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AE Concepts Cheat Sheet (DRAFT) by

Pennstate AE 202 intro to AE concepts cheatsheet for exam 2

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Defini­tions

Conduction
It is the transfer of heat through a material
Radiation
It is energy transm­itted directly through space
Convection
It is the transfer of heat by the movement of fluids such as air or water
Emissi­vity(ε)
ratio of the radiation emitted by the surface at a given temper­ature to the radiation emitted by a blackbody at the same temper­ature.
blackbody
The idealized surface that emits radiation at this maximum rate
Kirchh­off’s Law (1860)
At the thermal equili­brium, the power radiated by an object must be equal to the power absorbed.
Heat
It is the form of energy that can be transf­erred from one system to another as a result of temper­ature differ­ence.
Thermo­dyn­amics
We can determine the amount of heat transf­erred using a Thermo­dynamic analysis alone. It deals with equili­brium states and changes from one to another.
Heat Transfer
It deals with systems that lack thermal equili­brium. It is the science that deals with the determ­ination of the rates of such energy transfers is called heat transfer. Unit is Btu/hr, or Watt (1 W = 3.41 Btu/hr)
Infilt­ration
s the accidental heat loss/gain due to air leaking through the envelope, doors, windows etc.
Ventil­ation
is the delibe­rate, designed introd­uction of air into/out of a space required for healthy buildings
Heat Loss(B­tu/hr)
The heat transfer through each element to outdoor in winter season.
Peak Heating Loads(­Btu/hr)
the amount of heat lost to the outdoor enviro­nment at design outdoor and indoor condit­ions, which must be made up by the HVAC system to maintain occupant comfort.
Annual Heating Energy­(Btu)
The energy consum­ption during winter heating season. It will consider the heat gains from lights, human activi­ties, applia­nces, etc.
When will the peak heating loads happen?
Lowest weather temper­ature • At night (no solar) • No internal gains • Ignore thermal mass
When will the peak cooling loads happen?
Highest weather temper­ature • Maximum solar gains (window orient­ation) • Maximum internal heat gains • Ignore thermal mass
 

Approp­riate terms and questions

The heat (loss or gain) during a day is about #____?
B. Btu, D. Joule
The heat flow rate in this situation is # ____?
C. Btu/hr
#____ (heating or cooling) loads for a year will be needed
B. MBtu, D. Joule
#____ peak heating loads are docume­nted.
B. MBtu, D. Joule
R
sub
t
Total thermal resistance - Ability of a constr­uction assembly to insulate heat, including air films
U
Overall coeffi­cient of heat transm­ission - Ability of a constr­uction assembly to transfer heat, including air films
When will the peak heating loads happen?
• Lowest weather temper­ature • At night (no solar) • No internal gains • Ignore thermal mass
When will the peak cooling loads happen?
• Highest weather temper­ature • Maximum solar gains (window orient­ation) • Maximum internal heat gains • Ignore thermal mass
Why do we need to calculate Peak heatin­g/c­ooling loads
To size the heatin­g/c­ooling equipment, ducts, etc.
Why do we need to calculate these Annual heatin­g/c­ooling energy
To estimate the annual energy use by a system so we can tell the building owners how much it will cost to operate a building with a proposed system.

Thermal Gradient

Calcul­ations

U value calcul­ation
U=1/Su­m<R­>=Btu/h ft2 0F
 

Calcul­ations

U value calcul­ation [Btu/hr ft2 0F]
U=1/Su­m<R>
U value with frames [Btu/hr ft2 0F]
U=1/Su­m<R> where R = Rstud % area stud of sample + Rinsul­ation % area ins of sample
Emissivity
Qemit = εδAT^4 where ε = emissivity of surface
Air Space
1/E= 1/εsub1 + 1/εsub2 - 1
Heat Flow (q) [BTU/hr]
q = u x A x deltaT
Thermal Gradient [BTU/hr]
q = u x A x deltaT
Heat loss through slab-o­n-grade floors
q= F2 x P x deltaT
Heat flow through windows
𝑞 =𝑈𝐴(𝑇𝑖𝑛 −𝑇𝑜𝑢𝑡)
Heat flow through windows pt2
q = ASHGC Et
Heat flow by infilt­ration
qv = V x 1.08 x ΔT
Latent Heat by Infilt­ration or Ventil­ation
qlatent = 4840 x V x ΔW
Simple heat loss calcul­ation
total heat loss = Qwin + Qwalls + Qdoor + ... ...+ Qinfil­tration
Annual Energy Estimation
E heating = UAref ×(HDD) ×(24) / k where UAref = Q heat loss / ΔT
Annual Energy Estimation pt2
Efuel = Eheating / V
F2 (this is not U-value)
heat loss coeffi­cient from above (Btu/h­-ft-F)
Eheating:
Annual heating energy in Btu
UAref : average heat loss rate from a building
HDD: the degree days at the reference temper­ature
k: heating system efficiency
U = U-factors of window assemblies (Btu/h ft2 F)
Q = rate of heat flow (Btu/hr)
SHGC= solar heat gain coeffi­cient
Et= total incident irradiance
deltaW is found on the psycho­metric chat in-out (right side)
Efuel: Amount of fuel
V: heat value of fuel