# VFD's - On MUA units

Im am trying to figureout how to calculate savings using a VFD -
Variable Frequincy(Speed) Drive

Direct energy savings easy

I am trying to Calculate the savings in AIR FLOW/+/Air temp-differerance

Not exausting 75'F air outside at say 10,000 CFM - And not bringing in 30'F Air in the winter at the same CFM's

I am not looking for a direct answer im am looking for equations/examples? such as. Cost to heat 1 CF of Air per Degree F , Without going into too much detail I can use some assumptions (efficency of heating sorce etc.)

## Answers and Replies

minger
Science Advisor
??????????

What are the ??????? for

what dont you understand ?

I figured it all out :rofl:

Basically assume 10,000 CFM Fan

Values
Total CFM 10,000

Tatal CF - Day 14,400,000

1 CF air = 0.075 lbs 1,080,000

To heat 1 lbs air = 0.24
BTU's per Degree ferinhight A) 259,200

Delta T (Temp Change) B) 50

BTU's Per day A*B 12,960,000

1000 BTU = 1 Cubic foot gas 12,960

1 cubic metre = 0.0283 cubic foot 366.77

Cost Per cubic metre of gas $0.50 Air cost per day for 10,000 CFM fan Using Gas$183.38

BOOH YEAH

minger
Science Advisor
Luckily your calculations make more sense than your grammar. Yes though, your calcs look decent.

Well Im sorry MINGER that my grammer is not up to par with yours - Actually I could care less :tongue2:

But thank you for the reply's

And if I wanted to be really specific Im pritty sure I would also need to take into account the moisture/humidity , the efficiency of the heating sorce , Envelope of the building , Solar heat ...

Thanks for that info on that BIN program all take a look at it.

minger
Science Advisor
That was much better, good luck!