Ventilation

Question 1

Air Change Rate

Answer 1

The ventilation rate (m3/h) divided by the volume (m3) of the enclosed space expressed in air changes per hour (ACH). The number of times that the total air volume in a room or space is completely removed and replaced in an hour.

Question 2

Air Infiltration

Answer 2

The air ingress under ambient conditions that enters a building through cracks and gaps in the building envelope.

Question 3

Exfiltration

Answer 3

Air Loss

Question 4

Airtightness

Answer 4

A measure of the air leakage rate through the building envelope for a given test pressure (typically at 50 Pa).

Question 5

Blower door

Answer 5

A device for pressure testing building
airtightness.

Question 6

Contaminant removal efficiency

Answer 6

This is a term used to describe the efficiency of the removal of contaminant in a space by ventilation. It can relate to the space as a whole or to individual locations.

Question 7

Dilution ventilation

Answer 7

Mixing

Question 8

Displacement ventilation

Answer 8

A mechanism by which fresh air is introduced to a location without mixing the fresh incoming air with the room air.

Question 9

Heat recovery

Answer 9

A process by which sensible ‘dry’ heat from the exhaust air supply is recovered and normally used to pre-heat the supply air. Latent heat can also be recovered with some systems.

Question 10

Latent heat recovery

Answer 10

A process by which latent heat from moisture in air is recovered.

Question 11

Mixing (or dilution) ventilation

Answer 11

A system by which incoming fresh air is thoroughly mixed with the air already in a space. This is a common approach for air-driven heating and cooling systems.

Question 12

Percentage persons dissatisfied (PPD)

Answer 12

Thermal comfort parameter: the percentage of people expressing dissatisfaction with the thermal environment in which they are exposed (e.g. too hot or too cold).

Question 13

Predicted mean vote (PMV)

Answer 13

Thermal comfort parameter: a measure by each occupant of their perception to thermal comfort varying from –3 for too cold to 0 for neutral and +3 for too hot.

Question 14

Pressure test

Answer 14

A method for testing the airtightness of
a building or a component such as ductwork.

Question 15

Recirculation

Answer 15

The blending of fresh air with extract
air for recycling back into a ventilated space. This
forms an important part of an air-driven heating or
cooling system.

Question 16

Specific fan power

Answer 16

The electrical energy used to drive each litre/second of air through a ventilation system (measured in watts per l·s–1).

Question 17

Task ventilation

Answer 17

A system by which fresh air is ducted directly to the point of need.

Question 18

Ventilation effectiveness

Answer 18

A term used to describe thedegree that fresh air is mixed in a space.

Question 19

Natural ventilation

Answer 19

This is the process by which airflow through ventilation openings is driven by the natural driving forces of wind (wind effect) and temperature difference (stack effect).

Question 20

Mechanical ventilation

Answer 20

These systems incorporate fans and control systems to drive the ventilation process. They are thus able to provide ventilation irrespective of the availability or suitability of natural forces. Mechanical systems are also often used to distribute thermally conditioned air as part of the building’s heating and cooling (air conditioning) system.

Question 21

Mixed-mode or hybrid ventilation

Answer 21

This utilises a combination of both natural and mechanical ventilation.