Calculating Attic Air Temperature in Winter From Thermal Resistances of Construction Materials
Calculating Attic Air Temperature in Winter From Thermal Resistances of Construction Materials
(OP)
Engineers:
If the inside surface temperatures of wall construction of an interior wall and an exterior wall can be determined from resistances of the materials and interior/exterior temperature differentials, can the temperature of the air in the space in a pipe chase (between the walls) in an attic be determined with reasonable accuracy?
If so, how? Do the calculated surface temperatures of the wall areas exposed to the pipe chase assist in determining the air temperature in the space? If so, how?
Thank you,
DCEngr1
If the inside surface temperatures of wall construction of an interior wall and an exterior wall can be determined from resistances of the materials and interior/exterior temperature differentials, can the temperature of the air in the space in a pipe chase (between the walls) in an attic be determined with reasonable accuracy?
If so, how? Do the calculated surface temperatures of the wall areas exposed to the pipe chase assist in determining the air temperature in the space? If so, how?
Thank you,
DCEngr1





RE: Calculating Attic Air Temperature in Winter From Thermal Resistances of Construction Materials
If so, how? Do the calculated surface temperatures of the wall areas exposed to the pipe chase assist in determining the air temperature in the space? If so, how? "
Not quite sure why you didn't post in the HVAC forum.
The temperature in attic is highly dependent on how much air circulates due to the louvers and intentionally constructed leakiness of the attic, as well as the thermal leakage to/through the ceiling of the floor below.
Define "reasonable"
Your second paragraph doesn't make much sense. Thermal equilibrium requires the temperatures to balance heat flows, so the temperature of a chase has to to dependent on the temperatures around it, since the only other possible heat source/sink is the pipe itself.
TTFN

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RE: Calculating Attic Air Temperature in Winter From Thermal Resistances of Construction Materials
T1 is temperature of the room.
T2a is temperature of the chase on the room side
T3 is exterior temperature.
T2b is the temperature of the chase on the exterior wall side.
T1:T2a is dependent on the materials of the inside wall.
T2b:T3 is dependent on the materials of the exterior wall.
This is only approximate.
RE: Calculating Attic Air Temperature in Winter From Thermal Resistances of Construction Materials
T_air (immediately under the ceiling) will be 3-4 degrees hotter.
But, without knowing air flow through the attic, you know nothing. (As stated above.) You could make lots of estimates and guesses, but you have to start somewhere - get the air temperature of the attic near the pipe chase over at least 3x 24-hour periods. That's what you really want to know.
Now, it's mid-March, your attic may not be -15 deg F as in mid-Dec or January, but you have to start somewhere.
RE: Calculating Attic Air Temperature in Winter From Thermal Resistances of Construction Materials
RE: Calculating Attic Air Temperature in Winter From Thermal Resistances of Construction Materials
Heat flow in = Heat flow out
H = U A dT
U = heat transfer coefficient of wall / roof / floor
A = Area of wall / roof / floor
dt = temperature difference
Let say outside is hotter than inside, so inside will gain heat.
H (from outside) = H (to inside)
Uo x Ao x (To - Tx) = Ui x Ai x (Tx - Ti)
"o" means outside
"i" means inside
if you have more than one wall / roof / floor exposed, just add, and work on your algebra.
[(Uo1 x Ao1) + (Uo2 x Ao2) + ....][To-Tx] = [(Ui1 x Ai1) + (Ui2 x Ai2) + ....][Tx-Ti]
You are looking for Tx
Red flag if I am doing it wrong.