Thermal consideration of a shed
Module: MEC10110 - Advanced Energy System
Lecturer: Prof. Jorge Kubie
Assessment type: Coursework
Hand in date: Friday, 28 November 2014
Group ‘J’
Name
Matric
Course
Arkadiusz Tyranski
-
Meng – Mechanical
Aymeric Mommaerts
-
Beng – Mechanical
Robbie Murdoch
-
Beng – Mechanical
Tomasz Sliwinski
-
Beng – Energy
Wojciech Zienkiewicz
-
Beng – Energy
1
Abstract
Investigation of the thermal performance of the shed is presented in the following report. It
highlights the importance of determining the optimum thickness of the insulation in order to
provide best performance/money solution. Factors such as ventilation losses, sensible and
solar gains were considered while providing the following analysis.
Number of assumptions had been listed and explained.
The work provided helps to reduce the overall energy demand of the shed, and helps to
reduce the CO2 emissions which are at a constant rise.
2
Contents
Abstract................................................................................................................................. 2
1.
Introduction .................................................................................................................... 7
2.
General Assumptions ..................................................................................................... 8
3.
Technical Work .............................................................................................................. 9
3.1
Design of the shed .................................................................................................. 9
3.2
Heat loss............................................................................................................... 11
3.2.1
Front panel (combined) – Heat transfer for an isothermal vertical plate.......... 11
3.2.2
Side Panel (Combined) – Heat transfer for an isothermal vertical plate.......... 13
3.2.3
Back panel (natural) – Heat transfer for an isothermal vertical plate. ............. 13
3.2.4
Side panel (natural) – Heat transfer for an isothermal vertical plate ............... 14
3.2.5
Roof (combined) – Heat transfer for an isothermal horizontal plate ................ 14
3.2.6
Floor (nautral) – Heat transfer for an isothermal horizontal plate .................... 15
3.2.7
Windows ........................................................................................................ 16
3.3
Solar/Sensible gains and ventilation losses .......................................................... 17
3.3.1
Solar Gains .................................................................................................... 17
3.3.2
Solar gains admitted through single and double glazing ................................ 18
3.3.3
Sensible Gains............................................................................................... 20
3.3.4
Ventilation Losses .......................................................................................... 21
4
Selecting Windows ....................................................................................................... 22
5
Environmental friendly insulations considered.............................................................. 23
5.1
Description of Insolation types .............................................................................. 23
5.1.1
Wool Fibre ..................................................................................................... 23
5.1.2
Cellulose ........................................................................................................ 23
5.1.3
Hemp batts .................................................................................................... 23
5.1.4
Wood Fibre .................................................................................................... 23
5.2
Selecting optimum thickness of the insulation ....................................................... 24
5.3
Payback Time ....................................................................................................... 24
5.4
Final Selection ...................................................................................................... 25
3
6
Regulations .................................................................................................................. 26
7
Results ..................................................................................................................... 28
7.1
Shed breakdown providing U values and heat demand ........................................ 28
7.2
Final Shed Heat Demand and Payback time ......................................................... 29
8 Discussion and limitations ............................................................................................... 30
9 Recommendations .......................................................................................................... 31
10 Conclusion .................................................................................................................... 31
11 References.................................................................................................................... 32
12 Appendices ................................................................................................................... 33
12.1.
Excel Clarification .............................................................................................. 33
12.2
Solar Gains ........................................................................................................... 34
12.3
Sensible Gains...................................................................................................... 35
12.4
Ventilation Losses ................................................................................................. 37
Figure 1- Shed dimensions
9
Figure 2 - Shed orientation and wind
10
Figure 3- Top view of the shed
10
Figure 4 - Combined Convection
11
Figure 5- Thermal Resistance Series Diagram
12
Figure 6 - Boundary Layer
12
Figure 7 - Natural Convection
13
Figure 8 - Roof Combined
14
Figure 9 - Floor natural
15
Figure 10- Double Glazing
16
Figure 11 - Losses vs Gains SG
19
Figure 12 - Losses vs Gains DG
19
Figure 13 - Comparison of Ventilation Losses
21
Figure 14 - Optimum Insulation Thickness
24
Figure 16 - Actual Heat Demand Comparison between sheep wool and no insulation
29
Table 1 - Front Panel
13
4
Table 2 - Side Panel
13
Table 3 - Back Panel Natural
14
Table 4 - Side Panel
14
Table 5 - Roof
15
Table 6 - Floor
15
