Pipe insulation

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Pipe insulation and building insulation shown together during construction and once finished in an apartment building in Ontario, Canada. Hallway insulation.jpg
Pipe insulation and building insulation shown together during construction and once finished in an apartment building in Ontario, Canada.

Pipe Insulation is thermal or acoustic insulation used on pipework.

Contents

Applications

Condensation control

Where pipes operate at below-ambient temperatures, the potential exists for water vapour to condense on the pipe surface. Moisture is known to contribute towards many different types of corrosion, so preventing the formation of condensation on pipework is usually considered important.

Pipe insulation can prevent condensation forming, as the surface temperature of the insulation will vary from the surface temperature of the pipe. Condensation will not occur, provided that (a) the insulation surface is above the dewpoint temperature of the air; and (b) the insulation incorporates some form of water-vapour barrier or retarder that prevents water vapour from passing through the insulation to form on the pipe surface.

Pipe freezing

Since some water pipes are located either outside or in unheated areas where the ambient temperature may occasionally drop below the freezing point of water, any water in the pipework may potentially freeze. When water freezes it expands and this expansion can cause failure of a pipe system in any one of a number of ways.

Pipe insulation cannot prevent the freezing of standing water in pipework, but it can increase the time required for freezing to occurthereby reducing the risk of the water in the pipes freezing. For this reason, it is recommended to insulate pipework at risk of freezing, and local water-supply regulations may require pipe insulation be applied to pipework to reduce the risk of pipe freezing. [1] [2]

For a given length, a smaller-bore pipe holds a smaller volume of water than a larger-bore pipe, and therefore water in a smaller-bore pipe will freeze more easily (and more quickly) than water in a larger-bore pipe (presuming equivalent environments). Since smaller-bore pipes present a greater risk of freezing, insulation is typically used in combination with alternative methods of freeze prevention (e.g., modulating trace heating cable, or ensuring a consistent flow of water through the pipe).

Energy saving

Insulated hot water supply and return hydronic piping on a gas-fired boiler Water Boiler Supply and Return Piping.jpg
Insulated hot water supply and return hydronic piping on a gas-fired boiler

Since pipework can operate at temperatures far removed from the ambient temperature, and the rate of heat flow from a pipe is related to the temperature differential between the pipe and the surrounding ambient air, heat flow from pipework can be considerable. In many situations, this heat flow is undesirable. The application of thermal pipe insulation introduces thermal resistance and reduces the heat flow.

Thicknesses of thermal pipe insulation used for saving energy vary, but as a general rule, pipes operating at more-extreme temperatures exhibit a greater heat flow and larger thicknesses are applied due to the greater potential savings. [3]

The location of pipework also influences the selection of insulation thickness. For instance, in some circumstances, heating pipework within a well-insulated building might not require insulation, as the heat that's "lost" (i.e., the heat that flows from the pipe to the surrounding air) may be considered “useful” for heating the building, as such "lost" heat would be effectively trapped by the structural insulation anyway. [4] Conversely, such pipework may be insulated to prevent overheating or unnecessary cooling in the rooms through which it passes.

Protection against extreme temperatures

Where pipework is operating at extremely high or low temperatures, the potential exists for injury to occur should any person come into physical contact with the pipe surface. The threshold for human pain varies, but several international standards set recommended touch temperature limits.

Since the surface temperature of insulation varies from the temperature of the pipe surface, typically such that the insulation surface has a "less extreme" temperature, pipe insulation can be used to bring surface touch temperatures into a safe range.

Control of noise

Pipework can operate as a conduit for noise to travel from one part of a building to another (a typical example of this can be seen with waste-water pipework routed within a building). Acoustic insulation can prevent this noise transfer by acting to damp the pipe wall and performing an acoustic decoupling function wherever the pipe passes through a fixed wall or floor and wherever the pipe is mechanically fixed.

Pipework can also radiate mechanical noise. In such circumstances, the breakout of noise from the pipe wall can be achieved by acoustic insulation incorporating a high-density sound barrier.

Factors influencing performance

The relative performance of different pipe insulation on any given application can be influenced by many factors. The principal factors are:

Other factors, such as the level of moisture content and the opening of joints, can influence the overall performance of pipe insulation. Many of these factors are listed in the international standard EN ISO 23993.[ citation needed ]

Materials

Pipe insulation materials come in a large variety of forms, but most materials fall into one of the following categories.

