×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# ASTM C680 Calculator

## ASTM C680 Calculator

(OP)
Hey everyone,

Does anyone know of a calculator based off the ASTM C680 standard? I would like to calculate the temperature gain over a run of ductwork. the formula listed in the ASHRAE HoF is t_gain = 0.2*[(q*P*L)/(V*C_p*row*A)], where the terms are:

* q = heat loss through duct wall (Btu/hr*ft^2)
* P = duct perimeter (in)
* L = length of duct run (ft)
* V = air velocity (ft/min)
* C_p = specific heat of air (Btu/lbm*F°)
* row = density of air (0.075 lb/ft^3)
* A = area of duct (in^2)
* 0.2 = conversion factor for length and time units

I understand how to calculator/estimate all the variables except q (heat loss through duct wall). The handbook vaguely recommends that I use a calculator/calculation based off the ASTM standard C680. When I internet search calculators based off the ASTM standard C680, I don't find any hits. Does anyone have any recommendations or help?
Replies continue below

### RE: ASTM C680 Calculator

I'm not sure of a calculator for this. This would be a heat transfer problem, I believe the equation that might work for you is:

Q=hA(T-T_inf)
Q=BTU/hr
A=surface area (square ft)
T=temperature of air inside the duct at specific point (°F)
T_inf=temperature of the air around the duct (°F)
h=convection heat-transfer coefficient (BTU/hr-sq.ft-°F) (this is a little difficult to find)

Then you could use that Q value to find the t_gain that you're looking for over a short distance, then just iterate. That's how I'd start looking at it at least.

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!