Level 1Review Flashcards
Describe the relationship between the % values of CO2 and O2 in the flue gas when you adjust the air shutter on a fan-assist burner during set-up?
The greater the amount of excess air, the higher the % of O2 and the lower the % of CO2
If three flue samples were taken, the first with 20% excess air, and the second with 32% excess air, and the third with 44% excess air which would contain the higher CO2 reading?
The sample with 20% excess air
If a natural gas appliance and a propane appliance were firing at the same rate and under the same conditions, which would have the greater air requirements and which would have the greater percentage of CO2 in the flue products?
Both have the same air requirements, but propane has higher CO2
When performing an analysis of the products of combustion using natural gas, what percentages of carbon dioxide and oxygen you would expect to find if the excess air is set at 30%?
8.3% CO2, 5% O2
A gas appliance is firing at 5,400 Mbh on propane gas and condensing all water vapor to a liquid state. Calculate the capacity of water produced each hour in US Gallons
38 US Gallons
What is the formula for perfect (stoichiometric) combustion?
Fuel + O2 + N2 = CO2 + H2O + N2
What is the formula for complete combustion?
Fuel + O2 + N2 + Excess Air = CO2 + H2O + N2 + Excess Air
How does tertiary air control NOx emissions?
It slightly cools the flame
What can be done to control NOX emissions from a burner?
Inject steam around the flame
What can be used to control the combustion air for a burner system?
A Variable Frequency Drive or Electronically Commutated Motor
List three factors that can create CO in the products of combustion?
Running too much fuel, not enough combustion air or a failing draft inducer
What is the maximum air-free CO level allowed to be produced during combustion?
400 ppm
How many pounds of CO2 are produced per hour from a 54,784,000 BTUH fuel oil fired boiler?
8765 lbs
How many pounds of CO2 are produced per hour from a 7,312,000 BTUH natural gas fired boiler?
856 lbs
According to legislation, how much ppm sulfur content does heating oil need to be below?
500 ppm
What chemical compounds from combustion are collectively called SOX?
SO2 & SO3
What are two results when NO2 reacts with other pollutants?
Ozone and Acid Rain
What chemical compounds from combustion are collectively called NOX?
NO & NO2
What is the main reason for performing combustion analysis on gas fired equipment?
To ensure the equipment is operating in a safe and efficient manner.
How often should your combustion analyser be calibrated to ensure accurate test readings?
Once per year.
Where should the sampling probe take a sample from on a gas fired appliance?
Upstream of any draft control device or just downstream of a stack economizer.
What is the correct way to allow combustion analysis samples to be taken with plastic S636 systems?
Installing an access tee with a ½” tapped bushing as close as possible to the flue collar of the appliance where either a plastic or brass plug can be inserted.
What is a Peltier cooler used for in a combustion analyzer?
To drive out moisture from the sample
The gas cells in a combustion analyser are of what type?
Electrochemical
What can shorten the life span of the toxic sensors in a combustion analyser?
High gas concentrations or insufficient purging
What is the chemical formula for the Perfect combustion of Natural Gas?
1CO2 + 2H2O + 8N2
What is the chemical formula for the Perfect combustion of Propane?
3C02 + 4H2O + 20N2
What is added to the combustion process to produce Complete combustion?
Excess Air
What is the expected percentage range of O2 produced by a forced draft burner with CH4 as the fuel?
3% - 6%
What are four characteristics of Carbon Monoxide?
Toxic, colourless, odourless and tasteless
What can cause too much draft in a venting system?
High stack temperatures
What percentage gain in efficiency is achieved by lowering stack temperature by 45⁰F?
Less than 1%
Calculate the net stack temperature if the ambient temperature is 72⁰F and the stack temperature is 420⁰F? Is this temperature within typically expected values?
348⁰F, Yes (330 - 500⁰F)
If the measure percent O2 reading is 4.1% and the measured NOx reading is 55 ppm, what would the NOx ppm be when corrected to standard?
58.58 ppm
If the measured CO reading is 38 ppm, and the measured %O2 reading is 4.2% what would the calculated air-free ppm reading be?
47.56 ppm
What is the power end of the Honeywell, Series 90 Modutrol used for?
It is used to drive linkages
What is the auxiliary end of the Honeywell, Series 90 Modutrol used for?
It is used to devices like auxiliary switches
In what orientation should motors with crankshafts be installed?
Horizontal
How is strain avoided on the motor and linkage of a fuel/air system?
The drive lever rotational start point is kept off of the shaft centerline
Fixed Stroke Actuators are available in what two opening ranges?
90⁰ or 160⁰
Adjustable stroke model actuators can be field adjusted between what range?
90⁰ - 160⁰
What controls the speed and the amount of rotation of the driven lever pivot point?
It is controlled by the starting position of both levers and the connection distance of the linkage to the lever pivot points
Placing the drive lever closer to the shaft centerline than the driven lever is placed will do what to the rotation of the driven lever?
It will be reduced
Placing the driven lever closer to the shaft centerline than the driver lever is placed will do what to the rotation of the driven lever?
It will be increased
How are precise changes made on the linkage for a fuel valve?
By adjusting the cam spring
The gas butterfly valve is used to control modulation and to stop gas flow?
TRUE / FALSE
FALSE, It is not used to stop gas flow
How can high and low fire be adjusted on a gas butterfly valve?
By using the stop screws
Where would you find information for making initial set up adjustments to linkages?
From the equipment manufacturer
What must be done while making any adjustments to linkages?
