Overview

The motivation for developing a series of TAB forms in spreadsheet form was to reduce clutter on the job site, increase legibility of the entered data, increase form functionality, especially in an inclement environment, and increase the productivity of field personnel.

The spreadsheets were developed in the MS Excel® environment because it is familiar to most people, customizable, portable to a number of platforms, and the data is easily exportable.

I developed the spreadsheets for use on a PDA but they could just as easily be loaded onto a laptop, netbook, or phone. You will need an MS Office emulator to run these spreadsheets on a PDA or phone. I use “Documents To Go” from DataViz.

I started using these spreadsheets in 2006 and quickly found them to be superior to paper forms in the field, especially outdoors in inclement weather. They are as easy to customize to a particular job as paper forms and provide the added functionality of automatic calculations, especially the duct traverse calculators and the adjusted airflow forms. For more information please see the paper “A Preliminary Evaluation of Electronic Data Collection in the Field” where I compare paper forms, spreadsheet-based forms, and a commercially available electronic TAB form program.

The following sections detail the various forms and how to fill them out and use them. The downloadable spreadsheets are in the ‘raw’ form and have not been customized with blanked or colored cells.

Fan Data Form

This form is used to record fan data and is fairly straightforward. All of the fields present on a standard TAB form are on the left-hand side.

The fan or unit designation goes in the upper row as shown:

Fan Data / AHU-1 SF / AHU-1 RF / AHU-2 SF / AHU-2 RF / FCU 1-2 / FCU 2-3

The form has three parts: The unit data, test data, and notes section. The fields in each section can be customized as the organization or job requires.

Brake Horsepower (BHP) Form

This form uses nameplate data to calculate brake horsepower for single and three-phase motors in all the common voltages. The nomenclature is defined at the top of the spreadsheet.

The formulas used to calculate the BHp are:

Single-phase: (E x I x Eff x Pf)/ 746

Three-phase: (E x I x Eff x Pf x 1.73)/ 746

Sheave Calculator

The sheave calculator form calculates the motor sheave pitch and drive belt length required to meet new system airflow requirements. The form also calculates new drive motor amp draw and fan RPM. The motor-to-fan centerline distance is also calculated.

The first column of the form consists of data entered by the tech with the exception of the centerline distance, which is calculated. It appears like so:

Existing
Unit CFM: / 1335
Motor RPM: / 1802
Fan RPM: / 1546
Motor Amps: / 2.5
Motor FLA: / 3.3
Sheave Pitch: / 2.4 / inches
Fan Pulley Pitch: / 3.2 / inches
Belt Length: / 27 / inches
Centerline: / 9.10 / inches

The sheave and pulley pitch may have to be looked up but my experience is that most experience TAB techs have memorized the data for the most common sheaves including the pitch range and number of turns for a given sheave. It is entirely possible to include a data base but that is beyond the scope and purpose of these forms.

The second column of the form gives the maximum parameters of which the system is capable. These parameters are usually determined by the FLA of the drive motor and this part of the form looks like this:

System Max
Unit CFM: / 1464
Fan RPM: / 1696
Sheave Pitch: / 2.5 / inches
Belt Length: / 27

The row spacing is uneven to preserve the field continuity across columns. This makes scanning and comparing data in the fields easier. All of the data in this section is calculated.

This third column is the ‘New’ section where new system data is calculated based on a new required system CFM. The ‘Motor Amps’ field will turn red if the motor FLA is exceeded for the required system CFM. This part appears like this:

New
Unit CFM: / 1500
Fan RPM: / 1737
Motor Amps: / 3.5
Sheave Pitch: / 2.7 / inches
Belt Length: / 27

The field formulas are:

Fan RPM: First Fan Law

Motor Amps: Third Fan Law

Sheave Pitch: First Fan Law. Specifically (RPM2/RPM1)*Pitch1

Belt Length: 2C+[1.57(D+d)]+((D+d)^2)/4C

Where: C = centerline distance between motor and fan

D = Large pulley pitch, usually the fan

d = Small pulley pitch, usually the motor sheave

Mixed Air Calculator Form

Use this form to calculate mixed-air temperature and percentage based on outside and return air temperatures. The nomenclature is explained on the form. An example is shown below:

Percentage of OA if temps are known
RA / 71
OA / 49
MA / 64.5
% OA / 30%
Temp of MA if % of OA is known
RA / 71
OA / 49
Supply CFM / 1600
OA CFM / 500
% OA / 0.31
MA / 64.1

Air Density Correction Form

While most electronic meters automatically correct for altitude and temperature, it is not always possible to insert a temperature probe into the air stream being measured. This form uses air flow temperature, site altitude, and duct size to calculate the actual airflow when the temperature of the air flow is unusually high, as in the case of combustion vents.

After filling out the temperature of the airflow to be measured (in °F) and the site altitude (in feet above sea level) the spreadsheet calculates the barometric pressure, air density, and correction factor. The barometric pressure calculation assumes that the measurements are taken under normal atmospheric conditions and not in say, a hurricane. The spreadsheet can supply normal barometric pressures to 4000 feet above sea level.

There are separate forms for round and square ducts and the duct dimensions are entered as the duct diameter (in inches) for a round duct and the linear dimensions (in inches) for a square duct. The spreadsheet then calculates the duct area in sq. ft.

There is a section to enter the readings taken in the duct and then a field for the total number of readings. Calculations for average velocity, corrected velocity, FPM and CFM are then made automatically. Please note that the data field for the average velocity calculation will have to be field-adjusted to account for the number of readings taken.

