Rethinking the Computer Enhanced Design Process

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Heat flow

• Heat is energy
• measured in Watts ( J/s)
• Temperature is the amount of heat in a material.
• Measured in degrees Celsius (Co )
• Measured in Kelvin (K)
• 0 K (-273 Co) material with no heat

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Heat flow

• Heat will flow from a hot substance to a cold
  substance.
• Heat can flow in three ways
• Conduction
• Convection
• Radiation

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Heat flow

• Vibration of molecules
• conduction
• convection

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Heat flow

• Electromagnetic radiation

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Heat flow

• Conduction
• Conduction occurs through the transfer of
  vibrational energy from one molecule to the next.
• Depends on
• The cross sectional area
• The conductivity of the material
• The temperature difference

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Heat flow

• Conduction

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Heat flow

• Convection
• Convection occurs from a solid to a fluid or gas
• As temperature increases, density in the fluid
  decreases
• The lower density fluid rises
• This results in convection currents

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Heat flow

• Convection

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Heat flow

• Radiation
• All object emit some electromagnetic radiation.
• The hotter the object, theshorter the wavelength
• A hot fire will emit infrared radiation
• The sun (much hotter) also emits short wave
  radiation

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Heat flow

• Radiation

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Heat flow through materials

• Heat flow through materials occurs mainly by
  conduction. The ability of a material to conduct
  heat varies
• Metals are good conductors
• Gases are poor conductors

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Heat flow through materials

• Heat flow through materials depends on
• Cross-sectional area
• Temperature difference
• Resistivity or conductivity of the material

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Heat flow through materials

• Resistivity of a material
• Ability to resist heat flow
• Conductivity of a material
• Ability to allow heat flow
• Resistivity is the opposite (inverse) of
  conductivity. If resistivity is low, conductivity
  is high.

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Heat flow through materials

• Measuring resistivity and conductivity
• Resistance is measures as a R-Value
• m2 K/W
• Conductance is measured as a U-Value
• W/m2 K
• R 1/U and U 1/R
• If R 2, then U 0.5

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Heat flow through materials

• Conductance How much energy (in watts) passes
  through the material?
• 1 m2 of a material
• subjected to 1 oC of temperature difference

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Heat flow through materials

• A building structure usually consists of
  different materials. The overall R-Value or
  U-Value can be calculated
• Two possibilities
• Materials in series
• Materials in parallel

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Heat flow through materials

• In series
• Resistances are added
• R R1 R2 R3
• In parallel
• Conductances are added
• U U1 U2 U3

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Heat flow through materials

• Cavities
• Cavities increase resistance
• Heat flow through the cavity
• Conduction depends on depth
• Convection depends on depth and height
• Radiation depends on reflectivity of internal
  surface

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Heat flow through materials

• Insulation
• Any material with low overallconductance
• Ways to reduce overall conductance
• Materials with air bubbles. E.g. glass fibre,
  mineral wool, polystyrene
• Reflective materials that reduce the absorption
  of infrared radiation

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Heat flow in buildings

• A typical building structure
• Many components
• Many building systems (e.g. walls, roofs)
• Many different thermal conductances
• In series and in parallel

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Heat flow in buildings

• A typical building structure
• Many components
• Many building systems (e.g. walls, roofs)
• Many different thermal conductances
• In series and in parallel
• What is the overall result?
• What is the overall heat loss for a building
• What is the overall heat gain for a building?

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Heat flow in buildings

• Cold climate

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Heat flow in buildings

• Hot climate

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Heat flow in buildings

• Heat loss heat out
• Through the building fabric
• Walls, floor, roof, etc
• Ventilation through windows and doors
• Heat gain heat in
• from outside sources (e.g. sunlight)
• from internal sources (e.g. people, lighting,
  equipment)

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Heat flow in buildings

• If heat loss is less than heat gain
• Building heats up
• AC is required
• If heat loss is greater than heat gain
• Building cools down
• Heating is required

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Heat flow in buildings

• There are six main types of heat loss/gain
• Fabric gains
• Indirect solar gains
• Direct solar gains
• Ventilation Gains
• Internal Gains
• Inter-zonal gains

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Heat flow in buildings

• There are six main types of heat loss/gain
• Fabric gains due to differentials in air
  temperature between inside and outside the space
• Indirect solar gains
• Direct solar gains
• Ventilation Gains
• Internal Gains
• Inter-zonal gains

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Heat flow in buildings

• There are six main types of heat loss/gain
• Fabric gains
• Indirect solar gains due to the effects of solar
  radiation on external opaque surfaces
• Direct solar gains
• Ventilation Gains
• Internal Gains
• Inter-zonal gains