Combustion analysis must be performed
How do we balance safety and efficiency when adjusting our linkages with the use of a combustion analyzer?
- Adding more oxygen reduces the chance of CO and increases safety
- Reducing oxygen increases our efficiency but has the potential to increase CO thus being less safe.
- Always prioritize safety
What advantage does a direct contact water heater have?
No loss out the stack, no lost condensation, no lost radiant heat.
Describe how an immersion burner works.
A submerged radiant tube heat exchanger is used to heat large volumes of liquid.
Describe how an indirect bath heater works.
It uses two separate, submerged heat exchangers to heat a fluid with one heat exchanger and transfer that heat from the fluid to the second heat exchanger.
What are three of the potential hazards of using a direct fired construction heater?
- Being too close to combustibles can lead to a fire
- The possibility of fire if used in a wood frame structure
- There is the potential for dangerous levels of carbon monoxide
What is a curing oven used for?
Used to generate some form of chemical reactions once a temperature setpoint is reached by a particular substance.
What is a drying oven used for?
It is used to remove moisture from materials.
What is a baking oven used for?
It is used to remove moisture from materials and to generate some form of chemical reactions once a temperature setpoint is reached by a particular substance.
What is the purpose of a CO2 generator?
To produce carbon dioxide required by plants in commercial green houses.
What is the typical temperature range of an industrial furnaces?
750 to 3,275 °F
What is the purpose of an exothermic generator?
To produce cover gasses as a non-oxidizing atmosphere for the heat treating of bright metals.
What is the purpose of an endothermic generator?
To provide a positive pressure in a heat-treating furnace, and a platform on which a carburizing or decarburizing environment can be formulated.
What is the purpose of tertiary air in the combustion process?
To add air to control emissions and flame shape
What type of heat transfer does an infrared burner utilize?
Direct radiation
What type of heat transfer does a low temperature indirect heating burner use?
It uses a fan to transport the heated air to the work
What type of heat transfer does a direct-fired burner use?
It uses a mix of radiation and hot gas convection
What type of heat transfer does a high temperature indirect-heated burner utilize?
Tubes or enclosed walls are heated and radiate heat to the work
A propane fired boiler has a low-fire input of 1,700,000 BTUH and a high-fire input of 22,100,000 BTUH. What is its turndown ratio?
13:1
What ratio of air/natural gas are most premix burners limited to for acceptable, normal operation?
10:1
What are three characteristics of a nozzle mix burner?
- Its ability to operate over a wide range of air/gas ratios
- To control the mixing of the gas and air without sacrificing clean combustion or flame stability
- To allow the ability to vary the flame shape
What methods can be used to atomize oil in an oil fired burner?
- Air atomizing
- Pressure atomizing
- Steam atomizing
How can the flame length of an oil-fired burner be modified?
Changing the oil nozzle spray angle
The main burner flame shall be proven at the furthest point(s) along its base from the source of ignition when the burner flame width is in excess of how many feet?
3 feet
From the combustion flow formula identify what each variable represents.
Q = flow rate (cubic feet per hour)
A = area of the orifice (square inches)
K = discharge coefficient of the orifice
∆P = pressure drop across the orifice (inches water column
Sg = specific gravity of the gas
What would be the most reliable source to find the specific gravity of natural gas?
From your natural gas utility
What is the purpose of an Orifice plate?
To measure a general approximation of flow rate
The higher the discharge coefficient of the orifice the less restriction there is to gas flow.
TRUE / FALSE
True
When using an Orifice plate what are three things that could skew the results?
- The location of the pressure taps
- The thickness of a square edge plate
- If the appliance is operating in low fire
A direct fired make-up air unit is designed for temperatures ranging from -5⁰F to 75⁰F. At what outdoor temperature (within design parameters) will the velocity across the burners be the greatest?
75⁰F
A direct fired makeup air heater has the same function as an RTU.
TRUE / FALSE
FALSE
What is the main benefit of a DFMAH?
No efficiency lost to a heat exchange
Referring to the B149.1 under what conditions can a DFMAH be used?
A DFMAH shall not be installed unless it is necessary to exhaust air and replace it with preheated air
What must be proved before the DFMAH can start?
Any inlet or discharge air louvres must be proved open through an interlock with the control the exhaust system is operating
What is the purpose of makeup air?
To replace the air exhausted by large exhaust appliances which, when properly designed, installed and maintained ensure a neutral pressure in the building
When a DFMAH is used in a kitchen it must be interlocked with the kitchen exhaust fan so that neither fan can operate without the other operating?
TRUE / FALSE
TRUE
List three things that could affect the external static pressure placed on a DFMAH.
Filters, Grilles, Ductwork
When the DFMAH is in operation the burner is always firing?
TRUE / FALSE
FALSE
What are the two modes of operation for a spray booth DFMAH?
Spray Mode, Bake Mode
In a DFMAH what is adjusted to control air velocity?
Profile Other than make up air for a kitchen or spray booth list three other applications for DFMAH.
plates
Other than make up air for a kitchen or spray booth list three other applications for DFMAH.
Shaft pressurization (stairwell or elevator), storage garage, mine shaft
For refractory classification what would be considered a normal fusion temperature for the following refractories:
Normal Refractories
Super Refractories
High Temperature Refractories
- Normal Refractories 1600⁰C
- Super Refractories 2200⁰C
- High Temperature Refractories 1900⁰C
For refractory compounds and materials, what materials classification group do the following fall under:
Silica
Graphite
Lime
- Silica Acid Materials
- Graphite Neutral Materials
- Lime Alkaline Materials
Why do alkaline and acidic refractory material need to be kept apart on installation?