Table 7 - Monthly Heat Demand SG/DG windows
18
Table 8 - Sensible gains summary
20
Table 9- Typical values for air change per hour (data from 3rd year energy notes)
21
Table 10- Payback Time Windows
22
Table 11 - Annual Heat Demand / Cost of Demand
24
Table 12 - Energy Savings and payback time of insulation
24
Table 13-Maximum U values for building insulation envelop; (Act, The Building (Scotland)
Regulations 2004 Handbook, 2004, p. 469)
27
Table 15 - Summary - no insulation
28
Table 16 - Summary - sheep wool
28
Table 17 - Final Payback Time of Insulation
29
Table 18- Monthly ventilation losses with no insulation
37
Table 19 - Monthly ventilation losses with insulation
37
5
Symbol
SI Unit
Quantity
𝑅𝑎𝐿
Rayleigh Number
̅̅̅̅𝐿
𝑁𝑢
𝑁𝑎𝑡𝑢𝑟𝑎𝑙
Nusselt Number, Natural
̅̅̅̅𝐿
𝑁𝑢
𝐿𝑎𝑚𝑖𝑛𝑎𝑟
Nusselt Number, Laminar
̅̅̅̅
𝑁𝑢𝐿 𝐶𝑜𝑚𝑏𝑖𝑛𝑒𝑑
Nusselt Number, Combined
̅
ℎ𝑖
𝑊/𝑚2 𝐾
Heat transfer coefficient, Inside
̅̅̅
ℎ𝑜
𝑊/𝑚2 𝐾
Heat transfer coefficient, Outside
𝑞
𝑊/𝑚2
Heat flux
𝑇𝑖
℃
Temperature, Inside
𝑇𝑜
℃
Temperature, Outside
𝑇𝑓𝑖
𝐾
Film Temperature, Inside
𝑇𝑓𝑜
𝐾
Film Temperature, Outside
𝑅𝑒
Reynolds Number
ℎ̅𝑐𝑎𝑣
𝑊/𝑚2 𝐾
Heat transfer coefficient, Cavity
𝑅𝑡,𝑇
𝑚2 𝐾/𝑊
Total Thermal Resistance
𝑈
𝑊/𝑚2 𝐾
Total Heat Coefficient
𝑄𝑙𝑎𝑚
𝑊
Heat Transfer, Laminar
𝑄𝑇𝑢𝑟𝑏
𝑊
Heat Transfer, Turbulent
𝑄𝑇𝑜𝑡
𝑊
Total Heat Transfer
ℎ̅𝑙𝑎𝑚;𝑡𝑢𝑟𝑏
𝑊/𝑚2 𝐾
Laminar and Turbulent Heat Transfer Coefficient
l
𝑊/𝑚 𝐾
Thermal conductivity, window
l’
𝑊/𝑚 𝐾
Effective thermal conductivity
𝑅𝑠𝑖
𝑚2 𝐾/𝑊
Internal surface resistance
𝑅𝑠𝑒
𝑚2 𝐾/𝑊
External surface resistance
𝐿2𝐷
𝑊/𝑚 𝐾
Thermal coupling of coefficient
𝑙𝑡𝑏
𝑚
Linear thermal bridge
𝑑𝑗
𝑚
Glass pane, thickness
𝑈𝑔
𝑊/𝑚2 𝐾
Total heat transfer, glass pane
𝑈𝑓
𝑊/𝑚2 𝐾
Total heat transfer, frame
𝐴𝑓
𝑚2
Total area, frame
𝐴𝑔
𝑚2
Total area, glass
ψ
𝑊/𝑚 𝐾
𝑈𝑤
𝑊/𝑚2 𝐾
Linear thermal transmittance combined glass and
frame
Total heat transfer, Window
6
1. Introduction
In today's world, the huge and increasing demand on energy is mostly composed of fossil fuel
gas, oil and coal. These resources are not infinite, environmentally friendly and the cost of
extracting them is at a constant rise.
The aim of this project is to provide a recommendation for insulating a shed. This will be
achieved by looking at the energy performance of the shed, the environmental impact of the
insulation type and the economic feasibility.
7
2. General Assumptions
In order to provide the calculations shown in the report, some general assumptions were
made:
-
Steady state flow, temperature does not vary with time
-
Heat flux is the same through the fabric of the shed, 𝑞𝐼 = 𝑞𝐶 = 𝑞𝑜
-
Temperature of air inside the shed = 19ºC
-
Wind-speed of 3 m/s
-
Wind direction East-West
-
The shed is standing on a concrete foundation
-
The study uses Glasgow as data reference; outside air temperature is taken as the
average monthly temperature.
-
The orientation of windows in the shed is assumed south to obtain maximum solar
gains
-
Natural convection was considered inside the shed.
-
For natural convection to occur inside the shed, it is assumed that there are no
ventilation losses presented for calculation purposes
-
The ventilation rate is not affected by the insulation type. It is also assumed that
changing from single glazed windows to double glazed windows have no effect on
the ventilation rate.
-
For the roof, front and one side panel, combined convection was considered. For the
side panel facing west and the back panel facing north, only natural convection was
considered. This is because it is assumed that the shed is well sheltered from those
sides, assuming no external wind. This can be seen in Figure 2.
-
It is assumed that the shed is used for 3hrs/weekdays resulting in total usage time of
60hrs per month.
-
The contact resistance was neglected as the overall resistance of the material stack
dominates the thermal resistance.
-
The external heating is provided by electric heater
-
Cost of electricity is taken as 11.15 pence per kW/h
8
3. Technical Work
3.1
Design of the shed
The shed is a timber construction with water prof barrier on the roof. The dimensions of the
shed are specified in Figure 1
Front/Back Pane Length
2.62m
Front/Back Panel Height
2.26m
Side Panel Length
2.09m
Side Panel Height
1.73m
Window Length
0.5m
Window Height
0.5m
Figure 1- Shed dimensions
The inclination angle of the roof is 66° (total of 132°). The thickness of the wooden walls along
the entire construction is 12mm. The windows are single glazed, measuring 500mm by
500mm. The shed is standing on the concrete foundation, which improves moisture, water
and frost protection.
The thickness of the wall will increase by 60mm due to addition of the insulation material
(50mm) and OSB board (10mm). OSB board will provide the cover for insulation and trap the
air inside to increase insulating properties.
9
To summarize the modified shed, the wall is composed of three sections:
o
OSB board (Inside)
o
Insulation Material (Middle)
o
Timber (Outside)
It also contains a desk, shell and a chair for office use purposes.
As shown below in Figure 2, the wind is blowing from East to West. The North and West
walls are enclosed.
Figure 2 - Shed orientation and wind
As shown in Figure 3, after modification of the shed the insulation decreases the total volume
of the room but does not restrict the space available for the occupant.
Figure 3- Top view of the shed
10
3.2
Heat loss
3.2.1
Front panel (combined) – Heat transfer for an isothermal vertical
plate.
Figure 4 - Combined Convection
In order to undertake this analysis, further assumptions had to be stated:
-
For calculation purposes cross wind is assumed
-
There will be forced convection occurring on the outside of the panel resulting in a
combined convection
-
All specifications for this panel are taken from wholesaler’s website. The dimensions
can be found in Figure 1- Shed dimensions (Anon., 2014)
The surface of the front plate is considered as isothermal vertical plate and the external
surface is affected by the cross wind. The free convection of the inside air flows parallel to the
surface similar to the free convection of an external plate. This implies that inside conditions
can be treated the same as outside. As the heat travels towards the roof, the material of the
shed begins to conduct and the heat transfers through the material. Free convection occurs
on the external side of the shed and the forced convection created from the crosswind merges
with the free convection resulting in combined convection. The process described above is
summarised in Figure 4.
