Mechanical, Electrical, Plumbing Flashcards
<p>Energy sources</p>
<p>natural gas:Âmethan isÂmost efficient, propane a little more expensive bc delivered in tanks</p>
<p>oil: grades 1 = $, 5 = cheap, dirty, all $ compared to other energy, light vs heavy in some grades, 2 used in residential/sm.Âcommerical, 4-5 in large commercial</p>
<p>electricity: means being urban, cheapest, $ at peak times, good for radiant heat</p>
<p>steam: where available, efficient for campuses</p>
<p>geothermal: only works in mild climates, need ground source heat pump</p>
<p>Natural energy sources</p>
<p>passive solar, active solar, PVs, geothermal, wind, tidal</p>
<p>though last ones not used directly in bldgs. much</p>
<p>Degree days - heating or cooling</p>
<p>number of days per year that heating is needed, with inside average being 65 deg F</p>
<p>65-average outside temp that day = degree days counted for that day</p>
<p>Furnaces</p>
<p>upflow: return air comes in at bottom</p>
<p>downflow: opposite</p>
<p>horizontal: for crawlspaces, tight spaces</p>
<p>boiler: water or steam heats air, tubes are in a combustion chamber</p>
<p>Compressive refrigeration</p>
<p>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)</p>
<p>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)</p>
<p>evaporative cooling: curtain of water falls over medium, air passes through, evaporation of water reduces air heat (only works in low humidity)</p>
<p>HVAC systems</p>
<p>DX/direct expansion systems/incremental units: air from outside is heated/cooled, sent ductless into room</p>
<p>Â</p>
<p>all air: ducts + heater + chillerÂat</p>
<p>constant volume:Âsingle duct, only dampers allow room control/no zones, for small bldgs</p>
<p>VAV: variable air volume, many thermostats, air flow can be separate from heat flow</p>
<p>high velocity dual duct: smaller ducts, hot + cold mixes at stat-controlled mixing boxes, most accurate, high initial cost and takes up space</p>
<p>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</p>
<p>multizone: like dual duct, but mixed centrally, in separate chambers for each zone, then delivered</p>
<p>Â</p>
<p>Â</p>
<p>all-water: hot/cold water tubes w fan coil unit via wall opening or window at each zone, cost efficient, can't control humidity</p>
<p>air/water: air is deliveredÂfor 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</p>
<p>electric systems: radiant grids, eg, very expensive, doesn't address ventilation needs, often used only as booster</p>
<p>Exhausting / discharge</p>
<p>things that make excessive particulates, heat, odor, fumes, smoke</p>
<p>where hazmats are stored</p>
<p>clothes dryers, cooking places</p>
<p>labs</p>
<p>conveying systems that carry dirty loads</p>
<p>sub soil that's less than ideal</p>
<p>energy recovery</p>
<p>smoke control</p>
<p>HVAC energy conservation</p>
<p>economizer cycle: uses cool outside air instead of chilled air, when possible (if outsideÂtemp is 60 deg F or lower), helpful in large internal load bldgs</p>
<p>dual condenser cooling: one for heat recovery, one for heat rejection</p>
<p>gas/steam-fired absorption cooling: just water, no bad refrigerants, less efficient, higher first cost bc a cooling tower is needed</p>
<p>solar-powered dessicant cooling: liquid or solid that absorbs water, is dried out by heat from solar panels</p>
<p>direct-contact water heaters: hot gas directly passes through water, higher first cost, good where hot water in constant demand</p>
<p>recuperative gas boilers: aka boiler economizer, fuel economizer, flue gas used to condense air, remove latent heat, preheat water/air going to boiler</p>
<p>displacement ventilation: supply from floor, return from ceiling</p>
<p>water loop heat pump: for each zone, same pipes run, can collect heat from hot places, deliver it to cold places</p>
<p>thermal energy storage: water, ice or rock beds that store heat for later</p>
<p>heat transfer: not great for ventilation</p>
<p>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</p>
<p>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</p>
<p>extract-air windows: double pane, gap, single pane, in the gap is air that controls perimeter temp w heat or coolth</p>
<p>ground-coupled heat exchangers: pipes in ground, works in low rise bldgs only, moderate effect</p>
<p>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</p>
<p>variable refrigerant flow system: compresser and condensor outside, w evaporators in each zone, refrigerant piped in to spaces, smaller, cheaper</p>
<p>BMS systems</p>
<p>Electrical system components</p>
<p>conductor (wires), current (electrical flow), +/- difference (voltage/electromotive force), resistance fo current flow, power: rate at which energy is used, and work done (Watts)</p>
<p>AC/DC</p>
<p>AC: induction current, conductor is moved in magnetic field (commonest)</p>
