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HVAC Template System Fan Size to Sizing, not Fan

asked 2018-03-04 18:44:37 -0500

bbrannon4 gravatar image

updated 2018-03-05 07:30:31 -0500

I just noticed that when a template system is set up (let's say a typical AHU) and a max flow rate for the supply fan is entered, that flow rate is set to the System:Sizing object only, but the actual fan and cooling coil are set to auto-size. Obviously this ends up with the right result, but is confusing when reviewing someone else's model (what I'm doing now). Is there a reason why the expanded IDF file is create this way and the flow rate isn't just set straight into the fan?

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answered 2018-03-05 01:12:13 -0500

TomB gravatar image

My understanding is that sizing info generally flows top-down. Mixing autosize and hardsize is unwise, for many reasons, including that the loop/system sizing routines don't account for hardsized components.

The Input output reference provides some guidance on autosizing and hardsizing. V8.7 There is also a Gard Analytics powerpoint presentations that have some nuggests of wisdom on the topic

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I guess that makes sense programatically, but not conceptually to me. Physically what I want to say is that a fan in the real world has been speced (or even exists), so I want to define that in the model. In that case, I don't even need a sizing object at all (at the system level), but I probably still do at the zonal level. Wouldn't it be more realistic for the template object to realize that sizes have been entered and then not generate the system sizing object at all?

bbrannon4 gravatar imagebbrannon4 ( 2018-03-06 18:49:34 -0500 )edit

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Asked: 2018-03-04 18:44:37 -0500

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Last updated: Mar 05 '18