DAB is a particularly complex algorithm that balances energy efficiency, comfort, and system protection. Since DAB is often converting a constant air volume system (CAV) into a zoned system, the protection aspect of DAB is very important.
To protect the system DAB implements two concepts.
- Normalization - This is the theory that in a CAV system, the system will never condition unless at least one zone requires it. If a single zone requires conditioning, there is no reason that a single damper should not be at 100% to deliver the maximum conditioning to the zone the needs it most.
E.g. in a three zone system. One zone requires all of the cooling and has a calculated damper position of 85%, the other two have calculated positions of 40%. In this scenario, normalization would add 15% to all three dampers leaving you with one at 100%, and two at 65%.
- Cumulative Damper Target - This concept is that since we are adding back pressure with zoning to a CAV system, we never want the overall average damper opening of the system to be below a certain threshold. By default, this is 70%.
E.g. in our three zone example above, the average damper opening was (100+40+40)/3=60%. 60% is below our cumulative target. So we will add 1% to each damper until our average target is 70%. So we would end with one damper at 100% and two at 50%.
These are the primary reasons your damper will open even if it seems illogical. It is the system balancing multiple factors to protect itself.