My local Trane contractor and I were discussing the use of an XL19i versus an XL16i for a zoned system. After received some feedback on this forum I decided to ask a Trane field representative who is employed with the Trane distributor.

He advised me that only the Trane Integrated Zone System has the ability to "talk" to the variable speed fan and modulating dampers. Based on this he said only the Trane proprietary zoning system would work properly with a VS fan. He also said that if a contractor used a non Trane zoning system he would lose all ability to control the fan and, as a result, the fan would operate at full CFM capacity.

He further said this would result in 'excess air' which can only be managed by gross duct oversizing or bypass. As the variable speed fan motor has the ability to overcome resistance to air flow generally up to 40% greater than non-variable speed, the negative effect of bypassing air (as in conventional zone systems) is compounded. An analogy is like driving you car with the gas pedal to the floor, and modulating your speed by how hard you depress the brake."

So his first response was to advise me about the advantage of the Trane zoning system when using a VS fan and the problems any other zoning system would have with a VS fan.

Then he responded to the XL19 versus XL16 issue.

He said that the Trane zoning system is instructed to modulate the CFM on an understanding there is a 50/50 split between first and second stage CFM, and that this more closely matches the split on the XL19 system. As the XL16i provides an approximate (depending upon selection) 70 / 30 capacity split, the Integrated Zone System will not offer the correct airflow distribution when matched with an XL16i, especially on 1st stage, which statistically is 70-80% of the equipment run time.

So his conclusion was that Trane really didn't have a good zoning product for the XL16i. Therefore go with the XL19i.

I've made up my mind on the system (zoned XL19, XV90 or 80).

I just wanted to see if there was any response to the Trane rep position on:

1) How zoning systems work with a VS fan (Trane system-good, others-bad). Are there other zoning system (Honeywell, etc.) that work well with VS?
2) Staying away from XL16 with zoning?