# Minimizing Building Heat Loss vo2

```Minimizing Building Heat Loss
Introduction
• Today we introduce the concept of heat loss
and how to prevent it, ways of increasing
building efficiency
• Heat loss mechanisms:
1. Conduction (heat flow on a molecular
scale. Medium at rest or moving)
2. Convection (heat conveyed as internal
thermal energy of mass that is displaced
by mean or turbulent motion)
electromagnetic waves such as infrared
or visible light)
1. The transmission of electromagnetic waves through the
oven is also known as the microwave oven.
2. The heat energy emitted by the radiator.
4. The light energy radiated by incandescent lamps.
5. The emission of gamma rays.
Conduction
• Conduction is the movement of heat energy directly through solid materials
from molecule to molecule.
• Thermal Conductivity (k) is the term used to indicate the amount of heat that
will pass through a unit of area of a material at a temperature difference of
one degree.
• The lower the “k” value, the better the insulation qualities of the material.
Units; US: (Btu.in) / (h.ft2.oF), Metric: W / (m.oC)
• Conductance (c) indicates the amount of heat that passes through a given
thickness of material.
• Conductance= thermal conductivity / thickness. Units; US: Btu / (h.ft2.oF) Metric: W/
(m2.oC)
Determination of Thermal Conductivity Coefficient for Different Wall
Systems (TS EN ISO 8990): Example
Thermal Resistance
(RSI for metric unit, R for US units)
It is that property of a material that resist
the flow of heat through the material. It is
the reciprocal of conductance;
R= 1/c
Thermal Transmittance (U)
It is the amount of heat that passes through
all the materials in a system. It is the
reciprocal of the total resistance;
U= 1/Rt
TABLE THERMAL PROPERTÄ°ES OF SOME MATERÄ°ALS (examples)
Convection
• While still air is a good insulator, moving air can carry heat from a warm
surface to a cooler one.
• A warmed fluid, such as air, will expand as it warms, becoming less dense
and rising as a result, creating a fluid flow known as convection.
• This is one of the principal modes of heat transfer through windows. It
occurs between the air and the glass on the inside and outside surfaces,
and, in double-glazing, in the gas trapped between the panes.
• The rate of heat transfer in convection depends on three factors:
• temperature difference (difference in temperature of the medium at the warmer
and cooler points)
• the rate of movement of the carrying medium in terms of kg/s or m3/s
• the specific heat of the carrying medium in J/kg degC or J/m3 degC
• Heat energy can be radiated, in the same manner as it is radiated from the sun to
the earth.
• The quantity of radiation is highly dependent on the temperature difference
between the radiating body and its surroundings.
• The amount of radiation also depends on the surface’s emissivity.
• Most materials used in buildings have high emissivity of approximately 0.9, that is,
they radiate 90% of the theoretical maximum for a given temperature.
• Other surfaces can be produced that have low emissivity.
• ‘Low-e’ coatings are now normally used inside double-glazing to cut radiated heat
losses from the inner pane to the outer one across the air gap.
• There are two basic types. ‘Hard coat’ uses a thin layer of tin oxide, giving an
emissivity of 0.15–0.2. ‘Soft coat’ uses very thin layers of optically transparent silver
sandwiched between layers of metal oxide and gives an emissivity of 0.05 or better.
Strategies of
climate
control
6 Steps for Calculating Heat Loss
1. Determine Design Temperature
2. Calculate Surface Area
3. Calculate R-Value and U-Value
4. Calculate Surface Heat Loss
5. Calculate Air Infiltration Heat Loss
6. Calculate Total Heat Loss
What is Thermal Insulation?
•
Thermal insulation is the reduction of heat transfer between
objects in thermal contact or in range of radiative influence.
•
In simple terms, we can say thermal insulation of buildings means
•
insulators within walls, roofs or floor can make your house
thermally insulated.
•
There are different type of material available in the market to add
to buildings and make them thermally insulated.
How can heat loss be reduced through
insulation?
1. Windows and doors
2. Cavity wall insulation
3. Solid wall insulation
4. Floor insulation
5. Roof and loft insulation
6. Draught-proofing
Doors and windows
Types of Thermal Insulation Materials
• Fiberglass
• Mineral wool
• Cellulose
• Polyurethane foam
Fiberglass
• Fiber glass insulating material made up of fine glass fibers.
