Air treatment plays a crucial role in creating optimal indoor comfort conditions, guided by standards like EN ISO 7730, DIN 1946, and ASHRAE Standard 55. These regulations ensure that temperature, humidity, and airflow are balanced to achieve a comfortable and healthy indoor environment for occupants. Let’s take a closer look.

The German word “Behaglichkeit” can be translated to English as “comfort” or “coziness.” In the context of environmental conditions or HVAC, “Behaglichkeit” typically refers to a state of thermal comfort, where the indoor environment is perceived as pleasant and comfortable by occupants.
“Behaglichkeitszustand” can be translated as “state of comfort” or “comfort condition.” This term refers to the specific conditions under which a space achieves thermal comfort, considering factors such as temperature, humidity, and air movement.
So, in summary:
- Behaglichkeit = Comfort or Coziness
- Behaglichkeitszustand = State of Comfort or Comfort Condition
The German term “Behaglichkeit” is particularly noteworthy because it extends beyond just temperature and humidity to also include air movement as a critical factor in achieving comfort. This comprehensive approach enhances overall comfort by creating an environment where all aspects of air quality are considered. Additionally, “Behaglichkeit” evaluates comfort by measuring the number of occupants who feel dissatisfied, providing a holistic view of how well a space meets the needs of its users.
What is Comfort?
Comfort is achieved when the indoor climate and air quality are just right, making a person feel at ease in a space. This applies to both summer and winter conditions and all the in-between seasons.
According to the European standard EN ISO 7730, additional comfort criteria are defined to fine-tune air distribution and room airflow, ensuring optimal thermal comfort. The main factors influencing comfort include room air temperature, the intensity of radiant heat, air movement or airspeed within the room, and the temperature gradient between the floor and shoulder height.
Although not specifically defined as criteria for thermal comfort in the standard, factors such as room acoustics and humidity levels also play a crucial role in achieving overall comfort.
Air States and the Mollier h-x Diagram
Air states
To truly understand air conditions and their properties, it’s essential to consider the physical relationships between temperature and humidity, as these two factors are closely intertwined and influence each other. Our own bodily sensations reflect this connection—when a room is heated, it often feels drier, and when the temperature drops, the air can feel more humid.
These intricate relationships between temperature and humidity are clearly illustrated in the h-x diagram, named after Richard Mollier. First, it’s important to distinguish between relative humidity and absolute humidity.
Relative humidity refers to the percentage of air saturation with water vapor. At 100% relative humidity, the air is fully saturated and cannot hold any more moisture. Any additional moisture will condense into liquid form, appearing as fog or mist—essentially tiny water droplets suspended in the air. These droplets can also settle on surfaces, forming dew. On the other hand, 0% humidity represents completely dry air that contains no water at all, not even in vapor form—this is a theoretical value rarely achieved in practice.
Absolute humidity indicates the total water content in the air, typically measured in grams of water per kilogram of air.
In the Mollier h-x diagram, besides temperature, absolute humidity, and relative humidity, the concept of enthalpy is also represented. Enthalpy is the measure of the energy content of the air, showing that warm, humid air naturally contains more energy than cold, dry air. Additionally, the diagram also depicts the density of the air, measured in kilograms per cubic meter. It’s clearly shown that warm air is lighter than cold air, and this relationship is almost independent of the air’s humidity level.
In the h-x diagram, temperature is represented vertically, while absolute humidity is displayed horizontally. The curves for relative humidity run from the lower left to the upper right, while enthalpy is represented as a straight line running from the upper left to the lower right. Air density is slightly inclined, decreasing as absolute humidity increases.
This diagram allows for the precise determination of any air condition and the relationships between temperature, absolute and relative humidity, and energy content—all relative to standard atmospheric pressure at sea level.
The range between 30% and 65% relative humidity and temperatures between 20°C and 26°C, limited by a maximum absolute humidity of 11.5 g/kg of air, is defined as thermal comfort according to DIN 1960.
Within this range, optimal indoor air quality is achieved under normal conditions (in living spaces, workplaces, and recreational areas), which is the goal for any ventilation or air conditioning system.
All air conditions can be plotted on the Mollier h-x diagram. There are no air conditions beyond the 100% relative humidity line, as air can only hold water in gas form up to this saturation point.
This line is also known as the condensation line. Any water exceeding the 100% humidity threshold will immediately appear in liquid form, first as tiny water droplets, which we see in nature as fog at ground level or as clouds higher up.
