Thermal Comfort: Temperature, Humidity and Air Speed

What is thermal comfort, and what does legislation say?

The employee who says "the office is too cold" and the one who says "I'm suffocating" often sit in the same room. Thermal comfort is the state in which a person is satisfied with the temperature of their environment, and it cannot be explained by a single thermometer reading. Thermal comfort measurement therefore looks not only at air temperature but at all the factors affecting the body's heat exchange together.

Annex 1 of the Regulation on Health and Safety Measures in Workplace Buildings and Annexes sets out the following principles on this subject:

• In workplaces, thermal comfort conditions must not disturb employees or adversely affect their physical and psychological state; the temperature of the working environment must suit the way of working and the effort employees expend (item 19).
• Rest rooms, changing rooms, canteens and first aid rooms are kept at a sufficient temperature for their intended use; heating and cooling devices are positioned so as not to disturb employees or create an accident risk (item 19).
• In ventilation systems, air flow must not disturb employees or create sudden, large temperature differences (item 18). Maintenance and filter changes of mechanical ventilation are carried out annually by competent persons (item 17).
• The TS EN 27243 standard may be used in measuring and assessing thermal comfort conditions (item 19).

For places where display screen equipment is used, the Regulation on Display Screen Equipment also requires that equipment does not give off uncomfortable levels of heat into the environment and that humidity is kept at a suitable level.

What temperature should a workplace be?

There is no fixed temperature value for workplaces in legislation; the regulation requires an environment "suited to the nature of the work". Standards define how the appropriate value is determined. The commonly used standard for seated office work is TS EN ISO 7730. This standard calculates the PMV and PPD indices, which predict what proportion of people in the environment will be dissatisfied with the temperature, and divides comfort into categories.

According to the table in EN 16798-1, which is based on this standard, for seated work at the normal level of expectation (category II), the target operative temperature is in the range of 20–24 °C in winter and 23–26 °C in summer. The table assumes heavy clothing (1.0 clo) in winter and light clothing (0.5 clo) in summer; this explains the difference between winter and summer. These values are a starting point: in a shop where people work standing, a warehouse where heavy work is done or a production area with hot processes, the appropriate range is different.

Legislation gives no number for workplace humidity either. The temperature ranges in the same table are calculated assuming 40 per cent relative humidity in the heating season and 60 per cent in the cooling season. When humidity moves significantly away from these levels, complaints increase: very dry air causes dryness of the eyes, nose and throat and static electricity; very humid air prevents sweat from evaporating, causing a stifling feeling and mould growth.

Thermal comfort measurement: which parameters are measured?

Thermal comfort depends on six factors. Four relate to the environment and two to the person:

The properties of measuring instruments and the measurement method are defined in TS EN ISO 7726. In places where people work seated, measurements are usually taken at ankle, waist and head height (about 0.1, 0.6 and 1.1 m), so that the temperature difference between feet and head can also be seen. The measurement also assesses radiant asymmetries, such as a cold window or a hot ceiling, and floor temperature.

Measurements are carried out by laboratories that hold a proficiency certificate from the General Directorate of Occupational Health and Safety covering this parameter. Bursa Sistemer does not have its own laboratory; we plan measurements with authorised laboratories and enter the results into the risk assessment. Art. 8/4 of the Regulation on Risk Assessment requires the necessary measurements to be made to determine exposure levels if no measurement has previously been made for physical hazards. For which measurements are mandatory, see our article on workplaces where environmental measurements are mandatory.

How do you read thermal comfort complaints?

Listening to complaints before measuring shows where the measurement should focus. Complaints often point to a specific cause:

An important point to know about air speed is this: the cooler the environment, the more uncomfortable people find the same air speed. For seated work in category II, EN 16798-1 gives a maximum mean air speed of 0.16 m/s in winter and 0.19 m/s in summer (assuming 40 per cent turbulence). In other words, in winter even an air flow of less than 20 centimetres per second can lead to draught complaints, while in summer the same speed may feel refreshing.

Collecting complaints with a short survey and marking them on a floor plan shows whether the problem is in one area or across the whole floor. Thermal comfort complaints are often addressed together with office ergonomics; for desk and screen layout, see our article on office ergonomics.

Practical fixes for winter

• Entrance doors: Fit a draught lobby or air curtain at shop and office entrances; move tills and reception desks out of the door's direct air flow.
• Cold surfaces: Move desks away from external walls and large windows; use curtains or blinds.
• Floor: Use insulating mats at points where people stand on concrete floors.
• Heater placement: If warm air collects at the ceiling, mix the air with a ceiling fan or by adjusting the vents.
• Portable heaters: Electric or fuel-burning portable heaters carry fire and poisoning risks; if they are used, their locations and rules are defined. For details, see our article on heaters and carbon monoxide poisoning.
• Dressing in layers: Allow employees to adjust their clothing to the environment; clothing is one of the factors determining comfort.

Practical fixes for summer

• Solar control: Use blinds, awnings or solar control film on sun-facing facades.
• Heat sources: Separate heat-generating equipment such as printers, photocopiers and servers from desks.
• Air conditioning settings: Direct vents so that they do not blow straight at employees; avoid low settings that create an excessive difference between indoors and outdoors.
• Ventilation maintenance: Have filters and maintenance done annually by competent persons; a clogged filter both reduces the flow rate and increases complaints.
• Water and breaks: Make access to drinking water easier during hot periods.

In office and retail businesses in Bursa and the surrounding provinces, we address thermal comfort complaints as part of our risk assessment service and, if necessary, plan measurements with an authorised laboratory. You can track measurement and maintenance dates with the OHS calendar. For lighting measurements, see our article on lighting measurement and lux values, and for sector-specific topics, our office and retail page.

Frequently Asked Questions

What temperature should a workplace be?

Legislation does not give a fixed value; it requires the temperature to suit the way of working and the effort employees expend. According to EN 16798-1, which is based on TS EN ISO 7730, for seated work at the normal level of expectation, the target is 20–24 °C in winter and 23–26 °C in summer; the appropriate range is different for heavy work and work done standing.

Is thermal comfort measurement mandatory?

Legislation does not set a fixed measurement frequency for thermal comfort. However, if no measurement has previously been made for physical hazards in the risk assessment, the necessary measurements are made; persistent complaints are also a strong reason to measure.

What should humidity be at the workplace?

Legislation does not give a number; the Regulation on Display Screen Equipment requires humidity to be kept at a suitable level. The temperature ranges in comfort standards assume relative humidity of around 40 per cent in winter and 60 per cent in summer. In heated offices in winter, humidity can drop markedly; complaints of dry eyes and throat are a sign of this and are confirmed by measurement.

What should be done about complaints of air flow from the air conditioning?

First, the direction and flow rate of the vent and the position of the desk are checked. If air is blowing directly onto the employee, the vent is redirected or the desk is moved; if the complaint persists, the air speed is measured and assessed.