مادة التحكم البيئي / الجامعه الاردنيه /صيفي 2015

1. Thermal Mass
Thermal mass is a material's resistance to change in temperature. Objects with high
thermal mass absorb and retain heat. Thermal mass is crucial to good passive solar heating
design, especially in locations that have large swings of temperature from day to night.
Thermal mass is the ability of a material to absorb and store heat energy. A lot of heat
energy is required to change the temperature of high density materials like concrete, bricks
and tiles. They are therefore said to have high thermal mass. Lightweight materials such as
timber have low thermal mass. Appropriate use of thermal mass throughout your home can
make a big difference to comfort and heating and cooling bills.
Incorporating thermal mass is especially efficient in climates where there is a large
temperature swing over the course of a day; studies have shown substantial energy savings
for thermal mass homes in hot areas like the Arizona desert. For colder climates, the
potential for savings drops off and insulation becomes the most important part of the
equation.
Effective building materials for thermal mass applications generally have high density, high
specific heat (the capacity for absorbing heat), and low thermal conductivity.

2. How thermal mass works?
Thermal mass acts as a thermal battery. During summer it absorbs heat during the day and
releases it by night to cooling breezes or clear night skies, keeping the house comfortable. In
winter the same thermal mass can store the heat from the sun or heaters to release it at
night helping the home stay warm.
Thermal mass is not a substitute for insulation Thermal mass stores and re-releases heat;
insulation stops heat flowing into or out of the building. A high thermal mass material is not
generally a good thermal insulator.
Thermal mass is particularly beneficial where there is a big difference between day and night
outdoor temperatures.
Thermal mass, correctly used, moderates internal temperatures by averaging out diurnal
(day−night) extremes. This increases comfort and reduces energy costs.
Poor use of thermal mass can exacerbate the worst extremes of the climate and can be a
huge energy and comfort liability. It can radiate
heat to you all night as you attempt to sleep during
a summer heatwave or absorb all the heat you
produce on a winter night
To be effective, thermal mass must be integrated
with sound passive design techniques. This means
having appropriate areas of glazing facing
appropriate directions with appropriate levels of
shading, ventilation insulation and thermal mass.

3. Density and thermal mass
Density is the mass of a material per unit volume. In the Imperial system, density is given as
lb/ft3; in the SI system, it is given as kg/m3. For a fixed volume of material, greater density
will permit the storage of more heat.
High density materials such as concrete, brick, tiles, earth and water require a lot of heat to
increase in temperature. They also lose heat slowly and are referred to as having high
thermal mass
Low density, lightweight materials such as timber or timber products require little heat to
increase in temperature but lose heat rapidly. These are referred to as low thermal mass
materials
A material suitable for thermal mass must have:
high heat capacity
high density
low reflectivity (i.e. a dark, matt or textured finish)
Note that thermal mass is not the same as insulation, which, in building terms, describes a
building’s ability to reduce the conduction (or flow) of heat between indoors and outdoors.
In effective house designs, thermal mass and insulation work in harmony
Designing with Thermal Mass
Common architectural implementations of thermal mass storage are concrete floor slabs,
water containers, and interior masonry walls such as the back of a chimney. However, many
materials can be used
Climates and Thermal Mass
Thermal mass is most useful in locations that have large swings of temperature from day to
night, such as desert climates. Even if the thermal mass does not prevent heat energy from
flowing into or out of occupied spaces, like insulation would, it can slow the heat flow so
much that it helps people's comfort rather than causing discomfort.
In climates that are constantly hot or constantly cold, the thermal mass effect can actually
be detrimental. This is because all surfaces of the mass will tend towards the average daily
temperature; if this temperature is above or below the comfortable range, it will result in
even more occupant discomfort due to unwanted radiant gains or losses. Thus, in warm

4. tropical and equatorial climates, buildings tend to be very open and lightweight. In very cold
and sub-polar regions, buildings are usually highly insulated with very little exposed thermal
mass, even if it is used for structural reasons .
Winter
Allow thermal mass to absorb heat during the day from direct sunlight or from radiant heaters. It re-
radiates this warmth back into the home throughout the night.
Summer
Allow cool night breezes and/or convection currents to pass over the thermal mass, drawing out all the
stored energy. During the day protect the thermal mass from excess summer sun with shading and
insulation if required.

