# VFD's - On MUA units

1. Mar 9, 2009

### thebigjg

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.)

2. Mar 9, 2009

??????????

3. Mar 9, 2009

### thebigjg

What are the ??????? for

what dont you understand ?

4. Mar 9, 2009

### thebigjg

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

5. Mar 9, 2009

### Staff: Mentor

That looks pretty good, yeah. The difficulty is in getting more precise - you need weather data to know what the actual delta-T is on an hourly basis. I use a piece of software called Binmaker: http://www.interenergysoftware.com/binM/pro/BMPAbout.htm

6. Mar 10, 2009

### minger

7. Mar 10, 2009

### thebigjg

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.

8. Mar 10, 2009

### minger

That was much better, good luck!