Section 3 060203a-db Flashcards
Name the two types of hydronic systems
Gravity systems
Forced flow systems
How do gravity systems work
Circulation relied on natural convection with the heated water rising in the supply and the denser, cooler water dropping in the return piping
What are the 2 major drawbacks to gravity systems
Large diameter piping
Slow response time
What are forced flow systems
Addition of circulator
What are the two advantages to forced flow systems
Very Efficient
Smaller pipe diameters
What are the 4 types of forced flow systems
Monoflow systems (one pipe system)
Reverse return (two pipe systems)
Direct return (two pipe systems)
Series loop (one pipe system)
What does a monoflo system have that others don’t
Venturi tee
What does a Venturi tee do?
Reduces pressure at the outlet of the Venturi causing a flow of fluid from the convector into the header (typically on the outlet side)
What are the advantages and disadvantages of monoflo systems?
ADVANTAGES: less piping, and each unit can be controlled individually.
DISADVANTAGES: limited sizes of Venturi tees,temp of fluid decreases after each unit, and heat transfer units with high resistance don’t work well with this system
What is a direct return system
First supply, first return
What are the advantages and disadvantages of direct return systems
ADVANTAGES: all units get the same temperature, and size of piping can be reduced as flow requirement is reduced.
DISADVANTAGES: unequal length of each circuit, prone to short circuits, and must have balancing valves.
What is a reverse return system
First supply last return
The distance for each unit on a reverse return is the nearly the same (true/false)
true
What are the advantages and disadvantages of a reverse return system?
ADVANTAGES: easy to balance, individual units can be controlled.
DISADVANTAGES: more piping, expensive to install.
What is a series loop?
All fluid flowing through the circuit flows through each series-connected baseboard.
What are the advantages and disadvantages of a series loop?
ADVANTAGES: reduces the amount of piping.
DISADVANTAGES: first convector gets the highest temperature fluid, downstream units may have to be increased.
What kind of valves are used for isolation
Gate and ball valves are a good choice
What valve is used for balancing
Globe valve
Where are balancing valves installed in a heating system?
Either the supply or return (preferably on the return)
Stem on valve has to be installed with the valve stem in a ___________ position to prevent air from being trapped.
Horizontal
What is a wild loop
A connection between the supply and return piping that allows for continuous flow
When using a wild loop what is required to prevent dead-head
A bypass
What are radiator valves
Used to stop or reduce circulation at each heat emission unit.
What are zone valves
Allow flow to specific areas or zones
A zone valve is usually normally closed (true/false)
True. But can be either normally open or normally closed
Trapped air in a heating system can cause poor ___________.
Circulation
What is entrained air
Trapped air
What makes it easier for air to be released from fluid
Higher temperature, lower pressure
What do boiler fittings do
Direct air that is collected at the top of the boiler to a cushion tank
What are the three types of air elimination devices
Boiler fittings
Air scoops
Auto and manual air vents
How much piping is required to create laminar flow
4x pipe diameter
What are auto air vents
Float operated devices that allow for air to be vented from the system at any point of accumulation
What are manual air vents
A vent that is manually opened to vent air out of the system at high points (normally closed)
Where is a vent placed if piping drops
At the top just before it drops down
How many dual purpose appliances can be used in a heating system
1
How often should a dual purpose recycle water to prevent stagnation of water?
Every 7 days
Every boiler must have at least __ temp-actuated control (also known as safety shut off)
1
What are the two types of water boilers
High temp
Low temp
BHP
Boiler horsepower
What is equal to 1 BHP
34.5 lb
What is Net rating
75% of gross
How do you find efficiency
Gross/Netx100
1 BTU=____ F
1
How do you calculate BTU
BTU= EDR x 150BTU/hr
How do you calculate EDR
EDR= BTU / 150BTU/hr
What is the max pressure for cast iron boilers
207 kpa (30 psi)
What is the max temp and pressure for low temp boilers
120 C (250F)
1100kpa (160psig)
What are the three types of boilers
Fire tube boilers (high mass)
Water tube boilers (low mass)
Cast iron sectional boilers (high mass)
What is critical when boilers are fired
Continuous flow through heat exchanger
What are the advantages and disadvantages of high-mass boilers
ADVANTAGES: stable supply temp, reduces susceptibility to thermal shock.
DISADVANTAGES: slow recovery rate, risk of explosion, require low water cut off if over 400000 BTU
What are advantages and disadvantages of low mass boilers
ADVANTAGES: directly heat domestic water, quick recovery rate, higher velocity
DISADVANTAGES: susceptible to damage in case of no flow or low flow conditions,
What is used to prevent boiler from firing in case of no flow through heat exchanger
Flow switch
What is the most important when installing a boiler
Clearance to combustibles
What must installation of a boiler conform to
1- authority having jurisdiction
2- CGA B149 natural gas and propane code
3- CSA standards B214-01 installation code for hydronic heating systems
4- manufactures recommendations
What does VI and I mean
ASME stamps
What is a pressure relief valve set to go off at
30 psi
What is a limit control
A redundant control that only operates if the operating control fails
What is an operating control
Set to cut off fuel supply when the liquid temp reaches operating limit
What are pressure gauges used for
Determining pressure drop over the system and the flow characteristics of the circulator
What do all boilers need to have
1 pressure gauge and 1 thermometer
What are flow control valves used for
Preventgravity circulation from occurring within the piping system
What are expansion tanks
Allow for continuous expansion and contraction of fluid
What cross-connection is always the case for boilers
Severe (due to the use of chemicals)
What is used to prevent cross-connection
RP or air gap
What is the size for an air gap
1” or 2 times the pipe opening whichever greater
How often is an RP tested
Annually
PRV
PRESSURE REDUCING VALVE
How much psi do you lose for every foot of height
0.433 psi
What is the final form of protection
Safety relief
A PRV is installed ________ a boiler
above
What are the 2 types of switches
Float-activated
Probe-type
_______ and _________ can be damaged from condensate
Cast and copper
What does a condensate neutralizer do
Reduces acidity before draining into sewer
What must you do to all valves regularly
Exercise
If a safety relief valve is faulty what would happen
Leaking due to overpressure
What is the most common form of energy used to move a liquid
Pressure
Feet of head
Height of a column
What is the ideal velocity in a heating system
2-4 ft per second
What is the best type of flow
Laminar
What causes friction in a pipe
Viscosity
Pipe wall
Size and type of pipe
Number and type of fittings
Temperature
Velocity
What is erosion
Wearing away a metal due to the high temp, high pressure, and high velocity
If the velocity nis doubled what happens to the head pressure
Increases about 4 times
If the flow rate is halved what happens to the head pressure
Goes way up
Where is the expansion tank located
Upstream of the circulator
What is cavitation
Water changing to steam
How is the total equivalent length calculated
Total distance times 1.5
How is a wet rotor line-mounted circulator lubricated
Internal circulating liquid
How often and what do you do when you check a circulator
Annually check for leaks and unusual noise
