The method
Before using the result
- Steady one-dimensional conduction at supplied U-values. Equivalent annual hours at the chosen ΔT are an assumption, not weather modelling.
Worked examples
These original training examples illustrate the method for Certified Energy Auditor (CEA). Use the matching “Load example” button above to explore a variation; example values are not equipment settings or prescribed criteria.
1. Worked example
Compare envelope heat transfer using before-and-after U-values. Treat annual equivalent hours as an explicit assumption rather than a weather prediction.
- Heat-transfer area
- 100 m²
- Inside − outside temperature
- 20 K
- Existing U-value (W/m²·K)
- 1.5
- Proposed U-value (W/m²·K)
- 0.3
- Equivalent annual time at this ΔT
- 2,000 h
- AΔT = 2000 m²·K.
- Before = 1.5 × 2000 W; after = 0.3 × 2000 W.
- Annual difference = 2400 × 7200000 J.
- Existing heat transfer: 3,000 W
- Proposed heat transfer: 600 W
- Heat-transfer difference: 2,400 W
- Annual energy difference: 17,280,000,000 J
2. Comparison example
Compare a different supplied condition using the same method. For Energy Cert Exam, the important check is that the input meaning, units and method assumptions still match the problem.
- Heat-transfer area
- 100 m²
- Inside − outside temperature
- 20 K
- Existing U-value (W/m²·K)
- 1.5
- Proposed U-value (W/m²·K)
- 0.2
- Equivalent annual time at this ΔT
- 2,000 h
- AΔT = 2000 m²·K.
- Before = 1.5 × 2000 W; after = 0.2 × 2000 W.
- Annual difference = 2600 × 7200000 J.
- Existing heat transfer: 3,000 W
- Proposed heat transfer: 400 W
- Heat-transfer difference: 2,600 W
- Annual energy difference: 18,720,000,000 J
Check your understanding
1. Which relationship is used?
Heat loss = UAΔT; energy difference = (Ubefore − Uafter)AΔT × equivalent time.
2. Which assumption should you check first?
Steady one-dimensional conduction at supplied U-values. Equivalent annual hours at the chosen ΔT are an assumption, not weather modelling.
3. How should you verify a different unit system?
Convert every input to the displayed calculation units first. Equivalent physical inputs must give equivalent results; a unit label alone does not convert a number.
Continue with the matching exam topic
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