Does adjusting fan speed affect superheat/subcooling setpoints?
Scenario: A DX rooftop unit is installed and started up, with the supply fan set to 60hz.In the process of TAB, we might lower the fan to 50 or 40hz. At what point is it necessary to re-check subcooling? Wouldn’t the TXV need to be adjusted to compensate for the less evap airflow? My colleagues can’t give me a good answer.
Do TAB contractors typically report coil temp data? I’ve seen some TAB guys use an infrared thermometer to report coil temps. Seems like totally useless info, because you can’t conclude anything from it.
Who is sizing the equipment? Why are these units requiring such drastic airflow reductions?If the equipment and its associated ductwork was sized correctly, it should not need much adjustment.
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I recently did some units that had a prelim measurement of over 200% of design airflow.I’m pretty sure they oversize equipment based on global warming predictions.
That is not how equipment should be sized..Need a commercial load calculation, commercial equipment selection and commercial duct sizing.
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Txv should not need adjustment. If it does not turndown with load, sizing is the issue. Subcooling would be lower , but should not needadjustment.
Global warming predictions? Seriously?
Officially, Down for the countYOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET
I know enough to know, I don’t know enough
Why is it that those who complain the most contribute the least?
MONEY CAN’T BUY HAPPINESS. POVERTY CAN’T BUY ANYTHING
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HVAC sizing by Jackleg JimOriginally Posted by 2sac
Global warming predictions? Seriously?
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Well I don’t have a clue how engineers in their Dilbert cubicles size these AC systems. When I went to college, we learned to use fancy load calculation software that takes a gazillion inputs parameters and gives you a load number per zone. And now you’re supposed to use Manual D which undersizes everything for efficiency, blah blah….In reality, engineers would rather oversize systems than have them be too small and get complaints.
But I work for a TAB company, so I have no say in the design process. We’re supposed to make these systems work, regardless of the redneck engineering process.
And like you said you are the TAB company. The mechanical contractor is responsible for the units if they need adjustments to the refrigeration components.There is only so much the mechanical contractor can do if the engineers are clueless.
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