Module 7: Understanding Residential Construction – Mechanical Systems Flashcards
Voltage
This is the potential energy of any electrical system, and it is measured in volts. Most houses are equipped
with a 240-volt system that provides 240 or 120 volts.
Resistance
This is the tendency of any material (such as copper) to resist the flow of electricity, and it is measured
in ohms. Conductive materials are those with low resistance.
Current:
: This is the rate at which electricity is flowing, and it is measured in a unit called ampere, simply known as
amp
Watts
The power is measured in watts and is calculated by multiplying the voltage by the current
Electrical service entrance cable (overhead or buried)
he electrical service entrance cable brings electrical
service to the property from the street. A typical house
has 240 volts brought in through an overhead cable or
buried wires from the street supply. The size of the
electrical service is largely determined by the diameter
of this cable.
Older electrical systems were 60 amp, while modern
ones will be 100 or 200 amp. 60amp systems may
have problems running modern appliances (such as
dryers, microwave ovens, computer systems, and so
on) because the amperage required to run the
Electrical main disconnect
The electrical main disconnect is the first switch that
the electrical service entrance cable connects to. It is
used to shut off all power to the structure. Frequently,
the electrical main disconnect is incorporated into the
distribution panel. There are two types of distribution
panels. One contains fuses and the other contains
circuit breakers, but they both serve the same purpose
(and will be discussed later).
Distribution panel
The distribution panel distributes electricity through
individual circuits to various parts of the house. A
circuit is an unbroken loop of conductive material
(such as copper wire) that allows electricity to flow
through. Each circuit will have one or more outlets
(such as wall outlets, light fixtures, and so on)
connected to it.
Outlet
Electrical outlets are where electrical appliances
connect to the electrical power supply. The two types
of outlets are:
Ungrounded outlets: These older types of plugs
contain two slots of equal size and are not grounded.
Grounded outlets: Grounded means that the plugs
have an extra wire to send current to earth (or ground)
in the event of a power surge or other fault. Grounded
plugs became common after the 1960s.
Ground fault circuit interrupter (GFCI)
A ground fault circuit interrupter is a device that shuts
off the power to a circuit when a small amount of
current (as little as .005 amps) is leaking or flowing out
of the circuit. This could cause a harmful electric shock
to anyone standing nearby. The ground fault circuit
interrupter compares the electricity flowing from both
the wires. If the difference is more than .005 amps, the
system will be shut off.
These devices are normally used anywhere within
three feet of water to avoid electrocution. So, they are
often used in bathrooms and kitchens, and with
exterior outlets. They have a reset and a test button on
them.
Circuit breakers and fuses
Circuit breakers and fuses are safety devices found in
the main distribution panel and are designed to
prevent an overload of the electrical system.
In a typical modern home, most of the circuits are
rated at 15 amp using wire that is able to safely supply
that level of electricity. If two appliances were plugged
into the same circuit (and combined, they drew more
than 15 amps), the fuse would blow, or the circuit
breaker would trip and cut off the electricity to that
circuit.
Aluminum wiring
Aluminum wiring can present problems. For example,
aluminum is softer than copper and, when being
installed, it may be nicked or crushed by the installer.
This damaged wire will create local hot spots that can
lead to overheating.
Another problem is known as creeping, which is when
the aluminum wire creeps out from under the terminal
screws that hold the wire in place on the electrical
outlet. Each time an appliance is turned on, electricity
flows through and heats the wire; when the appliance
is turned off, the wire cools.
When heated, aluminum wire expands more than
copper, so the daily use of electricity in a home will
result in repeated expansion and contraction of the
wire. The creeping of the aluminum wire results in a
loose connection and overheating.
Ungrounded outlets
Ungrounded outlets can cause several problems, such
as:
• Electrical fire – Without a ground wire, a problem
with an outlet could cause arcing (electricity
jumping between a loose wire and a terminal) or
sparks, which could result in a fire with nearby
combustible material.
• Risk of shock – A person operating electronics or
appliances plugged into an ungrounded outlet
runs the risk of receiving a shock if there is a
problem with the outlet.
• Damage to appliances – Faulty ungrounded
outlets can short out appliances and make them
useless
Ungrounded outlets can cause several problems, such
as:
• Electrical fire – Without a ground wire, a problem
with an outlet could cause arcing (electricity
jumping between a loose wire and a terminal) or
sparks, which could result in a fire with nearby
combustible material.
• Risk of shock – A person operating electronics or
appliances plugged into an ungrounded outlet
runs the risk of receiving a shock if there is a
problem with the outlet.
