Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

VFD's - On MUA units

  1. Mar 9, 2009 #1
    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. jcsd
  3. Mar 9, 2009 #2


    User Avatar
    Science Advisor

  4. Mar 9, 2009 #3
    What are the ??????? for

    what dont you understand ?
  5. Mar 9, 2009 #4
    I figured it all out :rofl:

    Basically assume 10,000 CFM Fan

    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

  6. Mar 9, 2009 #5


    User Avatar

    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
  7. Mar 10, 2009 #6


    User Avatar
    Science Advisor

    Luckily your calculations make more sense than your grammar. Yes though, your calcs look decent.
  8. Mar 10, 2009 #7
    Well Im sorry MINGER that my grammer is not up to par with yours :frown: - 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.
  9. Mar 10, 2009 #8


    User Avatar
    Science Advisor

    That was much better, good luck!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook