Download Module 6 How to implement thermal insulation to HVAC Services

Energy Efficiency
E-modules - Guidance
Application of Thermal Insulation to HVAC Services in Public
Sector Buildings
Application of Thermal Insulation to HVAC Services in Public Sector Buildings | 2
CONTENTS
1
Introduction
3
2
Learning Objectives and Outcomes
3
2.1
Learning Objectives
3
2.2
Learning Outcomes
3
3
Overview and Principles of Thermal Insulation
4
3.1
Conduction
4
3.2
Convection
4
3.2.1
3.3
4
Thermal Convective Heat Transfer Coefficient
Overall Heat Transfer Coefficient
Thermal Insulation of HVAC Services
4
5
7
4.1
Scottish Building Regulations
7
4.2
Common Opportunities
8
4.2.1
Values, Flanges and End Caps
8
4.2.2
Hot Water Tanks
8
4.2.3
Plate Heat Exchangers
8
4.3
Common Factors in Installation Improvement Projects
9
4.4
Possible Risks
9
5
Useful Links and References
11
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1 Introduction
This guidance follows the format of the e-module “Application of Thermal Insulation to HVAC
Services in the Public Sector” and provides further details on the subjects covered in the
module.
Please note that module users working in a healthcare environment should always refer to
the relevant Scottish Health Technical Memorandum (SHTM) prior to considering installation
of the measures suggested in the module. The advice given in the SHTM may conflict with
the advice given in this module, as it has been developed for the wider public sector. The
relevant SHTM can be found on the Health Facilities Scotland website.
2 Learning Objectives and Outcomes
2.1 Learning Objectives
The learning objectives for this module are to:
 Understand the benefits of thermal insulation for HVAC services; and
 Understand the applications of thermal insulation for HVAC services.
2.2 Learning Outcomes
The learning outcomes for this module are to:
 Describe the principles of heat loss and the effects of thermal insulation;
 Identify opportunities for implementing thermal insulation to HVAC services installed in
Scottish public sector sites and buildings;
 Be able to carry out an insulation survey of HVAC thermal insulation and identify
opportunities for savings;
 Be able to prioritise the opportunities for applying thermal insulation of HVAC systems in
public sector buildings; and
 Understand the key aspects in relation to thermal insulation of HVAC systems when
building a business case.
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3 Overview and Principles of Thermal Insulation
Whenever there is a temperature difference between two objects, or an object and a fluid,
in close proximity, heat transfer will take place. There are three methods of heat transfer:
 Conduction is where heat moves through a solid object;
 Convection where heat is moved around in a fluid or gas, for example water or air; and
 Radiation where heat is transferred between objects by electromagnetic waves (primarily
infrared).
With regard to insulation, all three of these methods of heat transfer are important.
Insulation can reduce heat conduction by slowing the rate that heat is passed from the
source to the receiving medium.
Convection can be reduced by slowing the movement of the air or liquid to slow the rate of
heat movement. An example is stopping draughts.
Radiation can be decreased by changing the nature of the radiating surface. This is why
many surface insulation coverings have a shiny surface. The property of the surface that
affects this is called emissivity.
3.1 Conduction
Heat is transferred between two regions of a solid object with a temperature gradient. This
leads to variation in temperature in two regions. An example is the heat transfer occurring
through the metal in a pipe from inner diameter to outer diameter.
The conductive heat transfer can be calculated using the following formula:





Where
Where
Where
Where
Where
is the heat transfer
is the thermal conductivity of the material ( ⁄
)
is the heat transfer Area
is the temperature difference across the material
is the material thickness
3.2 Convection
Heat is transferred between a solid object and a fluid at the object surface. The convention
heat transfer can be calculated using the following formula:
 Where
 Where
is the heat transfer
is the convective heat transfer coefficient ( ⁄
 Where
 Where
is the heat transfer Area
is the temperature difference across the material
)
3.2.1 Thermal Convective Heat Transfer Coefficient
The thermal convective heat transfer coefficients are determined for any fluid depending on
a number of factors including velocity and fluid mechanical properties.