• A reinforced plastic material composed of glass fibers embedded in a resin matrix.
• Because of how it is made, by effectively weaving fine strands of glass into an insulation
material, fiberglass is able to minimize heat transfer.
• It can be easily moulded into any shape and has mechanical strength that is so
strong and stiff. It lasts for long time. No maintenance required . It is anti-magnetic,
fire resistant, good electrical Insulator, fireproof.
• It needs to be re-gel coated every 5 years. It may not work if it is wet or damp
during installation.
• Installing it requires safety precautions.
Examples of Installation
Mineral wool
• Mineral wool is a fibrous material drawn from molten mineral
or rock mineral.
• Mineral wool is a general name for fiber materials that are
formed by spinning or drawing molten minerals (or &quot;synthetic
minerals&quot; such as slag and ceramics)
• It is installed as sheet into walls.
• It is fire resistant, Noise resistant.
• it is very expensive material.
Examples of
Installation
Cellulose
• Cellulose insulation is plant fiber used in wall and roof cavities to insulate, draught proof and
reduce free noise. It is often made by hammer milling waste newspaper. The newspaper is
treated with chemicals, such as boric acid, to retard the spread of fire.
• Four major types of loose-fill cellulose products have been developed: dry cellulose, spray
applied cellulose, stabilized cellulose, and low dust cellulose.
• Cellulose insulation is treated with boric acid which makes them fire resistant and makes
them unpalatable.
• Have long term thermal insulating properties.
• Are cheaper than fiberglass. Normally health risk is less.
• Creates enormous amount of dust when installed.
• Cellulose insulation absorbs moisture easily and decreases the long-term insulating
properties
.
Examples of Installation
Polyurethane foam
• Polyurethane foam insulation is made up by reacting polyols
and diisocyanates, both products derived from crude oil.
• These foam insulation are spread on walls and roofs and
then it solidifies to make an insulating material.
• It has good thermal insulating properties, low moisturevapor permeability, high resistance to water absorption,
relatively high mechanical strength and low density.
• Reduces HVAC capacity requirements and have stable
insulation over time.
• Reduces air and moisture Infiltration resulting in a more
consistent temperature.
Examples of Installation
POLYSTYRENE (Styrofoam)
• Styrofoam is a good insulator because the plastic foam contains billions of
trapped gas bubbles.
• Gases hinder heat conduction because their molecules are very far apart
making it difficult for other molecules to collide with them.
• Insulation foam – are used for a variety of applications because of its
excellent set of properties including good thermal insulation, good damping
properties and being extremely light weight.
• From being used as building materials to white foam packaging, expanded
polystyrene has a wide range of end use applications.
• foam is durable, strong as well as lightweight and can be used as insulated
panel systems for facades, walls, roofs and floors in buildings
Examples of Installation
Other options for heat Insulation of roofs
• False ceilings with an air gap
can be built internally.
• Water sprinkling on roof .
• White-washing the roof before
summer.
• Applying reflecting materials
on the roof.
Heat insulation of exposed walls
• Construct wall of sufficient thickness. A brick wall of 23 cm thickness is
• Thermal performance can further be improved by providing cavity
walls (gap between two walls) and hollow bricks.
• Constructing a wall with suitable lightweight materials.
• Applying a light colour on the external surface.
What is Passive Design strategy?
• It is based upon climate considerations
• Attempts to control comfort (heating and cooling) without
consuming fuels
• Uses the orientation of the building to control heat gain and heat
• Uses the shape of the building (plan, section) to control air flow
• Uses materials to control heat
• Maximizes use of free solar energy for heating and lighting
• Maximizes use of free ventilation for cooling
• Uses shade (natural or architectural) to control heat gain
Differentiating Passive vs. Active Design
Passive design results when
• building is created and simply works “on its own”
• The plan, section, materials selections and siting create a positive
energy flow through the building and “save energy”.
Active design uses equipment to modify the state of the building,
create energy and comfort; ie. Fans, pumps, etc.
• Passive buildings require active users (to open and shut windows and
blinds...)
What is the
Solar
Geometry ?
Why Solar Geometry for passive design?
Advantage of studying Solar Geometry for passive design
Solar geometry works for us because
the sun is naturally HIGH in the
summer, making it easy to block the