5. Thermal Mass for Solar Gain
passive design.solar gainThermal mass is often critical to direct
High thermal mass materials conduct a significant proportion of incoming thermal energy
deep into the material. This means that instead of the first couple of millimeters of a wall
heating up 5–10 degrees, the entire wall heats up only 1–2 degrees. The material then re-
radiates heat at a lower temperature, but re-radiates it for a longer period of time.
This helps occupants stay more comfortable, longer. When the internal temperature of the
space falls at night, there is more energy still stored within the walls to be re-radiated back
out.
The larger the area of thermal mass receiving direct sunlight, the more heat it receives, so
the faster it can heat up, and the more heat it can store.

6. Thermal Properties of Materials
Every material used in an envelope assembly has fundamental physical properties that
determine their energy performance like conductivity, resistance, and thermal mass.
Understanding these intrinsic properties will help you chose the right materials to manage
heat flows
Thermal Conductivity (k)
A material’s ability to conduct heat.
Each material has a characteristic rate at which
heat will flow through it. The faster heat flows
through a material, the more conductive it is.
Conductivity (k) is a material property given for
homogeneous solids under steady state
conditions
It is used in the follow equation
where
q = the resultant heat flow (Watts)
k = the thermal conductivity of the material (W/mK).
A = the surface area through which the heat flows (m²)
∆T = the temperature difference between the warm and cold sides of the material (K), and
L = the thickness / length of the material (m)
Units for conductivity
Imperial – BTU*in/h ft ºF: In the Imperial system, conductivity is the number of British
thermal units per hour (Btu/h) that flow through 1 square foot (ft2) of material that is 1 in.
thick when the temperature difference across that material is 1ºF (under conditions of
steady heat flow)

7. SI - W/m ºC or W/m K: The System International (SI) equivalent is the number of watts that
flow through 1 square meter (m2) of material that is 1 m thick when the temperature
difference across that material is 1 K (equal to 1ºC) under conditions of steady heat flow.
?what`s the defference between insulation and thermal mass
The following is the fundamental differences between them:
Insulation
The basic function of insulation is impede the transfer of heat. This can be accomplished by
addressing any combination of the three basic forms of heat transfer:
1. Conduction
Insulation slows down how quickly thermal energy will migrate from one side of a material
to the other. All materials allow heat to "move through" at different rates.
Example: The same amount of heat will pass through a one inch thick steel plate a lot faster
than it will through one inch of cork. Therefore, cork is a better insulator than steel.

8. Convection2.
Air movement through building envelopes cause drafts and is a major source of heat
gain/loss. Good insulation systems address this issue of air leakage.
sulation and polyicynene spray foam insulation do a pretty similar job ofExample: Batt in
3.3 per inch). However,-allowing heat to conduct through them (both are typically about R
anthe spray foam expands to fill in stud cavities and prevent air gaps while batt insulation c
settle and allows air to pass between itself and the building framing. Therefore, regarding
convection, spray foam is a better insulator than batt insulation.
Radiation3.
can "jump"All objects radiate and absorb thermal energy to a certain degree. Radiant heat
from one material to another across an air space in a building system. But if a material can
heat, then it can serve as a better insulator with regard toabsorbrather thanreflectbetter
thermal radiation.
faced OSB sheathing (foil-located in a hot climate, foilExample: In an unconditioned attic
facing the inside of the attic) can reduce radiative heat transfer much better than regular
OSB sheathing.