These droplets can also settle on surfaces that are at or below the dew point temperature. In buildings, this phenomenon appears as damp surfaces, which can promote mold growth due to the presence of liquid moisture. To prevent mold formation, it is important to ensure that no wall surfaces in a room fall below the dew point temperature.
Mollier h-x Diagram
We have prepared a basic Description of the Mollier h-x Diagram:
Axes
– Horizontal Axis (x-axis): Represents the specific humidity or *absolute humidity typically ranging from 0 to 20 grams of water per kilogram of dry air (g/kg).
– Vertical Axis (y-axis): Represents the dry-bulb temperature, usually ranging from 0°C to 50°C.
Relative Humidity Curves
– Curved lines on the diagram indicate relative humidity levels, labeled from 0% to 100% in increments (e.g., 10%, 20%, …, 100%).
Thermal Comfort Zone Boundaries
– Temperature Range Draw vertical lines at 20°C and 26°C to represent the lower and upper temperature bounds.
– Relative Humidity Range: Identify the 30% and 65% relative humidity curves.
– Absolute Humidity Limits: Horizontal lines can be drawn at approximately 6 g/kg and 12 g/kg to represent the typical absolute humidity range.
Additional Elements
– Enthalpy Lines: Diagonal lines representing constant enthalpy can be included, though they are not primary boundaries for the comfort zone.
– Annotations:Label the axes, curves, and shaded comfort zone for clarity.
Comfort Zone
The thermal comfort zone on the Mollier h-x diagram typically falls within the following coordinates:
– Temperature (x-axis):Generally between 20°C to 26°C (68°F to 79°F).
– Absolute Humidity (y-axis): Typically between 6 g/kg to 12 g/kg of dry air.
This zone is further bounded by:
– Relative Humidity Curves: Between 30% and 65%.
– Enthalpy Lines: Enthalpy values usually range from about 30 kJ/kg to 50 kJ/kg within this comfort zone.
These coordinates represent the conditions where most people feel thermally comfortable, as defined by various standards, including DIN 1960. The exact boundaries can vary slightly depending on specific requirements or the demographic being considered (e.g., climate, clothing insulation, activity level).
In a Mollier h-x diagram, this thermal comfort zone would appear as a distinct area within these temperature and humidity limits, typically showing where occupants are likely to experience the highest levels of comfort under normal indoor conditions.

Thermal Comfort Zone Sensor: real-time indoor comfort assessment
At Andivi, we’ve engineered a sensor that goes beyond simply measuring temperature, humidity, and pressure. Our advanced sensor also computes dew point, enthalpy, and the density of moist air, providing a comprehensive overview of indoor environmental conditions.
But we didn’t stop there. We’ve enhanced this sensor by integrating thermal comfort indicators, enabling it to assess whether an environment falls within:
– The Optimal Comfort Zone (reflecting ideal conditions for maximum wellbeing),
– The Extended Comfort Zone (representing acceptable comfort levels), or
– Outside the Comfort Zone (indicating conditions that may compromise comfort).
This sophisticated capability allows us to monitor the comfort levels in various zones—whether rooms or open spaces—over time, offering valuable insights into the overall comfort within a building.
Moreover, the sensor helps maintain optimal humidity levels by issuing alerts if the indoor climate becomes too dry or too humid. This serves as a critical data point for triggering actions such as humidification or dehumidification, ensuring that indoor environments remain comfortable and conducive to wellbeing.
All the data points mentioned are calculated directly within the sensor and are grounded in the definition of the thermal comfort zone as specified by DIN 1960.
This standard ensures that, under typical conditions—whether in living spaces, workplaces, or recreational areas—the environment maintains optimal indoor air quality.
This alignment with DIN 1960 means our sensor not only provides real-time comfort assessment but also supports the precise control of ventilation and air conditioning systems, ensuring that they consistently meet the highest standards of comfort and wellbeing.
EN ISO 773
The international standard EN ISO 7730 focuses on the evaluation of thermal comfort in indoor environments. The standard provides methods for predicting and assessing thermal comfort using a combination of physical measurements and human factors. The key concepts covered by EN ISO 7730 include:
Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD):
– PMV: The standard introduces the Predicted Mean Vote (PMV) index, which predicts the average thermal sensation of a large group of people in a given environment. The PMV scale ranges from -3 (cold) to +3 (hot), with 0 representing a neutral thermal sensation.
