Final Flashcards
What the formula to convert watts to amps?
Amps = Watts/(1.73 x Volts x PF)
PF = power factor
1 watt is how many BTUs?
1 watt = 3.41 BTUs
1 ton of AC is how many BTUs?
1 ton of AC = 12,000 BTUs
Formula for heat gain through a window in BTUs
BTU = (temp difference) x (U-value) x (SF of exterior surface area)
How do you request power for building from utility company?
Must write a “Load Letter” which summarized electrical demand.
Why do you have to ground?
So you don’t get shocked by stray currents
How do you ground?
Wires run to a grounding rod, which is embedded in the earth. Alternatively, you can attach to copper pipes or structure
What does GFCI stand for?
Ground Fault Current Intercepter
What does a GFCI outlet do?
A gfci outlet measures current and shuts off outlet if abnormal current flow occurs.
Where are GFCI outlets used?
Typically are used in any environment that might have water.
For an outlet that has three slots, what do each of them do?
one fin is the “hot” line, the other fin is a neutral, and one is a ground
How does a wires gauge relate to maximum current?
the larger the wire gauge, the higher the max current (amps) can be
What is electrical diversity?
the reduction in the calculated electrical load to account for non-simultaneous requirements
Why is AC used over DC?
It’s a cheaper method for transmitting large amount of wattage, low amps- high watts, power can be transformed between voltages as needed
What is three-phase power?
electricity flow that has three sine waves of current offset by 120 degrees so there is no point at which there is no power.
How can you tell if you have three phase power?
There will be three wires coming into the electrical panel
What phase of power do most residential homes have?
single-phase
What is a demand charge for electricity?
an additional fee for peak 15 min KW usage in any one month, used to pay for total capacity required by a power plant
What is load shedding?
A method for reducing the electrical demand lad,ad thus, the peak KW usage. Non critical devices are shut down when not in use. Tied to building management systems
List common wires systems and explain what they are
- BX - wires with armored cable
- greenfield - flexible armored cable (no wires)
- conduit - pipe to carry wires, used for security and grounding
- EMT - thin walled conduit
How are wires pulled through conduits or tubes?
Using wire fish tape
How many spares should be on a panel board?
about 25%
why does each floor have it’s own panel?
panels should be close to the loads, and there are voltage drops for long runs of wire.
What is a circuit breaker and where are they located?
a device on a circuit that shuts off the circuit if there is a surge in current to protect the devices connected. They are located within the electrical panels
are is the watt load balanced in the panel?
the watt load is balanced over the three phases of power as best as possible
what is a bus duct?
A duct to run wires to each floor of a building from the main distribution panel
what is daisy chaining?
having multiple outlets on a single circuit
Name three self-contained power systems
- generator
- UPS (uninterrupted power supply)
- Cogeneration
what is a generator?
a device that powers a building using some sort of fuel (oil or nat. gas) when main electric is lost. Takes 10-12 seconds to start
what is UPS (uninterrupted power supply)?
a battery system used to bridge any power loss, typically used in computer rooms, can only last for 10-20 minutes
what is cogeneration?
supplemental power generated from surplus heat
What are some methods to test the electrical systems?
test amperage, test voltage, test resistance (megger meter), test heat (thermal imaging)
what is the lighting unit of measurement?
foot-candles or flux
list 4 type of light bulbs
- incandescent - very inefficient
- Flourescent - more efficient, but causes ballast heat output
- LED
- metal halide - has color problems
list some methods to reduce energy usage for lighting
- occupancy sensors
- time clocks
- day light sensors
- use of more day light
- more efficient bulbs
name the NYC local law dealing with energy consumption benchmarking
LL 133
What does BTU stand for and what does it mean?
British thermal unit; a measurement that is used to describe heat gain/loss
What is the historical meaning of BTU?
the amount of heat required to raise one pound of water 1 deg F
list some sources of heat in a space
solar radiation, people, lighting, computers, equipment, conductive heat gains, air infiltration
what load is the AC designed for?
peak hour load
What’s the formula for solar load through a wall?