The same process applies when dealing with non-insulated panel. The only difference is that
the overall thickness of the panel is lower resulting in a lower thermal resistance which implies
higher heat loss.
This heat transfer analysis applies for 4 of the 7 components respectively, front panel, window,
side panel and roof.
11
1/hi
LOSB/kOS
Lins/kins
Ltimber/ktimber
1/ho
Figure 5- Thermal Resistance Series Diagram
Figure 5- Thermal Resistance Series Diagram shows the resistances in series and the effect the
materials stack has on the temperature. A large drop in temperature can be seen from T 2 to
T3.
Figure 6 - Boundary Layer
The critical length of the boundary layer seen in Figure 6 - Boundary Layer in the coldest month
is calculated to be larger than the length of the front panel (2.2m, blue line) therefore the
boundary layer is considered laminar.
𝑅𝑒 =
𝑈 ∗ 𝑥𝑐𝑟
= 5 ∗ 105
𝜈
Transpose for 𝑥𝑐𝑟
𝑥𝑐𝑟 =
5 ∗ 105 ∗ 𝜈 5 ∗-
=
= 2.48𝑚
𝑈
3
12
The abbreviated results for the front panel are shown in Table 1 - Front Panel. Total results
can be found in the excel spreadsheet in the folder ‘insulation’ labelled ‘Front Panel’.
Table 1 - Front Panel
Comparison table - Front panel
Average Annual U (W/m²K)
Average Annual Q (W)
Average Annual Heat Demand (kW/h)
3.2.2
No insulation-
Wood fibre-
Hemp batt-
Cellulose-
Sheep Wool-
Side Panel (Combined) – Heat transfer for an isothermal vertical plate
The same methodology used for the front panel has been applied to the side panel using the
relevant dimensions. The air flow of 3m/s was considered an updraft and was used to calculate
the forced convection resulting in combined convection. Table 2 - Side Panelsummaries the
results of the side panel.
Table 2 - Side Panel
Comparison table - Side Panel
No insulation Wood fibre Hemp batt
Average Annual U (W/m²K-
Average Annual Q (W-
Average Annual Heat Demand (kW/h-
3.2.3
Cellulose-
Sheep Wool-
Back panel (natural) – Heat transfer for an isothermal vertical plate.
Figure 7 - Natural Convection
Looking at the orientation of the shed presented in Figure 2 - Shed orientation and wind it can be
seen that the shed is well sheltered from external wind hence the assumption is made that
only free convection occurs. The methodology and shed dimensions are exactly the same as
the front panel but due to the assumption made above forced convection do not merge with
13
free convection. Figure 7 shows that without wind, the boundary layer is parallel to the external
surface of the panel.
Table 3 - Back Panel Natural
Comparison table - Back Panel Natural
No insulation Wood fibre Hemp batt
Average Annual U (W/m²K-
Average Annual Q (W-
Average Annual Heat Demand (kW/h-
3.2.4
Cellulose-
Sheep Wool-
Side panel (natural) – Heat transfer for an isothermal vertical plate
The methodology for the side panel (natural) is exactly the same as the back panel using
relevant panel dimensions. Table 4 summarises results.
Table 4 - Side Panel
Comparison table - Side Panel
No insulation Wood fibre Hemp batt
Average Annual U (W/m²K-
Average Annual Q (W-
Average Annual Heat Demand (kW/h-
3.2.5
Cellulose-
Sheep Wool-
Roof (combined) – Heat transfer for an isothermal horizontal plate
Figure 8 - Roof Combined
As shown on Figure 8 - Roof Combinedthe inclination is greater than 60° therefore the internal
and external surfaces are considered to be horizontal planes. The combined convection
process of the external surface it shown in Figure 8 - Roof Combined.
The critical length has been calculated to be 2.48m (red line) which is smaller than the overall
length of the roof resulting in a mixed boundary layer as shown in Figure 6.
14
Table 5 - Roof
Comparison table - Roof
No insulation Wood fibre
Average Annual U (W/m²K)
Average Annual Q (W)
Average Annual Heat Demand (kW/h)
3.2.6
Hemp batt
Cellulose
Sheep Wool
-
-
-
-
-
4.70
3.03
3.03
3.04
3.06
Floor (nautral) – Heat transfer for an isothermal horizontal plate
Figure 9 - Floor natural
The heat transfer occuring at the floor is considered free convection. Lateral lossses are
neglected and the floor was only treated as a composite wall.
Table 6 - Floor
Floor
Average Annual U (W/m²K)
Average Annual Q (W)
Average Annual Heat Demand (kW/h)
No insulation-
For all the components described below, to obtain the results, data for average temperature
in Glasgow was used. For the floor, ground temperature for Glasgow was considered.
15
3.2.7
Windows
The calculations for the windows have been calculated based on ISO- as well as
on the class notes. The ISO standard includes both, the glass thermal transmittance (UG) and
the frame thermal transmittance (Uf) but the class notes omit the frame transmittance.
The glass thermal transmittance has been calculated three times:
a) Calculations based on ISO10077 standard for a double glazing window with the
dimensions of 4-9-4mm as shown in Figure 10. As shown in the excel tab
‘WindowISO10077’ and also following the EN673 (ISO), the thermal transmittance of
the glass (Ug) for the double window has been determined as 2.53W/m2K. It should
be noted that EN673 does not take in account the temperature but the internal and
external surface resistance respectively Rsi and Rse.
