Thermal Comfort Flashcards
Human comfort range
comfort: 65-80 deg F
tolerance: 60-85 deg F
Target temp for IBC/IMB
68 deg F
Types of temperatures
dry bulb = just a thermometer
wet bulb = plus wet cloth, swung around, aka sling psychrometer
hygrometer sensor = electronically sense humidity
relative humidity = ratio of current:max, comfort is 30-65%, tolerable is 20-70%
more humidity at >85 deg F, feels v hot bc evaporative cooling is ineffective
Wind speed vs temp
greater wind speed, lower apparent temp bc of increased convection
Surface temps
changes apparent temp by engaging bodies in radiative heat transfer, v important in cold rooms
Black globe thermometer
detects air temp + emissive heat radiation from objects
can collect MRT, mean radiant temperature
Effective temperature
takes into account temp, humidity, air movement
Surface radiation measurements
viewed angle = how much of the hot/cold surface is viewable
emissivity = ability to absorb/emit heat
emittance = ratio of heat emitted by that obj:heat emitted by a black body
Types of ventilation
to unoccupied space: to prevent mold
to occupied spaces: to provide breathable air, remove noxious gases, moisture
natural ventilation: must have 4% of room’s floor area equal to operable windows, or if an adjoining room is added, 8% of both room’s floor area, not less than 25 sqft
mechanical ventilation: tables based on occupancy (not the same ones as for egress) determines air flow rates in cfm/sf (cubic foot minutes)
Comfort charts
combine temp, humidity, other factors for setting ventilation goals
if humidity is high, then temp needs to come down
if temp is down, then radiation needs to increase
psychrometric chart is best example
Psychrometric chart
warm air holds more moisture than cold air
vertical lines = dry bulb temp
lines sloping upper left/lower right = wet bulb temp
curved lines from lower left/upper right = relative humidity
100% humidity = saturation line/dew point line = wet bulb/dry bulb temps are the same
upper left side shows enthalpy = total amt of sensible and latent (water phase stored) heat
enthalpy is the total amt of heat that must be removed by HVAC systems
Heat loss calculations
thermal conductivity = k, the rate at which heat passes through 1 sq ft of a 1 in. thickness of a material when heat difference is 1 deg f
conductance = C, is the same, but with varying thicknesses
resistance = R, is the inverse of C
U value = overall heat transmission coefficient is sum of resistances, inverted
total heat loss, q = U*A*temp change
heat loss via air infiltration: q = Vol(1.08)*temp change, where 1.08 is specific heat of air, vol is volume of air flow
Latent vs. sensible heat
sensible = you can feel it
latent = stored in water phase changes
people produce both!