They react with each other under high temperature and form salt
What is the main purpose of refractory material?
To contain the heat generated by the combustion process
Properly selected, mixed and installed what percentage of fuel costs could refractory save.
5% - 7 %
Broadly speaking, what are the two refractory types?
Shaped and Unshaped
Refractory helps shape the burner flame in the combustion chamber?
TRUE / FALSE
TRUE
What is the most important factor that affects the lifespan of refractory?
Refractory Dry-out
What schedule must be followed for curing and dry-out of refractory?
Follow Manufacturer’s Instructions
What can cause horizontal crack formation in refractory?
Thermal cycling, Stress accumulation, creep
What four factors affect the flow of gas through a piping system?
Type of gas, diameter of pipe, length of pipe, pressure drop
What factor determines which of the two formulas are used to develop the code tables?
System Pressure
Pipe sizing tables in the B149.1 used to size low pressure piping systems make an allowance for a reasonable number of fittings. How is this accomplished?
By adding a hidden 20% to the displayed code zone lengths (as noted in the formula in the code book)
Plastic pipe is approved for use in a liquid propane system.
TRUE / FALSE
FALSE (B149.1.20, 6.2.16)
In what two ways can the volume of gas required for an appliance be determined?
The appliance rating plate, or the appliance manufacturer when the rating is not shown on the appliance (B149.1.20, 6.4.2)
What shall not be done if piping or tubing is located in an area where a corrosive chemical is used?
It must not be concealed (B149.1.20, 6.7.3)
In British Columbia, piping of NPS 2 ½” and over shall have welded pipe joints.
TRUE / FALSE
FALSE. BC Gas Safety Regulations - 2.3 Clause 6.9.2 of CSA B149.1-20 is repealed and the following substituted: 6.9.2 Piping of NPS 2-1/2 to 4 shall be either press-connect fittings certified to CSA 6.32(ANSI LC-4) or welded pipe joints. Piping greater than NPS 4 shall be welded pipe joints.
If a gas piping system requires welding, who can perform this welding?
Welding of gas piping systems shall be performed in accordance with a procedure and by an operator registered under the applicable provincial or territorial legislation.
When can piping or tubing enter a building below grade?
Only when permitted by the Authority Having Jurisdiction (good luck) (B149.1.20, 6.15.8)
What are the three ways that piping or tubing can be identified by in a care, detention occupancy, commercial, industrial or assembly building?
The entire piping or tubing system shall be painted yellow, The piping or tubing system shall be provided with yellow banding that has a minimum width of 1” and is marked at intervals not exceeding 20’, or the piping or tubing system shall be labelled “GAS” or “PROPANE” utilizing yellow label s or markings.
Can a quick disconnect device be used instead of a manual shut off valve?
NO (B149.1.20, 6.18.7)
What is the minimum diameter gauge allowed to be used for a pressure test on a gas piping system?
3 inch (B149.1 - 6.22.2 (b))
Using good engineering practices, what type of fluid should be used to pressurize a piping systems 4 inches and larger that contain a combustible gas?
inert gas (B149.1 6.22.2)
What is the minimum test pressure as per code requirements for 372’ of 8” NPS schedule 80 steel pipe (yellow jacket) installed underground operating at a gas pressure of 40 psig?
100 psig (B149.1
When pressure testing a gas piping system, what is the maximum range the pressure gauge shall exceed the test pressure by?
at least by 15% but not more than 300% (B149.1 6.22.2 (b))
What is the maximum diameter purge point opening when purging NPS 2”?
1/2 inch
What is the maximum pipe size that can be purged using air or fuel gas as the purging agent if the length of the pipe is 45 feet?
2-1/2 inch (B149.1 Table 6.4)
What is the recommended pressure used when purging with nitrogen?
0.5 or 14” w.c.
What is the recommended purge velocity through the piping system?
200 ft/min
What is the reason for purging at the correct velocity through a piping system?
completely scrubs the walls, no stratification, faster than flame speed
Why is purging using an inert gas a requirement when exceeding the pipe lengths for the diameters given in Table 6.4 of the B149.1?
larger volumes of piping cannot withstand an internal explosion from a gas air mixture
What does TOE stand for in a TOE nipple?
Thread One End
During a nitrogen purge, what velocity must be maintained at the purge outlet?
200 ft/sec
When purging outdoors, what is the minimum distance from a building intake allowed?
10 feet
Identify the type of flame represented in the following images:
a. Figure 1 type A
Identify the type of flame represented in the following images:
b. Figure 2 type C
Identify the type of flame represented in the following images:
c. Figure 3 type E
Identify the type of flame represented in the following images:
d. Figure 4 type F
Identify the type of flame represented in the following images:
e. Figure 5 type H
What style of burner is represented by the following images:
a. Gun burner
What style of burner is represented by the following images:
b. Lance burner
What style of burner is represented by the following images:
c. Cane burner
What style of burner is represented by the following images:
d. Immersion burner
In order to increase regulator accuracy, the pitot tube senses pressure at what point?
Lowest outlet pressure point
Which regulator will have the least amount of droop under flow conditions?
A pilot operated regulator
Critical flow in a regulator occurs when the velocity of the gas reaches what threshold?
Sonic Velocity
What does a double-ported balance regulator use to sense downstream pressure?
A downstream sense line
Where is the sense line connected on a proportional regulator?
