Commercial HVAC Flashcards
What is the relationship between straight duct and hoods or elbow fittings?
Both hoods and elbows should be 2 gauges heavier than straight pipe.
Can dash stops ever be removed, overrided or modified?
No
What is the average face velocity at which air is drawn through the face to the hood exhaust?
60-100 fpm
What must always be provided for a local exhaust system?
A make up air unit
The key to designing an industrial exhaust system is?
Speed
What type of ducts are recommended for industrial exhaust systems?
Smooth and round
Before it enters the fan, how many diameters should duct be straight for?
At least 2 diameters
What is the biggest resistance on an exhaust system?
The filter
What 2 types of fans are used in an industrial exhaust system?
Axial-propeller
Centrifugal-draws air into the centre of the fan and exhausts it at 90 degrees.
Straight blade fans move?
Curved blade fans move?
Material
Air
Exhaust stacks should be located how far away from a buildings fresh air intake?
50’
How far from a roof line should exhaust stacks be located?
10’
Air velocity should be how many fpm out of an exhaust stack?
3000 fpm
Where should clean out or access doors be provided on an industrial exhaust system?
Near elbows or close to any other change in direction of the duct
What is the face velocity for hazardous materials?
50 fpm
How does a variable air volume hood maintain constant face velocity?
By slowing down or speeding up the air
Three types of workplace ventilation are:
Indoor air quality ventilation
Dilution ventilation
Local exhaust ventilation
Velocity is measured in?
FPM feet per minute
Volume is measured in?
CFM cubic feet per minute
What is the formula to find CFM?
CFM=FPM x area
Hoods located 4” from a source will require how many times the amount of CFM to provide the same degree of capture as a hood located 2” from the source?
4x
What 2 factors need to be considered when sizing a fan to ensure it can overcome resistance in the exhaust system?
Appropriate size and type
For velocities of 2500 fpm or less, how many diameters of straight on fan discharge should there be?
2.5 D
Duct hangers and supports should be of sufficient capacity to carry the weight of the system if what?
If half of the system is filled with material
What are explosion doors used for?
To provide instantaneous pressure discharge
How far should a hanger be from a joint?
At least 2 duct diameters
What is the minimum distance in inches that a draw band joint should be?
4” minimum
Why are expansion joints used?
To provide stress relief and absorb movement during extreme temperatures
A blast gate or slide damper is used for what?
When a positive seal is desired and to close off or isolate parts of a system when they are not in use
Name 3 types of longitudinal seams?
Groove seam
Butt weld seam
Spiral seam
Which seam can be used for all five duct classes?
Butt weld seam
Screws or rivets should be 6” maximum Center to Center?
True
How many inches of lap should there be on commercial pipe?
2”
Class 1 only and 2 gauges heavier than chart values describe what?
Aluminum duct
Elbows should have a centreline radius of what?
No less than twice but preferably 2.5 times the pipe diameter
All branches should enter the main duct at what angle?
Not to exceed 45 with 30 degrees being preferred
Branches should be installed in what orientation?
On their side or on the top
For transitions, every 1 unit of change requires how many units in length?
5
For fan outlets, what can be provided if an elbow inlet is necessary?
An inlet box or turning vanes
When designing an industrial exhaust system, if pipe size falls between 2 numbers you should go with the bigger size?
No, to maintain velocity revert to the smaller pipe size
When sizing a blow pipe system, is it possible to not include certain types of machines?
Yes, if the machine is seldomly used it is not included in sizing.
Eg. floor sweep
What type of duct is used for class 5?
Plastic or stainless as the application consists of corrosives such as acid
If a stack extends more than 10’ above a roof, what may be required?
A guy wire set which may be 3 wires minimum
What is the result of exhausting large amounts of air without a proper make up air unit provided?
Carbon monoxide
What built up in a duct can increase the risk of flash fire or explosion?
Static electricity
What can be used to avoid static buildup in a system?
Aluminum or copper ground wire
What is the purpose of a well designed industrial exhaust system?
Eliminate undesirable contaminants where protection of workers health is required
Why do some industrial exhaust systems require special piping or duct work?
There may be the possibility of corrosion or abrasion
What 4 provisions must be considered when designing/installing industrial exhaust duct?
Cleaning
Maintenance
Fire protection
Drainage
What is the maximum face velocity when exhausting toxic fumes?
