aftercooler, check valve and water separators) to measure compressor flow and it is widely accepted throughout the world.

WHAT IS ISO 1217 ANNEX C ?

Compressed Air Flow is nothing but the volume flow rate of Air with reference to ambient conditions or Normal Conditions or Standard conditions and so on

For ISO 1217, the manufacturers refer to below mentioned reference conditions to calculate FAD

Ambient temp. = 20ºC

Bar pressure = 1 bar

Relative Humidity = 0%

There are other measurement types used by manufacturers mostly from oil & gas industry like Normal Conditions, Standard Conditions or Inlet conditions

WHAT ARE NORMAL CONDITIONS ?

Volume flow rate of gas compressed and delivered at the standard discharge point, but with reference to Standard/ Normal conditions for temperature, pressure and inlet gas composition (humidity).

Temp. = 0ºC

Bar pressure = 1.013 bar

Relative humidity = 0%

CONVERSION – NM3/HR TO M3/HR

We will use universal gas equation to convert from Nm3/Hr to M3/Hr

PsVs/Ts = PnVn/Tn

Ps- Ambient Pr at site

Ts-Max Ambient temp at site

Rh- Avg Relative Humidity

Vs – Flow at Site – To be calculated

Normal Conditions:

Pn- Pr at normal conditions

Tn-Temp at Normal conditions

Vn – Flow ate Normal Conditions

WE WILL USE BELOW MENTIONED FORMULA TO CALCULATE SITE PRESSURE

• Ps = Pa – RH x Pvs to calculate dry air pressure at site

Ps- Ambient Pr at site – ?

Pvs – Vapour Pressure - 0.1234 bar @ 50 C

Rh- Avg Relative Humidity – 43%

Pa – Ambient Pressure – 1,013 Bar

Hence Ps = 1.013 – 0.43 X 0.1234

Ps = 0.959 Bar

CONVERSION CALCULATIONS

Ps- Ambient Pr at site – 0.959 Bar

Ts-Max Ambient temp at site – 50 °C (considering Oman conditions)

Rh- Avg Relative Humidity – 43%

Vs – Flow at Site – To be calculated

Normal Conditions:

Pn- Pr at normal conditions – 1.013 bar

Tn-Temp at Normal conditions – 0 °C

Vn – Flow ate Normal Conditions – 154 Nm3/Hr ( Given by Customer)

PsVs/Ts = PnVn/Tn

(0.959XVs)/323 = (1.013X154)/273

Vs = 192.5 Mr/Hr

Hence we concluded that the correct flow to be taken into consideration for sizing compressors will be 192.5 Mr/Hr

64 7 Comments Like Like Celebrate Support Love Insightful Funny Comment

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Share Aritra Kumar Biswas 3y

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It might be good idea to consider the moisture mass as well in the calculation before defining the capacity. It will be significant!!

Like Reply 1 Reaction 2 Reactions Mian Usman Consultant 3y

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Excellent Work !

Like Reply 1 Reaction Geron Farro 5y

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Hi Mr. Prashant Bawane, i'm just wondering if the above information regarding properties of Air is correct at normal condition (NTP)?...hoping for your further clarification...;)

Like Reply 1 Reaction Ratheesh manhacheri 5y

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so 192.5 Mr/Hr is the FAD value? why pressure is not associated with it? Suppose the customer specifies 154 Nm3/Hr at 9 bar discharge pressure. So the compressor vendor will use 192.5 m3/hr at 9 bar for model selection?

Like Reply 1 Reaction 2 Reactions AIR TECH COMPRESSEUR POWERAIR DU GROUPE ATLAS COPCO) 5y

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Dear Prashant thanks for that information. I have a question a customer gave me machines data 22600 NL/mn and pressure of 7 bars. He and asked me which compressor for that need. Firstly, I have to calculate the Air flow rate in L/S taking into account pressure 7 bars? I see in above formula the working pressure is not included? Thanks to help me

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