About Overheating Risk Assessment
The overheating risk assessment tool checks summer thermal comfort against the CIBSE TM59 and TM52 adaptive criteria, with EN 15251 and ASHRAE 55 comfort models also supported. It is used by building physicists and designers to demonstrate that free-running and mixed-mode spaces will not overheat.
Describe the room, glazing, thermal mass, ventilation strategy, and climate; the tool runs an hourly thermal simulation, derives the adaptive comfort limit, and reports a pass or fail against each criterion with a peak-day temperature profile.
How It Works
- Set the standard, room type, ventilation strategy, glazing, thermal mass, and monthly climate data.
- Compute the running mean outdoor temperature and the adaptive comfort temperature limit.
- Run an hourly single-zone simulation to estimate indoor temperatures across summer months.
- Evaluate the TM52 criteria (hours of exceedance, daily weighted exceedance, absolute deltaT) and the TM59 bedroom limit, then report pass or fail.
Worked Example
With a running mean of 21 C under TM52/TM59, the comfort temperature is Tcomf = 0.33 * 21 + 18.8 = 25.7 C and the upper limit is 28.7 C. A peak indoor temperature of 31 C gives deltaT = 31 - 28.7 = 2.3 K, which passes Criterion 3 (deltaT <= 4 K).
Formulas
- Adaptive comfort temperature
Tcomf = 0.33 * Trm + 18.8- Upper comfort limit
Tupper = Tcomf + 3- Running mean outdoor temperature
Trm = 0.50 * Tm + 0.33 * Tm1 + 0.17 * Tm2- TM52 absolute exceedance (Criterion 3)
deltaT = Tindoor_max - Tupper
Standards & References
- CIBSE TM59
- CIBSE TM52
- EN 15251
- ASHRAE 55
Frequently Asked Questions
Which overheating standards does this tool assess?
It assesses CIBSE TM59 and TM52, plus the EN 15251 and ASHRAE 55 adaptive comfort models, applying the relevant comfort coefficients and exceedance criteria for each.
What are the three TM52 criteria?
Criterion 1 limits hours of exceedance to 3% of occupied hours; Criterion 2 limits the daily weighted exceedance to 6 K-hours; Criterion 3 limits the absolute temperature above the comfort limit to 4 K. A space must satisfy at least two of the three.
How does TM59 differ from TM52 for bedrooms?
TM59 adds a fixed bedroom criterion: the operative temperature must not exceed 26 C for more than 1% of annual night-time occupied hours, in addition to the TM52 criteria.
Is the overheating risk tool free to use?
Yes, it runs entirely in your browser at no cost and stores none of your input data.