• Damage to appliances – Faulty ungrounded
outlets can short out appliances and make them
useless
Knob-and-tube wiring has several problems:
• It cannot accept three-pronged appliances
because it has no ground wire.
• It poses a fire risk because it has no ground wire.
Therefore, there is no protection when a fault
occurs.
• As it ages, the insulation becomes brittle and may
come off if something is stuck against it.
• It poses a fire hazard when bare wire is near
combustible material.
• There is a very real danger of shock or
electrocution to anyone who comes into contact
with bare wire.
Frequently blown fuses or tripped circuit breakers
If the fuses or circuit breakers in the distribution panel
are frequently blown or tripped, this is an indication
that something is wrong in the electrical system. This
can indicate:
• Overloading – a circuit is trying to draw more
current than it can handle. This can happen when
appliances with high amperage ratings are being
used on the same circuit.
• A short circuit – caused by the hot wire and
neutral wire in a circuit touching each other. They
could be the result of one or both wires coming
loose from a terminal.
• A ground fault – occurs when the hot wire and
ground wire come into contact. This could be the
result of one or both wires coming loose from a
terminal.
Hot or charred electrical outlets
If electrical outlets are hot or charred, this is an
indication that there is a problem with the wiring in or
near the outlet. This could be caused by aluminum
wires creeping out from under the terminal screw
resulting in arcing
Flickering/dimming lights
Flickering or dimming lights indicate a serious problem
with the wiring system, possibly caused by a heavy
load on the circuit (such as dining room lights dimming
as soon as the microwave is turned on). The wires may
be creeping out from under the terminal screws
resulting in a loose contact.
Electrical shocks when plugging in appliances
Shocks from a faulty appliance is one of the five
common causes of an electrical shock. Faulty
appliances do not always channel electricity as well as
they used to. When an appliance has damaged
circuitry, frayed wiring, or broken cords, electrical
currents become unstable. When you plug one in, the
unstable electricity can ruin your appliance, as well as
shock you
Light bulbs burn out quickly
There are many possible reasons why a light bulb
burns out quickly. The more common could be the
power supply voltage may be too high, bulbs may be
loose or connected improperly, excessive vibrations
may be causing the filament to break to name a view
Too many extension cords in use
If there are a number of extension cords used in a
house, it is an indication that there are insufficient
outlets to meet the homeowner’s needs. Extension
cords are designed for temporary use, not as a
permanent solution.
Benefits of solar panels
Solar panels are an excellent way to supplement a
conventional electricity service. Benefits include:
• A renewable energy source with minimal
environmental impact
• Low maintenance costs and lower utility bills
• Usability in areas without access to the energy
grid
Financial incentives for using solar panels
here are also financial incentives for using solar
panels:
• Homeowners can install a net metering system to
produce their own clean renewable energy.
• During periods when excess energy is produced
that isn’t needed by the homeowner (such as
summer when there are longer periods of
sunlight), the excess energy can be fed back to
the consumer electrical grid. Credits will be
provided, which can be used to buy electricity
when needed (such as on cloudy days or during
the winter season with shorter periods of
daylight)
Houses that aren’t suited for solar panels
Some houses may not suit solar panels, including:
• Houses that are surrounded by shade trees that
may not receive enough sunlight for effective
operation
• Houses with inadequate roof space
• Houses without enough south or southwest
facing roof space
• Houses with old roofs in need of continual repair
Heating and Cooling Systems
the primary requirements of any heating system are:
• Size: Large enough to provide adequate heat on the coldest day
• Reliability: Reliable and safe
• Cost: Economical to install and operate
• Equal heating distribution: Capable of heating all parts of the home equally
Capacity
Input capacity: This tells us how much fuel energy
is consumed for every hour of operation. It is
measured in British Thermal Units (BTU) per
hour. A BTU is the amount of heat required to
raise the temperature of one pound of water by
one Fahrenheit degree.
• Output capacity: The output capacity tells us how
much usable heating or cooling the unit provides
to a home. Any system will have inefficiencies in
it that lead to it turning less energy into heating.
For example, many furnaces take quite a lot of
energy to get them started without producing
any heat. Heat can also escape up the chimney.
Efficiency
The efficiency of a heating system takes the input
capacity and output capacity into account. Given as a
percentage, it tells us how efficiently a system actually
heats the home. If the input capacity and output
capacity of a system were the same, that would make
it 100% efficient. Most heating systems are
considerably less than 100% efficient as inevitably,
energy is lost somewhere
Efficiency ratings
Efficiency ratings tell us how well the energy put into a
heating system heats the home. It is based on the
Annual Fuel Utilization Rating (AFUE) rating, which
measures how much fuel is converted to heat in a
heating system.
