37201089
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Fichas por Kara Biczykowski, actualizado hace más de 1 año
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Creado por Kara Biczykowski
hace más de 2 años
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| A (sf) = area of bldg assembly C (Btu/hr-sf-°F) = conductance e (hr-sf-°F/Btu) = emittance Eᵗ (Btu/hr-sf) = total solar radiation hₒ (Btu/hr-sf-°F) = coefficient of heat transfer k (Btu/hr-sf-°F) = thermal conductivity (1" of thickness) | q (Btu/hr) = rate of heat loss qᵥ (Btu/hr) = rate of sensible heat loss or gain due to infiltration or ventilation R (hr-sf-°F/Btu) = resistance ΔT (°F) = temperature difference Tₑ (°F) = sol-air temperature Tₒ (°F) = outdoor dry-bulb temperature |
| U (Btu/hr-sf-F) = coefficient of heat transmission V (ft3/min) = volumetric airflow rate a = absorbance ε = thermal emissivity | *nomenclatures for equations |
| 1) human comfort is based on: 2) the body's heat production is measured in metabolic mets, what is a "met?" 3) one met = | 1) temp, humidity, air movement, temp radiation to & from surrounding surfaces, air quality, sound, vibration, light 2) the energy produced per unit of surface area per hour by a seated person at rest 3) 18.4 Btu/hr-sf, so avg surface area of resting adult = 360-400 Btu/hr |
| 1) what are the main 3 ways the body loses heat? 2) convection is: 3) when/how does the body lose heat thru convection? | 1) convection, evaporation, radiation 2) the transfer of heat thru the movement of a gas or liquid 3) when air temp surrounding a person is less than body's skin temp, around 85F - body heats surrounding air, heated air rises & is replaced w/ cooler air |
| 1) when does heat loss thru evaporation occur? 2) what is radiation? 3) when does the body lose heat thru radiation? 4) what is conduction? | 1) when moisture changes to a vapor as a person perspires or breathes 2) the transfer of heat energy thru electromagnetic waves from one surface to a colder surface 3) to a cooler atmosphere or surface 4) transfer of heat thru direct contact btwn 2 objects of different temps |
| 1) on avg, a gen comfortable air temp range is btwn: 2) a tolerable range is btwn: 3) IMC & IBC req any space for human occ. provide: 4) what is "effective temperature?" | 1) 69°F - 80°F 2) 60°F - 85°F depending on relative humidity 3) an active or passive space-heating system that can maintain min indoor temp of 68F 3 ft abv flr on heating day 4) val. that combines effects of air temp, humidity, & air movement |
| 1) what is dry-bulb temperature? 2) what is wet-bulb temp? 3) in dry air, moisture evaporates rapidly & causes wet-bulb temp to read as: 4) in moist air, a wet-bulb temp reads as: 5) what new technology measures relative humidity? | 1) temp measured w/ a std. thermometer 2) measured w/ a sling psychrometer - device w/ a moist cloth around bulb of a std. thermometer to measure humidity 3) a low wet-bulb temp 4) a high wet-bulb temp 5) can use a hyrometer sensor instead of a sling psychormeter now |
| 1) what is relative humidity? 2) comfortable relative humidity range: 3) tolerable range: 4) when humidity goes up like in the summer, why does someone feel hotter than temp indicates? | 1) ratio of % of moisture in air to the max amt of moisture air can hold at a given temp w/out condensing 2) 30% - 65% 3) 20% -70% 4) becomes more difficult for perspiration to evaporate |
| 1) air movement tends to increase (__) & (__) thru convection 2) wind speeds from (__) to (__) are acceptable for cooling w/ annoying drafts | 1) evaporation / heat loss - why a person feels more comfortable in high temps & high humidity w/ a breeze but also is cause of the "windchill effect" where tolerable cold air temps become unbearable in wind 2) 50ft/min - 200ft/min |
| 1) if surface temp around body is colder than skin temp, the body: 2) if the surface temp is warmer: 3) rate of radiation depends on: 4) what is the "viewed angle?" 5) ^ Ex person next to fireplace feels warm because: | 1) loses heat thru radiation 2) body gains heat thru radiation 3) surface temp of body & object, viewed angle, & emissivity 4) the solid angle formed btwn the measuring position & the outer edges of the object 5) they exp. high radiant heat b/c fireplace occupies a large angle of view relative to the body |
| 1) the "emissivity" of an obj. is it's ability to: 2) the "emittance" of an obj, is the: 3) what type of objects have low vs high emissivity? | 1) absorb & then radiate heat 2) ratio of radiation emitted by obj/ mat. compared to that by a black body at same temp. 3) shiny obj.'s have low, so don't absorb or radiate heat like black obj.'s, & is used to reduce heat transfer |
| 1) what is "mean radiant temp" (MRT)? 2) MRT is important comfort factor in winter & cold rms b/c as air temps decrease: 3) what is a globe thermometer? | 1) weighted avg of various surface temps in a rm & angle of exposure of occ. to these surfaces + any sunlight present 2) body loses more heat thru radiation than evaporation 3) a thermometer in a black globe that can acct for both air temp & radiant effects from surrounding surfaces |