9. Thermal Mass
This isheat.The basic function of thermal mass is to collect, store, and release
of heat. Threetransferfundamentally different than insulation's purpose of reducing the
important characteristics of thermal mass are listed below:
Solar Absorptance and Emissivity1.
re radiation (higher solarmoabsorbIn simple terms, darker opaque materials will
Also, every material's surfacethan lighter surfaces (lower solar absorptance).absorptance)
radiation at a given surface temperature (emissivity).emithas a different ability to
itsimproveto a thermal mass toExample: A "selective surface" may be applied
that it increases solarperformance. This black foil application is optically selective in
radiation of the heat derived from solar-reduces rewhile its low emissivityabsorptance
l exposed to direct solar radiation would wantabsorptance. Any sort of insulation materia
low solar absorptance and high emissivity.-the exact opposite
Heat Capacity2.**
Heat capacity expresses the amount of heat that can be stored in a material.
150 times more thermal energy thanstoreExample: Per cubic foot of volume, concrete can
batt insulation. This exemplifies another glaring difference between thermal mass and
insulation.
Conductivity3.
circle. Thermal conductivity is the measure of heat-comes fullcomparisonHere, the
conduction through a material. As mentioned above, insulation wants totransferred by
Conversely, thermal mass wants to allow conductivity ittransferimpede conductive heat
because the faster the material can import thermal energy from the collection point at its
ce, the more efficient the thermal mass will be at storing and distributing heat.surfa
Example: Heat will conduct through one inch of concrete roughly 60 times faster than
through one inch of extruded polystyrene (see illustration above)

10. tance (C)Thermal Conduc
Conductivity per unit area for a specified thickness. Used for standard building materials
In basic building materials, heat flow is usually measured by conductance (C), not
conductivity. Conductance is a material's conductivity per unit area for the object's thickness
(in units of W/m²K for metric and BTU/hr•ft2•°F for Imperial
Conductance is an object property and depends on both the material and its thickness.
Many solid building materials such as common brick, wood siding, batt or board insulation,
and gypsum board are widely available in standard thicknesses and compositions. For such
common materials, it is useful to know the rate of heat flow for that standard thickness
instead of the rate per inch
Factor (U)-U
Overall conductance of a building element. Used for layered building assemblies
In layered assemblies, conductances are combined into a single
number called the "U-factor" (or sometimes the “U-value")
U-factor and conductance translate conductivity from a material
property to an object property
U is the overall coefficient of thermal transmittance, expressed in
terms of Btu/h ft2 ºF (in SI units, W/m2 K). This is the same unit as conductance because it’s
a measure of the same thing: conductance is used for a specific material, U-factor is used for
a specific assembly. Lower U-factors mean less conduction, which means better insulation
For instance, the overall U-factor of a window includes the conductances of the glass panes,
the air inside, the framing material, and any other materials in their different thicknesses
and locations. Except in special cases, the conductances of the materials cannot be added to
determine U-factor of the assembly
The U-factor is an overall coefficient of heat transfer, and includes the effects of all elements
in an assembly and all sensible modes of heat transfer (conduction, convection, and
radiation), but not latent heat transfer (moisture related)
The term U-factor should be used only where heat flow is from air on the outside of the
envelope, through the envelope assembly to air on the inside. It should not be used on
basement walls, for example.

11. value = 1/U)-Thermal Resistance (R
A material’s ability to resist heat flow.
Designated as R (R-value), thermal resistance indicates how effective any material is as an
insulator.
The reciprocal of thermal conductance, R is measured in hours needed for 1 Btu to flow
through 1 ft2 of a given thickness of a material when the temperature difference is 1ºF. In
the Imperial system, the units are ft2•°F•hr/BTU. SI units are m²K/W.
Thermal resistance values are sometimes tabulated for both unit thicknesses and for a
sample of material with a known thickness. For example, the resistance of pine may be
given as 1.0 ft2•°F•hr/BTU per inch, or values may be tabulated for a 2x6 pine stud as 5.5
ft2•°F•hr/BTU. For a homogeneous material such as wood, doubling the thickness will
double the R-value. R-values are not typically specified for assemblies of materials. U-
factors are used for assemblies.
Insulation, which prevents heat flow through the building envelope, is often measured by its
R-value. A higher R‐value indicates a better insulating performance. When looking at spec
sheets, be sure you are reading the R-value in the right units, as the units are not always
explicitly written.
values in practice-factors and R-Using U
The variety of terms used so far to express thermal properties is potentially bewildering.
When dealing with complex layered building constructions, it’s useful to combine thermal
properties into a single overall number for specifying envelope design criteria.
For the total building envelope, this is often expressed as a U-factor. That said, windows are
often expressed with U-factor and walls are often expressed with R-values. There is no strict
rule.
Calculating the overall U-factor starts with adding resistances. U-factors are calculated for a
particular element (roof, wall, etc.) by finding the resistance of each constituent part,
including air films and air spaces, and then adding these resistances to obtain a total
resistance. The U-factor is the reciprocal of this sum (Σ) of resistances: U= 1/ Σ R