To the top of the diaphragm
When zero governor regulators are used for burners that are to be operated under positive or negative combustion chamber conditions, how can the combustion chamber pressure be counterbalanced?
Connecting a pressure reference line from the combustion chamber to the top diaphragm chamber of the zero governor
What type of regulator is pictured below?
Double-ported balanced regulator
In the above image what is the purpose of connecting the sense line?
To sense outlet pressure
In the above image at what point is the sense line connected to the main supply piping?
Downstream to the top of the piping
What type of regulator is pictured below?
Atmospheric regulator
What type of regulator is pictured below?
Pilot operated regulator
What would happen if the regulator shown below was installed backwards?
It will pass no flow
What would happen if the above regulator was installed upside down?
It would provide lower downstream pressure
When selecting a regulator for a gas piping system, what regulator inlet pressure should you assume there to be when the system is under no flow?
Static pressure (system setting)
Referring to the image below, what must be done to create a proportioning regulator with the use of the regulator shown?
Cross-connect an impulse line from downstream of the combustion air control valve to the top of the regulator diaphragm
When an impulse line is used for a proportional regulator system, what is the minimum pipe diameter the line should be installed from the shaft of the combustion air control valve?
5 Pipe diameters
When an impulse line is used for a proportional regulator system, what is the minimum pipe diameter the line should be installed from any pipe tee or elbow (change in direction)?
3 Pipe diameters
If it is absolutely necessary to locate the connection of an impulse line less than the recommended pipe diameters downstream of the combustion air control valve, how should the hole be drilled in the pipe?
Parallel to the to the shaft of the valve on the side of the pipe
How should a cross-connection impulse line from the combustion air to the regulator be installed?
With no dips in the line to avoid trapping water and pitched towards the combustion air line
Referring to the figure above, what is the purpose of the limiting orifice?
It limits gas flow to the maximum burner rate
Referring to the figure above, how is low fire adjusted and set?
By adjusting the spring in the regulator
Referring to the figure above, what can be done to correct the regulator action affected from variable combustion chamber pressures or any combustion chamber pressures higher or lower than the room pressure adjacent to the regulator?
An impulse line can be cross-connected from the combustion chamber to the air/gas ratio regulator
For nozzle mix burners, when is a cross-connected impulse line from the regulator’s vent to the main combustion air line required?
When the minimum gas inlet pressure exceeds the maximum air pressure by 3.5 or more inches water column
If the minimum gas pressure at the proportional regulator inlet is not more than the maximum air pressure at high fire, what can be done to compensate for this?
Install a two-pipe bleeder and set it so the maximum impulse pressure is 4 iwc less than the gas inlet pressure
When is an overpressure protection device required by code?
When the inlet pressure to a main pressure regulator exceeds the pressure rating of any downstream component or accessory
What method of overpressure protection will interrupt flow of gas in the event of an over pressurization?
Automatic shut-off system
Which type of over pressure protection system must be manually reset after it has been activated?
Automatic shut-off
Referring to the figure below, this is an example of which type of over-pressure protection?
Pressure relief
Referring to the figure below, if the main diaphragm ruptures, what is the likely result?
The relief valve will provide reduced flow rates
Referring to the figure below, what method of overpressure protection is represented?
Upstream monitor system
Referring to the figure below, how can we easily change which regulator is the worker and which is the monitor?
Switch the set points on the regulators
A separate line relief valve shall be installed where in relationship to the regulator?
As close as possible downstream from the regulator
Why do air requirements differ for appliances with and without draft control?
Units with draft control require dilution air
An atmospheric gas appliance has an input of 390 Mbh and is equipped with a draft hood. It is to be installed in a building that complies with code clause 8.2.1. A or B. What size duct is required to provide air to this appliance?
9”
A furnace room complies with code clause 8.2.1. (a) or (b). It contains a 260 Mbh furnace without draft control and a 120 Mbh hot water heater with a draft hood.
Size the combustion air duct based on a length of 21’
7”
A boiler room contains the following five pieces of equipment:
- one 3500 Mbh boiler with draft control
- two 450 Mbh hot water heaters with draft hoods
- two 750 Mbh duct heaters without draft control.
Calculate the required free area of the combustion air duct.
436 in2
The following gas appliances are installed in a mechanical room:
- one 1400 Mbh steam boiler with a barometric damper
- one 550 Mbh hot water heater with draft hood
- two 600 Mbh direct fired make-up air units
Select a square grill for the combustion air opening in the boiler room wall that will meet the minimum requirements of the B149.1 gas code (grills rated at 67% free area).
18” x 18” (314.507 in2)
The air supply to a 20,000 Mbh boiler, using a force draft burner, is provided by mechanical means through a horizontal duct 42 feet in length. What is the quantity of air required to be supplied to the boiler?
600,000 ft3 (30 ft3 for every 1,000 btu/h)
A 2,752 Mbh forced draft natural gas boiler is operating in a mechanical room, excess air set at 40%. What is the required free area for the combustion air duct?
92 in2
A structure is equipped with a boiler rated at 5,300 MBH and a hot water tank rated at 400,000 Btu/h. Both pieces of equipment are equipped with draft controls and the air supply is ducted from outdoors. What is the size of the free ventilation air opening?
47.9 in2
A structure is equipped with a boiler rated at 750 kW and a barometric draft control. What is the free area of the combustion air supply opening in mm?
162,750 mm2
A structure is equipped with appliances rated at 1,900 MBH. None of the appliances is equipped with draft control devices and the air supply is ducted from outdoors. What is the free area of the ventilation air opening?
