Exam Review Flashcards
Pipe is thicker wall than tubing for threading purposes…tubing cannot be threaded
There should be approximately 7 to 10 perfect (not nicked or broken) threads and 2 or 3 imperfect threads for each joint (connection)
4 tools needed to cut and thread pipe
Hack Saw or Pipe Cutter
Reamer
Die- (Cuts the threads on gas line)
Holding Tool (Chain Vise, Yoke Vise or Pipe Wrench)
Heat Cont.
Heat is Measured in BTU’s
BTU stands for = British Thermal Unit
BTU defined = The amount of energy (heat) it takes to raise one pound of water 1°F
3 Essential Elements for Combustion
- Fuel – Any Substance that has carbon and hydrogen
- Heat – To raise the substance to it’s ignition (burning) point
- Air – Contains 78% nitrogen, 21% oxygen
Fuels
Can be solid, liquid or gas
Common Fuels in the HVAC industry
1. Oil
2. Natural Gas = Made of mostly Methane
3. Propane Gas
Natural Gas
Also called Methane
Always comes in a gas state (no liquid)
Ignition Temp = 1163°F
Specific Gravity usually = .60
Operating Pressure = 3.5 “ WC (inches of Water Column)
Dry atmospheric air specific gravity = 1.0
Nat Gas is 60% the weight of air; therefore, Natural Gas rises when released to the atmosphere (Nat Gas is lighter than air)
Burn 1 CF (1 ft³) of Nat Gas = approximately 1000 BTU
Nat Gas in it’s pure form is Odorless and Colorless. An odorant (sulfur) is added for smell.
Propane Gas
Sometimes called Liquid Propane
Shipped/stored as a liquid. Turned to vapor for burning
Operating Pressure = 11 “ WC
Ignition Temp = 920 - 1020°F (more volatile (explosive) than Nat Gas)
Specific Gravity usually = 1.52
Dry atmospheric air specific gravity = 1.0
LP is 1.5 times heavier than air; therefore, LP Gas falls when released to the atmosphere
Burn 1 CF (1 ft³) of LP Gas = approximately 2500 BTU
LP gas must not be used for a gas furnace set up for Natural Gas. The results are overfiring and Soot buildup
Three types of Combustion
Perfect
Complete
Incomplete
Causes of Carbon Monoxide in a home
Max allowed by ASHRAE
Maximum allowable CO in a living area = 9 ppm
Maximum allowable CO in Flue Gas = 400 ppm
Max allowed by OSHA
50 ppm
Two Soot Causes
Lack of combustion air
Impingement
Types of Combustion Air
Secondary Air – Air that is mixed at the flame for combustion
Primary Air – Air Mixed before the flame for combustion.
Good Combustion (needed)
- Oxygen (air)
- Fuel
- Heat (or ignition)
OSHA defines “Confined Space” as….
Have limited access for entry and exit
Large enough for a person to enter
Are not intended to be continuously occupied by humans
Upflow
Most Popular
Heat exits the furnace at the top of furnace.
Return air (cold air) enters the bottom of furnace
Downflow
Heat exits the bottom of the furnace.
Return air (aka: cold air) enters top of furnace
Most often used where furnace is located on a first floor and supply duct exits into a crawl space
Multi-positional Furnace
nvented about 25 years ago.
These furnaces, unlike the others, can be placed in multiple positions without damaging the equipment.
Seasonal Belt Adjustment
The HVAC industry standard is to change the motor pulley to adjust belt driven air flow.
Larger Motor Pulley = More Air
Smaller Motor Pulley = Less Air
Regulator
Keeps constant pressure to burners and Gas valve
Nat Gas – 3.5 Inches water Column (“ W.C.) exiting regulator (going into the burners)
LP Gas – 11”WC from outside tank to furnace
11”WC to burners
Thermocouple
Used on gas furnaces, stoves, fireplaces, clothes dryers, water heaters, etc
What’s a Redundant Gas Valve?
It’s a combination gas valve that has two or more coils for allowing gas to exit the valve…it’s has multiple safeties (shut-off seats).
Pilot Burner Orifice
Very small opening for metering in gas for pilot
Can clog easily with lint, carbon and junk.
Burner Orifice
Meters in the proper amount of gas into burner
One orifice for each burner
Typically one burner for each heat exchange cell
They come in different opening sizes. This one is a number 45
Burners
- Drilled Port burner
- Slotted burner
- Ribbon Burner
- Inshot Burner (Single Port Burner)
Single Port Burner
Upshot Burner
Inshot Burner
Crossover Igniter
Makes sure all the burners light at the same time.
