Measurement of pressures and flows in the field & troubleshooting

Calibration of pressure measuring devices

• Layout done quickly and easily on a simple schematic of the system
• Can generate many simple systems in three mouse clicks
• Allows system of any complexity
• Detemines for itself whether a duct is a branch, submain, or main and whether it is part of a subsystem.
• Simple to change layout: just change the schematic
  Layout can be changed at any time without re-inputting other information (program automatically re-computes based on the new layout)
• Allows two laterals on a junction fitting (a real boon to rational layout)
• It is so fast and simple that ex-users of competing programs are sometimes confused because they "couldn't believe it was that easy".

• Allows use of round, rectangular, or flat oval ducts
• Selects intial round duct sizes from user-editable files of available duct sizes
• Allows user to over-ride program choices
• Can display duct dimensions on schematic
• Makes optimal re-sizing relatively easy (see Optimization)

• Extensive user-editable defaults drastically reduce number of required inputs
• Loss coefficients choices shown when and where needed. Progam computes many for itself based on simple user inputs.
• Entire run of ducts described at once (e.g., number of 90 degree elbows in this branch), which is much faster than describing each and every component individually as other programs require
• Pressures and flows re-computed instantly with every input you make, giving helpful feedback on effects of design choices
• Makes psychrometrics easy. Requires only that you input the dry bulb temperature and one other parameter (e.g., relative humidity). Elevation effects done automatically (table of elevations for most U.S. cities included)
• All computations done the most robust way possible -- not by using the approximations necessary for hand calculations.
• The pressures computed are what you should expect to measure in the system. Oddly enough, the values computed in manuals, text books, and other programs are not. They fail to correct for the complex interactions between branch pressure requirements and are computed for locations that are inimical to accurate measurements.

The schematic can display several parameters that are helpful in optimizing system design. The most important are Percentage of Ideal Airflow and Percentage of Target Velocity. The values appear as a label on each duct on the schematic, giving a easily understood view of which ducts should be re-sized or otherwise modified.
Just as importantly, it is so easy to make changes to the system that you can quickly try a change, then look at the flow at the fan and see if your change was a good idea. If not, change it back. It takes only a few key strokes or mouse clicks, so just try different combinations until you are completely satisfied you have done the best that can be done (i.e., ideal airflow at the fan approaches 100%).

In that regard, note that the author's damper balancing procedure produces the least possible energy costs and involves the least possible time to adjust dampers (second rounds rarely necessary)

First 3 steps same as "Redesign" above.
In Heavent, set to "balance with dampers."
3) Input the new airflows you would like to see in each hood.
4) Heavent predicts ratio of hood static pressure to pressure at the end of the duct (SPH/SPend) that will exist if the dampers are each adjusted correctly.
5) Adjusting dampers in the field: Adjust each damper in turn until the observed value of SPH/SPend is nearly the same as the predicted ratio. One round of adjustements should be sufficient.
6) Measure airflow at fan inlet, then adjust fan rotation rate (w) so that:

Note: this procedure should give the best possible distribution at the lowest possible energy use and take far less time than other methods.

I

Installation

II

III

 Aids in calibrating digital pressure manometers.

The auxiliary programs are explained in Heavent Manual.