Figure 10- Double Glazing
ISO10077 estimates the glass transmittance (Ug) at 2.6 for ‘one pane coated’ for a
window dimension of (4-9-4 mm) with air as the insulating gaz.
b) The thermal transmittance of glass has also been determined as 1.48 W/m2K
considering the window as a composite wall and natural flow inside and outside. As
discussed in the general assumptions, the flow should be considered to be forced
convection resulting in higher heat transfer coefficients (hi,ho) and thus higher thermal
transmittance. Comparing the heat transfer coefficients between natural and combined
convection, the heat transfers coefficients for combined are about 3 times higher. By
multiplying the natural heat transfer coefficient by 3 to simulate a combined convection
the thermal transmittance of glass has been determined as 2.05 W/m2K which
converges towards the ISO value.
16
c) The thermal transmittance has also been taken as 5.6W/m2K (Anon., 2012) for a single
glazing window.
The thermal transmittance of the frame (Uf) has been determined next. The technical drawings
of the shed did not include any dimensions concerning window frame size hence dimensions
were assumed as shown in the excel tab ‘Window-ISO10077’.
Once both, the glass (Ug) and frame (Uf) thermal transmittance have been determined the
overall heat loss through the window (Uw) can be calculated as:
Following the standard the overall heat lost (Uw) has been determined for the three cases.
3.3
Solar/Sensible gains and ventilation losses
3.3.1
Solar Gains
Solar gains are those admitted to the building through windows and fenestrations. Solar gains
are greater for single glazed windows than for double. However, the design specific heat load
will be greater for a building with single glazed windows.
To provide a comparison of the shed performance, when considering single and double
glazing, solar gains must be considered. Data included in Solar Gains provides a monthly
breakdown of the solar gains admitted to the building through single and double glazing. As
stated in general assumptions the shed is only used for 3 hours per day. Rough
approximations were used to determine the solar gains. These include:
Taking daily solar gains provided by Tom Grassie and dividing them by 24 to obtain a
value per hour. This value was then multiplied by 3 to achieve the total amount of
solar energy in the time period when the shed will be used. This assumes that the
solar irradiation admitted to the building is constant throughout the day, which is not
true.
After the above estimation was implemented, the number obtained was multiplied by
20, in order to obtain the total monthly solar energy admitted to the shed in the time
when it is used. As before, this is not accurate as the solar irradiation changes every
day.
17
Excel Spreadsheet which enables to determine the exact value of the solar irradiation, for
each hour of the day, for 365 days was obtained from Tariq Muneer. As the group has agreed,
amount and detail of work required to determine these parameters exceeded the allocated
time. The solar gains are very small and will not have a great impact on the final results.
3.3.2
Solar gains admitted through single and double glazing
Table 7 represents data obtained for single and double glazed windows.
Table 7 - Monthly Heat Demand SG/DG windows
Base Temperature
Month
January
February
March
April
May
Jun
July
August
September
October
November
December
Annual Heat Demand SG
Annual Heat Demand DG
Annual Gains SG
Annual Gains DG
Monthly Heat Demand (kW/h)
19
C
Average Temp ( C )
Heat Demand Single (kW/h)
3,5
2,08
3,3
2,10
5
1,88
7,4
1,55
10,1
1,19
12,9
0,82
14,2
0,64
14,2
0,64
12,2
0,91
9,5
1,27
5,4
1,82
3,9
2,02
Heat Demand Double (kW/h)
1,14
1,15
1,03
0,85
0,65
0,45
0,35
0,35
0,50
0,70
1,00
1,11
16,94
9,-,87
28,14
From the above table it can be seen that the total annual amount of solar gains exceed the
annual heat demand in both single and double glazing windows. This analogy can be miss
directing as the amount of solar gains admitted for summer months offsets the demand for
winter months. Further comparison providing a monthly breakdown, representing solar gains
against losses is provided in the Figure 11 and Figure 12.
18
Single Glazing-
Losses (Sg) kW/h
Gains (Sg) kW/h
Figure 11 - Losses vs Gains SG
Double Glazing-
Losses (Dg) kW/h]
Gains (Dg) kW/h
Figure 12 - Losses vs Gains DG
It can be seen that amount of gains during summer, is greater that the losses through both
single and double glazing. This will result in offsetting the heat demand for the summer
months, and as proven in further calculations, it will contribute for making the shed selfsustained when heating is considered.
19
3.3.3
Sensible Gains
Sensible gains are heat inputs to the building that are derived from the occupants and from
equipment used. The shed consist of only one occupant, with a small number of appliances,
resulting in overall sensible taken as 11 kW/h. Results are summarised in Table 8, Calculations
carried to obtain the results are summarised in the Sensible Gains.
Providing a value for sensible gains is very difficult as it requires a lot of assumptions to be
stated but the data provided is closely related to the notes provided by Tom Grassie.
Table 8 - Sensible gains summary
Component
Rating (W)
Heat Gain per 3 hours (W/h)
Heat Gain per 20 days (kW/h)
15
54
1.080
20
72
1.440
Laptop
52.5
30
0.6
Printer
80
3.3
0..66
390
7.800
Desk Lamp with
Fluorescent bulb
Lamp with
Fluorescent bulb (x1)
Occupant
Total
10.986
20
3.3.4
Ventilation Losses
Ventilation rate can be different for different areas in the house. For the simplicity, it can be
assumed as 1, but in the Table 9, there are some typical values of ventilation rate for different
areas in the house:
Table 9- Typical values for air change per hour (data from 3rd year energy notes)
Area
Kitchen
Bathroom
Room
Hall
Ventilation Rate (a.c/hr)
2
1.5
0.5
1.5
This data indicates a typical value taken when considering the ventilation losses in the house.
Due to the shed’s fabric, consisting of many air gaps, it can be estimated that the overall
ventilation rate would be greater from these specified for the house. The ventilation rate is in
order of 5.5 a.c/h without insulation and 3.5 a.c/h with insulation.