An example of a filled-out spreadsheet is given below:

Standard density / 0.075
Degrees F / 283
Altitude / 700
Barometric press. / 29.38
Actual density / 0.053
Correction Factor / 1.19
Duct Dia. / 6
Duct area (sq. ft.) / 0.196
Measured Velocity
125
130
160
185
165
189
175
185
No. of Measurements / 8
Average Velocity / 1314
Corrected Velocity / 1557
FPM / 195
CFM / 38

Duct Airflow Form

This form contains calculators to find duct airflow (cfm) and velocity pressure for round and square duct. There is also a calculator for the Second Fan Law. Duct dimensions are entered in inches and pressures are entered in inches water gauge.

An example of the round duct calculator:

Round Duct
CFM if VP is known
VP / Size / CFM
0.6 / 6 / 609
VP if CFM is known
CFM / Size / VP
609 / 6 / 0.60

And for the square duct calculator:

Square Duct
Dimensions
Height / 12
Width / 12
CFM if VP is known
VP / CFM
0.6 / 3102
VP if CFM is known
CFM / VP
3100 / 0.60

The calculator for the Second Fan Law appears like so:

Static Pressure and Airflow
SP if CFM is known
Old SP / Old CFM / New CFM / New SP
0.30 / 100 / 150 / 0.68
CFM if SP is known
Old SP / New SP / Old CFM / New CFM
0.3 / 0.68 / 100 / 151

Duct Traverse Form

The Duct Traverse Form contains calculators for rectangular and round ducts. For the rectangular traverse I chose to use the equal-area method for a couple of reasons. The primary reason was that the equal-area method is more forgiving and gives better results in situations where the traverse location is less than ideal. The secondary reason is that every TAB tech I’ve ever worked with has used the equal-area method. It uses an easily remembered formula so it is hard to get it wrong.

I used the log Tchebycheff method for the circular traverse because it has been shown to be significantly more accurate in round ducts than the equal-area method. A paper titled “Duct Flow Surveys, Where Should Those Points Be? “ produced by FlowKinetics LLC in 2008 makes the case for this rather convincingly.

The first worksheet of the form gives general guidelines for rectangular duct traverse and gives the general formula for calculating traverse points. The second sheet is the rectangular traverse calculator. My convention in distinguishing the two axes of the traverse was to label one side of the duct the ‘hole side’; the side that the holes for the traverse are drilled in, and label the other side the ‘measurement side’; the axis along which the pitot tube is run. On the worksheet it looks like this:

Duct dimensions
Hole side: / 36 / inches
Measurement side: / 24 / inches
Area: / 6 / sq. ft.

To determine the number of holes for the traverse and the number of measurement points I used the following conventions: if a given dimension is

≤ 30”, 5; 31” – 36”, 6, and >36”, 7. This information is on the first page of the workbook.

To use the calculator the only information that needs to be entered is the duct dimensions using the previously mentioned nomenclature. A sample worksheet looks like this:

Hole side data:
Use / 7 / holes
First hole at / 2.57 / inches
Traverse point every / 5.14 / inches
Measurement side data:
Use / 5 / measurements
First measurement at / 2.40 / inches
Measurement every / 4.80 / inches

This example is based on the dimensions entered above. There is also a decimal-to-English conversion table at the bottom of the worksheet.

For the round duct traverse sheet one need only enter the duct diameter in inches and the calculator does the rest. A sample worksheet looks like this:

Duct diameter: / 8 / inches
Area: / 0.349 / sq. ft.
Traverse Points
6 readings: / N/A / N/A / N/A / N/A / N/A / N/A
8 readings: / 0.17 / 0.94 / 1.47 / 2.76
5.24 / 6.53 / 7.06 / 7.85
10 readings: / 0.15 / 0.62 / 1.22 / 1.74 / 2.89
5.11 / 6.26 / 6.78 / 7.38 / 7.85

The points for the 8 and 10 reading sets are stacked to make them easier to see on the screen of a PDA. I have set up the calculator so that the 6 point set is only valid for duct diameters of 6 inches or less, like so:

Duct diameter: / 6 / inches
Area: / 0.196 / sq. ft.
Traverse Points
6 readings: / 0.19 / 0.81 / 1.93 / 4.07 / 5.19 / 5.81
8 readings: / N/A / N/A / N/A / N/A
N/A / N/A / N/A / N/A
10 readings: / N/A / N/A / N/A / N/A / N/A
N/A / N/A / N/A / N/A / N/A

Like the rectangular duct calculator there is a decimal-to-English converter at the bottom of the worksheet.

Adjusted Airflow Calculator

The purpose of this form is to simplify the calculation of the grille airflows when the system capacity is adjusted. The design system airflow and grille airflows are entered and then the actual system total airflow. The target grille airflows are then calculated based on the actual system total. This form removes a lot of tedious calculations when system airflow is adjusted.

System Total / Grille CFM / Percentage / Adjusted Total / Adjusted Grille CFM
2380 / 160 / 0.07 / 1666 / 112
160 / 0.07 / 112
160 / 0.07 / 112
300 / 0.13 / 210
300 / 0.13 / 210
300 / 0.13 / 210
200 / 0.08 / 140
160 / 0.07 / 112
160 / 0.07 / 112
160 / 0.07 / 112
160 / 0.07 / 112
160 / 0.07 / 112

Grille Balancing Form

I have been experimenting with a spreadsheet-based grille balancing form for a while. The idea is to quickly show which grilles are out-of-range and which ones need to be cut when the initial system readings are taken. The major problem is to present information, especially grille totals when the fan is adjusted, in such a way as to make the form easy to use and useful without cluttering up the display area, especially on a screen the size of a PDA or phone.

I welcome thoughts and ideas on this. If you are interested, contact me and I will send you what I have.