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3.3 Overall Heat Transfer Coefficient
The overall heat transfer coefficient can be calculated using the following formula:
⁄
⁄
⁄
⁄
 Where
is the heat transfer per unit time
 Where
 Where
is the contact Area of each side
is the thermal conductivity of the material
 Where
is the individual convection heat transfer coefficient for each fluid
 Where
⁄
⁄
⁄
is the wall thickness
The value of U is representative of the convection with each fluid on either face of the solid
and the conduction through the solid. Once U is calculated the overall heat transfer can be
simplified using the following formula:
 Where
 Where
is the heat transfer
is the heat transfer per unit time
 Where
 Where
is the contact Area
is the temperature difference
⁄
Even a simple heat transfer calculation can be complicated, involving many variable
parameters including the temperature of the surface, the temperature of the surrounding air
and the properties of the materials. With regard to insulation, the simple reality is that
insulating anything that is hot will lead to energy savings that will likely pay for itself in a
short time period.
The theory can be shown using an example. Figure 3.1 shows the annual saving from
insulating 1 metre, of 80 millimetre diameter, heating pipework with different thicknesses of
insulation, based on typical values and operating 24 hours per day all year round. From a
loss of £77 per annum, adding just 5 millimetres of insulation would reduce the heat loss by
over 60% (or £46). Adding a further 5 millimetres of insulation would reduce the loss by a
further 13% (or a further £10). However increasing the insulation by a further 15
millimetres of insulation would only save an extra £5. The return diminishes for each
incremental increase in insulation thickness, with the additional saving from increasing the
insulation from 15 millimetres to 50 millimetres only saving an extra £8 per year.
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Figure 3.1 - Insulation Thickness and Heat Loss Cost
This example shows it is better to have all hot surfaces insulated in some way, than only
some insulated to a high level. In other words insulating a lot a little, is better than
insulating a little a lot.
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4 Thermal Insulation of HVAC Services
In 1999, the Thermal Insulation Manufactures and Suppliers Association (TIMSA)
commissioned a study to assess the contribution of pipe insulation to possible further
energy saving in the UK. It found that the use of pipe insulation was already saving in
excess of 300 million tonnes of CO2 equivalent annually. However, there remained
considerable opportunities to make further savings by insulating otherwise uninsulated
pipes, with over 30% of the opportunity in the UK for retrofitting insulation in the area of
commercial heating and hot water systems.
A review of Scottish Public Sector Carbon Management Plans by the Carbon Trust found that
the third most common improvement projects identified were related to insulation, including
HVAC. Within the HVAC sector, installing valve insulation was found to have one of the best
impacts with regard to return on investment and magnitude of carbon savings.
4.1 Scottish Building Regulations
The Scottish Building Regulations stipulate when, where and how insulation must be applied
in new installations. The Building Regulations Non-Domestic Technical Handbook Section
6.4.1 (Insulation of Pipes and Ducts) states that:
“Pipes and ducts used for heating and cooling should be insulated to reduce
uncontrolled heat loss in the case of the former and uncontrolled heat gain in the
case of the latter.”
This is not necessary where the pipes or ducts always contribute to the heating or cooling
demands of the room or space, and the pipes or ducts are located at a height of 3 metres or
less above the floor.
Pipes that are used to supply hot water should be insulated against uncontrolled heat loss.
This is to conserve heat in the hot water pipes between frequent successive draw-offs.
Insulation for pipes and ducts should follow the guidance given for insulation thickness in
BS5422, Method for specifying thermal insulating materials for pipes, tanks, vessels,
ductwork and equipment operating within the temperature range -40°C to +700°C. For
example the selection of insulation thickness should be representative of the environmental
and fluid temperatures of the pipework.