| 1) what is operative temperature? 2) human comfort std.'s are based on wearing clothes, so to quantify effects the unit "clo" was developed which = 3) where are 2 types of ventilation req.'s designed for? | 1) an avg of air temp of space & MRT of space to measure effects of surface temps on human comfort 2) 1 clo = thermal insulation given by typ suit or about 0.15 clo / lb of clothing 3) unoccupied space like attics & occupied |
| 1) when natural ventilation is used, IMC & IBC req area that can be opened to outdoors be = to: 2) when rm is ventilated thru adjoining rm: 3) when mech ventilation is used, rate of supply air into rm must be: | 1) at least 4% of flr area being ventilated 2) opening onto adj rm must have min 8% of interior rm flr area, & not less than 25sf 3) = to rate of return/ exhaust air, but some cases prefer positive air pressure like in stair core to prevent smoke during a fire |
| 1) w/ mech ventilation, amt of OSA brought in depends on: 2) "comfort charts" show the relationships btwn: 3) chart shows as humidity increases, to prvd same amt of comfort at lower humidity levels, air temp must: 4) if temp drops blw recommended levels, what is needed to maintain comfort? | 1) type of use & occ. load (table in IMC - not same thing used for egress req.'s in IBC) 2) temp, humidity, & oth comfort factors Fig16.2 3) decrease, & air movement is req.'d 4) radiation in form of sunlight or mech radiation |
| 1) what is a "psychrometric chart?" 2) what is psychrometry? 3) this chart is used to make calcs for determining: | 1) Fig16.3 - a graphical rep. of the complex interactions btwn heat, air, moisture 2) the study of the water vapor content of air 3) how much heat & moisture needs to be added or removed by an HVAC system for comfort |
| 1) can hot or cold air hold more moisture? 2) on chart, the 100% relative humidity line is also known as: 3) what is "enthalpy?" | 1) hot air 2) the saturation line or dew-point line b/c it indicates when water vapor will form when saturated air comes into contact w/ a surface at or blw air's dew-point temp 3) total amt of both sensible & latent heat in air-moisture mixture |
| 1) what is enthalpy line on chart used for? 2) what is sensible heat? 3) what is latent heat? 4) what is humidity ratio? | 1) to determine total amt of heat that must be removed or added from conditioned air -both sensible & latent heat 2) just the heat represented by air temp 3) contained in the air moisture 4) amt of moisture by weight w/in a given weight of air |
| 1) what climate only do evaporative coolers (aka swamp coolers) work? 2) external loads that cause heat loss: 3) external loads causing heat gain: 4) internal loads causing heat gain: | 1) hot, dry climates - b/c they reduce air temp but not enthalpy (total heat) 2) air temp & wind 3) air temp & sunlight 4) people, lights, equipment |
| 1) conduction is transfer of heat thru: 2) convection is transfer of heat thru: 3) conduction is transfer of heat thru: 4) in order to determine the size of a heating system for a bldg: 5) how is heat lost in a bldg? | 1) direct contact btwn molecules 2) movement of air 3) electromagnetic waves from one surface to a colder surface 4) total amt of heat lost per hr must be calculated 5) thru the bldg envelope & air infiltration |
| 1) a mat.'s "thermal conductivity" (k), is the rate heat passes thru: 2) "conductance" (C) is the ^ same property when: 3) "resistance" (R) of a mat. is the # of hrs needed for: 4) total conductance & total resistance are related, equation is: | 1) 1sf of 1in of thickness of mat. when the temp differential is 1°F 2) the mat. is a thickness oth than 1in 3) 1 Btu to pass thru a mat. of a given thickness when the temp differential is1F 4) R = 1/C * k, C, R values for mat.'s are given in tables in ASHRAE handbook - will be prvd on exam for any heat loss calcs |
| 1) when bldg assembly consists of more than one mat., value to calc heat loss is: | 1) w/ the "overall coefficient of heat transmission" or "U" - this value isn't the sum of all individual mat. conductance *use equation: U = 1/ΣR |
| 1) amt of heat loss thru 1 unit of area of bldg mat. is dependent on the coefficient of heat transmission of mat. & temp differential btwn inside & out - for entire area of one mat. type, value is multiplied by total area to get total heat loss "q" | q = U A ΔT *in order to calculate heat loss for entire rm or bldg, all different heat losses (walls, wndws, roof, etc) must be solved for & then added together |
| 1) how is the value of ΔT (change in temp) found? 2) heat loss calcs & psychrometric charts are used to avoid condensation on: | 1) by subtracting the outdoor design temp from the desired indoor temp (which is typ 70°F) 2) interior surfaces & inside bldg const. by finding the dew pt of moisture in air - Ex air at 70°F & 35% humidity has a dew-pt of 41F so moisture will condense on surfaces blw this temp |
