Mechanical Insulation Simple Calculators: A Guide to the Temperature Drop for Air in an Insulated Duct or Fluid in an Insulated Pipe Calculators

Ronald L. King

Ron King is a Past President of NIA, the World Insulation and Acoustic Congress, and the Southwest Insulation Contractors Association. He was awarded the NIA’s President’s Award in 1986 and again in 2001. He is a 50-year veteran of the commercial and industrial insulation industry, during which time he held executive management positions at an accessory manufacturer and specialty insulation contractor. In 2004, he retired as the Chairman, CEO, and President of a large national insulation distributor/fabricator. He currently serves as a consultant to NIA on a variety of educational, outreach, and governmental initiatives, including coordinating many association alliance-partnership activities, serving as Chairman and Past Chairman, respectively, of the National Institute of Building Sciences’ National Mechanical Insulation Committee and Consultative Council, and as NIA’s liaison to the Federation of European Insulation Societies (FESI), which represents the European mechanical insulation market. He can be reached at RonKingRLK@aol.com.

September 1, 2013

This article continues our series featuring the
?Simple Calculators? from the Mechanical Insulation Design Guide (MIDG). The
calculators are part of the Mechanical Insulation Education & Awareness
Campaign (MIC), which was started by the Department of Energy’s (DOE’s)
Advanced Manufacturing Office to improve the energy efficiency of the U.S. industrial and commercial sectors. The
National Insulation
Association (NIA) and its Alliance partners
collaborated with the DOE to design, implement, and execute the MIC.

The MIC seeks to increase
awareness of the energy efficiency, emission reduction, economic stimulus
potential, and other benefits of mechanical insulation. An integral component
of the MIC was the development of the Simple Calculators. The calculators,
listed on the left, provide users with instantaneous information on a variety
of mechanical insulation applications in the industrial/manufacturing and
commercial markets.

  • Condensation Control—Horizontal Piping

  • Energy Loss, Emission Reduction, Surface
    Temperature, and Annual Return

  • Financial Returns

  • Estimate Time to Freezing for Water
    in an Insulated Pipe

  • Personnel Protection for Horizontal Piping

  • Temperature Drop for Air in an Insulated Duct or Fluid in an Insulated
    Pipe

The calculators are online as
part of the National Institute of Building Sciences’ MIDG, www.wbdg.org/midg.
You can also access them through a link on NIA’s website: www.insulation.org.
The calculators are fast, free, and functional tools that make it easy to
discover energy savings, financial returns, and other information for the
design of mechanical insulation systems for above- or below-ambient applications.

Insulation systems are often
designed to minimize variation of temperatures in processes. This article will
provide an overview and guide to use the Temperature Drop for Air in an
Insulated Duct or Fluid in an Insulated Pipe Calculators.

Temperature Drop Calculator for Air Ducts

This calculator estimates the temperature drop (or
rise) of air flowing in a duct (Reference: 2009 ASHRAE HoF, Chapter 4, Equation
48, page 4.21). The calculator requires data for 6 input variables. Results are
updated as each input variable is entered. Input information may generally be
obtained from design documents or field measurements. The impact of duct leakage
is not taken into consideration.

Following are the instructions
and additional information for each input variable. Note that the default
values for each input are highlighted in a box after each prompt.

  • Line 1.
    Enter the temperature of the air entering the duct, °F: 120

    The default value is 120°F; however, you should
    enter the actual initial temperature in degrees Fahrenheit for the air entering
    the duct.

  • Line 2.
    Enter the ambient temperature (the average temperature of the air surrounding
    the duct), °F: 75

    The default
    value is 75°F; however, you should enter the average ambient temperature in
    degrees Fahrenheit for the area surrounding the duct.

  • Line 3.
    Enter the flow rate of the air carried by the duct in cubic feet per minute
    (cfm): 500

    The default
    value shown is 500 cfm; however, you should enter the expected/designed flow
    rate.

  • Line 4.
    Enter the length of the duct run in feet: 50

    The default
    value is 50 feet; however, you should enter the actual length of the duct run
    in question.

  • Line 5.
    Enter the perimeter of the duct in inches: 48

    The default
    value is 48 inches; however, you should enter the perimeter of the duct in
    question.

