10
Parallel
Fan-Powered
VAV-SLM005-EN CONFIDENTIAL DOCUMENT. FOR INTERAL USE ONLY.
Feature
Evaluation
Analog Controls
Analog controls are a reduced cost solution for the end-user… or are they? Analog
VAV controllers have a similar cost as DDC VAV controllers. What they lack is the
ability to:
Monitor remotely
Provide diagnostic data
Provide feedback to building control panel
DDC systems can recognize something is broken before it is even noticed by the
occupants. By the time occupants notice a problem, a service technician can already
be on the way.
Leverage energy-saving strategies such as static pressure optimization (required by
ASHRAE 90.1) or Ventilation Reset. (See
www.Trane.com/commercial/issues/iaq/
ashrae.asp.com for additional details)
Acoustics
Make sure you are doing an “apples to apples” comparison. Don’t let the competition
use a less stringent sound power assumption or show cooling only information if re-
heat is to be used.
Sound Power
–if specifying a particular spectrum shape for a particular
manufacturer, this is the same as being a proprietary specification. This is not advised.
NC (Noise Criteria)
–NC level is determined by taking the sound power generated
using ARI 880-98, and applying a transfer function. The transfer function assumptions
in ARI 885-98 standard are significantly different than the 90 standard. On average, the
same unit operating at the same conditions will show a 4 NC improvement if the
older, superceded 90 standard is used. Don’t let the competition catch you in this trap.
Said another way, if your customers specified NC 40 in the space prior to the 98
standard being written, that is now equivalent to NC 44 with the current standard
ARI Certification
–Are the units that are specified ARI certified?
Titus has a quantity of 19 valve/fan combinations, however on the ARI website only 14
are listed as certified units.
Nailor has a quantity of 22 valve/fan combinations listed in their catalog, however on
the ARI website only 14 of those are listed as certified units.
Trane has a quantity of 19 valve/fan combinations, 19 of which are listed on the
ARI website.
If sound is going to be critical on specific units, make sure the units that we are
comparing to are listed on the ARI website
www.ariprimenet.org .
UL Rating for Electric Heat
Our units have been tested, approved, and listed with UL as an entire assembly. Most
VAV manufacturing companies have their units ETL listed in accordance with UL
standards.
Electric Reheat kW/Voltage/Staging options
To better answer this questions as to why units with electric reheat are not able to
reach certain higher kW’s on 2- and 3-stage or have certain number of stages, 3-phase
units when some are able to reach kW’s on some 1-phase, 1-stage units. There are
many reasons why, but the two major limiting factors are wire size and the units
discharge dimensions.
A heating element requires a certain length, a certain 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 end up needing 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.
