Series
Fan-Powered
CONFIDENTIAL DOCUMENT. FOR INTERAL USE ONLY. 40VAV-SLM005-EN
Electric Reheat kW/Voltage/Staging Options
There are many reasons why units with electric reheat are not able to reach certain
higher kWs with 2- and 3-stage, or have certain number of stages with 3-phase units.
The two major limited factors are wire size and the units discharge dimensions.
A heating element requires a certain length and diameter, and the correct number of
elements in order to obtain the correct staging. This determines the ohmage
(resistance) needed to provide the desired kW. Since resistance and kW are inversely
proportional for a given voltage, higher kW heaters need very little element material,
which means changing either the length or the diameter of the wire.
However, there are safety issues, UL and NEC regulations, and manufacturing
practices that limit the diameter from getting too small. Hence, only one alternative
exists and that is to change the length of the wire, which may not be long enough to
fill the discharge area of the heater. Filling the discharge area is important to building a
heater, because it will minimize stratification and will increase the longevity of the
heater by minimizing hot spots.
Factory-Commissioning
Factory-commissioning is more than just factory installed controls! Trane takes great
pride in being the industry leader in factory-commissioned DDC controls. The
following table differentiates these concepts and indicates where options can be
obtained (either the field, or the factory.):
Factory-installed Factory-commissioned
Transformer optionally installed X X
Wires terminated in reliable/ consistent setting X X
Controller mounted X X
Electric heat contactors and fan relay wired X X
Testing of heater contactors and fan relay X
Controller addressing and associated testing X
Minimum & Maximum airflows (occupied/unoccupied) X
Minimum & Maximum temperature setpoints
(occupied/unoccupied) X
Minimum ventilation requirements
(used to calculate ventilation fraction) X
Thumbwheel enable/ disable X
Heating offset X
Factory-commissioned controllers provide the highest quality and most reliable
controllers for your VAV system. Additional testing verifies proper unit operation
including occupied/unoccupied airflow, temperature setpoints, communication link
functionality, and output device functionality. The benefits of factory-commissioning
are standard on VariTrane terminal units with Trane DDC controls.
Perforated Liners
The intended use of the perforated liner was for units that had a Mylar or Tedlar
insulation. Mylar and Tedlar insulation was found to have long-term durability
problems and would erode into the airstream over time. The perforated liner was
designed to hold the insulation with the idea to improve acoustical performance over
a dual-wall construction.
Today, if a perforated liner is specified, it is generally used to prevent possible tearing
of the insulation during installation. However, the perforated liner will still allow air to
penetrate the insulation and loft fibers. Our best solution is to use a foil-face or dual-
wall insulation option.
Feature
Evaluation