Mineral wool

Mineral wools, including rock and slag wools, are inorganic strands of mineral fibre bonded together using organic binders. Mineral wools are capable of operating at high temperatures and exhibit good fire performance ratings when tested. [5]

Mineral wools are used on all types of pipework, particularly industrial pipework operating at higher temperatures. [6]

Glass wool

Glass wool is a high-temperature fibrous insulation material, similar to mineral wool, where inorganic strands of glass fibre are bound together using a binder.

As with other forms of mineral wool, glass-wool insulation can be used for thermal and acoustic applications. [7]

Flexible elastomeric foams

These are flexible, closed-cell, rubber foams based on NBR or EPDM rubber. Flexible elastomeric foams exhibit such a high resistance to the passage of water vapour that they do not generally require additional water-vapour barriers. Such high vapour resistance, combined with the high surface emissivity of rubber, allows flexible elastomeric foams to prevent surface condensation formation with comparatively small thicknesses.

As a result, flexible elastomeric foams are widely used on refrigeration and air-conditioning pipework. Flexible elastomeric foams are also used on heating and hot-water systems.

Rigid foam

Pipe insulation made from rigid Phenolic, PIR, or PUR foam insulation is common in some countries. Rigid-foam insulation has minimal acoustic performance but can exhibit low thermal-conductivity values of 0.021 W/(m·K) or lower, allowing energy-saving legislation to be met whilst using reduced insulation thicknesses. [8]

Polyethylene

Polyethylene is a flexible plastic foamed insulation that is widely used to prevent freezing of domestic water supply pipes and to reduce heat loss from domestic heating pipes.

The fire performance of Polyethylene is typically 25/50 E84 compliant up to 1" thickness.

Cellular Glass

100% Glass manufactured primarily from sand, limestone & soda ash. Cellular insulations are composed of small individual cells either interconnecting or sealed from each other to form a cellular structure. Glass, plastics, and rubber may comprise the base material and a variety of foaming agents are used. Cellular insulations are often further classified as either open cell (cells are interconnecting) or closed cell (cells sealed from each other). Generally, materials that have greater than 90% closed cell content are considered to be closed cell materials.

Aerogel

Silica Aerogel insulation has the lowest thermal conductivity of any commercially produced insulation. Although no manufacturer currently manufactures Aerogel pipe sections, it is possible to wrap Aerogel blanket around pipework, allowing it to function as pipe insulation.

The usage of Aerogel for pipe insulation is currently limited.

Heat flow calculations and R-value

Heat flow passing through pipe insulation can be calculated by following the equations set out in either the ASTM C 680 [9] or EN ISO 12241 [10] standards. Heat flux is given by the following equation:

Where:

In order to calculate heat flow, it is first necessary to calculate the thermal resistance ("R-value") for each layer of insulation.

For pipe insulation, the R-value varies not only with the insulation thickness and thermal conductivity ("k-value") but also with the pipe outer diameter and the average material temperature. For this reason, it is more common to use the thermal conductivity value when comparing the effectiveness of pipe insulation, and R-values of pipe insulation are not covered by the US FTC R-value rule Archived 2007-12-31 at the Wayback Machine .

The thermal resistance of each insulation layer is calculated using the following equation:

Where:

Calculating the heat transfer resistance of the inner- and outer-insulation surfaces is more complex and requires the calculation of the internal- and external-surface coefficients of heat transfer. Equations for calculating this are based on empirical results and vary from standard to standard (both ASTM C 680 and EN ISO 12241 contain equations for estimating surface coefficients of heat transfer).

A number of organisations such as the North American Insulation Manufacturers Association and Firo Insulation offer free programs that allow the calculation of heat flow through pipe insulation.

Related Research Articles

The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by , , or and is measured in W·m−1·K−1.

<span class="mw-page-title-main">Thermal insulation</span> Minimization of heat transfer

Thermal insulation is the reduction of heat transfer between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with specially engineered methods or processes, as well as with suitable object shapes and materials.

