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
operative temperature
average of air temperature of a space and the MRT of the space ;; can be measured using a black globe thermometer
British thermal unit (Btu)
the amount of heat required to raise the temperature of 1 lbm water by 1 degree F
U (coefficient of heat transmission)
the overall rate of heat flow through any combination of materials, including air spaces and air layers on the interior and exterior of a building assembly;; it is the reciprocal of the sum of all the resistances in the building assembly
C (conductance)
the number of BTUs per hour that pass through 1 ft^2 of homogeneous material of a given thickness when the temperature differential is 1 degree F
k (conductivity)
the number of BTUs per hour that pass through 1 ft^2 of homogeneous material 1 inch thick when the temperature differential is 1 degree F
dew point
the temperature at which water vapor in the air becomes saturated and begins to condense into drops of water
dry-bulb temperature
the temperature of the air-water mixture as measured with a standard dry-bulb thermometer
enthalpy
the total heat in a substance, including latent heat and sensible heat
latent heat
heat that causes a change of state of a substance, such as the heat required to change water into steam;; the amount of heat required to change the state of a substance is much greater than the heat required to raise the temperature of the substance (sensible heat). The average value of latent heat per pound of moisture is 1061 Btu.
resistance
the number of hours needed for 1 Btu to pass through 1 ft^2 of material or assembly of a given thickness when the temperature differential is 1 degree F;; it is the reciprocal of conductance.
sensible heat
heat that causes a change in temperature of a substance but not a change of state;; the sensible heat needed to raise the temperature of 1 lbm of water from 50 deg F to 100 deg F is 50 Btu. In contrast, the latent heat needed to change liquid water at 212 deg F to steam at 212 deg F is 1061 Btu.
specific heat
the number of BTUs required to raise the temperature of a specific material by 1 deg F;; specific heat is a measure of a material’s capacity to store heat as compared with the storage capacity of water.
wet-bulb temperature
the temperature of the air as measured with a sling psychrometer;; the wet-bulb temperature is a more critical measure of heat in high humidity because it is an indicator of physical stress caused when the human body is near the upper limits of temperature regulation by perspiration.
mean radiant temperature (MRT)
the uniform temperature of an imaginary surrounding enclosure in which radiant transfer from the human body would equal the radiant heat transfer in the actual nonuniform enclosure;; MRT is a calculated variable and cannot be directly measured
cross-ventilation vs. stack ventilation
Natural ventilation. Cross-ventilation is driven by windows and relies on narrow plans with large openings on either side; it is naturally compatible with daylighting. Stack ventilation depends on very low openings to admit outside air and high openings to exhaust it; it’s generally weaker than cross-ventilation except when there is no wind.
actuator
a device in a building control system that receives commands from a controller and activates a piece of equipment
annual fuel utilization efficiency (AFUE)
the ratio of annual fuel output energy to annual input energy;; this includes nonseasonal pilot light input losses
coefficient of performance (COP)
a unites number that is a rating of the efficiency of heating or cooling equipment;; it is derived by dividing the steady-state rate of energy output (or the rate of heat removal, in the case of cooling equipment) of the equipment by the steady-state rate of energy input to the equipment. The output and input values must be in equivalent units, such as watts out to watts in.
controller
a device that measures, analyzes, and initiates actions in a building control system
deadband
in a building control system, the range of temperatures within which neither heating nor cooling is needed
