environmental comfort Flashcards
variables that affect comfort in building?
-room temp
- airflow
- humidity
- radiation
- indoor air quality
what temps does body feel most comfortable?
- winter: 22.2 - 25.5
- summer: 22.2 - 24.4
what is humidity?
- moisture in the air
- high humidity less heat absorbed from body
- low humidity more heat absorbed from body
airflow?
- rate of air motion
- increased air flow increases heat evaporation from body keeping it cool
radiation?
- heat flows from hot to cold surface
- comfort can be increases by directing warm air towards cold surfaces, why most heating elements are located under windows
HVAC designed for?
- thermal conditioning
- adequate count of outdoor air
two types of humidity?
- absolute humidity
- relative humidity
dry air?
no water vapour
moist air?
some water vapour
saturated air?
max amount of water vapour
how is relative humidity measured?
hydrometer
how to dehumidify air?
cool it
what is the dew point (DPT)
temp of air/water vapour mixture when fully saturated
frost point temp?
when dew point is below freezing creating frost instead of dew
condensation?
process of removing liquid from air
effect of temp on humidity
- moisture holding capacity
- warm air holds more than cold air
dry bulb temp (DBT)
temp of the mixture of air and moisture at rest, measured with thermometer
wet-bulb temp?
- by comparing the dry and wet bulb temperatures we can determine the temp and humidity of air
specific volume?
ratio of unit volume of air per weight of dry air
enthalpy
quantity of heat contained in air under specific conditions
psychrometric chart
graphical representation of thermodynamic properties of moist air
what is relative humidity
ratio of actual water to max amount of water at the same temp and pressure
what two ways does air contain thermal energy
- temperature
- water vapour
sensible heat?
heat is associated with temp change
temperature is a measurement of what
sensible heat
what are all the material states
- solid
- liquid
-gas
latent heat?
release or storage of heat associated with change in phase of substance
water vapour is measurement of what?
also latent heat
heating cooling is change of what
change od sensible heat
humidification and dehumidification is change of what
is a change of latent heat
sensible heating (cooling)
when temp of air water mixture is raised, but moisture remains the same
cooling and dehumidification
lowering temp and humidity ratio
evaporating cooling
sensible heat converts to latent heat in the added vapour
heating and humidification
desiccant dehumidification
chemical or physical absorption of water vapour to dehumidify air
what fluids does the HVAC system carry to transport heat and cold
- air
- water
- steam
- refrigereant
what is heat measured in
british thermal units (BTU)
what is 1 btu
the heat to raise 1lb of water 1F
heating loads?
how much heat is lost and must be made up
cooling loads?
how much heat must be removed
what is critical condition design
- outside weather
- solar effects
- inside temp
- humidity
- status of building operations
critical deasign for heating occurs when
with super cold weather
critical design for cooling is when
with super hot conditions
what does the amount of ventillation depend on?
- type of occupancy
- number of occupants