<p>DC: galvanic current, single direction flow, comes from battery or from AC generator via rectifier, used in elevators and signals</p>
<p>energy measured in Watt-hrs (kW-hrs), is power mult by time</p>
<p>ampacity = ability to conduct current</p>
<p>Flexible layout</p>
<p>underfloor ducts (raceways in slab), cellular metal floors (metal decking as raceway), under-carpet wiring (low-voltage only)</p>
<p>Electrical wires</p>
<p>many wires: cable</p>
<p>non-metallic sheathed cable, romex: coated in plastic, can be conduit-less</p>
<p>flexible, metal-clad cable: BX, wires are in plastic, steel taped, no conduit, good for renovations</p>
<p>single wire/cable in thermoplastic rubber, must go in conduits, for safe support and to protect from fire</p>
<p>conduit types: rigid steel, intermediate, flexible (least safe), limit the number of bends, number of conductors in conduit to prevent heat build up</p>
<p>too many wires in a cable makes it inefficient, so busbars (Cu bars) in series used instead, aka bus duct, busway</p>
<p>Path of electrical travel</p>
<p>transformer (oil, silicone or dry, requires cooling, often loc in concrete vault)</p>
<p>goes to main building connection/master distribution panel, sent toÂ</p>
<p>switch gearÂ(poss. smaller transfomers), metering, power distribution to separate panels, master switch and circuit breaker is here</p>
<p>distribution panels, go to separate systems, zones, circuit brakers and further distribution here</p>
<p>to local power supply, where surge protection, harmonic protection, power conditioning units, active line conditioning units occur</p>
<p>Safety outlets</p>
<p>GFCI: ground fault circuit interrupters, detects small current leaks, near all wet areas</p>
<p>AFCI: arc fault circuit interrupters, for many receptacles in a series</p>
<p>Receptacles/switches</p>
<p>most common wiring device is a receptacle</p>
<p>12"-18" AFF, 15" for ADA</p>
<p>usu 15 amps, but 20 A required for heavy appliances</p>
<p>switches also common, can be toggle (normal), rocker, push/button, key, dimmer, automatic timer, programmable</p>
<p>normal is 2-way, 3-4-way requires addl conductors</p>
<p>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</p>
<p>power line carrier system: low voltage that carries signals for switch controls</p>
<p>multilevel lighting control: different groups and levels for luminaires to prevent over-lighting in different conditions</p>
<p>daylight compensation control: times of day controller, occupant sensor, starting to become code required, along with more switches in more places</p>
<p>Emergency power</p>
<p>for life/safety</p>
<p>standby power: to keep a business running</p>
<p>from a battery (need lots) or from a back-up generator</p>
<p>Water sources</p>
<p>issues to deal w 'raw water': sedimentation, coagulation, flocculation (alum, aggregate particles)</p>
<p>filtration: gravity, pressure, membranes, cartridges, sand, diatomaceous earth</p>
<p>ion-exchange: reverse osmosis, electrodialysis (charged membranes)</p>
<p>chlorination, chloranine, ozonation, UV, nanofiltration</p>
<p>distillation, aeration (improves taste), oxidization</p>
<p>municipal water: treated, then pumped at 50 psi (varies 40-80)</p>
<p>Private water extraction</p>
<p>wells, springs, rain water</p>
<p>5-10 gpm needed for residences, may need storage tank/pressure tank to reach that</p>
<p>pumps: suction (shallow only), submersible (common), jet (for deep), turbine (for deep + high capacity)</p>
<p>Solar water heating</p>
<p>need a solar collector, storage tank, piping, back up heater for dark days</p>
<p>if you add a pump it's 'active', if not 'passive'</p>
<p>direct: open-loop, water used = water heated</p>
<p>indirect: closed loop, water heated then heats the water that's used, can use antifreeze for heating liquid (good in cold climates), need a heat exchanger, active version of this is the most common configuration</p>
<p>batch system: black painted tank in glass box</p>
<p>thermosiphon: uses natural movement of heated H2O to run supply</p>
<p>drain down/drain backÂsystem: pump, removes H2O if freezing temp arrive,Âpump puts water back in when temps back up</p>
The energy produced per unit of surface area per hour by a seated person at rest
1 met (metabolic unit) = 18.4 Btu/hr-ft^2
Factors: air temperature, humidity, air movement, surface temperature, clothing, ventilation
Factors in thermal comfort
Relative humidity
Percent moisture in the air : maximum amount of moisture the air can hold at a given temperature without condensing
emissivity
measure of an object’s ability to absorb and radiate heat (emittance: ratio of the radiation emitted by an object at a given temperature to the radiation emitted by a black body at the same temperature)
mean radiant temperature (MRT)
a weighted average of all surface temperatures in a room and the angle of exposure of the occupant to these and any sunlight present
