Thermal studies U Vlaues

1. Tools: For now you will need….
Pen
Paper
Calculator
Put bags under tables
Context…

2. Salford City
College
Construction
&
Engineering
Nationals
In
Construction

3. Construction science and materials After this
next session is over you will be able to :
• Calculate the "U" value of a concrete roof slab
150 mm (0.15m) thick, asphalted 30 mm
(0.03m) for rainwater protection and the soffit
faced with plasterboard 12 mm (0.012)thick on
50 mm softwood battens, the void filled with
50mm (0.05) Glass fibre quilting .
• K Concrete = 1.0 W/m² °C
K Asphalt = 0.25 W/m² °C
K Plasterboard = 0.35 W/m² °C
K Glass fibre Quilt = 0.035W/m² °C

4. You will also…..
• Know about heat gains
and losses in buildings
Where is heat lost in a dwelling?...

5. Next – Heat Losses in Homes

6. Heat
Losses In
Homes
Give an example
of steps you can
take to save
energy …
Coming Next – Construction Techniques

7. Construction
Techniques
DG

8. Double galzing…
Next:Note taking…
Next note taking …Factors affecting energy use

9. Name things which can increase or
decrease energy usage …
• climate: • Usage:
• • the way that the property is
Location used including space and
• solar radiation heating requirements
• Wind
• degree of exposure • internal temp causes :
• domestic appliances
• desired internal temp.
• Building • heating system and its
Characteristics efficiency
• shape and size The Total Heating Load…
Coming Next – the Total Heating Load

10. The Total Heating Load
Roof
Solar
Gains
Cooking
Windows
Fuel
Supply
Electrical
appliances
Walls
Ventilation
Flue
losses
Boiler
Hot water Floor
Next slide…FHL + VHL = SHL

11. • Gains
Total Heat Load
• Losses
• How is heat lost from a
• What types of things heat a
house up? building?
•
• Solar effect • Fabric Heat Loss
• Cooking
• Ventilation Heat Loss
• Hot water
• Specific Heat Loss
• Electrical appliances
• In what ways does heat flow? ...

12. THERMAL STUDIES
• HEAT FLOW
 Radiated heat flow through air such • The current Building
Regulations carry a
as the rays from the sun section relating to the
 Convection as fluid, gas or liquid. It conservation of
expands on heating becoming lighter energy
and is forced upwards by cooler fluid
taking its place and therefore creates • Someone has to know
circulation how to add up the
amount of heat loss
 conduction by passing heat from one
molecule to another, this is the source • So who does it and
of most heat loss in buildings. how is it done?..
K…

13. What is the standard unit of THERMAL
CONDUCTANCE?
("K" value)
• In physics, thermal conductivity, k, is the property of a
material that..
• …indicates its ability to conduct heat. It appears primarily in
Fourier's Law for heat conduction.
Coming Next – values for common materials

14. • K values vary with good insulators
having a value of around 0.003 W/m² °C
and up to 400 W/m² °C for good
conductors.
• (Don’t try to remember these numbers
they are set out in industry tables)….

15. Material K value (W/m2 0C )
K values
• Aluminium alloy 160
•
•
Asbestos cement sheet
Asphalt roofing
0.4
0.8
for
•
•
•
Brickwork
Concrete (regular)
Concrete (lightweight)
1.83
0.84
0.19
common
•
•
Copper
Corkboard
160
0.042
building
materials:
• Fibre insulating board 0.05
• Glass 1.0
• Glass wool (mat or fibre) 0.04
•
•
Hardboard
Mineral wool
0.13
0.039 adapted
• Gypsum plaster 0.46
•
•
Plasterboard
Polystyrene (expanded)
0.16
0.033
from the
•
•
•
Polystyrene (solid)
Polyurethane foam
0.17
0.026 CIBSE
PVC flooring 0.04 chartered institute of building service
engineers
• Carbon steel 150
•
•
Sandstone
Softwood timber
1.3
0.13 guide
• Hardwood timber 0.15
• Woodwool slab 0.085
Reciprocal of K is R…

16. Resistivity & Conductivity
• K values are good but • How do you find
so is the opposite of resistance?
conductance,which is… • Resistivity =1/K value
• Resistance • materials are not always
• to show how a material supplied in one-metre
resists heat a blocks, using the
Resistivity (r) value can resistivity you can look
be found. This is the at the thickness of the
reciprocal (opposite) material and calculate
of a K value the "resistance" (R)
What if you have lots of Rs …

17. HEAT LOSS FROM BUILDINGS
• Finally to find how much heat energy is being
conducted we use a thing called the unit of
"Thermal Conductance" used …
• U = 1/total resistance expressed in Watts per metre²
What does the U-value represent?…..