Recently, the Scottish Building Regulations have been extended to cover the insulation
requirements for work on existing systems. The Building Regulations Non-Domestic
Technical Handbook Section 6.4.3 (Work on Existing Buildings) states that:
“Where a new boiler or hot water storage vessel is installed or where existing
systems are extended, new or existing pipes, ducts and vessels that are accessible
or exposed as part of the work should be insulated as for new systems. Replacement
hot water storage vessels should be insulated as for new systems.”
Where pipes, ductwork or vessels are being replaced in part, or being extended, the existing
system should be improved to meet current standards. Guidance on the extent to which
improvement should be made is given in Annex 6.G ‘Improvement to the energy
performance of existing building services when carrying out building work’.
It is recognised that complete insulation will sometimes not be possible, such as where
services pass through or around structural building components for example floor joists, or
where existing systems are wholly or partially retained as part of conversion works. In such
cases, insulation should be fitted as for new systems as far as is reasonably practicable.
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Table 4.1 shows different types of insulation that can be commonly applied to HVAC
services.
Table 4.1 – Applications of different types of insulation
Type of Insulation
Maximum
Temperature (°C)
Application
For hot services:
Glass mineral fibre, aluminium
foil faced, preformed
230
Internal, concealed services
Glass mineral fibre, aluminium
clad
230
Internal services, exposed to damage
and external services open to the
weather (joints sealed)
830
Internal, concealed services
830
Internal services, exposed to damage
and external services open to the
weather (joints sealed)
Rock mineral fibre aluminium
faced, preformed
Rock mineral fibre aluminium
foil faced, preformed,
aluminium clad
For services at ambient
temperature or below:
Polyethylene foam
80
Internal and external (joints sealed)
4.2 Common Opportunities
4.2.1 Values, Flanges and End Caps
Although pipework is normally insulated, there remains a large opportunity for insulating
valves, flanges and end caps. An exposed valve is equivalent to 1 metre of un-insulated
pipe of the same diameter. It may be that they have never had insulation, or that it has
been removed at some time in the past during maintenance and was not been reinstated or
replaced. In this instance it is recommended that new jackets are installed which make
replacement easy after maintenance tasks, for example Velcro or hook and eye fastening.
The savings achievable will vary depending on the diameter of the pipework and the
temperature of the water. Using standard rules of thumb, the cost savings from fitting a
valve jacket in a school boilerhouse range from £3 for a 10 millimetre valve to £25 for a 150
millimetre valve. However, installing insulation in a building with extended hours of
operation, such as a care home would lead to a quicker return on investment. In this
example, the savings are over 3 times higher than in a primary school, with an annual
saving of £95 for 150 millimetre valve.
4.2.2 Hot Water Tanks
Hot water tanks are another common opportunity. Although the hot water tank will almost
certainly be insulated, inspection hatches are often exposed, again due to insulation being
removed at some time in the past during maintenance and was not reinstated or replaced.
It is recommended that new jackets are installed with Velcro or hook and eye type
fastenings.
4.2.3 Plate Heat Exchangers
Another common opportunity is the plate heat exchangers. They may have been installed as
part of an energy saving project, but they often do not have an insulation jacket which
negates the benefit of their reduced size over hot water tanks. Once again it is
recommended that new jackets are installed with Velcro or hook and eye type fastenings.
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A quick and relatively easy method of assessing the performance of existing insulation, or to
assess whether inaccessible pipework is insulated, is to use a thermal imaging camera. The
images in Figures 4.1 show a thermal image of insulated steam pipework.
Figure 4.1 – Thermal image of insulated steam pipework
The insulation is performing less well on the middle pipe and in certain areas the insulation
has deteriorated quite considerably. In this case, it may more cost effective to undertake
targeted replacement or upgrade sections of the insulation.
4.3 Common Factors in Installation Improvement Projects
Opportunities for insulation can be prioritised based on a few factors:
1.
2.
3.
4.
5.
6.