In order to obtain ventilation losses in kW/h, degree days had to be considered. Data
summarised in Ventilation Losses show a monthly breakdown of ventilation losses for the shed
with and without insulation.
Figure 13 provides comparison of ventilation losses with and without insulation.
Ventilation Losses (wiht and without insulation-
No Insulation kW/h
With Insulation kW/h
Figure 13 - Comparison of Ventilation Losses
21
4 Selecting Windows
In order to provide further analysis of the shed, the window type which will be considered has
to be determined. Table 10 shows the energy savings and payback time when considering
replacement of already installed single glazing to double glazing windows.
Table 10- Payback Time Windows
Single Glazing
258.55
Actual Heat Demand
Energy Savings (kW/h)
Price of Electricity (£)
Cost of Installing DG window (£)
Money Saved (£)/year
Payback
0.1115
Double Glazing-
To provide payback calculations, annual heat demand had to be considered. Non insulated
shed was used for the calculation purposes. This methodology is true for all insulation types
as the difference in the heating demand will remain the same when analysing windows. All
ventilation losses and gains were considered.
Greater number of solar gains admitted through single glazing windows, and also due to the
assumption that the ventilation losses are not affected by the type of glazing, the difference of
the annual heating demand for single and double glazing units is very small. This implies that
the overall energy savings are also very small, which provides a very high payback time of
276 years.
This payback time seems very unrealistic, but considering overall heat demand for the shed
in order of 286,66 kW/h and energy savings of 14.91 kW/h (1,66 pounds) per year it can be
justified.
The conclusion taken from that analysis implies that the payback time for double glazed
windows will reduce, when considering bigger buildings consisting of greater areas of glazing
and also greater heat demands.
It can also be stated that replacement of single glazed windows for double glazed windows
will have an environmental impact on the shed related to installation, manufacturing and
transportation. Life cycle analysis will be required to justify this statement, but from previous
experiments undertaken for different subject and consultation with Tariq Muneer allow this
statement to be made.
22
5 Environmental friendly insulations considered
5.1
Description of Insolation types
5.1.1 Wool Fibre
Wool fibres (Thermal conductivity 0.042W/mK) are hygroscopic by nature and will have a
moisture weight content of up to 35%, dependent on the relative humidity of the surroundings.
While absorbing this moisture, wool releases energy in the form of heat, thus raising the
temperature of its surrounding areas. By naturally releasing this moisture in the warmer
seasons, wool creates a cooling effect in the surroundings. It does not slump or reduce in
thickness over the years unlike polyester or fiberglass. It takes up to 15% less energy to
produce when compared to fiberglass and it is fully biodegradable. (EcoMarchent,- Cellulose
Loose cellulose insulation made from recycled newspaper combined with a mineral fire
retardant offers a sustainable and cost effective way to insulate floors and lofts as well as the
walls. With an installed density of 40kg/m3 cellulose has a high thermal performance (Thermal
conductivity 0.039W/mK) and also improves sound control of the building. It fills the smallest
gaps, even around wiring and does not encourage the growth of fungi, mould or bacteria while
providing cheap insulation solution. (EcoMarchent,- Hemp batts
Hemp batts is a natural fibre thermal insulator (thermal conductivity of 0.040 W/mK.) which
contains 95% of natural hemp and 5% of recycled adhesive binder (although content
proportion may vary). It is highly sustainable insulation (2 tonnes of CO2 taken away for one
tone of hemp harvest), which comes from waste straw from hemp harvest. Easy application
and durability makes it attractive solution for shed insulation. (EcoMarchent,- Wood Fibre
Wood fibre batts come from sustainable forestry and have a heat capacity of more than twice
that of mineral wool (Engineering tool box). The heat capacity of a material, tells us how much
thermal energy is stored in a material. Higher the heat capacity, the greater the thermal inertia,
which means that it is harder to get the temperature to change. Wood fibre batts are easy to
install and can be applied on walls, roofs and floors. Thermal conductivity of 0.040 W/mK and
its heat capacity gives very good overall thermal performance. (EcoMarchent, 2014)
23
5.2 Selecting optimum thickness of the insulation
In order to determine the optimum thickness of the insulation which will be used for the shed,
analysis of how the heat loss changes accordingly to the insulation thickness was undertaken.
This is summarised in Figure 14
Figure 14 - Optimum Insulation Thickness
The curve presented in the Figure 14 - Optimum Insulation Thicknessshows that change in
thickness from 0-50mm provides the greatest heat loss difference (65W). The heat loss
difference between 50-100mm is almost four times lower (20W). Because of the market
availability and the results obtained from the above figure, 50mm of insulation thickness was
selected as appropriate.
5.3 Payback Time
Payback time of four different isolation types are provided in Table 11 and Table 12
Table 11 - Annual Heat Demand / Cost of Demand
No insulation
Wood Fibre + OSB
Hemp Batt + OSB
Cellulose + OSB
Sheep Wool + OSB
Annual Heat Demand - No Gains (kW/h) Cost of demand (£-
Table 12 - Energy Savings and payback time of insulation
Wood Fibre + OSB
Hemp Batt + OSB
Cellulose + OSB
Sheep Wool + OSB
Energy Savings (kW/h-
Isolation Cost (£-
24
Money Saved (£-
Payback Time (years-
When calculating the heat demand and the payback time, solar and sensible gains were not
included as it will not affect the presented comparison. It can be seen on Table 12 - Energy
Savings and payback time of insulation that the difference in energy demand and energy savings
is very small, and that only cost of insulation has an impact on the payback time.
The high payback time results from small energy demand resulting in small energy savings.
