Mechanical insulation, although important to facility operations and manufacturing processes is often overlooked and undervalued. National standards, universal energy policies or generally accepted recommendations as to what should be insulated, what insulation systems are acceptable for a specific use and application best practices do not currently exist. As a result, the value of mechanical insulation is not being realized to its potential in reducing our dependency on foreign energy sources, improving our environment, improving our global competitiveness and providing a safer work environment.
Insulation is applied but rarely engineered. With the best intentions, but not necessarily with thorough knowledge, many specifications have evolved over the years primarily based upon modification of old documents. This practice combined with the lack of mechanical insulation educational and awareness programs as to the value in having a properly engineered, installed and maintained mechanical insulation system has led to the underutilization of mechanical insulation in energy conservation, emission reduction, process and productivity improvement, life cycle cost reduction, personnel safety, life safety, work place improvements and host of other applications.
In response, the National Institute of Building Sciences (NIBS) formed a Committee to bring together major governmental agencies, private industry and organizations that are concerned with the design, installation and maintenance of mechanical insulation. This committee, referred to as the National Mechanical Insulation Committee (NMIC) offers the opportunity for a constructive public and private partnership in the examination of mechanical insulation practices, the development of recommendations, and the promotion of education regarding the merits and value of mechanical insulation.
National Mechanical Insulation Committee
Individuals from the following government agencies and industry associations worked together in the development of the Mechanical Insulation Design Guide with funding being shared equally between government agencies through NIBS and industry through NIA.
- American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
- Architectural Computer Services Inc. (ARCOM - Masterspec)
- General Services Administration (GSA)
- Midwest Insulation Contractors Association (MICA)
- National Institute of Building Sciences (NIBS)
- National Insulation Association (NIA)
- North American Insulation Manufacturers Association (NAIMA)
- Oak Ridge National Laboratory (ORNL)
- United States Army Corp of Engineers (USACE)
- United States Department of Energy (DOE)
- United States Department of Veterans Affairs (VA)
- United States Naval Facilities Engineering Command (NAVFAC)
National Mechanical Insulation Committee (NMIC) Objective
The overall objective of NMIC is to identify, develop and disseminate information related to mechanical insulation in commercial and industrial applications by examining current policies, procedures and practices; identifying research or testing needs; developing recommendations utilizing the best science and information available; providing education and awareness programs as to the merits and value of proper insulation systems and to establish a roadmap to implement improvements in design, insulation system selection and establish application best practices.
The first initiative is the development of an internet based Mechanical Insulation Design Guide (MIDG) and to make it available through the NIBS Whole Building Design Guide. The MIDG is to be continually updated as deemed necessary and appropriate by the NMIC to reflect current and state of the art information.
Mechanical Insulation Market Definitions
MECHANICAL INSULATION is defined to encompass all thermal, acoustical and personnel safety requirements in:
- Mechanical piping and equipment, hot and cold, applications
- Heating, Venting & Air Conditioning (HVAC) applications
- Refrigeration and other low temperature piping and equipment applications
Mechanical insulation in the BUILDING SECTOR is defined to include education, health care, institutional, retail and wholesale, office, food processing, light manufacturing and similar type applications. This Sector is often referred to as the Commercial Sector.
Scope of the Design Guide
The scope of this design guide includes the design, specification, installation, and maintenance of insulation systems for use within the markets defined above. Specialized insulated air handling products (flex-duct and duct board products) are not considered to be mechanical insulation industry from the perspective of this guide and accordingly are not addressed.
MIDG is part of the NIBS WBDG-Whole Building Design Guide®. The Whole Building Design Guide is an evolving web-based resource intended to provide architects, engineers, facility managers, project managers etc. with design guidance, criteria and technology for "whole buildings". The WBDG is continually augmented with updated and new information and is structured as a "vertical portal", enabling users to access increasingly specific information as they navigate deeper into the site. The Mechanical Insulation Design Guide has been developed within the same principles as the WBDG.
Using the Mechanical Insulation Design Guide
As the name implies, the Mechanical Insulation Design Guide is primarily intended to assist designers, specifiers, facility owners and users of mechanical insulation systems. The engineering design process is generally divided into a number of phases along these lines:
- Identify the need or define the problem
- Gather pertinent information
- Identify possible solutions
- Analyze and select a solution
- Communicate the solution
For an insulation design project, these phases could be expanded and restated as follows:
- Identify the design objectives (Why insulate?)
- Identify what is to be insulated (What?)
- Identify the location and appropriate ambient design conditions (Where?)
- Identify the materials and systems available (How?)
- Analyze and determine the acceptable solutions (How To? and How Much?)
- Write the specification
For insulation, the design process boils down to developing answers to six basic questions:
Why?, What?, Where?, How?, How To? and How Much?
Example problems which illustrate the insulation design process, as well as the use of the Mechanical Insulation Design Guide can be viewed below.