18. • The term ‘U’ represents overall thermal
conductance from the outside to inside
covering all modes of heat transfer.
• What use is this in relation to the whole?
• An average U-value can be calculated

19. • The U-Value is an important concept in building
design.
• It represents the air-to-air transmittance of an element
(part or fabric). This refers to how well an element
conducts heat from one side to the other, which makes
it the reciprocal of its thermal resistance.
• So if you calculate the thermal resistance of an element,
we can simply invert it to obtain the U-Value..
• U=?
•U = 1/total resistance expressed in Watts per metre²
Lets work some out…

20. Example
• Calculate the "U" value of a brick wall, plastered one side
with 20 mm background and 3 mm of hardwall gypsum
finish, where "K" values for Brickwork = 0.55 W/m² °C,
background = 0.6 W/m² °C, hardwall plaster = 0.9 W/m² °C.
Material L (Thickness) K Value R=(1/k) x L
Brickwork 0.103 0.55 0.187
Background 0.020 0.6 0.033
Gypsum 0.003 0.9 0.003
Total Resistance 0.223
U value = 1/Total Resistance = 1/0.233 = 4.484 W/m² °C
Coming Next – further examples…

21. • Calculate the "U" value of a concrete roof slab 150 mm (0.15m) thick,
asphalted 30 mm (0.03) for rainwater protection and the soffit faced
with plasterboard 12 mm (0.012)thick on 50 mm softwood battens, the
void filled with 50mm (0.05) Glass fibre quilting .
• K Concrete = 1.0 W/m² °C
K Asphalt = 0.25 W/m² °C
K Plasterboard = 0.35 W/m² °C
Example K Glass fibre Quilt = 0.035W/m² °C
• Work to 3 decimal places.
Material L K R=(1/k) x L
Concrete 0.15 1.0 0.15
Asphalt 0.03 0.25 0.12
Glass Fibre 0.05 0.035 1.426
Plasterboard 0.012 0.35 0.034
U value = 1/Total Total R
Resistance = 0.58 W/m² °C
1.73
Coming Next – air layers & cavities

22. BOUNDARY STILL AIR LAYER & CAVITIES
• In any construction • This boundary still air layer
between the fabric and has an insulating quality
the internal/external that can be included in the
environment there will heat loss calculation.
be a layer of air which• The exterior surfaces of
is "trapped" by the buildings are usually
surface roughness of rougher than the internal
the materials used faces
Coming Next – thermal properties of cavities

23. CAVITIES
• cavities are used to keep heat in
• To increase the width of a cavity will not necessarily
produce any significant improvement in heat
retention-meaning…
• You only need a small gap
Coming Next – standard values…

24. BOUNDARY STILL
AIR LAYER & CAVITIES
• Standard Internal Resistance value 0.123 W/m²
°C
• Standard External Resistance value 0.055
W/m² °C
• Standard Cavity Resistance value 0.18 W/m²
°C
Coming Next – further standard values

25. HEAT AS A FORM OF ENERGY
• Total heat loss per second =
Area x "U" x Temperature
difference.
• Calculations to determine the total
heat loss for a particular building for
a particular period for a particular
temperature difference can now be
made
This session completed…

26. • Average U value = total exposed surface area / total
exposed surface area

27. Heat load calculator
• http://www.shophmac.com/info-center/hvac-ca
• STOP

28. Material L (Thickness) K Value R=(1/k) x L
Brickwork 0.103 0.55 0.187
Background 0.020 0.6 0.033
Gypsum 0.003 0.9 0.003
Total Resistance 0.223
U value = 1/Total Resistance = U value = 1/Total Resistance = 1/0.233 = 4.484 W/m² °C
Coming Next – further examples…