60-125 fpm
What is another name for an auxiliary air fume hood?
Makeup air fume hood
What is incorporated to maintain a desired face velocity on a variable air volume fume hood?
A closed loop control system
What is the basic principle on how dilution ventilation works?
Blow clean air in and exhaust dirty air out
List 5 basic components in a local exhaust ventilation system?
Hood Duct Air cleaning device Fan Exhaust stack
What type of pressure is found in a local exhaust ventilation duct?
Slightly negative pressure
What occurs if face velocity in a hood exceeds 125 fpm on a capturing hood?
Turbulence
What is a blast gate also known as?
Slide damper
When is plastic or PVC duct used on an industrial exhaust system?
For corrosive or toxic fumes are to be conveyed
What is the best practice regarding centreline radius and number of gores on elbows used for an industrial exhaust system?
Centreline of 2.5 and 7 gores
What can be added to maintain velocity in a constant volume exhaust system in a building that has a variable air volume ventilation system?
Bypass dampers
What can be installed to reduce energy consumption in a building that employs a large amount of exhaust systems?
Heat recovery system
What is the recommended face velocity for a hood under normal conditions?
100 fpm
What is the function of a kitchen canopy or hood?
Capture plume of heated air that is rising
What are two main categories of commercial kitchen exhaust hoods?
Type I
Type II
What are Type I hoods designed to handle?
Heat and grease laden effluents
What are the two broad categories of Type I hoods?
Standard and Listed
What does a Type I hood capture that a Type II does not?
Grease
What are two basic styles of hoods?
Canopy and non-canopy
List 4 types of canopy hoods?
Island
Wall
Corner
Slotted
List two types of non-canopy hoods?
Back shelf
Eyebrow
List 4 items that could be part of the grease removal system?
Filters
Baffles
Air washers
UV technology
What 4 codes must a grease removal system meet when installed?
Alberta building code
NFPA
Manufacturers specs
Authority having jurisdiction
What is installed to suppress a flare up prior to having heat damage in a grease removal system?
Fire suppression system
In what orientation should commercial kitchen exhaust ducts be installed?
Vertically
What is the minimum air velocity through commercial kitchen exhaust ducts be according to the NFPA?
500 fpm or 152.4 m/minute
How much make up air is required in a commercial kitchen?
100%
What is a control interlock panel used for in a commercial kitchen?
To ensure that when the exhaust fan is on, the make up air unit is also on and vice versa
How much overhang must a commercial kitchen canopy have in regards to the cooking equipment?
At least 6” per exposed side
What gauge of mild steel can be used in the construction and installation of a commercial kitchen canopy?
Stainless steel?
18 gauge mild steel
20 gauge stainless
At what length on a commercial kitchen exhaust canopy is it desirable to have two take offs on top for discharge?
When the canopy exceeds 10’
What gauge of mild steel can be used in the construction of commercial kitchen exhaust duct?
Stainless steel?
16 gauge mild steel
18 gauge stainless
Where shall access doors, for the purpose of cleaning and inspection, be installed on commercial kitchen exhaust duct?
Side or top
How much extra weight needs to be accounted for in commercial kitchen exhaust duct if the cross sectional area exceeds 24”?
800 lbs
How much clearance must a commercial kitchen exhaust duct have to combustibles?
18”
How far away from adjacent buildings, air intakes or property lines must a commercial kitchen exhaust duct terminate outside?
10’
How far from a roof surface must the outlet for a fan discharge be?
40”
What is the maximum storage capacity of the grease collector?
1 US gallon
What type of force extracts grease through a baffle tape grease filter?
Centrifugal force
What is the optimum operating velocity of air through a baffle type grease filter?
150-300 fpm
What takes precedence over original drawings and specs?
Addenda and revisions
What is the purpose of a spec?
To describe the work to be done
What is the purpose of a schedule?
To provide information on what goes where
What is a change to a blueprint called?
A revision
What is a change to a specification called?
An addenda
What should always be read before starting a job?
The mechanical general notes
What point are all elevations derived from?
The datum point
What are changes to drawings referred to as?
As builds
What does BIM stand for and what does it include?
It stands for building information management and includes all of the information used to construct a building
What must carefully be studied when compiling a job takeoff?
The plans and specifications
What is ACTS?
The Alberta construction tendering system
What does a bid bond guarantee?
If the contractor is the low bidder that they will honor the bid
