S1, N1, U1 & U2 Flashcards
What is the usual “watts per unit length” rating of standard density baseboard heaters?
820W per meter
Where in a room should baseboard heaters be mounted?
At floor level, centred along a wall and preferably under a window
What type of heater is installed at ceiling height?
A Unit heater
Residential electric furnaces are usually available in both single-phase and three-phase ratings from ______ kw to _____ kw
4kw to 50kw
What type of heater unit can be used with certain oil-fired, force air furnaces?
A Plenum Heater
Residential water heaters are commonly available in ____ kW and ____ kW
3kW and 4.5kW
What are three types of thermostats commonly used is residential space heating applications?
Line Voltage
Low Voltage
Electronic
If a heat lamp using a medium-base lampholder is installed in a residential bathroom, does it have to be on a separate heating branch circuit? Y or N
No
Where are the supply registers of force-air furnace normally located?
Around the perimeter of each room
What is the purpose of the heat exchanger in a gas-fired furnace?
To separate the products of combustion from the air
The typical efficiency of a gas-fired furnace is between ____ % - ___ %
70%-80%
How many conductors are commonly needed between the furnace and the room thermostat? And what is the magnitude of the voltage that they carry?
2 or 3c
24v
Which does the room thermostat control directly, the gas valve or the blower motor?
Gas Valve
After the thermostat opens, which shuts off first, the blower motor or the gas burner?
The gas burner
What is the purpose of the anticipator resistor in the room thermostat?
To limit the set point overshoot to an acceptable value
What is the purpose of the thermocouple? Is it necessary?
It uses thermoelectric generation to create a small voltage when heated.
No.
List three conditions that may cause overheating of the heat exchanger
Room thermostat contacts stuck
Blower does not run
Insufficient air flow
What prevents the heat exchanger from overheating?
The high limit over heat safety thermostat will close the gas valve
What are the Typical settings for the blower control/overheat safety thermostat?
- Blower off 90 degrees
- Blower on 130 degrees
- High limit off 104 degrees
Where should an electronic air cleaner be installed on a furnace?
In the return air duct
Describe how an electronic air cleaner filters the air?
The ionizing section charges the dust particles which are then attracted to the charges collection plates
Why should the electronic air cleaner be interlocked with the blower motor?
To prevent the accumulation of ozone
What is the purpose of a damper?
To regulate air flow
Wiring for HVAC control components is usually ____v
24v
To double the airflow rate, the fan hp should be increased ____ times
8 times
What are the failsafe positions for the outside, exhaust and return air dampers?
Outside exhaust damper (Normally Closed)
Air damper (Normally Open)
How does the damper actuator achieve its failsafe position?
When power fails
What are two methods of providing mechanical cooling in an HVAC system?
Chilling cooler tower
Refrigeration
What is the typical set point for a mixed air controller?
13 degrees
The purpose of the minimum position device
Prevents the outside air damper from closing
What does the term economizer control mean?
When the outside air is warmer than the return air
What are the typical fail safe positions for the hot and chilled water valves?
Hot water Valve Normally Open
Chilled water valve Normally Closed
Describe the function of a duty cycle function?
Switches equipment off for short intervals during occupied periods, saving electrical energy.
Functions of an optimal start/stop program?
Adjusts the warm up and cool down timing
A programmable thermostat combines the features of?
A standard thermostat and a electronic time clock
What is demand limiting?
Reduces peak electrical demands of the building by turning off non essential loads during peak hours
Three problems that can cause a pilot light to go out
Backdrafts
Insufficient gas flow
Thermocouple not fully flamed
Two problems that could prevent a DSU system from lighting
Short electrode or conductor
Spark path not crossing the gas burner
A photovoltaic cell is made up of?
A semiconductor material such as silicon
Domestic electric water heaters are mostly rated at?
3kW
MI cables are mostly used as resistance elements in?
Heating cables
The control transformer in a gas fired furnace is typically rated at ____v
120/24V
What is the correct sequence of control for a complete heating cycle of a low efficiency gas fired furnace?
Fan On
Burner On
Burner Off
Fan Off
Purpose of a thermocouple in a gas furnace?
Indicates the presence of a pilot flame
The anticipator in a thermostat is used to?
Prevent the room temperature from rising too far above set point
A heat pump is used to?
Provide both heating and cooling in the same unit
Which type of water heater is the most common in homes?
Storage tank water heaters
What type of water heater that must have a large electrical capacity is?
Indirect water heaters