If all the burners do not light at the same time, one or more burners may “delay” ignite and cause a large boom. This is called “delayed Ignition”
Heat Anticipator
Built into heating thermostat
A small heater that fools the thermostat into shutting off the furnace early to prevent temperature override.
Fan Control
This component only allows the blower to come on when heat exchanger is warm enough.
Limit Control
Safety N.C. SWITCH
It prevents the furnace from over heating
The Limit Safety
All furnaces have a Safety Limit.
The safety limit will trip open if the furnace overheats
What would cause a furnace to overheat?
1. Lack of air across the Heat Ex.
2. Furnace over firing
Combination Fan/Limit Control
This control is typically (but not always) seen on the standing pilot furnaces.
High Efficiency Furnace Components
Induced Draft Motor (AKA: power vent or Mechanical Draft)
Heat Exchanger
Burners
Electronic Ignition
Secondary Heat Exchanger
Med or High Efficiency Furnaces
Medium (80+ %) and High Efficiency (90+%) gas furnace have an induced draft blower motor that is often called a power vent motor or Mechanical Draft motor
In-Shot Burner
AKA: “jet burners”
Saves space on the gas furnace
Allows the furnace to be shorter
Also, allows the furnace to be multi-positional
Used in modern
induced draft
furnaces
90+% Gas Furnace Results
- Lower flue temperature
65 -70% furnace = around 500°F
80% eff furnace = around 280-350°F
90+% eff furnace = around 120°F - Produces Condensate – because flue temperature is below dew point (dew approximately 300°F)
Pilot Orifice
If the pilot orifice becomes clogged, always replace it with a new, identical pilot orifice
What may happen if Burner Orifices are not sized properly
If the burner orifices are too large (LP gas with Natural Gas sized burner orifices) , this will let too much gas into the burners and HX. This will create excessive soot and possibly crack the heat exchanger (HX)
Personal Protective Equipment – PPE
PPE refers to equipment worn by a worker to minimize exposure to specific hazards and to help ensure personal safety
Ladder Safety
- Make sure the ladder extends at least 3 feet above the support point
- Needs to lean out ¼ of the height
- Always keep three points of contact will the ladder when climbing
Lockout/Tagout
An aggressive lockout/tagout (LOTO) program is one of the best ways to prevent electrical shock.
Electrical Safety
The severity of the electric shock is determined by the amount of current flow through the body as well as the path the current takes as it passes through the body.
Two categories of furnaces when for venting
Natural Draft (draft diverter)
Induced Draft (Power vent motor AKA: Mechanical Draft
What are the three items needed for combustion?
Heat (ignition)
Fuel
Air (oxygen)
Motors
Belt Driven–
Change speeds by changing motor pulley diameter size.
Larger motor pulley = more air
Smaller Motor Pulley =
Less air
Variable Speed Blowers Motors
More efficient than standard motors (uses less $$$)
Greater number of speeds
Constant air flow
Constant torque
Constant speed
4 types of Gas Burner Ignition
Standing Pilot – You are already familiar
Intermittent Spark – sparker lights pilot
Direct Spark – sparker lights burners directly
Hot Surface Ignition (HSI) – “Glow Plug” lights either pilot or burners directly
Intermittent Spark
Thermostat calls for heat, sends 24v to spark module telling the module we want heat.
Spark module sends 24v to PV (Pilot Valve) portion of gas valve to send gas to pilot
At same time 10,000v is sent to sparker
Pilot should light
Direct Spark
Very similar to the Intermittent spark, only there’s no pilot, the 10,000v spark ignites the burner
How to Check Flame Rectification
Place your Multi-Meter to the micro amps (μA) setting, remove the wire to the flame sensor and place the Multi-Meter in series.
Integrated Control Board
The modern IC Board is responsible for controlling all the furnaces functions.
Why is there a pressure drop in the gas line system?
The pressure resistance (pressure drop) in a natural gas or L.P. gas line
Why do Cat IV Appliances produce a condensation water?
The secondary Heat Exchanger is removing the extra heat from the flue gases to the point where the moisture in the flue gas turn from a vapor to a liquid (Condeses)
Combustion Air
NOx is pronounced NOX
California requires all gas furnaces to have a special NOX filter installed by the HVAC contractor
Tramp Air
Uncontrolled air which leaks into the combustion side of the heating appliance through any opening not designed by the manufacturer.
Checking a Pressure Switch
- Ohm the switch out with induce draft motor off
- Ohm the switch out with induce draft motor on
- Check for 24v voltage across switch with motor off and then on
Duct Work
Foil back fiberglass
Bubble wrap
Duct liner
Sheet Armor Flex
