Theory Flashcards
What angle must you have when drilling stainless?
135 degrees
How is spring back compensated when bending stainless?
Over bending
What method of power braking should be used with stainless?
Air bending
From where are Alberta outdoor design temperatures taken?
The Alberta building code January 2.5%
What is design temperature difference ?
The difference from indoor design temperatures to outdoor design temperatures
Which way does heat travel?
Hot to cold
Define effective temperature.
Effective temperature could be defined as how a person feels at a set temperature
What 4 factors affect building temperature?
- building envelope
- mechanical systems
- occupants
- appliances
What fibre has the greatest r value ?
Glass fibre
True or false. Above and below grade have the same r value.
True
What 3 factors are used to find the correct infiltration factor?
- site exposure
- penetrations
- air tightness
Duct passing through an unconditioned space must be ______.
Insulated
Define Ventilation ( fresh air ) loss
Ventilation losses are direct loss to the appliance and need to be added to the total conductive heat loss to ensure the correct appliances are selected.
Where is the summer design temp found?
July chart. Temp is factored off of 75 degree indoor temp
Does radiant head add a load to the building ?
Yes
When must a solar adjustment be made ?
When the summer mean temp is greater than 8 degrees Celsius
What is the solar adjustment for fully shaded walls and doors?
-11*F
What is the default when calculating heat gains and losses ?
No shades and drapes are used
What must be done if the direction of the house is unknown?
The wall with the most windows shall be calculated as if it were facing east or west
1 ton of cooling = _____btuh
12 000
What are cooling units sized in relation too?
The heat gain calculation
A properly sized cooling unit will be within ____ %to ____ % of the buildings total heat gain calculation.
80% - 125%
How far are supply air outlets from the wall?
8”
How many supply airs must be in a unfinished basement for every 430ft squared?
1
How many return air inlets should be on each floor ?
1
Where should return air inlets never be installed ?
Kitchens, bathrooms, laundry rooms, utility rooms and crawl spaces
What are 2 things to consider when ventilation air is introduced to residential HVAC system ?
- fresh air inlet size
- mixed air temperature
What are 2 things to consider when it comes to ventilation air inlet sizing ?
The connection shall be between the nearest return air branch and the blower.
The connection shall be at least 10’ from the blower or connected using an acceptable mixing device
What temperature should the mixed air ( return air ) be ?
No lower then 60F or 16c
What 4 factors must you consider when designing an HVAC system?
- proper duct size
- ducts running through unconditioned spaces
- zoning for houses with special heating and cooling needs
- combustion and dilution air
What must happen to duct that passes through an unconditioned space ?
-sealed air right. Must be insulated. Vapour barrier on warm side of insulation. If supply more then 50ft long increase size by 10% airflow
How much air should be collected from the basement ?
50% of the supply airflow to the basement
What is the heating airflow proportioning factor ?
A portion of the cfm required to deliver 1 btuh of heat at the heating flow rate
Where is the room heating load taken from ?
Heat loss / gain calculation sheets
True or false. It is good trade practice to have more than 1 return air per floor.
True
What is acceptable air velocity for the main supply ?
700-900 fpm
To determine inlet and supply openings
2x4 walls
Number of openings= floor return air cfm / 120
2x6 walls you divide by 180
What are 3 advantages of continuous blower operation?
- improved air filtration
- increased building comfort
- reducing cold areas in the building
True or false duct systems will be different sized for heating than for cooling.
True
Why is it important to balance a residential HVAC system?
If a system is not balanced there will be cold areas in the building
What do Dwyer meters measure ?
They measure pressure in water columns not CFM
What do manometers measure ?
They are for low pressure. Inclined manometers are more accurate than u tube manometers
What are the 2 basic types of anemometers ?
Thermal and rotating valve
What is atmospheric pressure at sea level?
14.7 “ w.c.
What is static pressure ?
Air will exert pressure on the walls of the vessel in which it is confined
What causes dynamic pressure losses ?
Dynamic pressure losses are the result of changes in the direction and velocity of air flow. They occur when an airstream makes turn or has changes.
What is the aspect ratio ?
4:1
What is equivalent length ?
The comparison of the calculated pressure drop through a fitting to the pressure drop through a straight length of duct the same size
How is the radius ratio of an elbow calculated?
By using the centre line radius ( one half the width of an elbow + the throat radius) of the elbow dividing it by the width of the elbow
Why are splitters installed in elbows?
To reduce the dynamic pressure losses
What is the maximum angle of an eccentric diverging fitting ?
30*
What is the maximum angle of a concentric diverging fitting ?
60*
Where are two piece streamliners used ?
In areas where the ductwork cannot be made to offset around an obstruction and that would exceed 20% of the cross sectional area of the duct.
How do you calculate air velocity ?
V= 4005 square root PV
What two requirements does the Alberta Building code state about fuel fired appliances installed on the roof of the building or any location outside the building ?
1.2m from property line, measured horizontally
3m from an adjacent wall same building.
What is sensible cooling load?
Refers to the dry bulb temperature of the building and the latent cooling load refers to the wet bulb temperature of the building.
Which location is duct velocity taken ?
The trunk air velocity is recorded at a location closest to the equipment
What is outlet throw ?
Usually displayed in feet . Is the distance the air travels from the centre of the diffuser outward to a point where the air velocity drops to 50 fpm
What 2 factors are plotted onto a ductulator or friction table when finding the diameter of a supply air branch duct ?
Adjusted duct pressure and outlet flow rate
What are the 2 classes of fans ?
- axial ( propeller)
- centrifugal ( radial)
Define axial fans.
Air enters and leaves the impeller in a direction parallel to the fan axis. All of the static pressure comes from the change in velocity as the air passes through the impeller. More suited for low volumes and pressures.
The wheels of axial fans
K wheel- blades can’t be adjusted
A wheel- blades can be adjusted only when fan is on
C wheel - blades can be adjusted when fan running
What are the 3 types of axial fans ?
- propeller
- tube axial
- vane axial
What are the most commonly used fans ?
Propeller fans
What are the 4 types of fan blades ?
- forward curved blades
- backward inclined blades
- airfoil blades
- radial blades
The backward inclined airfoil fan is a refinement of the flat bladed backward inclined centrifugal fan in what respect ?
It has better static efficiency and it is quieter
What type of fan blade arrangement is usually used in air pollution control applications with high particulate loadings?
Radial blades
Which fan should never be used in a ductless system?
Forward curved blade centrifugal fan
What is the best fan to use on a blowpipe system in a sawmill?
Radial blades centrifugal fan
The most accurate volume control of air is obtained by using what type of damper?
Opposed blade damper
What is an accepted method of determining the length of a splitter damper ?
1 1/2 times the width of the small duct
Which damper is generally used in locations where it is either fully opened or fully closed?
Parallel blade damper
Which fans provide right angle airflow in a rectangular shape and are useful in applications such as air curtains over doorways?
Cross flow fans
What dampers are the best for modulating air flow ?
Parallel blade dampers
One foot of water equals ____ PSI
0.433 PSI