BTU = peak hour solar load x exposed surface area of wall
what’s the formula for BTU’s for temp difference through glass?
BTU = (temp difference) x U-value x area of glass
What is the U-value?
heat transfer coefficent; measure of heat loss through a building’s element (wall). High U = poor thermal performance. Low U = good thermal performance
how does the R value relate to the U value?
R-value = 1/(U-value)
What is NYC LL 32?
law implemented in 2020 to increase the thermal efficiency of buildings by 8% today and then 13% by 2030.
What is ASHRAE?
American Society of Heating, Refrigerating and Air Conditioning Engineers; prof. organization that sets HVAC standards
Is an HVAC system designed for the worst case scenario?
no, peak conditions only happen one or two times a year and would significantly increase the size/cost of a system if designed for it.
List six air conditioning system types
chilled water, condenser water, air cooled, ice storage, geothermal, co-generation
what is the second law of thermodynamics and how does it relate to AC systems?
2nd law states heat will flow from a hot surface to a cooler surface and this principle is used to cool refridgerant/coolant/water in an AC system
what is commonly used to remove heat from AC systems?
water
What is a PTAC system?
a packaged terminal air conditioning system
How does a home AC unit work?
air is cooled through evaporator, then refrigerant is compressed by compressor, then is cooled some in the condenser, then travels back to evaporator
How does a chilled water system work?
system has two loops: a chilled water loop and a condenser water loop. Chiller cools water, which cools building on chilled water loop. Heat from the chiller is taken away by the condenser loop and temps are reduced in the cooling tower
what is a direct expansion AC system?
evaporator is in direct contact with the air stream cooling coil (the evaporator)
how does a condenser water system with DX units work?
each floor has own DX unit to cool, condenser water runs through each unit and is cooled in a cooling tower
what are some benefits of a condenser water system with DX units?
less duct work, no operating engineer required, less penetrations, better control of space, easier to maintain, redundant equipment
why does condenser water that runs through a cooling tower have to be treated?
it is an open sytem and if untreated can cause legionnaires disease, clog pipes, corrode pipes, and evaporate
what type of maintenance is done to a cooling tower?
water chemically treated for corrosion inhibitors and biocides, water is tested 3 days per week, samples are taken to determine condition of pipes, systems are “bled” to revitalize water
what is ice cooling refrigeration?
ice is stored in tanks then warm is blown over to cool it
how does a geothermal system work?
compressor has a ground loop that can heat or cool refrigerant depending on if its a heating or cooling system
Why is a variable air volume system preferred over a constant volume system?
VAV is more energy efficient
How does a constant air volume system work?
air flows at a constant volume and the temperature is controlled by changing the temperature of the blown air
How does a variable air volume system work?
the blown air temperature is held constant and the room temps are adjusted by varying the airflow
how is airflow measured?
cubic feet per minute (CFM)
formula for calculating required airflow through duct?
CFM = BTU/[(Troom - Tduct)x1.08]
How is air returned in a building?
either through a return duct or the plenum space
how do you control temperature in a building?
a thermostat
Whats a variable frequency drive?
system that allows air flow to be adjusted to meet demand if lower than system capacity (i.e. reduce airflow to 15000 cfm from 20000 cfm)
how is the air delivered in an hvac system?
duct work
what things are considered when designing duct work?
cfm needed, velocity of airflow (for noise), size restrictions. insulation
Why do you need to insulate ducts?
keep temperature stable, eliminate condensation, reduce noise
what is air balancing?
a check to make sure the actual airflow is the same as the designed airflow
Why does a building need to be ventilated?
to replace oxygen, dilute CO2, dilute odors, dilute any chemicals in furniture or finishes
what can be done to reduce noise from an AC system (or any other system)?
use a concrete pad and spring isolators
what are some common heating systems?
boilers, warm air, heat pumps, solar cells, geothermal, co-generation