Method
Steady one-dimensional thermal resistance, U-value and Q=UAΔT.
Equations
Rn = dλeach layer
RT = Rsi + Σ(d / λ) + Rso
U = 1RT
Q = U · A · ΔT
Symbols and units
| Symbol | Quantity | Unit |
|---|---|---|
| Inputs | ||
| A | Area | m² |
| ΔT | Inside-outside temperature difference | K |
| Rsi | Inside surface resistance | m²K/W |
| Rso | Outside surface resistance | m²K/W |
| Layers: one row each | ||
| d | Layer thickness | m |
| λ | Layer thermal conductivity | W/m·K |
| Results | ||
| Rn | Resistance of each layer | m²K/W |
| RT | Total resistance | m²K/W |
| U | U-value | W/m²K |
| Q | Heat transfer | W |
| Q | Heat transfer | kW |
Assumptions and limits
- Film resistances are supplied, not defaulted.
In practice
- Enter one row per layer, in any order. Surface resistances are inputs: take them from the standard your project follows.
Worked example
The input values are the calculator's own verification test, run through the calculator. They show the working; they are not design values.
Inputs
| A | Area | 10 m² |
| ΔT | Inside-outside temperature difference | 20 K |
| Rsi | Inside surface resistance | 0.13 m²K/W |
| Rso | Outside surface resistance | 0.04 m²K/W |
Layers
| d (m) | λ (W/m·K) |
|---|---|
| 0.1 | 0.5 |
Results
| Rn | Resistance of each layer | 0.2 m²K/W |
| RT | Total resistance | 0.37 m²K/W |
| U | U-value | 2.7027 W/m²K |
| Q | Heat transfer | 540.541 W |
| Q | Heat transfer | 0.540541 kW |
A preliminary check for engineer review, not an engineering approval. The project calculation to the applicable codes, authority requirements and specification governs.