If a heating system has an AFUE rating of 60%, then 40
cents of every dollar spent on heating are being
wasted.
Forced air
A forced-air central heating system is one which uses air
as its heat transfer medium. It relies on metal ductwork
and vents to distribute air, separate from the actual
heating and air conditioning systems. The supply duct
directs air from the central unit to the rooms that it is
designed to heat. The return duct carries air back to a
central air handler for reheating. A thermostat is used to
control the temperature in a forced air heating system.
Advantages:
• Can heat the house more quickly than radiant
systems
• Can use the same ductwork as air conditioning
systems
Disadvantages:
• Less energy-efficient than a steam or hot water
system due to heat being lost as it travels through
ductwork to different parts of the house
- May require more regular maintenance than radiant
systems
• Bad for people with allergies due to circulation of
allergens and dust, which become airborne and are
released from the vents
Steam
In a steam heating system, a boiler furnace heats water
by means of a gas or oil-fired burner and turns it into
steam. The steam travels through pipes to cast iron
radiators or convectors, which give off heat and warm
the room. As the steam cools, it condenses back into
water and returns to the boiler by gravity to be heated
again. Steam is rarely used in new construction.
Advantages:
• Quiet and provides consistent heat
• Good for people with allergies due to not involving
the movement of air
Disadvantages:
• Less energy-efficient than some systems due to
heat being lost as it travels through pipes to
different parts of the house
• Expensive to install
• Components often insulated with asbestos, which
have serious health and safety concerns
• Air conditioning unable to be added to the system
Hot water
A hot water system is a system that heats water and
distributes it throughout the house by way of piping to
cast iron radiators. Even though a boiler may be used
to heat the water, it is not actually boiled but heated to
approximately 71°C.
Common in older houses, hot water systems can use
gravity or force to circulate heated water through the
system. The system may have one pipe or two.
In a one-pipe system, the hot water passes through
each radiator, returns to the main, and mixes with the
hot water as it goes to the next radiator. The cooler
water returning reduces the temperature of the main
water.
The two-pipe system has a separate pipe for the return
of the cooler water from the radiator to the boiler.
Advantages:
• Quiet and provides even heat
• Doesn’t circulate allergens like a forced air
system does, which is good for people with
allergies and sensitive skin
Disadvantages:
• More expensive to install than forced air systems
• Can become blocked over time with rust and
mineral deposits
• Components often insulated with asbestos,
which have serious health and safety concerns
Electric.
Two main types of electric heating systems are found
in homes, baseboard resistance heater and radiant
heating cables or coils that are placed in the ceiling or
floor. This type of heating allows for a thermostat to
control each room’s temperature individually.
Advantages:
Radiant
Radiant heating systems supply heat directly to the
floor, or to panels in the wall or the ceiling of a house.
The systems depend on the transfer of heat directly
from the hot surface to objects in the room via
infrared radiation. Radiant heat warms the house by
circulating water through pipes embedded in the floor.
Ground source heat pumps
Aground-source heat pump or geothermal system
uses the earth, groundwater, or both as the source of
heating the winter and as the sink for heat removed
from the home in the summer. Liquid (usually
antifreeze) circulates through a loop under the ground.
The heat collected from the ground is distributed
through the house with an air handling system.
Air source heat pumps
An air-source heat pump is a system that transfers heat
from outside to inside a building, or vice versa. Air
source heat pumps work similarly to ground source
heat pumps, except that they extract heat from the air
rather than the ground and use it to heat the house.
The heat collected from the air is distributed through
the house with an air handling system. Their
advantages and disadvantages are similar to those of
ground source heat pumps.
Advantages:
• Environment-friendly
• Low maintenance once installed
• Can save money on heating bills
Disadvantages:
• Expensive to install
• Significant disruption during installation similar
to ground source heat pumps
Electric furnace
An electric furnace converts electricity to heat and as a
result does not need a heat exchanger, burner, or
chimney. These components are replaced by electric
heating elements sitting directly in the air stream. The
blower simply forces air across the heating elements
and the warmed air returns to the rooms via ductwork.
Advantages:
• Lower upfront costs than gas or oil furnace
systems
• Quiet
• Low maintenance
Disadvantages:
• More expensive to operate than gas or oil
furnace systems
• Takes longer to heat up the house than gas or oil
furnace systems
Gas furnace
A gas furnace burns natural gas, which heats up a heat
exchanger. Cold air passes through the heat exchanger
and is blown through the heat exchanger and into the
ductwork. Products of combustion are released
through the side of the house via an exhaust pipe.
