Sizing gas line

[caluna]

Hi,

I am sizing a gas line to several (10) different-size units on rooftop. Some of the rooftops will be operating at a real-life maximum load LESS (say half) that of the standard supplied gas heating capacity.

In those cases, may I size the gas line for my anticipated design loads, rather than the rated manufacturure's maximum (which will never be reached at my % FA and design conditions?)

Thank you,

Caluna

 

[TBP]

The gas code for your jurisdiction will likely set out the required line sizes, based on the heat input value assigned by the manufacturer of the units. Probably, by the time you try to downsize the pipe size requirements, show all the calculations, and get it approved (assuming that you even CAN get the code variance approved), it will cost more than just running the line sizes as specified in the code.

 

[ChrisConley]

I agree with TBP. Gas lines should be sized for maximum load regardless. Most rooftop units never run past 75%, but the gas lines still need to be sized for the design day, or else Murphy's law says you'll be short pressure at the worst possible time.

If the RTU's are oversized, and you're trying to save a few nickles by dropping the pipe size... how about sizing the RTU smaller then?

 

[chicopee]

I would base my gas line on the total rated capacity of all rooftop units. Price differential for increaing size of gas line should not be significant.