Pneumatic controls vs. DDC

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Is there a way to model an upgrade of HVAC controls from pneumatic to DDC?  Is the performance unaffected, and the justification purely based on lower maintenance costs?

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We have wrestled with this as well for pneumatic to DDC conversions.  The basic change should be a better throttling range.  The primary difference is in the ability to incorporate better controls, such as discharge air temperature reset from space, improved VAV box controls, or demand controlled ventilation.  I have searched for ideas as well, and not found much help, other than anecdotal responses; "saved 30%",etc.  For older systems we sometimes add a 5% to 15% HVAC energy penalty manually to reflect controls out of calibration, etc., and remove the penalty as part of the upgrade.  The 5% to 15% penalty varies based on if the entire system is pneumatic (15%) or just the VAV boxes.  Good Luck.

Bob Towell at CxE Group

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