There are four levels of efficiency for gas furnaces:
conventional, mid-efficiency, high-efficiency, and highefficiency pulse. As of 2010, all gas furnaces must be of
high efficiency. In areas where no gas is available,
propane is often used.
Advantages:
• Lower operation costs than electric or oil furnace
systems
• Heats up faster than electricity
• More energy-efficient than electric furnace
Disadvantages:
• Can be expensive to install
• Natural gas network not available in every area
• Emits low levels of carbon monoxide, which need
to be vented to the external environment
Oil furnace
Similar to gas furnaces, oil-fired furnaces have a
burner and combustion chamber, and emit exhaust
through a flue pipe in a chimney
Advantages:
• Last longer than gas furnaces
Easier to service than gas or electric furnaces
• Not dependent on pipeline infrastructure
Disadvantages:
• Large storage tank necessary
• Can take up prime space if located in the
basement
• Can cause environmental problems if buried in
the yard
• Less energy-efficient than gas furnace
• Fuel price higher than gas furnaces
• Generates more pollution than gas and requires
more cleaning and maintenance
• Tank replacement necessary every 10 years at a
cost of about $3,00
Gravity furnace
A gravity furnace (sometimes called an octopus
furnace) is found in older houses and is no longer
installed in new builds. They work similarly to a
conventional furnace except that there is no fan to pull
house air into the furnace, blow it through the burner,
and push it out through the air registers. It may be
fueled by either gas or oil.
Instead, the system works on gravity—on the principle
that hot air rises and cool air falls. Warm air rises
through the supply ducts and cool air settles back
through the return ducts to the furnace. As a result,
gravity furnaces are the least efficient form of furnace.
Boilers
Open boilers: Open boiler systems, which are no longer commonly used, use an expansion tank
located above the highest radiator in the structure. This tank allows space for water
to expand when water is heated and has an overflow pipe. Open systems use
gravity rather than a circulating pump to move the water.
Closed boilers: In closed boiler systems, there is water in the boiler, piping, and radiators. The
water is pressurized a few pounds higher than what is required to force it up to the
highest level within the structure. Closed systems typically have a circulating pump
to force the water through the system.
Central Air Conditioning Systems
Central air conditioning systems distribute cooled air throughout a structure. The basic function of any air
conditioning system is that a refrigerant is put under pressure by a compressor until it becomes liquid, which is
cooled by a condenser and then evaporated again. This evaporation process cools the air around it, which provides
a cooling effect. This cooled air is distributed throughout the structure via ductwork
Ductless Air Conditioners
Homeowners can also put individual air conditioning units in different rooms, each of which cools the room directly.
These units work on the same principles as central air conditioning systems, but do not distribute cooled air through
ductwork. Like a central system, they have an outdoor component containing a compressor, fan, and condenser
coils, and an indoor component that cools air by blowing it over an evaporator coil.
Clogged filters
All heating and cooling systems are dependent on an
intake of air to function correctly. Dirty or clogged
filters can restrict the flow of air and reduce the
effectiveness of a system and, if not cleaned or
replaced regularly, can lead to costly repairs. Another
problem can be ice developing on the evaporator coil
on the air conditioner.
Faulty thermostat
Thermostats can malfunction, leading to over-heating
or under-heating the house. If they are battery
powered, a low battery will affect their performance.
Cracked heat exchanger
A cracked heat exchanger can leak carbon monoxide,
which can be fatal, and soot, which is injurious to
health. It is important to schedule regular maintenance
to check for a cracked heat exchanger.
Undersized or broken fan in distribution system
If a fan is not large or powerful enough to distribute air
through a heating/cooling system or is broken in some
way, it can lead to poor or inefficient operation.
Leaking refrigerant
Leaking refrigerant will cause inefficient cooling, since
the refrigerant can no longer absorb as much heat
from the outside, causing warmer air to come from the
vents. It will also lead to elevated electricity bills due to
the need to turn the air conditioning up higher to
achieve the same effect.
Leaking refrigerant will cause inefficient cooling, since
the refrigerant can no longer absorb as much heat
from the outside, causing warmer air to come from the
vents. It will also lead to elevated electricity bills due to
the need to turn the air conditioning up higher to
achieve the same effect.
If there are holes in the ductwork or gaps where it
connects, this will reduce the efficiency of the system,
leading to higher energy bills. All ductwork should be
sealed, caulked, and free of holes. Leaking ducts also
suck up debris and distribute it throughout the house,
creating air quality problems and dust.
Leaks or drafts in the walls, windows, and doors of the house
The house itself must be sealed well and free of drafts
and leaks for heating and air conditioning to work
effectively and efficiently
