Deck 11: Condensation in Buildings

Question 1

Using a Psychrometric chart or a sketch of one, without calculation or use of tabulated data, which air condition do you expect to have a higher vapour pressure than the air in the room you are in now?

A)35^oC d.b., 32^oC w.b.
B)20^oC d.b., 50% Percentage Saturation
C)10^oC d.b., 80% Percentage Saturation
D)-5^oC d.b., 100% Relative humidity
E)40^oC d.b., 10% Percentage Saturation

Answer 1

A

Question 2

Why does condensation occur within a building?

A)Users leave taps running, baths full, water evaporates and deposits onto room surfaces, making air moist
B)Evaporated water within the building meets surfaces at below dew point temperature
C)Kettles, cooking, fish tanks and open bowls of water evaporate more water vapour into room than ventilation can remove
D)Porous building materials provide pathways for cold moisture to ingress a warm building and make indoor surfaces damp
E)Cyclic variation of indoor surface temperatures always produces below dew point locations

Answer 2

B

Question 3

What is air, in terms of condensation risk?

A)Dry gas needed to ventilate humidity out of buildings
B)Mixture of oxygen, nitrogen and carbon dioxide
C)Mixture of dry gases and water vapour
D)That which causes the problem
E)Humans and animals breathe out humid air

Answer 3

C

Question 4

What is the movement of humidity through a building called?

A)Mass transfer
B)Ventilation
C)Natural or mechanical ventilation
D)Condensation
E)Evaporation

Question 5

What drives moisture flow through a structure?

A)Percentage saturation difference
B)Air temperature difference in ^oC d.b.
C)Vapour pressure difference in Pascal's
D)Air moisture content difference in kg H₂O/kg dry air
E)Wet bulb air temperature difference in ^oC w.b.

Question 6

In the context of condensation in building, what does Rv stand for?

A)Volumetric resistance of a material
B)Resistance value
C)Resistance volume
D)Vapour resistivity
E)Total vapour resistance

Question 7

How can a porous wall or roof have its' vapour resistance improved?

A)Replace with new materials
B)Wallpaper internal surfaces
C)Drill ventilation holes to ventilate structure
D)Add a layer of polythene film
E)Cannot be done so increase heating within building

Question 8

Which is true?

A)MN s/g m = GN s/kg m
B)10³ kN s/g m = GN s/kg m
C)10³ N s/g =MN s/g
D)10⁶ N s/kg = MN s/g
E)kN s/kg = MN s/g

Question 9

Why are thermal and dew point temperature gradients for a structure calculated and drawn?

A)Calculate thermal admittance of the structure
B)Decide where additional thermal insulation or vapour barrier improves performance
C)Discover dynamic behaviour of the structure
D)No need to do it anymore as computers do all design
E)Calculate optimum thickness of thermal insulation

Question 10

Which are the units of moisture mass flow rate through a building structure used to calculate condensation risk?

A)kg/s
B)kg/m² s
C)grammes/hour
D)kPa/m²
E)N s/kg