10 in2
A structure has a mechanical room into which air must be ducted from outdoors. It contains the following appliances:
- One boiler rated at 3,000 MBH, equipped with a barometric damper
- Two duct heaters without draft controls rated at 950,000 Btu/h each
- Two hot water tanks rated at 250,000 Btu/h each. Both tanks are equipped with draft hoods
What is the free area of the combustion air supply opening?
385 in2
A structure has a mechanical room into which air must be ducted from outdoors. It contains the following appliances:
- One boiler with no draft control rated at 500 kW
- One boiler with draft control rated at 4,000 MBH
- One duct heater with no draft control rated at 125 kW
- One hot water heater with a draft hood rated at 800,000 Btu/h
What is the free area of the combustion air supply opening?
485.37 in2
A mechanical room is equipped with gas appliances with a total input of 3,200 Mbh. All appliances are equipped with draft control devices. The louvre specified for the combustion air opening has a free area of 70%. What is the size of the opening required to fit the louvre?
428.58 in2
What is the minimum opening size on a screen used on a combustion air-supply opening?
1/4”
On a combustion air louvre with dampers the dampers must be controlled in what way?
Automatically
What interlock is required for an automatically adjustable combustion air louvre?
Normally Open contact interlocked with burner control
What two fan styles are commonly used for mechanical air supply systems?
Axial and Centrifugal
When air is provided by mechanical means what type of switch must be used?
The code does not specify the type. Air proving switch (sail or differential)
What three factors would lead you to want to pre heat combustion air?
Prevent the freezing of pipes, prevent thermal shock of the boiler, maintain appliance efficiency
What do ICI Appliance manufacturers do for high altitude installations? (above 4500 feet)
Increase blower motor horse power
What is the relationship between static pressure and air flow?
As static pressure goes up air flow goes down
What three factors have the greatest affect the static pressure in ducting?
Cross sectional area, length, number of fittings
What is the static pressure ranges of the following combustion supply-air ducting systems?
a. Low Pressure:
b. Medium Pressure:
c. High Pressure:
a. less that 3” w.c.
b. 3” to 6” w.c.
c. 6” to 10” w.c.
Referring to the figure below, what type of actuator is used to drive the vent damper?
Linear
Referring to the figure below, what type of actuator is used to drive the vent damper?
Rotary
When an automatic flue damper used on an appliance equipped with direct-spark ignition falls fully open upon loss of driving medium, the fuel supply to the appliance needs to be shut off.
False
What type of tubing is used to connect a differential pressure transducer used to control a damper actuator to the flue stack probe?
Silicon
What is the typical maximum distance a differential pressure transducer used to control a damper actuator should be connected to the flue stack probe?
6 feet
Referring to the figure below, What should distance ‘A’ be to improve accuracy?
3 times the vent diameter
If a CO sensor is used in a boiler room, how high above the floor should the sensor be mounted?
4 to 6 feet
When CO sensors are installed in an 28,250 ft2 boiler room, a total of how many sensors are required?
4
What would be the calculated theoretical draft developed by a stack 55 feet in height with an average temperature of 310°F, and the ambient temperature is 70°F?
0.246” w.c.
A boiler is firing natural gas at 4,000 Mbh with 30% excess air. What would be the calculated the volume in cubic feet per minute of flue gases leaving the flue outlet if the temperature is 450°F, and the outside air temperature is 70°F?
1603 cfm
A natural gas boiler is firing at 3 million Btu/h with 40% excess air. The ambient air temperature is 66°F and the stack temperature is 410°F. What would be the calculated velocity of the flue gas if the boiler is equipped with a 16-inch diameter stack?
889 fpm
If a stack has a velocity of 1000 fpm, what would be the calculated draft produced?
0.06 w.c.
A boiler equipped with a power burner is firing at 11 million Btu/h with 35% excess air. The combustion air duct is sized to meet the Gas Code requirements. What would be the calculated velocity through the combustion air duct if the boiler is operating at full input, the ambient air temperature is 70°F, and the stack temperature is 460°F?
972 fpm
You are called on to commission an installation of a 4,750,000 Btu/h natural gas boiler.
- Excess air set at 30%
- Stack diameter 18 inch
- Combustion chamber and heat exchanger pass volume 188 ft3
- Gross stack temperature 485 deg. F
- Ambient temperature 76 deg. F
Based on this information what is the expected draft in the stack?
0.0762” w.c.
What factors would achieve the highest draft in a chimney?
Tall chimney, hot combustion products, hot ambient (outside) air
A mechanical draft produced by a device upstream from the combustion zone of an appliance is a definition of what type of draft?
Forced draft
A mechanical draft produced by a device downstream from the combustion zone of an appliance is the definition of what type of draft?
Induced draft
What reading would the draft pressure gauge indicate when measuring in the combustion chamber of a gas fired appliance using a force draft burner?
Positive pressure
What reading would the draft pressure gauge indicate when measuring in the combustion chamber of a gas fired appliance using a fan-assisted burner?
Non-positive pressure (Negative over-fire pressure)
What does a balanced draft system incorporate?
A forced draft burner and an induced draft fan
What type of draft control does a gas-fired appliance incorporate when using a forced draft burner?
Internal damper
Why is the draft reduced when using flue gas recirculation to control NOx?
Lower flame temperatures
Why is the draft reduced when using a scrubber (air pre-heater)?
Heat is removed from the flue gases
Referring to the figure below, to maintain a draft of 0.08” w.c. at E what will the draft pressure need to be across the damper B?
