HVAC Flashcards
Why do we ventilate?
- reduced CO2 levels
- reduce virus/bacteria count
- remove dangerous dust, gas, vapour
- prevent condensation
- remove odours
- remove moisture
- air movement
- introduce cooler air
Surface condensation
Occurs where the surface temperature of a room surface falls below the dew point temperature of the moist room air
Interstitial condensation
Occurs within the fabric of the building, wherever the temperature falls below the dew point temperature
Natural ventilation
- driven by wind and stack effects
- harder to predict and control
- air unfiltered
- low energy use
Mechanical ventilation
- driven by fans
- controllable
- effective in deep plan buildings
- high air change rates can be achieved
Saturated vapour pressure
The vapour pressure of the water vapour in an air sample that contains the maximum amount of vapour possible at that temperature
Vapour pressure
The partial pressure exerted by the molecules of a vapour
Dew point
The temperature at which a fixed sample of air becomes saturated
Hygrometer or psychrometer
Instruments which measure the humidity of air
Vapour resistivity
A measure of the resistance to the flow of water vapour offered by unit thickness of a particular material under standardised conditions
Vapour resistance
The resistance of a specific thickness of material
Radiator pro and cons
Low maintenance
Good temp control
Simple and compact
Slow thermal response
Uneven temperature gradient
Heat loss through windows
Convectors pro and cons
Quick warm up time compared to radiator
Good air movement
Reduce risk of burning
Dust collects
Requires cleaning
Maintenance required and power supply
Underfloor heating pros and cons
Overcomes cold surface
Invisible heating system
Even heat distribution
Not suitable for offices that require underfloor services
Leaks in hot water systems
Slow response in heat change
