F4: Hydronic Control System Flashcards
What is the point of a second heat exchanger in a boiler?
It scrubs the latent heat from the flue gases = increases AFUE / allows to operate at a lower temp
What does AFUE stand for?
Annual Fuel Utilization Efficiency
Primary / Secondary piping have replaced what types of piping?
Series loop
2 - pipe direct / reverse return piping
Monoflow tee
How does a primary / secondary system operate?
through the principle of hydraulic separation for proper flow rates
Why are closely - spaced tees / hydraulic separators used?
So that pumps that are connected to the same water system won’t have an effect on each other.
What ensures min pressure drop between the tees?
Placing tees no farther than 4 pipe diameters from each other
What are parallel - multizone / zone valves?
Same heating fluid temp to all zones
- Common supply / return piping are used
- One circulator for all zones
How does a 2 pipe direct return system move water?
By one pump
How are zone valves controled?
Through a thermostat
What senses domestic hot water
an aquastat
How does a pump and boiler burner operate on a Low mass boiler?
Circuit only energized if a zone valve proved open
How does a pump and boiler burner operate on a High mass boiler?
does not need flow through it / burner circuit could always be energized
What does cold start mean?
Can’t fire to keep it self hot unless there is a call for heat from the system
What does a schematic diagram show?
Shows the components as they might appear physically
What does a ladder diagram show?
Only electrical symbols for components
What does the R terminal indicate?
external power supply to the thermostats / end switches
What does C terminal indicate?
Connects internally to neutral side of the 24V AC transformer
is also the external ground connection for burner / zone valve circuits
What does the G terminal do?
outlet sides of end switches connects to it
feed internal relay coil / externally feeds power to burner circuit
What would W and Y terminals indicate?
There is another internal relay for control of other devices (AC or furnace fan)
What water temp feeds Radiant floor panels?
90 F - 140 F
depending on the BTUH / ft2 and R value of floor coverings
What is a mixing valve?
has tempering of water through it
Are diverting valves installed in the same location as mixing valves?
No
Where are diverting valves located?
mounted on the return piping.
How many inlets does a mixing valve have?
2 inlets
1 outlet
How many inlets / outlets does a Diverting valve have?
1 inlet
2 outlets
True or False: diverting valves have less head loss than mixing valves.
True
What is a 2 way valve?
a throttling valve w/ a low head loss
controlled by a capillary tube connected to a bulb
What does the bulb do on a 2 way valve?
sense the temp in the radiant circuit
Why is a 4 way mixing valve a superior choice for tempering water?
has very low head losses through them
What does a heating curve calculate?
How much hotter the supply water will need to be as outdoor temp drops
What is thermal equilibrium?
Where indoor and outdoor temperatures are equal
What does WWSD stand for?
Warm Weather Shutdown Point
What does a Voltmeter containing VOM (volt-ohmmeter) tell us?
Where voltage is or isn’t present / its value
A voltmeter will always tell us the difference in what?
in volts between the two meter leads
Why would a voltmeter read 0?
1) no voltage present at all at either of the leads
2) 2 leads are being exposed to the same voltage
3) meter isn’t working properly
a minus sign appearing in front of the voltage measured on a digital multimeter would indicate what?
leads are reversed in polarity
No action needed –> meter isn’t being harmed
What does a tap test ensure?
the polarity is correct
meter pointer moves to the right = polarity is correct
Do the wires have to be disconnected when measuring voltage?
No
Voltmeter is used in parallel w/ circuit being tested
Ammeters must be installed is a what?
in a series with the circuit or components being checked
remove a wire and place meter leads to each end of wire
True or False: Wire leads must be at least as heavy in wire gauge as the wiring in the circuit being checked
True
What is the easiest way to check for amperage (current flow)?
use a clamp on ammeter