The draft at A should be 0.6’ w.c. and the draft losses through the appliance are as follows:
- C = 0.12” w.c.
- D = 0.11” w.c.
- Elbow = 0.05” w.c. each
Across damper B = 0.19 “w.c.
- calculation: 0.6 – (0.08 + 0.12 + 0.11 + 0.10) = 0.19
What can be the results of an improperly selected, sized and/or installed venting system?
Efficiency loss, Appliance damage, Increased appliance maintenance, damage to breeching & stack, Production downtime, Increased operating costs.
What is the draft source for a natural draft appliance? Explain how this draft source moves the products of combustion through the appliance and the venting.
Gravity is the source. It moves the products of combustion through the appliance and venting because the hot flue gases are lighter and naturally rise (buoyancy).
Define forced draft:
A mechanical draft produced by a device upstream from the combustion zone of an appliance
Describe the three general variations of Burner inlet blowers and the different pressures associated with each.
a. Blowers which operate with enough pressure to overcome the burner alone. The combustion chamber, appliance outlet and venting will all be under negative pressure
b. Blowers which operate with enough pressure to overcome the burner and combustion chamber. The combustion chamber will be under positive pressure, appliance outlet will be neutral or negative and the appliance venting will be under negative pressure
c. Blower which operates with enough pressure to overcome the burner, combustion chamber and part or all of the venting. All parts of the system past the burner are under positive pressure.
Define induced draft:
A mechanical draft produced by a device downstream from the combustion zone of an appliance
What is the pressure upstream of the blower when it is located on the outlet of the appliance?
Negative
What is the pressure downstream of the inducer blower located on the outlet of the appliance?
It will be positive immediately downstream but could be either negative, neutral or positive on the downstream side depending on the blower’s power and the venting system
In a venting or chimney system with mechanical draft what two types of draft can be present and what type of pressure is associated with each?
Forced draft – static pressure in the venting is positive
Induced draft – static pressure is the venting is negative
When a venting system was originally installed as a gravity system where is the best location for the blower to be located? Why?
A draft inducer located at the vent or chimney outlet will maintain a negative pressure in the venting. Which would be the pressure the system was originally designed for
What must be done when a power venter is used in place of a natural draft venting system.
Gas flow to the main burner must be prevented in the event of power venter failure
When must design registration take place when you are designing or modifying complex, technical, and regulated equipment in BC?
Before the construction and installation of the equipment
When are parallel blade damper used?
For open/closed operation
When are opposed blade dampers used?
For modulating operation
What must be done when an automatic flue damper is installed on an appliance with a continuous pilot?
Must have a fixed minimum opening of 20% of the flue area and be interlocked with the burner control system so the that damper is proved fully open before ignition of main burner and The fuel supply to the appliance will be shut off in the event of failure except where the damper will fail fully open.
What are three common ways to prove draft in an appliance or venting system?
A pressure switch, An integrated proven draft switch, A pressure transducer
What Category appliance has nonpositive pressure and a temperature above 140°F (60°C)?
Category I
What Category appliance has positive pressure and a temperature below 140°F (60°C)?
Category IV
What Category appliance has positive pressure and a temperature above 140°F (60°C)?
Category III
What Category appliance has nonpositive pressure and a temperature below 140°F (60°C)?
Category II
What Category appliance requires venting that is made of material that is intended to resist corrosion from condensing?
Category II & IV
What Category appliance requires venting to be sealed and pressure tight?
Category III & IV
What is that maximum temperature of 316L stainless venting?
550°F
What temperature can high temperature silicone go up to?
2000°F
A flue vent can be supported by the appliance it serves.
True/False
False
What is the typical grade for horizontal flue venting?
1/4” per foot
How should the flue venting be graded for a condensing type appliance when running the vent horizontally to the outdoors?
Towards the appliance
To maintain the flow of condensate in a condensing appliance’s flue venting, a horizontal change in size of the venting should be done with what type of increaser?
Eccentric type
When changing the size of vertical venting, it should normally be done with what type of increaser?
Concentric type
What is used on flue venting guy wires to allow for vent expansion and contraction without stretching the guy wires?
Spring loaded turnbuckles
What is the voltage limitation on the secondary side of a control power transformer for a safety control circuit of a gas fired appliance?
120 V
What type of transformer is used for power conditioning?
Isolation transformer
What is the primary purpose of the design of an isolation transformer?
To physically and electrically separate primary and secondary windings from each other.
What is protected by fusing the secondary side of a control power transformer?
The transformers secondary winding
Referring to the figure below, what type of transformer is represented?
Control power transformer
Referring to the figure below, what primary and secondary voltage is the transformer configured for?
Primary 480 V / secondary 120 V
What information is required from the loads energized to size a control power transformer?
Total inrush VA
What is the minimum ignition transformer secondary voltage required for direct spark ignition of main burner gas?
6000 V
What is the minimum ignition transformer secondary voltage required for ignition of an oil burner?
10,000V
What is the standard voltage used for industrial control circuitry?
120 volts
Why are separate ignition transformers used for industrial burner systems?
To generate a big and hot enough spark to ensure the fuel ignites quickly and efficiently
Are limit circuits wired in parallel or series?
In series
List four specific conditions that a limit in a circuit control can control for?
Temperature, Pressure, Liquid Level and Liquid Flow
What are the two types of reset for limit switches?
Manual or Automatic
Referring to Figure 1, what type of limit is represented?
A High pressure limit switch
What does an operating control do and what are the two most common limits associated with them?
An operating control turns the burner system on and off based on temperature or pressure.