12. Value-Total R
values In Series-Adding R
When materials are sandwiched together, perpendicular to the direction of heat flow, it is
called adding "in series". An example of this is a cavity-brick wall, with two layers of brick,
an air gap, and 1/2" (1.2 cm) of plasterboard, all in a row
The heat must pass all the way
through one material before it
gets to the next material, so any
heat flow blocked by one material
is blocked the rest of the way.
Mathematically, adding in series
is easy: simply sum all thermal
resistances (R-values)
values In Parallel-Adding R
When materials are sandwiched parallel to the direction of heat flow, it is called adding "in
parallel". The heat being transferred does not need to pass all the way through one
material before it gets to the next material; instead, it can take the path of least resistance.
An example of this would be a standard window in a well-insulated wall.
Mathematically, adding in parallel
means the overall R-value will be
one divided by the sum of the
reciprocals of all the individual
materials' R-values. A highly
conductive material can completely
short-circuit other insulative
materials and cause the total R-
value to be low.

13. ***
Specific Heat
High specific heat requires a lot of energy to change the temperature
Specific heat is a measure of the amount of heat required to raise the temperature of given
mass of material by 1º. In the Imperial system, this is expressed as Btu/lb ºF; in the SI
system, it is expressed as kJ/kg K. It takes less energy input to raise the temperature of a
low-specific-heat material than that of a high-specific-heat material
For instance, one gram of water requires one calorie of heat energy to rise one degree
Celsius in temperature. Water has a high heat capacity and, therefore, is sometimes used as
thermal mass in buildings.
)Thermal Lag (Time Lag
With high thermal mass, it can take hours for heat to flow from one side of the envelope to
the other
This slowing of the flow of heat is called "thermal lag" (or time lag), and is measured as the
time difference between peak temperature on the outside surface of a building element and
the peak temperature on the inside surface. Some materials, like glass, do not have much
of a thermal lag. But the thermal lag can be as long as eight or nine hours for constructions
with high thermal mass like double-brick or rammed earth walls

14. PropertiesGlazing
In transparent surfaces there’s even more to take into
account
Heat transfer through a window involves all three
modes of heat transfer; conduction, convection, and
radiation. The dominant mode of heat transfer is
always changing and depends on the time, the
ambient and interior temperatures, the exterior wind
speed, and the amount and angle of solar radiation
that strikes the window. The insulation capabilities of
windows are usually measured by their U-factors; see
the table on the Glazing Properties page. The U-
factor for a window is primarily a metric used to
calculate the conductive portion of the heat transfer
through the window.

