Ventilation Flashcards
What are the three methods to ventilate a house?
- Exhaust only
- Supply only
- Balanced
For supply-only ventilation systems, what is the ideal location for supply registers?
High level supply, 12 inches from ceiling
For a balanced ventilation system, how is fresh air introduced into a house?
- Its own dedicated duct system
- Into the cold air return plenum of the furnace
What is the average energy efficiency of a balanced ventilation system?
70% average (55-85% energy efficient)
What is the recommended air changes per hour with a balanced ventilation system?
1/3 ACH
List the components of a HRV
- Cabinet
- Heat exchanger
- inlet & exhaust fans
- duct system
- Flow measuring stations
- Controls
- Air filters
- Condensate system
- Defrost system
What are the different arrangements for the defrost system of a HRV?
- Supply preheated air with an electric duct heater
- Warm exhaust air is recirculated through the supply side (no fresh air during this time)
- Exhaust fan stops & supply intake blocked with a damper
- Supply fan turns off & exhaust fan moves warm air through HRV
Do all HRVs have a condensate system?
No. Some HRVs may transfer moisture to supply air
What are the control options for a HRV?
- Thermostat
- Humidistat
- Dehumidistat
- Manual switch
- Timers
- Fan speed controls
Where are flow measuring stations installed on a HRV?
On both the supply & exhaust warm side ducts, 12 inches away from the dampers
How should the supply intake termination be located on the exterior of a house?
- 6ft away from the exhaust termination
- 3ft away from gas meters
- 3ft away from other exhaust vents
- 18 inches above grade
- 40 inches away from corners of buildings
- Away from driveways & garages
Where are the cold side ducts located on a HRV?
- Exhaust duct from the HRV to the outdoors
- Supply duct from outdoors to the HRV
How should cold side ducts be installed?
- Short & straight
- If flex ducts are used, they should be supported every 3ft
- Exhaust ducts should be sloped downwards to allow condensation to discharge
How should warm side ducts be installed?
- uninsulated
- rigid metal construction
How much ventilation is needed for a roof?
- 1 sq ft of ventilation per 300 sq ft of attic floor
- 1 sq ft of ventilation per 150 sq ft of attic floor when no soffits and air barrier below insulation
What are the disadvantages of turbine vents?
- Don’t work without wind
- Can depressurize the attic on windy days
- Noisy
- Prone to seize & leaks
- Can cause bulk water leakage
How much ventilation is needed for crawlspaces?
1 sq ft of ventilation per 150 sq ft of crawlspace floor
What are the different types of heat exchangers in a HRV?
- Flate plate
- Rotary wheel
- Concentric tube
- heat pipe
- capillary blower
- heat pump
What are some clues that insulation has been added to flat roofs?
- plugged:
- holes in roof coverings
- holes in ceilings
- fascia boards
- vents added to the roof
- extra thickness to roof
- lower ceiling height than expected
What are some clues of moisture problems in flat roofs?
- sagging or spongy roof surface
- sagging ceilings
- mold or mildew on ceilings
- rusted nail heads on ceilings
What types of insulation are suitable for below grade?
- rigid fiberglass
- mineral wool
- polystyrene boards
What happens when the HRV is not interlocked with the furnace fan?
short-circuiting of airflow
Can a HRVs condensate drain discharge directly outdoors?
Not in cold climates; may freeze
Define “hydgroscopic”
Materials with the ability to absorb large amounts of water (i.e. wood)
If water absorbed > max capacity = rot develops
If water absorbed < max capacity = will dry out as temp rises
Define “thermal bridging”
Points where the insulation is not continuous
What conditions are required for mold growth?
- Oxygen
- Right temperature (4C - 38C)
- Moisture (20% moisture content in wood)
- Food (wood)
What is night sky radiation?
During the day the roof heats. At night, the roof looses all heat from radiation to the cold night sky. Due point is reached and condensation occurs on the roof sheathing, leading to mold growth overtime.