Referring to Figure 2, what is this the symbol for in a limit circuit?
Pressure switch
Referring to Figure 3, what is this the symbol for in a limit circuit?
Temperature switch
Referring to Figure 4, what is this the symbol for in a limit circuit?
Float switch
Referring to Figure 5, what is this the symbol for in a limit circuit?
Flow switch
Define an interlock:
An interlock is a feature that makes the state of two mechanisms or functions mutually dependent (one can’t work without the other).
What is one purpose of a permissive circuit?
To ensure two incompatible events don’t occur at the same time.
A DFMAH shall be ______ in such a way as to prevent its operation unless the exhaust system is functioning.
Interlocked
What must be proved when using automatically operated louvres for the inlet and discharge of a DFMA?
They must be proved fully open.
An airflow switch is an example of what type of interlock.
Running interlock
What is the purpose of a purge interlock?
To prove that the purge air flow rate is at maximum during the purge
The low fire start interlock permits the ignition of the pilot of main flame at an input of:
40% or less of the rated maximum input
Modern burner controls do not need to be continuously powered.
FALSE
What initiates the burner cycle?
The Control Circuit switches being completed
List some of the typical switches that could be found on the limit circuit of a boiler.
Manual switch, operating Aquastat, high limit Aquastat, low water cut-off, thermostat, DDC contacts, Pressuretrol, flow switch, aux-low water cut-off.
What is the purpose of an interlock?
To stop the burner from firing to prevent an appliance from damaging itself if a condition fails to be satisfied.
What must be done when a non-recycling interlock opens?
It must be reset manually
What feature shall be included on a low water cut-off that is an interlock for a water boiler that is located above the hot-water circulating system?
It must have a manual reset feature.
Define Permissive:
Conditions that need to be satisfied before you can start the equipment cycle.
Define Interlock:
Prevents an appliance from damaging itself if a condition fails to be satisfied.
List the common run interlocks:
Combustion Air Proving Switch (CAPS), Mag Starter Aux Switch, Low gas Pressure Switch (LGPS), High Gas Pressure Switch (HGPS), Oil Temp Switch, Low Oil Pressure Switch, Low Atomizing Media Switch
What type of interlock is required when combustion air is supplied by mechanical means?
A combustion air proving switch
What is the “normal” position of a combustion air proving switch?
Open (NO)
How many air changes of the combustion zone and flue passages must take place during the pre-purge period prior to the ignition cycle?
4
What is the purpose of the purge interlock:
To prove adequate air supply before the start of the pre-purge countdown timer and during the purge period.
What is the purpose of a low fire start interlock?
To prove combustion air damper and fuel valve are in low fire position before ignition.
When shall a proven low fire start be required?
On a variable input appliance that has an input in excess of 1,000,000 BTUH, unless otherwise approved.
List 4 types of pre-ignition interlocks:
Start interlock, fuel valve switch, proof of closure switch, overtravel proof of closure switch
Define proof of closure switch:
A factory sealed switch incorporated into a safety shut-off valve that includes at least one set of contacts, which close only after the valve port is closed and which open prior to the opening of the valve port.
What type of switch is pictured below?
Over Travel Proof of Closure Switch
Where are the potentiometers housed on a steam boiler with a single point positioning system utilizing a bridge circuit?
Modulation motor and modulating Pressuretrol
Referring to the figure below, what is the fixed resistance between points B & W of the bridge circuit?
135 Ω
Referring to the figure below, once released to modulate, what would cause the modulation motor to rotate open?
A decrease in resistance between R & B and an increase of resistance between R & W of the modulating control.
Referring to the figure below, what will happen to the firing rate if the wiper (R) in the modulating control moved towards (W)?
The burner firing rate will decrease
Referring to the figure below, what would indicate that the bridge circuit is balanced?
The motor stops rotating.
What is the purpose of the N.C. limit switches in the open winding and closed winding circuits of the modulation motor?
To prevent over rotation of the motor
What device is NOT part of the 4–20 ma control loop?
Sensor
For control point instrumentation, what does RTD stand for?
Resistance temperature detector
What type of RTD is mostly used in the industrial sector?
Coiled element RTD
The known electrical resistance at a specific temperature of the metal that makes up an RTD allows the RTD to be accurate within its temperature limits.
True/False
True
What metal is most commonly used in an RTD in industrial applications?
Platinum
How does an RTD work?
The resistance increases as the temperature of the sensor increases
Which is the most common RTD wiring configuration that gives a good combination of accuracy and convenience?
3-wire
A 4-wire RTD gives the best accuracy even though most industrial controllers/measurement devices cannot make a true four wire measurement.
True/False
True
What is the characteristic of a 3-wire RTD configuration?
It allows the measurement to factor out the resistance of the leads
What type of circuit is used in an RTD to measure the resistance?
Wheatstone bridge
How does a thermocouple interpret changes in temperature?
Change in voltage
RTDs are more sensitive than thermocouples thus they react faster.
False
A ____________ has wider operation ranges than an RTD.
Thermocouple
Which statement is true when comparing thermocouples to RTDs?
Thermocouples react faster than RTDs, but RTDs are more accurate
What can limit the maximum range of a thermocouple?
Its diameter
How does a pressure transducer work?
It converts pressure into an electrical signal
What produces the electrical signal in a pressure transducer?
Strain gauge
What types of electrical output is available for a pressure transducer?
Millivolt, 0-10 Voltage, 4-20 mA
How many platinum RTDs does a thermal mass flow meter use?
