Environment 2

Question 1

Energy Balance

Answer 1

To maintain a constant comfortable internal temperature known as the Steady State, building should achieve Thermal Balance.

(Balancing Heat Loss and Heat Gain)

Heat Loss:

• The major heat loss channels from a building are ventialtion, and transmission infiltration through e construction fabric
• Loss of warm, moist air by: Ventilation through ducts & flues, ventilation through gaps at doors and windows frames
• Transmission heat loss via: walls, floors, roofs, windows & doors

Question 2

Energy Balance:

Transmission

Answer 2

A building envelope has any potential gaps. Warm air can leave the fabric or cold air can penetrate from outside.

Question 3

Energy Balance:

Heat Loss

Answer 3

• Conduction Loss through the building is measured as a function of the material’s conductivity
• Convection Losses on both the inside and outside surfaces of any building layer is measured as the surface resistance
• Radiation heat loss is measured as the energy transmission at the surface resistance of an object

Question 4

Energy Balance:

Heat Gain

Answer 4

The major heat gains channels into a building are solar gain, incidental gains and heating inputs

• Sensible and Latent Gains by: Direct solar gain, Appliances, Lighting and Heating, people
• Transmission Heat Gain via: Walls, Roofs, Windows and Doors due to ambient air temperature

Question 5

Energy Balance:

Solar and Metabolic Gains

Answer 5

• Solar Gain: It is possible to predict passive solar gain by referring to Solar Flux values for your geographical region. (Solar Gain = 0.52 x Window Area x Solar Flux)
• Metabolic Gain: If a building is continually occupied, heat gain can be generated by users; this is referred to as Metabolic Gain

Question 6

Thermal Analysis:

U-Value

Answer 6

• Lack of precision in the way buildings are made mean that we must look to robust benchmarking methods to assess how thermally efficient buildings are
• one method is U-Value Calculation
• U-Value: establishes the rate of heat loss through walls, roofs and floors using the thermal conductance of building elements.

Question 7

Thermal Analysis:

K-Value

Answer 7

• The conductivity of a material is expressed as its K-Value
• It is determined by a calculation of the amount of heat transmitted through 1m² of the surface of a material that can cause a temperature change of 1ºC from one side of the material to the other
• The lower the K-Value for a material, the better it insulates
• K-Values are predetermined and an be found in reference tables or manufacturers data, Units are W/mK

Question 8

Thermal analysis:

r-Value

Answer 8

• The Resistivity of a material is expressed as its r-Value
• Resistivity is the ability of a building material to resist the flow of heat. It is the inverse of conductivity and is expressed as the reciprocal of conductivity
• The formula for calculating Resistivity is: r = 1/K
• r = The Thermal Resistance per unit area of a piece of material (m²K/W)
• K = represents the conductivity of the material (W/mK)

Question 9

Thermal Analysis:

R-Value

Answer 9

• The resistance of a material is expressed as an R-Value, it is a measurement of a building materials resistance to heat flow
• The higher the R-Value, he greater the insulation
• Resistance is calculated as the inverse of Conductivity x the actual thickness or depth of the material
• R = L x r
• R = Resistance measured in m²K/W
• L = Thickness of material (always in meters)
• r = Resistivity of a material in mK/W

Question 10

Thermal Analysis:

Insulation Types

Answer 10

1. Quilt: In the form of Batts, Rolls, or Blankets. These are flexible products made rom glass, natural fibres or mineral fibres.
2. Blown: Loose-fill insulation includes loose fibres or pellets that are blown into building cavities using special pneumatic equipment.
3. Rigid: Fibrous materials or plastic foams that re pressed or extruded into board-like forms and moulded pipe-coverings.
4. Reflective Foil: Films fabricated from Aluminium foils with a variety of backings e.g. strong paper, plastic film, Polyethene bubbles or cardboard

Question 11

Measuring Thermal Performance

Answer 11

• Housing in Scotland governed by the Building Standards
• They require all new dwellings to meet a set target for carbon dioxide emissions known as the Target Emission Rate (TER). This includes calculating for heat loss and the efficiency of heating systems.
• To avoid excessive heat loss the following U-Values need to be achieved: External Walls (0.19 W/m²K), Floors (0.15 W/m²K), Roofs (0.13 W/m²K), Windows and Doors (1.50 W/m²K)