| 1) b/c of warmer inside temps, to avoid water vapor from inside bldg permeating the const. & condensing on surfaces like wood sheathing & causing damage to it or reducing effectiveness of insulation, what can be done? 2) what is a "thermal gradient?" | 1) placing a vapor barrier on the warm side of insulation, so the side facing the bldg interior 2) it shows the variance in temp thru a cross section of a const. assembly Fig16.4 |
| 1) heat loss thru infiltration is calculated w/ equation: *infiltration greatly affects energy use so codes req. use of air barriers to min. it | 1) qᵥ = V (1.08) ΔT * 1.08 Btu-min/ft3-°F-hr accts for specific heat of air AKA the amt of heat air at a certain density can hold V (volumetric flow rate) = air infiltration calc'd from volume of air lost via cracks, doors, openings |
| 1) heat gain thru bldg envelope can be calc'd like heat loss w/ equation q = U A ΔT except that: 2) design equivalent temp diff. (DETD) accts for: | 1) the temp differential isn't used directly, & instead the "design equivalent temp difference" (DETD) must be used 2) air temp diff., effects of sun, thermal mass storage effects of mat.'s, colors of finishes exposed to sun, & daily temp range (values are in ASHRAE tables) |
| 1) an alt to DETD is "sol-air temp" which is a value for: 2) in heat gain calcs, sol-air temp can be used in place of: 3) the sol-air temp calculation is: | 1) outdoor temp that combines effects of temp difference w/ solar radiation 2) ΔT 3) Tₑ = Tₒ + aEᵗ/hₒ - 7°F * this rep's heat flow is strongly affected by amt of solar radiation & color of surface, w/ dark colors = greater heat flow |
| SOL-AIR TEMP EQUATION Tₒ is outdoor dry-bulb temp "a" is surface's absorbance for solar radiation (light colors typ 0.45 & dark typ 0.90) Eᵗ is total solar radiation incident on surface in Btu/hr-sf | SOL-AIR TEMP EQUATION hₒ is the film coefficient of heat transfer by long-wave radiation & convection at the surface - typ assumbed to be 3.0 Btu/hr-sf-°F |
| 1) heat gain thru glazing is calc'd by: 2) "design cooling load factor" (DCLF) accts for: 3) occupants of a bldg produce which two kinds of heat? | 1) multiplying the area of glazing by the "design cooling load factor" (DCLF) 2) type of glazing, type of int. shading, outdoor design temp - factors published by ASHRAE 3) sensible heat & latent |
| 1) sensible heat gain from occupants is about (__) Btu/hr 2) total sensible heat is estimated by: 3) 1W (watt) = 3.41 Btu/hr so heat gains from lighting can be calc'd by multiplying: | 1) 225 Btu/hr 2) multiplying # of occ. by 225 Btu/hr 3) total wattage load of bldg's lighting by 3.41 *use 1.25 if fixtures are fluorescent |
| 1) why must latent heat be acct'd for in calc-ing heat gains? 2) in heat gain calcs latent heat is calc'd separately or % of total sensible heat which is based on: | 1) b/c for cooling purposes, moisture in air must be removed to maintain comfortable relative humidity level while sensible heat level is being reduced 2) exp & type of occ., typ about 30% of sensible heat gain in many occ.'s |
| 1) why is using bldg mat.'s w/ a high mass an effective passive method to mitigate effects of heat gain via solar radiation & air temp? 2) how do you calc sensible heat gain thru infiltration? | 1) b/c mat.'s like masonry, concrete, tile all slow transmission of heat into bldg - absorb heat & store it during the day & release it at night when air temp is cooler 2) sim to calc-ing heat loss - total heat gain is found by multiplying total area by an infiltration factor |
| 1) if a bldg is mech ventilated, vol of air brought into bldg is multiplied by: *see definitions P16-12 | 1) amt of heat that must be extracted to cool air & remove excess humidity *energy to do this in humid climates is alot |
| 1) "coefficient of heat transmission" (U) - overall rate of heat flow thru any combo of mat.'s, is the reciprocal of the sum of all the resistances in the bldg assembly 2) "conductance" (C) - # of Btu/hr that pass thru 1sf of same mat. of given thickness when temp differential is 1F | 3) "conductivity" (k) - # of Btu/hr that pass thru 1sf of same mat. 1in thk when temp differential is 1F 4) "dry-bulb temp" - temp of air-water mixture as measured w/ std. thermometer 5) "enthalpy" - total heat in a substance, both latent & sensible |
| 6) "latent heat" - heat that causes a change of state of a substance, like heat req'd to change water to steam (amt of heat req'd to change state of a substance is much greater than heat req'd to raise temp of a substance {sensible heat}) | 7) "resistance" - # of hrs needed for 1 Btu to pass thru 1 sf of mat. of given thkns when temp differential is 1F - reciprocal of conductance 8) "sensible heat" - heat that causes a change in temp of a substance but not state |
| 9) "specific heat" - # of Btu's req'd to raise the temp of a specific mat by 1F - it's a measure of a mat.'s capacity to store heat as compared w/ the storage capacity of water | 10) "wet-bulb temp" - temp of air as measured w/ a sling psychrometer - more critical measure of heat in high humidity b/c it's an indicator of physical stress caused when the human body is near limit of temp regulation by perspiration |
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