What are the Minimum Minimums for Digital Typical Controllers?

Minimum minimums are the minimum airflow limits Titus recommends for accurate airflow control on terminal unit inlets. Many customers have noticed that Titus’ 2014-15 Product Catalog contains updates regarding these values. In this entry, we will reference the “DESV - Digital Typical Controller” section found on pg. M14.

The original minimums that we established many years ago were based on factory-calibrated pneumatic controls. It was determined that factory-calibrated controls could maintain an accuracy of +5% if we did not try to set the minimum airflow limit too low. Of course, you can always order a unit set for full close-off because that is not really airflow control.

For the Titus II and IIA, we determined that a minimum airflow based on a sensor signal of 0.03 in wg could be controlled within +5%. The Titus I required a slightly higher sensor signal of 0.05 in wg in order to deliver the same accuracy. Later, analog and digital electronic controls were assumed to be equivalent to the Titus II and IIA controls with regard to the minimum control accuracy.

Here are the minimums for Titus I:

• Size 04 = 55 cfm
• Size 05 = 85 cfm
• Size 06 = 105 cfm
• Size 07 = 135 cfm
• Size 08 = 190 cfm
• Size 09 = 225 cfm
• Size 10 = 300 cfm
• Size 12 = 425 cfm
• Size 14 = 575 cfm
• Size 16 = 750 cfm
• Size 40 = 1800 cfm

Here are the previous minimums for Titus II, Titus IIA, TA1/TA2 and digital controls:

• Size 04 = 45 cfm
• Size 05 = 65 cfm
• Size 06 = 80 cfm
• Size 07 = 105 cfm
• Size 08 = 145 cfm
• Size 09 = 175 cfm
• Size 10 = 230 cfm
• Size 12 = 325 cfm
• Size 14 = 450 cfm
• Size 16 = 580 cfm
• Size 40 = 1400 cfm

During the preparation of our latest catalog, it was decided these minimum values should be reduced in recognition of the improvements that have occurred in digital electronic controls (specifically, their electronic flow sensors).

We reduced the minimums based on a sensor signal of 0.01 in wg. As always, the actual flow-control accuracy depends on the quality of the controller, but our lab testing has shown that some controllers can provide +5% accuracy down to a sensor signal of 0.005 in wg.

Here are the latest minimums for digital controls:

• Size 04 = 30 cfm
• Size 05 = 40 cfm
• Size 06 = 45 cfm
• Size 07 = 70 cfm
• Size 08 = 90 cfm
• Size 09 = 120 cfm
• Size 10 = 145 cfm
• Size 12 = 190 cfm
• Size 14 = 300 cfm
• Size 16 = 385 cfm
• Size 40 = 720 cfm

Titus’ minimum minimums for digital controls are much lower than they have ever been. This should be a welcome change for designers whom want accurate airflow control without increasing the minimum airflow volume to achieve it. We have redefined how low you can go!

Please direct questions toward Titus Communications (communications@titus-hvac.com) and/or Titus' Chief Engineer Randy Zimmerman (rzimmerman@titus-hvac.com).