Heat Loss Flashcards
why do we perform heat loss on a structure
to properly size the appliance, piping, duct work, and HDU’S (heat distribution units)
can heat transfer be stopped
heat transfer can only be slowed never stopped
how does heat move
heat moves from an area of higher concentration to an area of lower concentration by conduction convection or radiation
what is a BTU
the amount of energy needed to raise one pound of water one degree fahrenheit
what is transmission loss
heat loss through the envelope by means of conduction ex: windows doors etc
two factors that effect transmission losses
wall construction and delta T
explain infiltration
warm air leaves building cold air replaces it because the building psi is less than the outdoor psi
why is infiltration bad
heat loss from building leads to lower efficiency
five reasons infiltration is good :)
oxygen rich air removes moisture removes odors removes chemicals from cleaners removes outgassing
when is mechanical ventilation needed in winter
when there is less than .5 ACH
What is the R Value
number of hours it takes for 1 btu to pass through one square foot of material, with one degree delta T between the two sides
What is the U Value
number of BTU’s that will pass thru 1 sq. ft of material in 1 hour with 1 degree delta T between the 2 sides
why is solar gain not accounted for when computing heat loss?
our designed condition is for the winter (no sun)
table 1 is used to find what
outdoor design temp (ODT)
what does the 97.5 % column mean
it means that we are at or above that temp 97.5% of the time
table 2 is used to find what
HTM’s
what is the accepted IDT for calculating heat loss
70 degrees
please list 9 ways heat is lost from a building
roof - ceilings exposed walls doors and windows slab floors below grade walls partition basements floors ceiling to attic floor loss to crawl space duct loss to unconditioned space
4 ways heat is lost from a heating system
- Ducts in unheated spaces
- Vent air must be heated before entering space
- Bathroom and kitchen exhaust fans
- Outside air intake to feed combustion
when measuring windows and doors we round to the nearest
tenth (.1 )of a foot then the nearest square foot
wall length we round to
nearest foot
wall heights we round to
nearest half foot
gross exposed wall area round to
nearest sq foot
wind speed u factor table 2
15mph
