Selection of Correct Insulation Material Thickness for a Specified Application

1.1   Range of Insulation Materials – Indoor/Outdoor Applications

The following table illustrate the name of the insulation material and its temperature application.

1.2   Use of Data Sheets for Material Selection, Thermal Conductivity and Performance Criteria

The use of manufacturer’s data sheets in selecting the correct material is a vital part of the system design and installation procedures. The manufacturer’s data sheets generally contain information on the following:

• Conformity to standards.
• Description of the product.
• Environmental impact of the product.
• Performance and properties.
• Hazards associated with the product.
• Safety precautions.
• What to do in case of an emergency.

1.3   Effects of Environmental Conditions

To offset the effects of installing thermal insulation in various types of adverse environmental conditions, insulation materials should have:

• Resistant to attack by chemicals with which they may have come into contact with. If this is not practical, then the insulation should be provided with a resistant coating or jacket.
• Resistance to moisture sufficient that they do not deteriorate under wet conditions. This is particularly important when operating in the open.
• Resistance to vibration, mechanical shock, and abrasion or, as most insulants by their nature are mechanically weak, at least protection against damage by same.
• Weathering and protection for the purpose of elimination of ingress of moisture, protection against fire and mechanical damage and against corrosion.

1.4   Integration of New Technologies and Materials

New materials are being developed on a constant basis, which are more energy efficient and cost effective. Architects and engineers are using processes that are environmentally responsible and resource-efficient throughout a building's life-cycle: from design, construction, operation, maintenance and renovation. This practice expands and complements the classical building design concerns of economy, utility, durability, and comfort. Innovations and new technological advances in the research and design of insulation materials is playing a major part in the energy efficiency of “green” buildings.

2.0  Selection of Appropriate Material Thickness and Performance Criteria

2.1   Thickness Selection and Performance Requirements for Insulating Materials

In deciding on a certain type and thickness of insulation to be used for a particular application, a number of factors or performance requirements for the insulation system need to be considered. The selection of materials and the insulation thickness to be specified shall be determined according to the intended function of the insulation.
The performance requirements shall be specified in according with the appropriate clauses and tables of the British Standard BS5422:2001, which shall be determined from the following factors:

• System operating temperature.
• Design ambient air temperature.
• Relative humidity of the ambient air.
• Air Velocity
• Location of the plant (indoors or outdoors).
• Pipe Diameter (or flat surface dimensions).
• Orientation of pipes (horizontal or vertical).
• Vertical dimensions of flat surfaces.
• Emissivity of outer surface.

For refrigerated, chilled or other cold applications, the following performance requirements, if applicable, shall also be specified in according with the appropriate clauses and tables of this standard:

• Resistance of the insulation material to the passage of water.
• Permanence of any vapour barriers used.

Refer to BS5422:2001 page 81, for selecting the correct insulation thickness for a particular application.

2.2   Thermal Conductivity

Refer to module 4 – unit 2 – section 2.5

2.3   Multiple Layering of Insulation – Staggering of Joints.

Pipe work is usually insulated with pre-formed pipe section that should be fitted closely to the pipe, and any unavoidable gaps in circumferential or longitudinal joints should be fitted with, compatible insulating material. Total insulation thicknesses greater than 75mm should be applied in multi-layers with all joints in adjacent layers staggered. As shown in the drawing.
Typical method of staggering insulation sections on a straight pipe.
Each section should be held in place by circumferential bands or tie wire at not greater than 50mm to the end of the section. Over tightening of bands or wires should be avoided to prevent cracking of rigid material or opening of joints of flexible material. After tightening, the ends should be pressed into the insulating material to prevent damaging a vapour barrier (if in place) or an outer finishing material.

3.0  Calculation of Material Thickness to Achieve Heat Loss Values

3.1   Heat Loss Calculations

Pipe Insulation is thermal insulation used to prevent heat loss and gain from pipes, to save energy and improve effectiveness of thermal systems.
The benefits include, in addition to reducing costs and environmental impacts of energy consumption:

• Reducing or eliminating condensation on cold pipes.
• Protection from dangerous pipe temperatures.
• In domestic hot-water systems, the water temperature at the point of use can be closer to the temperature at the water heater, and wait time for hot water can be reduced.
• Control of noise.
• Reduction of unwanted heat gain to air-conditioned spaces.

The heat flow through pipe insulation with outer diameter do and inner diameter (of the insulation--equal to outer diameter of the pipe) di is

where  is the length of the pipe, k is the thermal conductivity of the insulation material, and ΔT is the temperature difference between the inner and outer walls of the insulation. If the insulation is sufficiently thick and has sufficiently low thermal conductivity, the outside surface of the insulation will be close to the ambient temperature, and ΔT may be approximated as the temperature difference between the temperature of the fluid in the pipe and the ambient temperature.

3.2   Area, Volume and Density

Area of a Square

The area of a Square  = Length of Side x Length of Side.
Example: Duct Size   =  0.6m x 0.6m.
Area of Duct = 0.36m square.

 Volume

The volume of a duct = Length of Side x Length of Side x Height.
Example: A duct section is 600mm x 600mm x 600mm long.
Calculate the volume of the duct = .6m x .6m x .6m long
Volume of duct = 0.216m³ or 0.216 cubic metres.

Density

Density is defined as mass per unit volume.
Density can be calculated using the formula: d = m ÷ v
where d = density, m = mass, v = volume
The greater the density, the more mass per unit volume.
The unit of density derived from SI units is kilograms per cubic meter, kg/m3 or kgm-3.

3.3   Heat Loss and Insulation Thickness

Insulation is available in nearly any material imaginable.  The most important characteristics of any insulation material include a low thermal conductivity, low tendency toward absorbing water, and of course the material should be inexpensive.   In the chemical industry, the most common insulators are various types of calcium silicate or fibreglass.  Calcium silicate is generally more appropriate for temperatures above 225 0C, while fibreglass is generally used at temperatures below 225 0C.
Since heat loss through insulation is a conductive heat transfer, there are instances when adding insulation actually increases heat loss.  The thickness at which insulation begins to decrease heat loss is described as the critical thickness.   Since the critical thickness is almost always a few millimeters, it is seldom (if ever) an issue for piping. 

Summary

Insulation is available in nearly any material imaginable.  The most important characteristics of any insulation material include a low thermal conductivity, low tendency toward absorbing water, and of course the material should be inexpensive.
The use of manufacturer’s data sheets in selecting the correct material is a vital part of the system design and installation procedures. Care should be taken when calculating heat loss through insulation to ensure that the correct amount and type of insulation is used.