Safety. If a hot (or cold) surface is a risk to the occupants, insulation can be used as a
control measure;
High temperatures. The higher the temperature, the greater the heat loss, and the
better the financial return from installing insulation;
Longer building operating hours will lead to higher savings;
Electrically or oil heated water. The cost of electricity and oil are significantly higher
than for natural gas, meaning heat loss costs more in water systems heated in this
way;
Plant rooms that have external walls, floors and roofs. Heat is not actually lost until it
leaves the building. Heat loss from an internal plant room will simply lead to
uncontrolled heat gain in the adjacent spaces. Plant rooms that are external to the
building or have external surfaces will offer higher savings from insulation; and
External pipe work and ducts. Insulating external pipework and ductwork generally lead
to higher savings due to the higher temperature gradient. Thermal insulation can also
help protect the exposed surfaces from the weather, for example from corrosion and
frost.
4.4 Possible Risks
Three key risks need to be considered for installation improvement projects: health and
safety; factors that could make implementation more expensive; and factors that could
reduce the achievable savings.
For example, if the surfaces to be insulated are at a higher vertical level, the contractor may
have to use items that may increase the overall project costs, such as fall arrest systems,
cherry picker hire, or scaffolding.
Asbestos is a common issue, particularity during re-insulating projects. The presence of
asbestos may make the project uneconomic, so reviewing the asbestos register is a priority
when assessing the proposed project.
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Other risks include working near hot surfaces and working in confined spaces. Factors to
consider that could affect the savings achieved against those predicted include:




Being overly optimistic in the original assumptions to improve the business case. This is
referred to as optimism bias and it is good practice to factor for this;
A reduction in the operating hours of the system after the insulation has been installed;
A fall in the cost of energy; and
Investments in energy efficiency measures.
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5 Useful Links and References
Title
Source
Link
Zero Waste Scotland
-
www.zerowastescotland.org.uk
How to Implement Thermal Insulation
(CTL145)
The Carbon Trust
www.carbontrust.com/media/147159/j8052_ctl145_how_to_imple
ment_thermal_insulation_to_hvac_services_aw.pdf
BS 5422:2009 Method for specifying
thermal insulating materials for pipes,
tanks, vessels, ductwork and equipment
operating within the temperature range 40°C to +700°C
Institute of British
Standards
www.bsigroup.co.uk
TIMSA Guidance for Achieving Compliance
with Part L Building Regulations –
domestic and Non-Domestic Heating,
Cooling and Ventilation Guide
TIMSA
www.timsa.org.uk/TIMSAHVACGuidance.pdf
Building Standards Handbook 2013 –
Non-Domestic Section 6.4 Insulation of
Pipes
Scottish Government
www.scotland.gov.uk/Resource/0043/00435261.pdf
Introduction to Heat Transfer
The Heat Transfer
Society
www.hts.org.uk/downloads/introductiontoheattransfer.pdf
How to implement thermal insulation
(CTL145)
The Carbon Trust
www.carbontrust.com/media/147159/j8052_ctl145_how_to_imple
ment_thermal_insulation_to_hvac_services_aw.pdf
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BS 5422:2009 Method for specifying
thermal insulating materials for pipes,
tanks, vessels, ductwork and equipment
operating within the temperature range 40°C to +700°C
Institute of British
Standards
www.bsigroup.co.uk
TIMSA guidance for achieving compliance
with Part L of the Building Regulations
Domestic and Non-Domestic Heating,
Cooling and Ventilation Guide
The Thermal
Insulation
Manufacturers and
Suppliers Association
www.timsa.org.uk
Building Standards Handbook 2013 - Non
Domestic Section 6.4 Insulation of pipes,
ducts and vessels
Scottish Building
Standards
www.scotland.gov.uk/Topics/Built-Environment/Building/Buildingstandards/publications/pubtech/th2013ndom6
Engineering Toolbox
Engineering toolbox
www.engineeringtoolbox.com/insulation-temperatures-d_922.html
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