15. WINDOWS & GLAZING
GLAZING
Glazing loses a significant amount of heat from a building, so this is an area
which should be monitored carefully to ensure its efficiency when insulating a
property.
WINDOWS
In the case of replacement windows in both domestic and non-domestic situations, there is
an alternative way of complying. Compliance can be achieved by installing a double-glazed
unit with a centre pane (glass only) U-value of not worse than 1.2 W/m²K. The frame
material type and its thermal performance are then irrelevant.
What is the U-value that windows need to meet?
The U-value to be achieved by windows, doors and rooflights refers to
the energy effeciency of the frame and the double-glazed unit
combined.
The average area standard U-values depend on the frame material of
the windows, doors and rooflights.
✓ PVC-U and Timber 2.0 W/m²K
✓ Aluminum And Steel 2.2 W/m²K
However, when designing buildings, architects and designers have the
option of 'trading off' between the insulation performance of different
building materials. This flexibility allows for lower performance in a
particular material to be compensated by a higher performance in
another.
What is the effect of the frame material?
The material your frames are fabricated from will have an effect on the
combined performance of a window. PVC-U and timber are generally
good insulators whereas metal frames tend to be less energy effecient.

16. Types of glass:
1. Annealed glass
is the most commonly used architectural glass. As it is not heat-treated
and therefore not subject to distortion typically produced during glass
tempering, it has good surface flatness. On the downside, annealed glass
breaks into sharp, dangerous shards
2. Heat-strengthened glass
has at least twice the strength and resistance to breakage from
wind loads or thermal stresses as annealed glass.It is a heat-treated
glass products, heated and quenched in such a way to create
residual surface compression in the glass. The surface compression
gives the glass generally higher resistance to breakage than
annealed glass. The necessary heat treatment generally results in
some distortion compared to annealed glass. Like annealed glass, heat-strengthened glass
can break into large shards.
3. Fully-tempered glass
is also a heat-treated glass product, fully-tempered
glass provides at least four times the strength of
annealed glass, which gives it superior resistance to
glass breakage.
Similar to heat-strengthened glass, the heat-
treatment generally results in some distortion. If it
breaks, fully-tempered glass breaks into many small fragments, which
makes it suitable as safety glazing under certain conditions.

17. 4. Insulating glass
units (ig units) consists of two or more lites of glass with a
continuous spacer that encloses a sealed air space. The
spacer typically contains a desiccant that dehydrates the
sealed air space.
The air space reduces heat gain and loss, as well as sound
transmission, which gives the ig unit superior thermal
performance and acoustical characteristics compared to single glazing.
Most commercial windows, curtain walls, and skylights contain ig units.
Most perimeter seals consist of a combination of non-curing (typically butyl) primary seal
and cured (frequently silicone) secondary seal.
The service life of an ig unit is typically determined by:
• the quality of the hermetic sealants installed between the glass and the spacers,
• the quality of the desiccant
5. Tinted glass
contains minerals that color the glass uniformly
through its thickness and promote absorption of visible
light and infrared radiation.
4. Laminated glass
consists of two or more lites* of glass adhered together with a
plastic interlayer. Because it can prevent the fall-out of
dangerous glass shards following fracture, it is often used as
safety glazing and as overhead glazing in skylights.
The plastic interlayer also provides protection from ultraviolet
rays and attenuates vibration, which gives laminated glass good
acoustical characteristics. Because laminated glass has good
energy absorption characteristics, it is also a critical component
of protective glazing, such as blast and bullet-resistant glazing assemblies.

18. Benefits of double glazing
Energy saving
Interior comfort
Sound Reduction
Dew Condensation
Triple glazing
Triple glazing is widely used in cold
climate countries like Sweden and
lowenergy-Norway, and the ultra
PassivHaus standard requires triple
glazed windows with a Uvalue of no
more than 0.8. To get a window with
value, you have to not-such a low U
ch to triple glazing but alsoonly swit
insulate the frame itself, as well as
using more expensive manufacturing techniques

19. :eferenceR
http://www.level.org.nz/passive-design/thermal-mass/how-thermal-mass-works
http://sustainabilityworkshop.autodesk.com/buildings/thermal-mass
http://sustainabilityworkshop.autodesk.com/buildings/thermal-properties-materials
http://danieloverbey.blogspot.com/2013/05/whats-difference-between-insulation
http://www.modernenviro.com
https://en.wikipedia.org/wiki/Thermal_mass
https://greenpassivesolar.com/passive-solar/building-characteristics/thermal-mass/
http://insulationlsa.weebly.com/windows--glazing.html