Boiler Test One Flashcards
Low Temp Boilers
Max temperature 250 F (120C)
Max pressure 160 psig (1100 Kpa)
With cast Iron heat exchanger (High mass 30 Psig)
Typically rated in BTU/hr or EDR
Usually Net rated
BTU
British Thermal Unit
amount of heat required to raise temp of 1 lb of water 1 F
BHP
Boiler horse power
High temp Boilers
Over 250 F (120C)
Rated in MBH or BHP
Gross rated
ASME 1
MBH
One thousand BTU’s British thermal units per hour
One BHP
The ability of a boiler to evaporate 34.5 pounds of water per hour
Input rating
Represents the amount of heat in the fuel that is burned by the burner
Output rating
represents the total heat output of the boiler, available as hot water
Net Rating
75% of the gross rating - losses - stack, system or pipe - Difference between net and gross is a deduction intended to cover typical installation losses
Caloric Value
Potential energy in gasses
One EDR of Hot water
150 BTU
One EDR of Steam
240 BTU
Gross Output
Total heat output of boiler available as steam or hot water
Low Mass Boiler
- Need to have fluid moving though tubes when burner is on
- Code states a flow switch must be added to, or can be installed alone instead of LWCO
- Commonly Copper, Aluminum or Stainless steel all of which are non- corrosive and resilient
High Mass Boilers
-Need to be Full of water when the burner is on
- Minimum code is LWCO (Float or Probe type)
-Cast Iron
If you drop the pressure on a liquid it becomes a
Gas
Efficiency =
Efficiency% = Gross output in BTU/ Input in BTU X 100
Condensing boilers
- Efficiency rate of 90%
-Achieved by cooling products of combustion to water vapor (steam) in flu then reverting to liquid water and water providing 970 BTU/lb of condensate
Latent heat energy is added to typical sensible heat of a mid efficient (83-85%) providing 90% efficiency
Considerations for Condensing Boilers
- High operating temperatures (above 140 F at exchanger inlet) may not allow water vapor to condense - reducing efficiencey
-Flu gasses have cooled and are no longer rising with convection so now a fan or direct vent system is needed
-Condensate is acidic & should be neutralized prior to disposal in the sanitary system
Conventional VS Condensing Boilers
Conventional - Need to leave heat behind in the flue gas so the gas is hot enough to rise up and out of venting system (convection)
Condensing - cools the flue gasses to condensation point and gains latent heat energy
Hot water Boiler Operator turns the Boiler on & off in response to regular heat demands, 3 types:
Microprocessor
Liquid sensing bulb fluid temperature control
Thermostat
Boiler Control: High Limit
Shuts Boilers fuel if the boiler gets to hot
- The temperature is set above the operating temperature range but never higher than the manufacturer states
- ASME states never higher than 250F
Code requires two temp controls for any boiler
1) Operating control
2) High limit
ABSA requires large boilers to have a manual reset
Manual reset has a small red button between 2 wires if it trips the boiler must be manually restored by pressing button
Safety Relief Valve (SRV)
- Last line of defence against over pressure and or explosion
- stem must be vertical
- must be officially approved
- No valves between heat source and discharge
- Discharge must grade and drain away from valve with no reduction in size
- No lower than 6” and no higher than 12” from floor
Air Removal Devices
Air vent - Manual or automatic
Air separation devices - Boiler fitting, Line scoop, Microbubble resorber
Manual Air vents
Located at piping high point to release trapped air from the piping
Automatic Air vent
Server same purpose as manual but must consider:
1) Include isolation valve for servicing
2) Pressure at highest point must be minimum of 4 psi to prevent air entrainment (sucking in )
Boiler fitting
Attaches directly to the HIGH MASS BOILER outlet nozzle & releases air from inside the boiler & allows water out to system
Line Scoop
The fitting increases in diameter to allow the fluid to slow and release air bubbles
- min of 5 pipe diameters of straight pipe needed at inlet and outlet to smooth flow out
- if a cushion type expansion tank is used, the air scoop is piped to this tank which is installed above the boiler
Micro Bubbler Resorber
- uses a screen like media inside for bubbles to attach to when they accumulate the fitting has a built in air vent that releases the gas
- they have no inlet outlet turbulence issues like the line scoop
Fluid Expansion
From filling to operating temperatures, water volume can be charged up to 5%
so we have 3 types of containers or expansion tanks
1) open expansion Tank
2) cushion Tank
3) Diaphragm Tank
Open Expansion tank
Open tank must be placed at least 3’ above the highest pipe because it is open to the atmosphere where water boils at 212 F these systems are limited to 180F
Cushion Tank
The Cushion tank is located in the boiler room above the boiler
the air scoop is piped to the cushion tank equal amounts of water return to the system
- similar to an open expansion tank except it does not have a vent to atmosphere
- it is closed under pressure 15 psi is typical for residential
Diaphragm Tank
Diaphragm tanks have rubber bladder between air and fluid
- they are pre charged, pressure must be charged to match system
- because there is a bladder separating, The Air scoop now has an auto air vent instead of pipe to tank
- can be located anywhere around boiler
-often best in high temp/ low pressure location
2 Types of centrifugal pups are used in hydronic systems
Conventional and Wet Rotor Circulator
Conventional Circulator (big red silver tip)
Air cooled
lubricated by oil and grease
Wet Rotor Circulator (Grundfos)
Cooled and lubricated by the heating system fluid
In the pump there is an impeller and a Volute
Impeller - is a disc used by both style pumps to move water or direct the flow of a moving fluid
Volute - spiral shaped pump casing with the purpose to convert liquids velocity to pressure as the impeller discharges the liquid through the casing nozzle
4 types of piping systems
1)Series or perimeter loops
2)Mono flow or one pipe system
3)Two pipe direct return
4)Two pipe reverse return
Series or perimeter loops
- a loop can only be one zone
- limited capacity 50 000 to 60 000 btu/hr
- heat emitters form part of piping
- water cools as it moves through circuit heaters near end have lower output
Mono Flow or one pipe system
- heaters can be zoned separately
-special venturi tees required on return
-fluid speeding through venturi nozzle draws fluid from side branch this moves heating fluid through the heater
Two pipe Direct
- “First supplied, first returned”
prone to short circuits
balancing valves on return are a must
Two pipe reverse return
-Most Balanced arrangement
- each heat emitter has equal piping lengths