  • Line 6.
    Enter the R-value of the selected duct insulation, ft: 6

    Enter the
    R-value of the selected duct insulation. Available R-values will vary,
    depending on the insulation products selected. If it is not known, it is
    suggested you consult the respective manufacturer data sheet.

Based upon the information
variables provided, the Results section displays the temperature drop (°F) and
the temperature of the air leaving the duct. In this example, the results were
2.4°F and 117.6°F, respectively.

Temperature Drop Calculator for Hydronic Piping

This calculator estimates the temperature drop (or
rise) of water flowing in a pipe. The calculator requires data for 9 input
variables. Results are updated as each input variable is entered. Input
information may generally be obtained from design documents or field
measurements.

Following are the instructions
and additional information for each input variable. Again, default values
appear in bold, underlined text after each prompt.

  • Line 1.
    Enter the temperature of the water entering the pipe, °F: 35

    The default
    value is 35°F; however, you should enter the actual temperature for the water
    entering the pipe (in degrees Fahrenheit).

  • Line 2.
    Enter the ambient air temperature (the temperature of the air surrounding the
    pipe), °F: 75

    The default
    value is 75°F; however, you should enter the average ambient temperature,
    (temperature in degrees Fahrenheit for the area surrounding the pipe).

  • Line 3.
    Enter the wind speed of the ambient air in miles per hour (mph): 15

    The default
    value is 15 mph. You should enter expected wind speed. If unknown, it is
    suggested you use 1 mph for indoor and 8 mph for outdoor applications.

  • Line 4.
    Enter the flow rate of the water carried by the pipe in gallons per minute
    (gpm): 40

    Note:
    The calculator does not screen for reasonable flow velocities; hydronic piping
    is normally sized for flow velocities between 5 and 12 feet/second.

    The default
    value is 40; however, you should enter the expected or designed flow rate in
    gpm.

  • Line 5.
    Enter the length of the piping run in feet: 100

    The default
    value is 100 feet; however, you should enter the actual length of the pipe run
    in question.

  • Line 6.
    Select the nominal pipe size (NPS) in inches: 2

    The default
    value is an NPS of 2 inches; however, by using the drop-down box you can select
    any pipe size from ½ inch to 24 inches.

  • Line 7.
    Select the nominal thickness of insulation in inches: 1

    The default
    thickness is 1 inch; however, you should use the drop-down box to select the
    desired thickness, from 0 to 4 inches (in half- or quarter-inch increments).

  • Line 8.
    Select an insulation material: Fiberglass
    (to 850°F)

    Note: The
    calculator does not screen for material temperature limitations.

    The
    default box indicates fiberglass; however, you may use the drop-down box to
    select 1 of 8 insulation materials: Calcium Silicate, Cellular Glass,
    Elastomeric, Fiberglass, Mineral Wool, Polyethylene, Polyisocyanurate, or
    Polystyrene.

  • Line 9.
    Select thermal emittance of the outer jacket material: 0.10 – Aluminium,
    oxidized, in service

    The default box indicates in service oxidized
    aluminium;
    however, you may use the drop-down box to select 1 of 11
    exterior surfaces. For a detailed discussion and definition of emittance,
    please refer to the MIDG. 

Based upon the information
variables provided, the Results section displays the temperature rise (°F) and
the temperature of the water leaving the pipe. In this example, the results
were 0.0°F and 35.0°F, respectively.

While the Simple Calculators may not address every insulation material
or application, they are an extremely valuable, easy-to-use tool that can
provide users with online, snapshot information on some the most frequently
asked-about benefits and design considerations of mechanical insulation
systems.

For both the novice and seasoned user, the MIDG—located at www.wbdg.org/midg—is
an excellent resource for basic insulation information and tools for designing
a complex insulation system. The MIDG is comprehensive and contains information
on every step of a project: from design, to selection, specification,
installation, and maintenance of mechanical insulation. The MIDG website is
regularly updated to bring users the most current and complete
information—including the convenient Simple Calculators,
designed to make the most common mechanical insulation calculations simple and
accessible to users of all levels. For further information
on this topic and the calculator please refer to the MIDG, Design Objectives—Process
Control section.