As a part of efforts by the Department of Energy’s Advanced Manufacturing Office to improve the energy efficiency of the U.S. industrial and commercial sectors, the National Insulation Association (NIA), in conjunction with its Alliance partners, worked to design, implement, and execute the Mechanical Insulation Education & Awareness Campaign (MIC).

As we have discussed in previous articles in this series, the MIC was a program to increase awareness of the energy efficiency, emission reduction, economic stimulus potential, and other benefits of thermal insulation for mechanical systems. An integral component of the MIC was the development of a series of “Simple Calculators.” The calculators, listed at  below, provide users with instantaneous information on a variety of 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 available online at www.insulation.org/designguide. 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.

This article will provide an overview and guide to use the Estimate Time to Freezing for Water in an Insulated Pipe Calculator.

Estimate Time to Freezing for Water in an Insulated Pipe Calculator

This calculator estimates the time it takes for a long, fluid-filled pipe (no flow) to reach freezing temperature.

It is important to recognize that insulation retards heat flow; it does not stop it completely. If the surrounding air temperature remains low enough for an extended period, insulation cannot prevent freezing of still water or of water flowing at a rate insufficient for the available heat content to offset heat loss. Well-insulated pipes, however, may greatly extend the time to freezing. Clean water in pipes usually supercools several degrees below freezing before any ice is formed.

After freezing begins, the latent heat of fusion must be removed. Note that the calculator estimates the time to reach the freezing temperature of water (32°F) and does not address the supercooling or latent heat of water. The calculator also ignores the thermal resistance and capacitance of the pipe wall. This calculator is based on the approach published in the 2009 ASHRAE Handbook of Fundamentals (Chapter 23, Equation 1). For further information on this topic and the calculator, please refer to the Design Guide’s section on Design Objectives—Freeze Protection web page.

Calculator Inputs

The calculator requires Input Information for 6 input variables. Results are updated as each input variable is entered.

Following are the instructions and additional information for each input variable.

• Line 1. Initial Temperature of Water in Pipe, °F 42

The default value is 42°F; however, you should enter the actual initial temperature for the water in the pipe.

• Line 2. Ambient Temperature, °F -18

The default value is -18°F; however, you should enter the expected ambient temperature in Fahrenheit. It is suggested you use a realistic worst-case scenario.

• Line 3. Select Pipe Sizes or Tubing Sizes, Pipe Sizes, NPS

The default selection is Pipe Sizes, NPS; however, you should use the drop-down box to select either Pipe or Tubing applications.

• Line 4. Select Nominal Pipe or Tubing Size, 6

The default value is a nominal pipe size of 6″; however, by using the drop-down box you can select a pipe or tubing size from ½” to 24″.

• Line 5. Select Insulation Thickness, 2

The default thickness is 2″; however, you should use the drop-down box to select the desired thickness. It offers a range from .5 to 4 inches.

• Line 6. Select Insulation Material, Polyisocyanurate (-297°F to 300°F)

The default material is Polyisocyanurate; 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. You will note each of the material options contains a general operating temperature range. The Simple Calculators do not have the capability of utilizing user-supplied thermal curves. Thermal conductivity values for the listed materials are based on ASTM material specification values.

Based upon the information variables provided, the Results section displays the estimated time to freeze point in hours; in this example the result was 10.6 hours.

In summary, the Simple Calculators are intended to provide the user with online, easily accessible, snapshot information on some the most frequently asked about benefits and design considerations of mechanical insulation systems. They do not address every insulation material or application condition, but they do provide guidance in a number of applications that are useful for the testing and evaluation of insulation projects and materials.

Whether you need basic insulation information or are designing a complex insulation system, the Design Guide, found online at www.insulation.org/designguide is an excellent resource for the novice or the experienced user. The Design Guide is continually updated and always has the most current and complete information, including the convenient Simple Calculators, which were designed to make common mechanical insulation calculations easy for users of all levels.

These tools can be very helpful in designing a mechanical insulation system and allow the user to easily determine the many benefits and value of thermal insulation for mechanical systems.

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