5.4 Final Selection
Decision matrix was constructed in order to help with selection of the optimum insulation
type. It can be seen below:
Total weighted - Case II
Total weighted - Case III
Total weighted - Case IV
3
3
3
3
5
0.7
0.7
0.7
0.7
Payback Time
4
3
4
4
2
0.3
0.3
0.3
0.3
Environmental impact
4
4
5
5
5
0.9
0.9
1.1
1.1
Ease of installation
4
4
2
4
3
0.5
0.5
0.3
0.5
Health impact
Fire risk
5
4
5
3
4
3
4
4
4
4
0.9
0.7
0.9
0.5
0.7
0.5
0.7
0.7
23
4
3.7
3.6
4
III-Cellulose
I- Wood fibre
IV-Sheep Wool
Energy Savings
II-Hemp Batts
Total weighted - Case I
Different Insulation
Requirements
Weight
Grand total points
-
-
-
4
RANKING
2
3
4
1
Scale
5
better
3
same
1
worse
25
All of the above insulation have good overall thermal performance. Their thermal conductivity
ranges between- W/mK. Although wood fibre bats have the highest heat capacity,
every insulation could be considered in different terms of properties. Bearing in mind initial
sustainability aspect of materials, sheep’s wool and hemp bats come from fast growing
sources while cellulose comes from easy to obtain, everyday use products.
Even though wood bats are obtained from sustainable forestry, it takes a very long time to
replenish them but they are easy to recycle. All of the products show fire retardant properties
and meet fire resistance classification requirements of Euroclasses (Commission
2000/147/EEC).
Sheep wool is covered with titanium based treatment, called “Thorlan”, which protects the
material against insects. It is also a 100% natural product and while absorbing the moisture it
releases the heat to the surroundings. During summer months this will have an opposite effect
and will provide cooling.
Technically each of the considered materials could be used to insulate the shed, but after
evaluating the decision matrix, and by looking at the description provided above, sheep wool
was selected as the best suitable insulation type.
6 Regulations
The initial use of the shed was not intended as an office hence the shed was not designed to
be heated and did not have to comply with ‘The Building (Scotland) Act 2003 and The Building
(Scotland) Regulations 2004 Handbook in relation to Climate change (Scotland) Act 2009’ as
it is part of an exception of this standard:
(a) Non-domestic buildings which will not be heated, other than heating provided solely
for the purpose of frost protection.
The shed is now being converted to an office hence during the heating season (October to
April) the shed will use some heater to keep the inside temperature at 19°C as stated in our
general assumptions.
Heating buildings not primarily designed to be heated will adversely affect energy efficiency
and because of this, the most demanding of measures are recommended when conversion
occurs. When converting an unheated building (shed) into a heated building (office) the same
standards to those for an extension to the insulation envelope should be achieved. (Act, n.d.,
p. 473)
26
Table 13 shows the maximum U-values for building elements of the insulation envelope
complying with BS EN ISO 8990:1996 –‘Thermal Insulation’.
Table 13-Maximum U values for building insulation envelop; (Act, 2004, p. 469)
Measurements/Calculations of U-values should also comply with BS8990 and be determined
for a steady-state thermal transmission. BS8990 defines the ‘U-values’ as a measure of how
much heat will pass through one square metre of a structure when the temperatures on either
side of the structure differ by 1 degree Celsius (expressed in W/m2K).
Table 13 summarises the U-values for the shed considering a temperature difference of 1°C.
The assumed temperature difference (ΔT) in the calculations is well above ΔT=1°C specified
in the regulations. Comparing the maximum U values for building insulation envelop; (Act,
2004, p. 469) is only possible after assuming new interior and outside temperature to obtain
satisfactory maximum 1° difference.
From the results obtain from Table 14 and Table 15 for which the annual average temperature
was used, it can be seen that the U value calculated not exceed the stated ones in regulations
and because they are close to them it is hard to assume but optimistically can be said that
they are comply with maximum U values. U value of the roof (0.81) is the exception as it does
exceed the specified regulations of 0.35.
27
7 Results
7.1 Shed breakdown providing U values and heat demand
Table 14 and Table 15 represent the U-value for every component of the shed and also
provide the annual heat demand.
Table 14 - Summary - no insulation
Component
Side Panel (Natural )
Side Panel (Combined)
Back Panel (Natural)
Front Panel (Combined)
Windows
Roof
Floor
Total Shed Heat
Demand (kW/h)
NO INSULATION
Average U value
Average Annual Heat Loss
(W/m²K)
(Q) ( W-
Annual Heat Demand
(kW/h-
273.52
Table 15 - Summary - sheep wool
Component
Side Panel (Natural )
Side Panel (Combined)
Back Panel (Natural)
Front Panel (Combined)
Windows
Roof
Floor
Total Shed Heat
Demand (kW/h)
Insulation - Sheep Wool (k=0.042 W/mK)
Average U value
Average Annual Heat Loss
(W/m²K)
(Q) ( W-
Annual Heat Demand
(kW/h-
126.13
The average U value has been calculated for every month as the average temperature
changes resulting different U values. As expected, the panels open to the wind have higher
heat losses than the one obstructed. The roof has the highest U-value and the biggest
area (5.91m2) resulting in highest heat losses.
28
7.2 Final Shed Heat Demand and Payback time
After all of the above calculations were conducted, providing optimal thickness of insulation,
insulation type and also the window selection, final calculation for heat demand of the shed
can be provided. It is summarised in Figure 15
Heat Demand No Insulation vs Sheep Wool-
No Insulation Heat Demand (kW/h)
Sheep Wool Heat Demand (kW/h)
Figure 15 - Actual Heat Demand Comparison between sheep wool and no insulation
Table 16 provides final payback time for the insulation type selected.
Table 16 - Final Payback Time of Insulation
No Insulation-
-
Annual heat Demand (kW/h)
Cost of Demand (£)
Energy Savings
Money Savings
Isolation Cost
Payback Time
Sheep Wool-
As previously discussed, the payback time is considerably high. This is because the difference
between the heat demand is small, resulting in small energy savings.
29
8. Discussion and limitations
Results presented above are final, but this does not imply that they are correct. Due to a great
number of limitations and assumptions made, these results needs to be examined very
carefully and critically commented on.
