J6 PPT 1-4 Flashcards
In a passive air supply system, there are no mechanical devices used to bring the air from outside to inside. True or False?
True
Passive air supply systems use dampers, grills and louvred vents to bring outside air in for combustion. True or False?
True
Ducting a fresh air supply near the the furnace or boiler burner provides all combustion air and _________ air if necessary.
Dilution
A hole in the wall may be used as fresh air instead of ducting providing the appliance is close enough and it complies with 8.3.1 (d). True or False?
True
Mechanical air supply is based on ____cuft per 1000btuh which is perfect stoichiometric combustion
30cuft per 1000btuh
Air can be split into 3 categories. What are they?
- Combustion
- Dilution
- Ventilation
The three parts to combustion air are?
- Primary
- Secondary
- Excess
What is the portion of air supplied to the initial stages of combustion and controls the rate of combustion?
Primary air
Primary air is ___ of stoichiometric combustion air and ____cutft per 1000btu’s
1/3
3.33
What is the portion of air supplied for the intermediate and final stages of combustion and controls combustion efficiency?
Secondary air
Secondary air is ____ of stoichiometric combustion air and ____cuft per 1000btu’s
2/3
6.67
What is the extra portion of air supplied to the combustion zone that is not required for complete combustion?
Excess air
Atmospheric appliances require ___% excess air. (50% of theoretical combustion). Therefor they require __cuft per 1000btuhs.
50%
5
Power burners require ___%-___% excess air or 2.5 cubic feet per 1000btuh
20-25%
Is dilution air apart of the combustion process?
NO
Why is dilution air required?
To slow and cool flue gases
Do all appliances require dilution air?
Only if they have draft control
The ambient air that is admitted to a
venting system at the draft hood, draft diverter, or draft regulator is known as?
Dilution air
Do fan assist appliances require dilution air?
NO
Dilution air is ___cuft per 1000btu
15cuft
Describe ventilation air
Air supplied by an opening or exfiltration to a space with an appliance to replace exhausted air
Excess air _______ complete
combustion.
ensures
High efficiency appliances require about ___% excess air
25%
Excess air is the air required ______ the amount needed for stoichiometric combustion
ABOVE
__________ appliances require 50% excess air added to stoichiometric air requirements (5ft per 1000btuh)
Atmospheric
Name two draft control devices?
- Draft hood
- Barometric damper (draft regulator)
Name three appliance configurations with no draft control
- Fan assist
- Forced draft
- Induced draft
Dilution air is added downstream of the heat exchanger at the draft control device. True or False?
True
Dilution air is not part of the combustion process. True or False?
True
Name three types of air duct covering/screens?
- Grill
- Louvre
- Screen
Grills/Louvres are usually made of galvanized iron, copper, aluminum or other rust-inhibited materials. True or False?
True
Air grills have efficiency ratings so they must be increased to allow for proper airflow. True or False?
True
Rectangular and round duct can come in sizes from __in to ___in
3in to 41in
Type of ducting material also determines _______
sizing
Name the two types of make-up air heaters. They operate generally in the same way.
direct fired
indirect fired
What are make-up air heaters designed to do?
Replace exhausted air at the desired temperature
Make-up air units have ___________ gas valves
modulating
The discharge air nozzle on a make air unit is adjustable. True or False?
True
Make up air units have two gas manifolds. Name them.
Main gas manifold
Pilot gas manifold
Velocity of a makeup air air steam?
2,500 - 3,500 fpm
Make-up air combustion system utilizes a ______- mixing type of line burner, in which a circulating air stream supplies all all air needed
nozzle
At which pressure is raw gas typically fed directly into the burner ports on a direct fired make up air?
5” w.c
For a DFMA, the fast air stream provides means of mixing the air and gas, as determined by the shape and size of holes in the baffles. True or False?
True
Proper combustion is achieved over a wide firing range, up to __:_ turndown ratio
30:1 turndown ratio
The air flow through the heater must be straight and have sufficient velocity to maintain adequate ________ and burner capacity within the space allowed
turndown
Where is the blower located on a make-up air?
downstream of the burner (negative side)
What is the purpose of having the blower on the negative side of a makeup air?
The pull through method helps to avoid airstream stratification, where the blower mixes excess air and combustion products
Any of these malfunctions will cause a burner safety shutdown (manual reset)
- pilot fails to ignite
- loss of flame after ignition
- high discharge temperature
- low cabinet temperature — outdoor
units only
- high air velocity through the profile
plate
- low air velocity through the profile
plate
True
Fan assisted BURNER overcomes the resistance of the burner only. True or False
True
Is a fan assisted BURNER equipped with a draft control?
Yes, fan only overcomes burner. Remaining flue rises out. Requires draft control and dilution air.
Fan assisted APPLIANCE has a draft through the entire appliance and is not equipped with draft control. True or False
True
Does a fan assisted appliance require dilution air?
No, because there is no draft control
Draft hood requires?
30cutft of air
15 dilution
10 combustion
5 excess
