Thermal environment
Thermal Comfort Assessment
Independent PMV/PPD thermal comfort assessments and continuous office temperature monitoring — to BS EN ISO 7730 and BS EN 16798-1 — diagnosing the workplace's most-reported complaint category.
More than just temperature
Thermal comfort is six variables — air temperature is only one of them
The single most-asked workplace IAQ question is: "what should the office temperature be?" The honest answer is that air temperature alone determines very little. The perception of thermal comfort is governed by six variables, four environmental and two personal: air temperature, mean radiant temperature (the temperature of surrounding surfaces), relative humidity, air velocity, clothing insulation (measured in clo units) and metabolic rate (met).
An office at 22 °C air temperature can feel cold if occupants sit next to a single-glazed façade (cold radiant asymmetry), draughty (high air velocity from a supply diffuser), or stuffy (low velocity and high humidity). A thermal comfort assessment measures all six variables and computes the Predicted Mean Vote and Predicted Percentage Dissatisfied per zone, giving a defensible engineering basis for any setpoint or remediation decision.
Thermal complaints are also the leading trigger for occupant interventions that wreck other systems: windows opened in winter (collapsing CO₂ control), supply diffusers blocked with cardboard (creating draught elsewhere), portable heaters under desks (overloading circuits). Solving the thermal complaint is usually the cheapest way to protect the rest of the building services.
Methodology
A thermal comfort assessment
- 1
Stage 01
Briefing & survey
Review of complaint log, HVAC zoning, occupancy density and dress code. Issue of the ASHRAE 7-point thermal sensation survey to occupants of affected and control zones.
- 2
Stage 02
Instrumented deployment
Calibrated temperature, globe-temperature, humidity and omnidirectional air-velocity probes deployed at three heights (0.1 / 1.1 / 1.7 m) across each zone for 5–10 working days.
- 3
Stage 03
PMV/PPD computation
Per-zone, per-hour PMV and PPD calculation in accordance with BS EN ISO 7730, with clo and met estimated from the survey.
- 4
Stage 04
Reporting & remediation
Written report with charted traces, benchmarking against BS EN 16798-1 Cat II, identification of draught/radiant-asymmetry hotspots and a ranked remediation plan.
Benchmarks
Thermal comfort targets
| Parameter | BS EN 16798-1 Cat II | Comfort criterion |
|---|---|---|
| Operative temperature (winter) | 21–23 °C | PPD < 10% |
| Operative temperature (summer) | 23–26 °C | PPD < 10% |
| Relative humidity | 30–60% | — |
| Air velocity (winter) | < 0.16 m/s | Draught risk < 20% |
| Air velocity (summer) | < 0.20 m/s | Draught risk < 20% |
| Vertical temp gradient (0.1–1.1 m) | < 3 °C | Local discomfort < 5% |
Symptoms & complaints
When thermal comfort tips into SBS territory
Persistent headache. End-of-day fatigue that lifts at the weekend. Dry, gritty eyes — particularly in over-heated, low-humidity winter offices. Inability to concentrate in the afternoon. Visible behavioural signs: occupants wearing coats indoors, portable fans in winter, blinds permanently lowered, blankets at desks.
These complaints sit on the boundary between thermal discomfort and Sick Building Syndrome. A thermal comfort assessment isolates the thermal contribution from the rest of the IAQ picture and shows which complaints can be solved by setpoint and balancing work alone, and which need full SBS investigation including ventilation, particulates and VOCs.
FAQ
Thermal comfort assessment — common questions
Too hot, too cold, too draughty?
Commission a six-parameter thermal comfort assessment to BS EN ISO 7730. Call 01322 555566.
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