# Thread: Please explain the terms in Q = 1.08 * CFM * dT for HVAC systems/AHU

1. It sounds like you understand the math but not anything about how to get the numbers used to plug into the formula.

One way to get your CFM would be to use the formula by knowing the other two factors which is not what you're wanting but that is a common way if you don't have other ways to measure it.
The other 2 common ways i can think of are:
1 - use a manometer & get your static pressure & match it up with a blower chart supplied by the manufacturer.
2 - use an anemometer & get your velocity in fpm & convert it to cfm after measuring the area of the duct.
You can also use an air balancing hood but it's more for balancing & not as good to find your total cfm since it's usually not practical to use on the main trunk.
A common ballpark used for design is 400 cfm per ton but that can vary greatly depending on the actual system setup & duct work.

As for dT that is just the temperature of the air out minus temp of air in.

75 degrees going into the unit & 100 degrees coming out = 25 dT

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The OP has started 3 very similar threads. The first one asked what is the role of Discharge Air Temperature in HVAC. The second was Calculate the energy used by and air Handler for 1 degree temperature change. The second concerned a museum. Now this one. I believe he is trying to do a heat load calculation and determine how efficient his HVAC equipment is. He has asked a number of questions but has not said what he really trying to achieve. Just a guess he's gotten several very large electric bills

Anagha Satish, what are trying to do and you may get some better help in understanding your problem

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Originally Posted by Anagha Satish
I'm a Computer Science Engineer, and do not have deeper knowledge on these areas. I'm into Data Analytics and working on developing a Prediction model, where the DAT is predicted for a given timestamp.

I need to calculate the energy consumed(Q) and hence I need to understand the parameters involved in it.
Q is not energy consumed.

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is dat kinda like swag? we need more know it all engineers that's for sure. I don't get it. should be called swagineers
Last edited by poppa; 10-14-2017 at 08:20 PM. Reason: spell

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Originally Posted by Anagha Satish
Hi,

Can someone please explain the terms used in the formula Q= 1.08*CFM *dT . What does these terms mean,? How are they calculated and what should be the unit for it?

How it is calculated for a HVAC or AHU
In my experience "Q" would be the output of the system being tested in BTUs. This formula is used when you have a known value of "Q". This is used to determine the actual cfm at the heat source.
CFM = (1.08 × Q) / dT

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I'm a Data Scientist (Computer Engineer), working on Energy management solutions. My task is to predict DAT temperatures using appropriate algorithms, thru which we can reduce the energy wasted and also the overall electricity cost.

I do not have much idea about HVAC systems and AHU (Air Handling Units) hence asking basic working principles and the calculations

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I'm not sure I am following this, but with a known BTU of heat you can determine the CFM(quantity of air) moved. Or for a known CFM, you can determine temperature change.
I use this to predict the temperture drop I can expect if I install exhaust fans in a server room, for example.

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Originally Posted by Anagha Satish
I'm a Data Scientist (Computer Engineer), working on Energy management solutions. My task is to predict DAT temperatures using appropriate algorithms, thru which we can reduce the energy wasted and also the overall electricity cost.

I do not have much idea about HVAC systems and AHU (Air Handling Units) hence asking basic working principles and the calculations
Good luck.

9. Originally Posted by Anagha Satish
I'm a Data Scientist (Computer Engineer), working on Energy management solutions. My task is to predict DAT temperatures using appropriate algorithms, thru which we can reduce the energy wasted and also the overall electricity cost.

I do not have much idea about HVAC systems and AHU (Air Handling Units) hence asking basic working principles and the calculations
My question to you is of what use is the DAT if you're concerned about reducing energy? Does the discharge air have to blow directly on something to keep it warm? It seems to me that you need to calculate the btuh loss of the structure at a given indoor & out door temperature, convert it to wattage needed & then cost.

10. Q=furnace BTU output

11. or air handler w/electric heat. late to the party i know

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