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  1. stern

    Heat Exchanger Problem

    Yes, Cp should be 1.005 KJ/Kg K and I found with an entropy balance m1s1 + m3s3 - m1s2 - m3s4 -Q/T =0 the answer. Thank you all..
  2. stern

    Heat Exchanger Problem

    Thank you Energymix, Im sure youre a very kind human being..
  3. stern

    Heat Exchanger Problem

    Hello I need some help with a heat exchanger calculations. A counterflow H Ex uses combustion gases to heat air for a process. The data T1 in(air)= 25C , T3 in (gases)=180C and T4 out (gases)= 85C air mass flow= 1 kg/s, gases m= 1.8 kg/s The combustion gases lose heat to the environment by 5...
  4. stern

    Design Conditions

    Thank you very much for your comments
  5. stern

    Electric Kiln Design

    Anybody that could help me to learn some basic design principles for electric kilns? I need to determine KW input required for a specific volume in ft3 , I think Im having some difficulty understanding radiation. I just have a space volume ( 15 x 7 x 3 mts) and a delta T 5 to 40 C how to...
  6. stern

    Design Conditions

    Hi all, I would like to ask why is that in the outside air design conditions for winter there are not included the wet bulb temperature or relative humidity as in summer? In summer with dry and wet bulb temps i go easily to my psychrometrics software and compute some data but for winter I just...
  7. stern

    Evaporation efectiveness at colder climates

    Thank you all!
  8. stern

    Evaporation efectiveness at colder climates

    Hi there, I was reading some theory of evaporative cooling equipment and learned that water requires sensible heat from air to evaporate (heat converted to latent heat). My questions are, for a cold weather with low RH like for instance 17.6 F db, 51% RH is it still possible for water to...
  9. stern

    Chimney in an indirect fired gas heater

    Thank you dvd
  10. stern

    Chimney in an indirect fired gas heater

    Hi guys, Is there a specific formula to calculate the area of chimney needed to exhaust flue gases from a x BTU/hr gas heater? If i need to provide more imformation please advice. Thanks, S
  11. stern

    CFMS vs Tons

    Thank you walkes, I agree with your simple explanation, in the field there are cases where loads are unknown and you have to give an estimate in A/C requirements so this rule could be a good start.
  12. stern

    CFMS vs Tons

    Forget about rules of thumbs, why manufacturers catalogs have cfm ranges about 400 cfm/ton ?
  13. stern

    CFMS vs Tons

    317069 thank you, you mentioned something very interesting " cfm for a zone could have any amount as long as the supply air condition is on the zone SHR line" Ive been searching some sites and the ACH method taking into account space volumes to determine cfms is much used, besides in my...
  14. stern

    CFMS vs Tons

    Yes sprinkler I agree with you, But now if the sensible load requires the 2000 cfms and the total load is for 10 tons, what air flow would the 10 tons AHU be handling? This was more or less the doubt since the beginning.
  15. stern

    CFMS vs Tons

    sspeare, Thanks, yes I know what a psychrometric chart is, I have used it for years and psychrometric software as well. I just was directing to the guys that answered me, not all the forum! I kept looking because their answers didnt satisfy me and I was sharing another guys thread that seems...
  16. stern

    CFMS vs Tons

    Yeah right guys, but the answer I was looking for I found it in another thread from Yeldud (Mechanical) and I think hes an engineer not a contractor :-) "The A/C unit only need to circulate enough air for the tons of sensible load ocurring in the spaces, because the latent load removal occurs...
  17. stern

    CFMS vs Tons

    Thanks IRstuff but the rule of thumb is 400 cfm per ton, I know this could vary with the application but I see everyone in A/C using this as general rule. Im using psychrometrics software to calculate tons required and the 2000 cfm is an input value. What I obtain is 10 tons required for total...
  18. stern

    CFMS vs Tons

    Hello there, I have a space that requires 2000 cfms according to room volume and air changes per hour but when I calculate the sensible plus latent loads 10 TR are required. The rule of thumb is 400 cfm per ton so how does this work? what is the logic of this? 10 tons would be 4000 cfm or...
  19. stern

    AIR MIX SELECTION

    Thank you quark, I see the calculator and its easy to use when you have both air stream conditions. The problem is when you dont have the return air measurements, I suppose we have to assume these conditions but Im not sure. Am I wrong?
  20. stern

    AIR MIX SELECTION

    Hello everyone, I have the following problem, outside air x conditions and its required 90% return air and 10% outside air to heat a building. Is there a rule of thumb on what conditions to consider for indoor air( return) to calculate the mix? I need to determine the BTU/hr required and need...

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