<span class="mw-page-title-main">Thermal mass</span> Use of thermal energy storage in building design

In building design, thermal mass is a property of the matter of a building that requires a flow of heat in order for it to change temperature. In scientific writing the term "heat capacity" is preferred. It is sometimes known as the thermal flywheel effect. The thermal mass of heavy structural elements can be designed to work alongside a construction's lighter thermal resistance components to create energy efficient buildings.

Conduction is the process by which heat is transferred from the hotter end to the colder end of an object. The ability of the object to conduct heat is known as its thermal conductivity, and is denoted k.

<span class="mw-page-title-main">Wetsuit</span> Garment for thermal insulation from water

A wetsuit is a garment worn to provide thermal protection while wet. It is usually made of foamed neoprene, and is worn by surfers, divers, windsurfers, canoeists, and others engaged in water sports and other activities in or on water. Its purpose is to provide thermal insulation and protection from abrasion, ultraviolet exposure, and stings from marine organisms. It also contributes extra buoyancy. The insulation properties of neoprene foam depend mainly on bubbles of gas enclosed within the material, which reduce its ability to conduct heat. The bubbles also give the wetsuit a low density, providing buoyancy in water.

<i>R</i>-value (insulation) Measure of how well an object, per unit of area, resists conductive flow of heat

In the context of construction, the R-value is a measure of how well a two-dimensional barrier, such as a layer of insulation, a window or a complete wall or ceiling, resists the conductive flow of heat. R-value is the temperature difference per unit of heat flux needed to sustain one unit of heat flux between the warmer surface and colder surface of a barrier under steady-state conditions. The measure is therefore equally relevant for lowering energy bills for heating in the winter, for cooling in the summer, and for general comfort.

<span class="mw-page-title-main">Heat sink</span> Passive heat exchanger that transfers the heat

A heat sink is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is dissipated away from the device, thereby allowing regulation of the device's temperature. In computers, heat sinks are used to cool CPUs, GPUs, and some chipsets and RAM modules. Heat sinks are used with other high-power semiconductor devices such as power transistors and optoelectronics such as lasers and light-emitting diodes (LEDs), where the heat dissipation ability of the component itself is insufficient to moderate its temperature.

<span class="mw-page-title-main">Heat pipe</span> Heat-transfer device that employs phase transition

A heat pipe is a heat-transfer device that employs phase transition to transfer heat between two solid interfaces.

In thermodynamics, the heat transfer coefficient or film coefficient, or film effectiveness, is the proportionality constant between the heat flux and the thermodynamic driving force for the flow of heat. It is used in calculating the heat transfer, typically by convection or phase transition between a fluid and a solid. The heat transfer coefficient has SI units in watts per square meter per kelvin (W/m2K).

A vacuum insulated panel (VIP) is a form of thermal insulation consisting of a gas-tight enclosure surrounding a rigid core, from which the air has been evacuated. It is used in building construction, refrigeration units, and insulated shipping containers to provide better insulation performance than conventional insulation materials.

<span class="mw-page-title-main">Trace heating</span>

Electric heat tracing, heat tape or surface heating, is a system used to maintain or raise the temperature of pipes and vessels using heat tracing cables. Trace heating takes the form of an electrical heating element run in physical contact along the length of a pipe. The pipe is usually covered with thermal insulation to retain heat losses from the pipe. Heat generated by the element then maintains the temperature of the pipe. Trace heating may be used to protect pipes from freezing, to maintain a constant flow temperature in hot water systems, or to maintain process temperatures for piping that must transport substances that solidify at ambient temperatures. Electric trace heating cables are an alternative to steam trace heating where steam is unavailable or unwanted.

In physics, thermal contact conductance is the study of heat conduction between solid or liquid bodies in thermal contact. The thermal contact conductance coefficient, , is a property indicating the thermal conductivity, or ability to conduct heat, between two bodies in contact. The inverse of this property is termed thermal contact resistance.

<span class="mw-page-title-main">Building insulation</span> Material to reduce heat transfer in structures

Building insulation is material used in a building to reduce the flow of thermal energy. While the majority of insulation in buildings is for thermal purposes, the term also applies to acoustic insulation, fire insulation, and impact insulation. Often an insulation material will be chosen for its ability to perform several of these functions at once.

<span class="mw-page-title-main">Building insulation material</span> Insulation material

Building insulation materials are the building materials that form the thermal envelope of a building or otherwise reduce heat transfer.

