HC220- residential electric heat Flashcards
during the summer insulation keeps heat _____________________
out
during the winter insulation keeps heat _____________
in
Home insulation material is referred to as _________________________ insulation
thermal
Thermal insulation is avalible as:
-bankets
-rigid and spray foams
-batts
-pouring wool
-blowing wool
-loose wool
Vapour barier is a plastic film that is ___________mils thick. or metal foil which has a high _________ to moisture
-6mils
-resistance
Does spray foam create its own vapour barrier
yes
When homes utilizing a forced-air heatinf method are undergoing a heating cycle, the home tends to have slightly ___________ air pressure relative to the outside atmosphere.
positive.
trapped moisture in vapour barriers can also cause:
-building
-“sick building syndrome” from mold
Vapour barriers prevent __________________ which stops the condensation problem
-air leaks
The vapour barrier is always installed on what side
on the warm side of the insulation
3 methods of satisfying the National Building Code
-6 mil poly film
-is sprayfoam is used, its used as its own vapour barrier.
-metal foils
What does the insulation value R represent
the heat-retaining ability of the insulation.
what does the R value define
-amt of resistance to heat flow through one square foot area of a given material for each one degree fehrenheight temp difference on each side of materieal.
The _____________ the R-value number the _____________- heat retaining ability of the insulation
-higher
-better
What are RSI values and how to convert
-metric equvialent to the imperial R-values.
-converted by multiplying the RSI value by 5.7 (RSI x 5.7)
How to convert to/from RSI values
1.convert to a common unit (mm/inches)
2.multiply/divide by 5.7
what is design temperature
a selected temp used in heat loss calculations
What is outside design temperature
temp of the outside air for the first time at which the heat loss is calculated
Design temp tables give the ____________ outside temp that might occur.
lowest
The design temp difference between the ________________ design temp and the ______________ design temp.
inside
outside
how to find design temp difference and what is it used for
- subtract outside by inside.
- is the actual temp difference is the actual temp difference used in heat loss calculation.
What is conduction
process of heat transfer through a material
What is infiltration
-describes any air leaks into a building from the inside.
2 methods to use to determine rate of infiltration and how is it used.
- “crackage” method.
-requires the estimation of the lineral footage of the cracks and windows and doors and the application of an appropreate factor. - amt of air in the building in meters cubed and assume that much air will infiltrate the building once each hour
what is the U factor used for and how to find.
- figuring heat loss
-found by dividing the sum of the R factors into 1( U= 1 divided by R1+ R2+R3….)
in the U factor the _________ the insulaltion value of the components the ________ the factor
-better
-smaller
Using heat trasfer factor how do you determine heat loss due to conduction
-heat transfered x by the area of exposed surface
When determining heater size what heat requirements for a room must be considered (8)
- area of the room
2.amt of exterior wall
3.wheater the room is over a heated space - if a room is under a heated space
- number and size of windows in the room
6.any doors and their size on exterior walls - infiltration losses (cold air entering through cracks around doors and windows)
8.extra heat must be provided to compensate for heat loss through chimneys.. ect
All heaters must be ________________ to meet CSA specifications
performance certified
what is the rule of thumb for heater sizing
-110 watts per square meter,
-approx 10 watts per square foor
what is thermal insulation
any material that resists the flow of heat from one surface to another
what are 3 types of thermal insulation commonly used in modern buildings?
- fibreglass
2.batts
3.spray foam
4.blowing wool
What is the purpose of the vapour barrier?
-protects insulation and structure of a building
-protects interior finish
what is a typical inside design temperature?
21 and 24 degrees celcius
Convection heaters use ________ in the room to ___________ the heat
- natural air circulation
2.circulate
where should convection heaters be installed and what is an example
-on or near the floor under windows where heat loss is the greatest
-baseboard heater
what are baseboard heaters designed to do
control room by room temperature control
where should baseboard heaters be installed
-near floor along exterior walls and below glass areas.