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Heat flow in buildings

• There are six main types of heat loss/gain
• Fabric gains
• Indirect solar gains
• Direct solar gains due to solar radiation
  entering the space through a window or void
• Ventilation Gains
• Internal Gains
• Inter-zonal gains

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Heat flow in buildings

• There are six main types of heat loss/gain
• Fabric gains
• Indirect solar gains
• Direct solar gains
• Ventilation Gains due to the movement of air
  through through cracks and openings in the
  building
• Internal Gains
• Inter-zonal gains

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Heat flow in buildings

• There are six main types of heat loss/gain
• Fabric gains
• Indirect solar gains
• Direct solar gains
• Ventilation Gains
• Internal Gains due to people, equipment (such as
  computers) and lighting
• Inter-zonal gains

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Heat flow in buildings

• There are six main types of heat loss/gain
• Fabric gains
• Indirect solar gains
• Direct solar gains
• Ventilation Gains
• Internal Gains
• Inter-zonal gains due to differentials in air
  temperature between zones

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Heat flow in buildings

• Designers job
• Reduce as much as possible the difference between
  
• heat loss and
• heat gain

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Heat flow in buildings

• What is HVAC?
• Heating, Ventilation and Air conditioning
• It is expensive!
• It uses a lot of energy
• What is HVAC for?
• To add or remove heat
• To make up for the difference between heat loss
  and heat gain

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Modelling with zones

• With lighting, it was possible to simulate just
  one room. This is not the case with thermal
  simulations.
• Spaces in the building interact with each other
• Must model all spaces in the building
• Therefore, thermal models must be highly
  simplified

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Modelling with zones

• The basic unit of a thermal simulation is the
  zone
• A zone is a volume of air that is relatively
  homogeneous
• Usually a room
• No holes or gaps (windows are OK)

Zone 1
Zone 2
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Modelling with zones

• The simulation software must calculate
• heat flow between zones
• Adjacency is important
• The construction may be different

adjacency
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Modelling with zones

• The enclosing surfaces must have thermal
  properties.
• For Ecotect these are
• U-values (U W/m²K)
• Specific admittance (Y W/m²K)
• Solar absorption (Abs 0-1)
• Thermal decrement (Decr 0-1)
• Thermal lag (Lag hrs)

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Modelling with zones

• U-values (U W/m²K)
• thermal conductance of materials and the
  convective and radiative effects of surfaces and
  cavities
• Specific admittance (Y W/m²K)
• ability to absorb and release heat energy
• Solar absorption (Abs 0-1)
• portion of solar radiation that is absorbed
• Thermal decrement (Decr 0-1) and lag (Lag hrs)
• dynamic thermal behaviour

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Modelling with zones

• A zone may contain partitions
• Partitions must be internal
• The air on both side must be similar
• Furniture can also be defined as a partition

partition
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Modelling with zones

• A number of properties can be set for each zone

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Modelling with zones

• A number of properties can be set for each zone
• Operation AC On/off times
• Comfort Band Max and min temperatures
• Occupancy Number of people and activity
• Air Change Rates Air infiltration, wind
  sensitivity
• HVAC system Type of HVAC system
• Heat Gains people, lighting, equipment
• Schedules daily and yearly behaviour

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Modelling with zones

• HVAC system
• None
• All the windows are doors remain shut
• Natural Ventilation
• Occupants may open the windows
• Mixed-Mode System
• A combination of heating, AC and natural
  ventilation
• Full Air Conditioning, Heating Only or Cooling
  Only
• Heating and/or AC. Windows are never opened.

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Modelling with zones

• Heat gains
• There are two types of heat gains
• Sensible heat gains
• lighting, computers, etc
• value given per square metre of floor area
• Typical office lighting 20 W/m2
• Typical office equipment 40 W/m2
• Latent heat gains
• This value is not used in Ecotect, so ignore it

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Modelling with zones

• Schedules
• operational schedules
• occupancy schedules
• Schedules allow you to assign different profiles
  to weekdays, holidays, weekends, etc
• a profile consists of a percentage for each hour
  in the day
• profiles are assigned to different days
• up to 12 different daily profiles can be created

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Thermal analysis

• Thermal analysis in Ecotect

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Thermal analysis

• Types of thermal calculation

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Thermal analysis

• Hourly Temperature Profile
• Outside temp the temperature outside
• Beam solar direct solar radiation
• Diffuse solar indirect solar radiation
• Wind speed typical wind conditions
• Zone temp the temperature inside
• Selected zone the selected zone is shown in bold

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Thermal analysis

• Hourly Heat Gains/Losses
• HVAC load overall cooling and heating
• Conduction through building fabric
• Sol Air through solar gains on opaque surfaces
• Direct Solar through transparent windows
• Ventilation through crack and openings
• Internal lights, people and equipment
• Inter-Zonal heat flow between adjacent zones

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