<span class="mw-page-title-main">Thermal bridge</span>

A thermal bridge, also called a cold bridge, heat bridge, or thermal bypass, is an area or component of an object which has higher thermal conductivity than the surrounding materials, creating a path of least resistance for heat transfer. Thermal bridges result in an overall reduction in thermal resistance of the object. The term is frequently discussed in the context of a building's thermal envelope where thermal bridges result in heat transfer into or out of conditioned space.

<span class="mw-page-title-main">Heat flux</span> Vector representing the energy passing through a given area per unit time

In physics and engineering, heat flux or thermal flux, sometimes also referred to as heat flux density, heat-flow density or heat-flow rate intensity, is a flow of energy per unit area per unit time. Its SI units are watts per square metre (W/m2). It has both a direction and a magnitude, and so it is a vector quantity. To define the heat flux at a certain point in space, one takes the limiting case where the size of the surface becomes infinitesimally small.

There are a number of possible ways to measure thermal conductivity, each of them suitable for a limited range of materials, depending on the thermal properties and the medium temperature. Three classes of methods exist to measure the thermal conductivity of a sample: steady-state, time-domain, and frequency-domain methods.

<span class="mw-page-title-main">Insulated pipe</span>

Insulated pipes are widely used for district heating and hot water supply. They consist of a steel pipe called "service pipe", a thermal insulation layer and an outer casing. The insulation bonds the service pipe and the casing together. The main purpose of such pipes is to maintain the temperature of the fluid inside the service pipes. Insulated pipes are commonly used for transport of hot water from district heating plants to district heating networks and for distribution of hot water inside district heating networks.

In heat transfer, thermal engineering, and thermodynamics, thermal conductance and thermal resistance are fundamental concepts that describe the ability of materials or systems to conduct heat and the opposition they offer to the heat current. The ability to manipulate these properties allows engineers to control temperature gradient, prevent thermal shock, and maximize the efficiency of thermal systems. Furthermore, these principles find applications in a multitude of fields, including materials science, mechanical engineering, electronics, and energy management. Knowledge of these principles is crucial in various scientific, engineering, and everyday applications, from designing efficient temperature control, thermal insulation, and thermal management in industrial processes to optimizing the performance of electronic devices.

<span class="mw-page-title-main">Heat flux measurements of thermal insulation</span>

Heat flux measurements of thermal insulation are applied in laboratory and industrial environments to obtain reference or in-situ measurements of the thermal properties of an insulation material. Thermal insulation is tested using nondestructive testing techniques relying on heat flux sensors. Procedures and requirements for in-situ measurements are standardized in ASTM C1041 standard: "Standard Practice for In-Situ Measurements of Heat Flux in Industrial Thermal Insulation Using Heat Flux Transducers".

References

  1. "UK Water bylaw pipe insulation requirements", UK Copper Board, "Archived copy" (PDF). Archived from the original (PDF) on 2015-06-30. Retrieved 2015-06-28.{{cite web}}: CS1 maint: archived copy as title (link)
  2. "Tips to Keep Pipes from Freezing".
  3. "Pipe insulation thickness guide", Thermal Insulation Manufacturers & Suppliers Association, http://timsa.associationhouse.org.uk/default.php?cmd=210&doc_category=98
  4. "Passiv Haus requires no heating or cooling pipes", PassivHaus UK, http://www.passivhaus.org.uk/index.jsp?id=668 Archived 2010-08-14 at the Wayback Machine
  5. "Rock wool technical description", Rockwool, http://guide.rockwool.co.uk/products/industrial-(rti)/pipe-section-mat.aspx Archived 2012-07-22 at the Wayback Machine
  6. "Industrial Rockwool insulation", Rockwool, http://guide.rockwool.co.uk/products/industrial-(rti)/process-pipe.aspx Archived 2012-06-18 at the Wayback Machine
  7. "Glass wool technical description", Knauf, http://www.knaufinsulation.co.uk/solutions/hvac/pipes/hvac_pipes_-_small_bore.aspx
  8. "Phenolic foam technical description", European Phenolic Foam Association, http://www.epfa.org.uk/properties.htm Archived 2016-05-23 at the Portuguese Web Archive
  9. "ASTM C 680 calculation standard". American Society for Testing and Materials.
  10. "EN ISO 12241 calculation standard". International Organization for Standardization.