-centred under a window
-center of blank exterior wall
baseboard heaters hsould be fastened __________ than snug to allow for expansion and contraction of ____________ metal. This would _________ associated noise
1.less
2.heater frame metal
3.reduce
Heating cable is ________ in plaster ceiling or ____________ between 2 layers of drywall with filler plaster
1.embedded
2.sandwiched
Where is heating cable used
-concrete floors
-side walks
-driveways
how is ceiling cable purchased
-calibrated length
-wattage/voltage rating stamped on cable reel
can heating cable be cut or shortened
no
How do fan forced heaters work and what do they range from
-fan motor to force the air across the electrically heated elements
500W to 35kW
where are small wall unit fan forced heaters used and how are they mounted
-bathroom
-kitchen
-door entrance
-surface mounted or recessed
advantage od a central electric heat fan forced unit and where is thermostat placed
-ease of connecting split system central air conditioning with room for the “A” coil.
-thermostat- central area away from exterior walls and sunlight
what are radiant heaters
-emit infrared rays that dont heat the air but heat objects or surfaces as they strinke
what are hydronic units (boilers), how do they work and what do the thermostats do.
-use water as heating medium.
-electric elements heat the water to a temperature adnd the circulatiing pumps move the water to rhe radiaters that emit heat.
-thermostats used to control zone values to certain areas or one central control.
what are duct heaters
-form of supply heat to an existing system.
how to advoid burn out of the exchanmger in a duct heater
-air flow switch to control elements
what are thermostats designed to do
-maintain a constant temp by regulating the heat supply to balance the rate of heat loss in the area being controlled
What are the most common types of thermostats
in line, extra-low voltage
where do thermostats have to be located
1.5 meters (5 ft) above the floor on inside walls.
How do in-line thermostats work
-temp sensetive element which activates line voltage switch controlling the power supply to the heaters
how to extra-low voltage thermostats work
activate a relay which opens an dcloses the cct to the electric heater
Heat exchangers have various recovery rates, but are about _____________ efficient
75%
Where is a exchanger found
-hung from floor joists in the basement
-if installed in a mechanical room, output returned to living area for circulation
where are air exchangers used
-ventalate bathrooms
-kitchen
-laundry
can you connect the range hood to the exausr unit of the fan or the dryer
no
the furnace blower in duct work systems must be interconnected with the ___________- through a normally open contact
-HRV
What are 3 conrolls that are provided with the heat exchanger
1.variable speed motor
2.de-humidistat
3.auto-defrost control
how do de-humidistat controls work and what is the recommended humidity setting
-controls humidity level in th ehome and when the humidity rises avove the pre-set level, the de-humidistat will bypass the speed conreol to operate the exchanger at the full flow rate
-recommended level is 40%
how do auto-defrost work
-senses incoming fresh air temp after it passes through the exchanger
-when outside temp drops below freezing. Frost will form on the core surfaces and decrease the efficency of the unit. after it senses this the intake fan will automatically stop, leaving the exaust fan runniing and it will warm the core and the frost will melt and run out of the condensation drain
where is the control dehimidistat mounted
in the hallway. push buttons are in bathrooms and other rooms with HRV exaust vents
what type of cable is used for the de-humidistat, push button controls, between HRV unit and central furnace
dehumoidistat- 18/4
push button- 18/3
between- 18/2
what is the difference between low and standard wattage density baseboard heaters?
low-lower W/FT rating (140W-180W/ft), heaters are approx 6ft, low in surface temp so can be installed under drapes and other heat sensitibve materials.
standard-240W-280W/ft, have higher surface temp, 1000W is more concentrated on standard. 4 ft long
what is typical size range of fan forced electric heaters?
500W-35kW
what is the premise of operation for radient heaters?
-ceramic elements heat to a high temp and emit infared rays
-target objects that absorb rays
-wave energy is converted to heat energy
-air not heated directly but becomes heated in a secondary way like conduction or convention
is a north, south,west, or east wall best for thermostats
north facing wall
why are air-to air heat exchangers necessary in modern homes
-they are air-tight so require fresh air.
-air becomes stale and oxygen depleted if not replaced regularly
what is line current
-amt of current in equipment required to do the work its rated for
according to the CEC the heating equipment for instilation standards cant be subjected to the temperatures exceeding _______ degrees celcius
90
what section of CEC do you find rules for fixed electric heating systems
62
for single phase fixed electric heaters how do you convert the electric heat load or equipment rating expressed in Watts into amps
I line=Power total divided by Voltage line and multiply by number of poles
how to find minimum allowable overcurrent devide required to protect the cct using the rating for contimuous operation for fixed electric heater
- I line divided by continous operation %
- table 13
the minimum allowable overcurrent device ___________ then the calculation
-must not be less
-round up
