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?
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.
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.