2
In a thermal mass flow meter, what task does each RTD perform?
One RTD measures the fluid temperature and the second maintains a constant temperature differential above the process fluid
What three things is an automatic O2 trim system designed to compensate for?
Fuel characteristics, temperature, barometric pressure
What sensor is the critical component used to reduce emissions in a modern biomass boiler?
O2 sensor
To give better control and more consistent/accurate positioning for a modulating burner, in what system are servo motors used?
In a parallel positioning system
What work does a power rectifier perform?
Converts alternating current (AC) in direct current (DC)
What work does a power inverter perform?
Converts direct current (DC) into alternating current (AC)
Where may a gasfitter see the use of a power converter?
Within the first stage of a variable frequency drive (VFD)
What electrical device(s) within the power rectifier converts alternating current (AC) to direct current (DC)?
Bridge rectifier
Where may a gasfitter see the use of a power inverter?
Within the last stage of a variable frequency drive (VFD)
What electrical device(s) within the power inverter converts direct current (DC) to alternating current (AC)?
Transistors and MOSFETs
In computer networking, what Does LAN stand for?
Local Area Network
In Computer networking, what does WAN stand for?
Wide Area Network
In computer networking, what is a LAN?
A group of computer devices connected with each other in a small place such as a home, school, campus, hospital, or a factory
In computer networking, what is a WAN?
A long-distance network that covers a country, continent, or the whole world
In computer networking, what is a MAN?
A larger networking area connecting Local Area Networks to a larger network of computers
In computer networking, what is the purpose of a firewall?
stops attacks from WAN to LAN
Even though it is old technology, what type of serial interface connection is still commonly used with industrial machines?
RS232
What type of ethernet connector is used in corrosive environments or when washdowns are needed?
M8 or M12 connectors
List the three types of guided or hard wired signal transmission mediums.
Optical fiber, Twisted pair, Coaxial cable
List the three types of unguided or wireless signal transmission mediums.
Radio, Wi-fi, Bluetooth
Historically, twisted pair cabling has been the most common type of network communication cable in the gas industry.
TRUE / FALSE
TRUE
What are three types of noise that can interfere with a data signal?
Crosstalk, RFI, EMI
How do we reduce the interference?
By using twisted pairs and shielding twisted pairs
Which category of LAN cable commonly used with HVAC equipment has the highest throughput?
CAT 6
What must be done to shielding to make it effective?
It must be grounded
Which end of the shielded cable is grounded?
Only the source end
What are the advantages of unshielded cable?
- Easier to install, no fragile shield to terminate.
- More flexible. STP Cable is ridged and Shield can be easily damaged from bending into too tight of a radius.
- Cost, UTP cable is cheaper.
Which of the unguided or wireless signal transmission methods has the longest range?
Cellular
What, commonly, can cause a power surge?
A Lightning Strike, High power draws, Tripped breakers
What is the definition of insufficient voltage?
The decrease of electrical power to 90% of normal for 1 minute or more
What is the most common cause of insufficient voltage?
An overloaded system
What is a short circuit?
A low resistance connection between two conductors supplying electrical power to any circuit
What could cause a short circuit?
Damaged insulation, a loose wire, faulty appliance wiring
What device is used to break the circuit when it detects and electric arc in the circuit?
An Arc Fault Circuit Interrupter (AFCI)
What could be a reason for a fuse to blow?
An overloaded circuit, a short circuit, a ground fault, an arc fault
What could be a consequence of corrosion on our electrical connection?
- Loss of material leading to loss of function
- Introduction of additional resistance leading to added heat and eventual failure
Which type of wire is the least resistant to corrosion?
Aluminum
What is the consequence of switching the neutral wire instead of the hot wire on an appliance disconnect switch?
The appliance will always be live, even when the switch is open. Leading to a risk of electrical shock for the technician
What is an arc flash?
The light and heat created from an arc fault explosion
What is an arc blast?
The pressure wave created after an arc fault
What is the major cause of an arc flash?
Voltage transients
Referring to the figure below, what is arc flash boundary 1 referred to as?
Arc flash protection boundary
Referring to the figure below, what is arc flash boundary 2 referred to as?
Arc flash limited approach boundary
Referring to the figure below, what is arc flash boundary 3 referred to as?
Arc flash restricted boundary
Referring to the figure below, what is arc flash boundary 4 referred to as?
Arc flash prohibited boundary
What is defined as an arc flash protection boundary?The calculated safe working distance from electrical equipment which would not expose the employee to the hazards associated with an electrical arc flash.
What is defined as an arc flash limited approach boundary?
The minimum permitted distance that unqualified and unprotected personnel may approach a live component.
What is defined as an arc flash prohibited boundary?
The boundary where no electrical worker is permitted unless proper procedures, PPE, training, energized work permits, and risk assessment are all in place.
What is defined as an arc flash restricted approach boundary?
The minimum permitted distance where personnel need to have been trained in shock protection techniques, be wearing the correct PPE, and have a written and approved plan for any work in the zone.
Referring to the figure below, what is the minimum power supply required for the 4-20 mA loop?
25 Volts
Referring to the figure below, the loop current is measured at 29 mA. What are the possible causes of the excess load on the loop?
Miswiring, ground loop, a problem with the transmitter
If two points in a 4-20 mA loop are grounded it can create an alternate pathway for the loop current to flow through.
TRUE / FALSE
True
Referring to the figure below, what should the resistance value be of the shunt resister given the following information?
- Source volts: 26
- Source current: 125
- Loop current: 20 mA max
248 Ohms