It is known that natural convection will not occur due to doors and windows being opened
throughout the day and also due to the shed fabric containing air gaps. This implies that
ventilation losses should be associated. For calculation purposes the inside conditions were
assumed to be natural convection only. In addition, the heat inside the shed is assumed to be
isothermal which is not realistic as the temperature will vary at different levels in the shed.
Hot air would rise and accumulate under the roof while cooler air would drop down to the floor.
If the flow inside the shed was treated realistically implying forced convection, the heat transfer
coefficients would be greater resulting in higher heat loss. This implies that the calculated heat
demand is under-estimated. As Table 15 shows the roof has the lowest annual U value
meaning that with hot air rising the heat losses would be even greater.
Obtaining the heat demand using the average daily temperature is also not accurate as the
temperature considered should be the temperature for the hours when the shed is being used.
This assumption has an important impact on ΔT and would increase significantly the heat
demand of the shed if used during cold hours.
The payback time for the insulation was approximately 11 years. Realistic conditions would
result in higher heat demand hence reducing the payback time of the insulation. This factor
should be taken into consideration with a careful approach.
It can be seen that there is no heating requirement during summer months for both insulated
and non-insulated conditions. During winter months the heat demand is approximately 3 times
greater without insulation.
30
9. Recommendations
To obtain more realistic results further analysis has to be taken which will not assume
ideal conditions,
When dealing with larger heat demands and larger areas of glazing, double glazed
windows could be considered, for the shed, replacement of single glazed windows is
not cost effective, and the payback time exceeds the lifetime of the shed. Therefore,
it is recommended not to replace windows,
Sheep wool is recommended for the insulation material,
50mm of insulation is recommended as it provides cost effective reduction of heating
load. Also, market availability of insulation limits the thickness to 50mm and 100mm.
When the shed is built, the orientation of the shed should be considered to provide
sheltering when possible and to maximise solar gains. This will reduce the overall
heating demand.
Carpets on the floor would increase insulation hence resulting in lower heat demand
Painting the external surface of the walls in black color would result in higher solar
radiation absorption hence lower heat demand.
10. Conclusion
From the report it can be concluded that installing insulation is a very effective way of
decreasing the heat demand. The overall annual energy demand was reduced by almost 2/3.
The relative long payback time of up to 12 years can be interpreted differently. When moderate
use of the shed is considered the payback time significantly decrease. For environmental
conscious person, the payback time would be neglected as the invested cost is around £260,
this amount is compensated by positive contribution to environment and the idea of
sustainability.
Further analysis in a form of life cycle assessment should be undertaken to determine the
exact environmental impact of the shed, insulations and windows.
Ventilation losses are almost half of the heat demand but the solar and sensible gains have a
considerably high impact and help to counterbalance the heat demand. Several assumptions
had to be stated to evaluate appropriate data which helped to understand importance of small
aspects while calculating heat demand for the shed. The project feasibility can be improved
by applying recommendations given.
31
11. References
Act, S. G., 2004. The Building (Scotland) Regulations 2004 Handbook, s.l.: s.n.
Act, S. G., n.d. s.l.: s.n.
Alisdair, M., 2014. Electrical design engineer at GDM partnership [Interview] -).
Anon., 2012. [Online]
Available at: http://www.doubleglazing.com/windows/double-glazing-benefits/energy-efficiency/
Anon., 2014. Shedwarehouse. [Online]
Available at: http://www.shedswarehouse.com/id-10377OXFORD_6ft_x_8ft_Premier_Reverse_Tongue_and_Groove_Apex_Shed_Higher_Ridge_(12mm_Tan
dG_Floor_and_Roof).aspx
[Accessed-].
ASHREA, n.d. ASHREA Handbook- Fundamentals. Cdr edition ed. 2011: ASHREA.
box, E. t., 2011. www.engineeringtoolbox.com. [Online]
Available at: www.engineeringtoolbox.com/heat-gains-lights-d_709.html
[Accessed-].
EcoMarchent, 2014. www.ecomerchant.co.uk. [Online]
Available at: www.ecomerchant.co.uk
Jan F. Kreider, P. S. C. A. R., 2010. Heating and Cooling of Buildings. 1 ed. s.l.:s.n.
32
12. Appendices
12.1. Excel Clarification
On the attached CD, a folder containing five excels spread-sheets can be found:
1. Heat Transfer calculations
2. Summary of the calculations
3. Losses and gains heat demand
4. Insulation market research
5. Insulation justification
1. Heat transfer calculations
The heat transfer calculations have been split into seven sections respectively, front panel,
window, side panel, back panel, roof and floor. Six sections composed of two sheets that
describe the heat transfer without insulation and with insulation. The seventh section
presents the calculations for the floor.
The structure of each spread sheet except windowiso10077 is as follows:
-
Inside Calculation
-
(Insulation Calculation)
-
Outside Calculation
-
(Combined)
-
Results
-
Data sheet section
Each sheet contains its own data sheet section as parameters are changing dependent upon
the panel. The datasheet section also contains a thermophysical properties table used for
interpolating.
The first tab contains a macro. First a suitable value should be inputted in the “outside
temperature cell” then pressing the button will iterate and provide a summary of results. Note
that, after the macro is run the assumed temperature is defined as 18.9, this value ensures
when the macro is run for a second time that the Rayleigh number is positive. As the macro
redefines the assumed internal wall temperature, the results are incorrect except for the
summary.
The macro was initially planned to be available for every tab, but due to time restriction it was
only implemented once.