The Mechanical Insulation Design Guide is organized to help develop these answers. The guide is divided into five sections as follows:
Example Design Problems
The following examples are intended to illustrate the insulation system design process as well as the use of the Mechanical Insulation Design Guide.
A light manufacturing facility near Midway Airport in Chicago is expanding. 150 psig steam will be required for several of the new processes, and multiple natural gas fired boilers will be installed to provide the required steam. These boilers will also serve as the energy source for space heating in the plant and in the adjacent office area. The new boilers will be located in an existing boiler house remote to the main plant. The main steam line is a NPS 8 steel and will be located in overhead pipe racks adjacent to a pedestrian walkway. Total length of the outdoor run is 150 ft. The task is to design the insulation system for the NPS 8 line.
Step 1 Identify the design objective. (Why)
Design objectives and considerations are discussed in Design Objectives section of the MIDG. After reviewing this section, it is determined that this project has multiple design objectives. First, operating costs are a concern as the energy costs are expected to be a significant portion of the unit costs of the manufactured product. In addition, the overhead pipe rack will include a pedestrian walkway. Personnel protection will therefore be important. Abuse resistance will be a design consideration due to the proximity of the steam line to the pedestrian walkway.
Step 2 Identify what is to be insulated. (What)
The main piping run will be steel piping and will be oriented primarily horizontally. The steam pressure in this line will be controlled to a set point of 150 psig. The temperature of this saturated steam will be 366 °F.
Step 3 Identify the location and appropriate ambient conditions. (Where)
The 8 NPS steel piping runs outdoors between the boiler house and the main plant. After reviewing the Resources section of the MIDG, we recognize that design weather data for the Chicago is available from the ASHRAE Handbook - Fundamentals. Annual average weather data is available via the National Climatic Data Center website. For energy calculations, we will use the average annual temperature and wind speed at Midway Airport (51 °F and 10 mph). For personnel protection, we will use the ASHRAE 0.4% summer design temperature of 92.3 °F and 0 mph wind speed.
Step 4 Identify the materials and systems available. (How)
Candidate insulation materials and systems are reviewed in the Materials and Systems Section. After entering the operating temperature of 366 °F into the Performance Property Guide (Table 1), there are seventeen available insulation materials that satisfy the operating temperature requirement of 366 °F. Selecting the material types that pertain to pipe insulations, we identify the following candidate materials:
- Cellular Glass (ASTM C 552)
- Mineral Fiber Pipe (ASTM C 547 Type I Fiberglass)
- Mineral Fiber Pipe (ASTM C 547 Types II - V Mineral Wool)
- Polyimide (ASTM C 1482)
- Calcium Silicate (ASTM C 533)
- Expanded Perlite (ASTM C 610)
Referring again to Table 1, these insulation materials differ in several key properties (e.g. density, thermal conductivity, and compressive resistance) but all would meet the thermal requirements for the project.
For jacketing/finishing systems, we note that the location is outdoors so weather protection is required. We also note that abuse resistance is a consideration for the design for the piping located in the pipe rack. Possible jacketing materials include metal, UV stabilized PVC jacket, synthetic rubber laminates, and multi-ply laminates. Since low water vapor permeance is not a consideration for this project, we will specify aluminum jacketing.
Step 5. Analyze and determine the acceptable solutions. (How Much and How To)
After reviewing the Design Data section of the MIDG, we utilize the NAIMA 3E Plus computer program to analyze the candidate systems to estimate the surface temperatures and heat losses. For these calculations, we assume horizontal pipe and a jacket emittance of 0.1 (corresponding to weathered aluminum). Starting with the personnel protection objective (with a max surface temperature criterion of 140 F) at the summer design condition of 92.3 °F and 0 mph wind speed, we calculate required thicknesses for each of the candidate materials.
Thickness Required for Personnel Protection NPS 8 Piping
|Material||Thickness, in.||Surface Temp. °F||Heat Loss, Btu/(h·ft)|
Based on these results, we conclude that approximately 2 to 2-1/2 inches of insulation will be required to keep the temperature of the outer surface of the insulation system at or below 140 °F.
The next step is to analyze the candidate insulation systems with respect to operating costs. Using the Cost of Energy function in the 3E Plus program, and using the expected cost of natural gas of $10/MCF with a boiler efficiency of 75%, we generate the following table:
Annual Cost of Lost Energy, $/ft/yr
|Thickness||Cellular Glass||Polyimide||Mineral Fiber (Fiberglass)||Mineral Fiber (Mineral Wool)||Calcium Silicate||Expanded Perlite|
Reviewing these data, it is apparent that there are significant cost savings available by going beyond the 2 to 2-½" thicknesses required for personnel protection. Using the default cost data from the Economic Thickness section of 3E Plus, with a labor rate of $60/hr, a discount rate of 8% and an estimated life of 10 years, we determine that a thickness of 4" insulation (single layer) minimizes the life cycle cost of the insulation system. This result, however, is dependent on the installed costs of the insulation material and could vary from the default values.
