Mechanical, Electrical & Plumbing Systems Flashcards
Energy sources
natural gas: methan is most efficient, propane a little more expensive bc delivered in tanks
oil: grades 1 = $, 5 = cheap, dirty, all $ compared to other energy, light vs heavy in some grades, 2 used in residential/sm. commerical, 4-5 in large commercial
electricity: means being urban, cheapest, $ at peak times, good for radiant heat
steam: where available, efficient for campuses
geothermal: only works in mild climates, need ground source heat pump
Natural energy sources
passive solar, active solar, PVs, geothermal, wind, tidal
though last ones not used directly in bldgs. much
Degree days - heating or cooling
number of days per year that heating is needed, with inside average being 65 deg F
65-average outside temp that day = degree days counted for that day
Furnaces
upflow: return air comes in at bottom
downflow: opposite
horizontal: for crawlspaces, tight spaces
boiler: water or steam heats air, tubes are in a combustion chamber
Compressive refrigeratrion
refrigerant (HCFCs, ammonia, SO2, propane) is precompressed to liquid, as it decompresses, it absorbs latent heat (takes in heat from one place via evaporations, deposits it in another, via condensation)
waste heat can be used in a salt solution absorption system, boiled off or evap off gas condensing down throws heat elsewhere (moving the water/latent heat elsewhere)
evaporative cooling: curtain of water falls over medium, air passes through, evaporation of water reduces air heat (only works in low humidity)
HVAC systems
DX/direct expansion systems/incremental units: air from outside is heated/cooled, sent ductless into room
all air: ducts + heater + chiller at
constant volume: single duct, only dampers allow room control/no zones, for small bldgs
VAV: variable air volume, many thermostats, air flow can be separate from heat flow
high velocity dual duct: smaller ducts, hot + cold mixes at stat-controlled mixing boxes, most accurate, high initial cost and takes up space
reheat-constant volume: air taken in, cooled/dehumidified, then heated 1) on demand at coils over rooms, zone reheat or 2) furnace-boiler, terminal reheat, both still $$ but initial cost lower
multizone: like dual duct, but mixed centrally, in separate chambers for each zone, then delivered
all-water: hot/cold water tubes w fan coil unit via wall opening or window at each zone, cost efficient, can’t control humidity
air/water: air is delivered for ventilation (good when contamination risks high, return air not taken back in), water is for heating/cooling, happens at fan coil units or chiller/boiler
electric systems: radiant grids, eg, very expensive, doesn’t address ventilation needs, often used only as booster
Exhausting / discharge
things that make excessive particulates, heat, odor, fumes, smoke
where hazmats are stored
clothes dryers, cooking places
labs
conveying systems that carry dirty loads
sub soil that’s less than ideal
energy recovery
smoke control
HVAC energy conservation
economizer cycle: uses cool outside air instead of chilled air, when possible (if outside temp is 60 deg F or lower), helpful in large internal load bldgs
dual condenser cooling: one for heat recoverly, one for heat rejection
gas/steam-fired absorption cooling: just water, no bad refrigerants, less efficient, higher first cost bc a cooling tower is needed
solar-powered dessicant cooling: liquid or solid that absorbs water, is dried out by heat from solar panels
direct-contact water heaters: hot gas directly passes through water, higher first cost, good where hot water in constant demand
recuperative gas boilers: aka boiler economizer, fuel economizer, flue gas used to condense air, remove latent heat, preheat water/air going to boiler
displacement ventilation: supply from floor, return from ceiling
water loop heat pump: for each zone, same pipes run, can collect heat from hot places, deliver it to cold places
thermal energy storage: water, ice or rock beds that store heat for later
heat transfer: not great for ventilation
heat recovery ventilation: air to air heat exchangers, waste air used to preheat incoming fresh air, via flat plane: thin walls of adj ducts or energy wheels: transfer water vapor from air stream to the other, or heat pipes: pipe of refrigerant, moves from cold to hot streams
water to water heat exchange: runaround coils, hot air over coils, heated water goes to cold intake air to preheat it, reduces air circ. problems
extract-air windows: double pane, gap, single pane, in the gap is air that controls perimeter temp w heat or coolth
ground-coupled heat exchangers: pipes in ground, works in low rise bldgs only, moderate effect
chilled beams: passive version, only via fins that bring in outside air temps, active version, use boiler/chiller and ventilation, but no ducts, fans, just coils and fins
variable refrigerant flow system: compresser and condensor outside, w evaporators in each zone, refrigerant piped in to spaces, smaller, cheaper
BMS systems
Electrical system components
conductor (wires), current (electrical flow), +/- difference (voltage/electromotive force), resistance fo current flow, power: rate at which energy is used, and work done (Watts)
AC/DC
AC: induction current, conductor is moved in magnetic field (commonest)
DC: galvanic current, single direction flow, comes from battery or from AC generator via rectifier, used in elevators and signals
energy measured in Watt-hrs (kW-hrs), is power mult by time
ampacity = ability to conduct current
Flexible layout
underfloor ducts (raceways in slab), cellular metal floors (metal decking as raceway), under-carpet wiring (low-voltage only)
Electrical wires
many wires: cable
non-metallic sheathed cable, romex: coated in plastic, can be conduit-less
flexible, metal-clad cable: BX, wires are in plastic, steel taped, no conduit, good for renovations
single wire/cable in thermoplastic rubber, must go in conduits, for safe support and to protect from fire
conduit types: rigid steel, intermediate, flexible (least safe), limit the number of bends, number of conductors in conduit to prevent heat build up
too many wires in a cable makes it inefficient, so busbars (Cu bars) in series used instead, aka bus duct, busway
Path of electrical travel
transformer (oil, silicone or dry, requires cooling, often loc in concrete vault)
goes to main building connection/master distribution panel, sent to
switch gear (poss. smaller transfomers), metering, power distribution to separate panels, master switch and circuit breaker is here
distribution panels, go to separate systems, zones, circuit brakers and further distribution here
to local power supply, where surge protection, harmonic protection, power conditioning units, active line conditioning units occur
Safety outlets
GFCI: ground fault circuit interrupters, detects small current leaks, near all wet areas
AFCI: arc fault circuit interrupters, for many receptacles in a series
Receptacles/switches
most common wiring device is a receptacle
12”-18” AFF, 15” for ADA
usu 15 amps, but 20 A required for heavy appliances
switches also common, can be toggle (normal), rocker, push/button, key, dimmer, automatic timer, programmable
normal is 2-way, 3-4-way requires addl conductors
low-voltage switching: 24V to individual switches, fed by central 120V switch, good for programming and automation, better than traditional switching, though in everday applications, is more expensive
power line carrier system: low voltage that carries signals for switch controls
multilevel lighting control: different groups and levels for luminaires to prevent over-lighting in different conditions
daylight compensation control: times of day controller, occupant sensor, starting to become code required, along with more switches in more places