33
12.2 Solar Gains
Area of Window (m²)
Month
January
February
March
April
May
Jun
July
August
September
October
November
December
0.5
Passive Gains Single South 90° (kW/h per m² per day-
Total passive gains/year (kW/h)
Area of Window (m²)
Month
January
February
March
April
May
Jun
July
August
September
October
November
December
Passive Gains 3h/day for month/ area-
0.5
Passive Gains Double South 90 (kW/h per m² per day-
Total passive gains/year (kW/h)
34
Passive Gains 3h/day for month/ area-
12.3 Sensible Gains
Assumptions:
Two fluorescent 20W bulbs, equivalent to two 100W bulbs
Desk lamp with fluorescent 15W bulb
Using fluorescent fixtures:
𝑞𝑒𝑙 = 𝑊 ∗ 𝐹𝑢𝑙 ∗ 𝐹𝑠𝑎
Fsa - Special allowance factor for fluorescent bulbs recommended value: 1.20 (ASHREA, n.d.)
Ful – Light use factor
W- Wattage
20𝑊 ∗ 1 ∗ 1.20 = 24𝑊
24𝑊 ∗ 3ℎ = 72𝑊ℎ/𝑤𝑜𝑟𝑘𝑖𝑛𝑔𝑑𝑎𝑦(3ℎ)
15𝑊 ∗ 1 ∗ 1.20 = 18𝑊
18𝑊 ∗ 3ℎ = 54 𝑊ℎ/ 𝑤𝑜𝑟𝑘𝑖𝑛𝑔 𝑑𝑎𝑦 (3ℎ)
Sensible and Latent Heat Gains from occupant:
Table 1, “Representative Rates at Which Heat and Moisture Are Given Off by Human Beings
in Different States of Activity” from ASHREA Fundamentals gives data for the heat gains
from a male office worker doing light seated work. (ASHREA, n.d.)
130𝑊/ℎ
130𝑊 ∗ 3 = 390𝑊ℎ/𝑤𝑜𝑟𝑘𝑖𝑛𝑔 𝑑𝑎𝑦 (3ℎ)
Total Heat Latent Heat Sensible Heat
130 W
45 W
70 W
Appliances
Heat released by computers, printers and other office appliances can be significant and
should be considered in heat gains calculations. “There is a considerable uncertainty in the
35
estimated heat gain from appliances owing to the variation in appliances and the varying
usage schedules. “ (Jan F. Kreider, 2010)
According to Heating and Cooling of Buildings a realistic approach is to take 50% of the total
nameplate ratings to show peak heat gain during maximum usage of the appliances,
therefore:
𝑄𝑔𝑎𝑖𝑛 = 0.5 ∗ 𝑄𝑛𝑎𝑚𝑒𝑝𝑙𝑎𝑡𝑒 𝑟𝑎𝑡𝑖𝑛𝑔
Actual heat output from laptop can be calculated from OHMS law.
-Li-ion battery, 10.8 V, 5-6 A
𝑃(𝑊) = 𝐸 ∗ 𝐼
10.8 𝑉 ∗ 5,5 𝐴 =- 𝑊
52.54 ∗ 0.5 = 26.27𝑊 ∗
*Some of that energy is converted to chemical energy not heat.
A fair assumption of 10W of Heat can be generated during moderated work of the laptop.
(Alisdair, 2014)
Printer (laser): 80W (assuming 10min/ 3h working day operation)
80𝑊 ∗ 0.5 = 40𝑊
40𝑊
= 3.3 𝑊ℎ/ 𝑤𝑜𝑟𝑘𝑖𝑛𝑔 𝑑𝑎𝑦(3ℎ)
12∗
*Value for Printer has to be added separately (only 5min operation time, 1/12 of and hour)
Total heat gains from Lights, occupant and appliances
24𝑊 + 18𝑊 + 30𝑊 + 130𝑊 = 185.3𝑊
185.3𝑊 ∗ 3ℎ = 546𝑊ℎ + 3.3𝑊ℎ (𝑝𝑟𝑖𝑛𝑡𝑒𝑟) = 549.3𝑊ℎ/ 𝑑𝑎𝑦
𝑇𝑜𝑡𝑎𝑙 𝑝𝑒𝑟 𝑑𝑎𝑦: 549.3𝑊ℎ/ 𝑤𝑜𝑟𝑘𝑖𝑛𝑔 𝑑𝑎𝑦(3ℎ)
Total month kWh (20 days each 3h):
0.549 ∗ 20 = 11 𝑘𝑊ℎ
36
12.4 Ventilation Losses
To calculate the air change specific heat loss, certain air change per hour for the whole shed
needs to be assumed. As mentioned in general assumptions, the air change per hour is in
order of 5.5 for no insulation and 3 with insulation. To determine the ventilation losses,
volumetric flow rate/sec (m3/s) was obtained. This multiplied by density, (1.2 kg/m3 at 20 C)
gives the mass flow rate. Mass flow rate multiplied by specific heat capacity (Cp = 1.0007
kJ/kg.K at 293K) gives the ventilation heat loss rate in kW/K.
Table 17- Monthly ventilation losses with no insulation
No Insulation
Base Temperature
Month
January
February
March
April
May
Jun
July
August
September
October
November
December
19
C
Average Temp ( C ) Degree Days Monthly Heat Demand (Jules) Heat Demand (kWh)
Annual Heat Demand
3,5
3,3
5
7,4
10,1
12,9
14,2
14,2
12,2
9,5
5,4
3,9
153,90
-
-,-,-,-,-,-,-,-,-,-,-,-,97
18,87
19,12
17,05
14,12
10,84
7,43
5,84
5,84
8,28
11,57
16,56
18,39
kw/h
Table 18 - Monthly ventilation losses with insulation
Base Temperature
19
Average Temp ( C
Month
)
January
3,5
February
3,3
March
5
April
7,4
May
10,1
Jun
12,9
July
14,2
August
14,2
September
12,2
October
9,5
November
5,4
December
3,9
Annual Heat Demand
83,95
With Insulation
C
Degree
Days
Monthly Heat Demand (Jules-
-,-,-,-,-,-,-,-,-,-,-,-,80
kw/h
37
Heat Demand
(kWh)
10,29
10,43
9,30
7,70
5,91
4,05
3,19
3,19
4,52
6,31
9,03
10,03