At this point the designer should recognize that the operating cost estimates for several of the candidates are sufficiently close to warrant additional analysis. Using the links in the Materials and Systems section, he could reference product data sheets for specific insulations to refine the analysis. The additional design consideration of abuse resistance may warrant the review of additional product properties (e.g. compressive resistance). After this review, he could prepare the specification around several of the best candidates and competitively bid the project.
Step 6. Write the specification
The final step is to communicate the design intent utilizing the specification (How To). The designer may have access to one or more guide specifications (e.g. ARCOM MasterSpec or UFGS 23 07 00) which could be utilized.
A standby diesel powered generator set is to be installed to provide backup power for a large hospital complex. The generator set is located in an unconditioned but ventilated detached building on the hospital grounds. Exhaust gases will be piped out of the building but will pass near high traffic walkways accessible to maintenance personnel. The generator set will be run periodically for testing and maintenance, but is designed to run continuously if needed. The exhaust gases are estimated to be about 1,000 F under full load conditions. Exhaust piping is NPS 12 steel.
Step 1. Identify the design objective. (Why)
Design objective are discussed in Section 1. The design objective here is personnel protection. Since we are dealing with exhaust gases ducted outside the building, energy conservation is not a concern. The insulation system will be designed to keep the surface temperature below 140 F at worst case conditions. Since the exhaust piping will be near a high traffic area, abuse resistance is a design consideration.
Step 2. Identify what is to be insulated. (What)
The 12 NPS steel piping in the generator building and has both horizontal and vertical runs. The temperature of the exhaust gases in this piping will vary depending on the load on the generator set. For the purpose of this example, we will assume full load conditions (1,000 F).
Step 3 Identify the location and appropriate ambient conditions. (Where)
The exhaust piping is located in the stand-alone generator building. This building is unconditioned during the summer months. Ventilation in the form of exhaust fans is provided. The thermal conditions in the generator building will vary with the outdoor weather and with internal loading.
For outdoor conditions, design weather data (ASHRAE Handbook—Fundamentals) shows four values for the outdoor design dry-bulb temperature for Charlotte.
Design Cooling Temperatures for Charlotte, NC
|Level||Design Dry-bulb Temperature, F|
|Mean of Annual Extremes||97.0|
The 0.4%, 1%, and 2% levels represent the annual cumulative frequency of occurrence. In other words, we could expect, based on the thirty-year weather record examined, that the outdoor dry-bulb temperature would exceed the 1% level 1% of the time (i.e. 88 hours per year). The exhaust piping, however, is not located outdoors. Conditions indoors may be warmer (particularly if the generator set is running at full load). How much warmer is difficult to determine, but it seems prudent to select an indoor design temperature of 95 F for this example.
Since this generator building would be ventilated during equipment operation, air movement around potions of the exhaust piping could be significant. However, since this is a personnel protection design, we will assume no air movement.
Step 4 Identify the materials and systems available. (How)
Materials and systems are reviewed in Section 2. Referring to Table 1, there are three currently available insulation products that satisfy the operating temperature of 1,000 F:
- Calcium Silicate Pipe (ASTM C 533, Type I)
- Mineral Fiber Pipe ( ASTM C 547, Types II-V)
- Expanded Perlite Pipe (ASTM C 610)
Referring again to Table 1, these insulation materials differ in several key properties (e.g. density, thermal conductivity, and compressive resistance) but all three would meet the thermal and physical requirements for the project.
For jacketing/finishing systems, we note that the location is indoors so weather protection is not required. We also note that this is an above ambient application so a vapor retarder is not required. Referring to Section 1, we note that personnel protection applications should utilize a high emittance surface to minimize surface temperatures. We also note that abuse resistance is a consideration for this design. We therefore identify painted metal as a candidate jacketing material.
Step 5 Analyze and determine acceptable solutions. (How Much and How To)
Utilizing the NAIMA 3E Plus computer program, we analyze the three candidate systems to estimate the surface temperatures assuming horizontal pipe.
Calculated Surface Temperatures of Three Insulation Options
|Thickness, in.||Calcium Silicate
ASTM C 533-04
ASTM C 547-06
ASTM C 610-05
Based on this analysis, we conclude that approximately 5 to 6 inches of insulation will be required. We also note that the calculated surface temperatures are very similar, all falling within a range of about 5 F. This again indicates that all three of these options would provide an acceptable solution. At this point the designer could reference product data sheets for specific insulation products to refine the analysis. Alternatively, he could prepare the specification around all three choices and competitively bid the project.
Step 6 Write the specification.
The final step is to communicate the design intent utilizing the specification. The designer may have access to one or more guide specifications (e.g. ARCOM MasterSpec or UFGS 23 07 00) which could be utilized.