– PPD: The Predicted Percentage Dissatisfied (PPD) index estimates the percentage of people likely to be dissatisfied with the thermal environment. It is derived from the PMV and provides an understanding of how well an environment meets thermal comfort requirements.
Thermal Comfort Criteria:
– Air Temperature: The standard considers the indoor air temperature as a crucial factor for thermal comfort.
– Radiant Temperature: The influence of surface temperatures, which can affect perceived comfort through radiant heat exchange, is also considered.
– Air Velocity: Air movement or air velocity in the space is taken into account, as it can influence how warm or cool a person feels.
– Humidity: While not a primary factor in PMV calculations, humidity can affect comfort by influencing sweat evaporation and overall perception of the environment.
– Clothing and Metabolic Rate: The standard also accounts for the impact of clothing insulation (measured in clo units) and metabolic rate (related to the activity level of occupants) on thermal comfort.
Categories of Thermal Environment:
EN ISO 7730 defines three categories of indoor environments based on the level of thermal comfort provided:
– Category A: High level of comfort, suitable for spaces where occupants have higher expectations, such as office buildings.
– Category B: Moderate level of comfort, acceptable for most standard indoor environments.
– Category C: Basic level of comfort, tolerable in spaces where less stringent comfort criteria are acceptable.
Application and Use:
EN ISO 7730 is widely used in the design and assessment of HVAC Systems, as well as in building certification processes. It helps engineers and designers create environments that are thermally comfortable for the majority of occupants by using the PMV and PPD indices as guidance.
In summary, EN ISO 7730 provides a comprehensive framework for evaluating and ensuring thermal comfort in indoor environments by considering a range of environmental and human factors. It is a key tool in creating comfortable and energy-efficient indoor spaces.
DIN 1960
DIN 1960 is not a specific standard; rather, it typically refers to a broad range of German standards. However, based on the context provided earlier regarding thermal comfort and air quality, it’s likely referring to guidelines within the framework of German standards that deal with indoor environmental conditions.
In the context of thermal comfort, DIN 1960 can be understood as part of the standards that define the optimal indoor climate conditions in terms of temperature and humidity for human comfort. Specifically, it establishes the following:
Thermal Comfort Range
Defines the acceptable range of indoor conditions that ensure a comfortable environment for occupants. This range typically includes relative humidity levels between 30% and 65%, and temperatures between 20°C and 26°C, with a maximum absolute humidity of 11.5 g/kg of air.
Application Areas
The standard applies to spaces like living areas, workplaces, and recreational facilities, where maintaining optimal indoor air quality is crucial for comfort and health.
Objective
The goal is to create an environment where occupants feel comfortable, without experiencing discomfort due to excessive heat, cold, dryness, or humidity.
This framework is used in the design and operation of HVAC systems to ensure that indoor spaces meet the defined criteria for thermal comfort, contributing to the well-being and productivity of occupants.
ASHRAE Standard 55
ASHRAE Standard 55, Thermal Environmental Conditions for Human Occupancy, sets the benchmark for designing indoor environments that prioritize occupant comfort. This standard outlines the essential factors that must be managed to ensure that indoor spaces meet the thermal comfort needs of the majority of occupants.
Understanding and implementing these guidelines is key to creating spaces that are not only comfortable but also adaptive, sustainable, and responsive to occupant needs.
Holistic Comfort Criteria
ASHRAE 55 emphasizes that thermal comfort is not merely a function of air temperature but results from a complex interplay of factors, including air temperature, radiant temperature, humidity, air speed, clothing insulation, and metabolic rate. The standard advocates for a comprehensive approach that considers all these variables to create environments where occupants feel comfortable and at ease.
Adaptive Comfort Model
Recognizing that comfort can vary depending on the climate, ASHRAE 55 introduces the Adaptive Comfort Model. This model accounts for the fact that people naturally adapt to their environments over time, particularly in naturally ventilated spaces. The standard provides guidelines for adjusting thermal comfort criteria based on outdoor temperatures and occupant expectations, making it more relevant to real-world conditions.
Environmental Control and Flexibility
ASHRAE 55 stresses the importance of allowing occupants some degree of control over their environment, whether through personal fans, adjustable thermostats, or window operability. This flexibility can significantly enhance perceived comfort by empowering individuals to tailor their immediate surroundings to their preferences.
Curious about the ongoing “office thermostat wars”? Find more about it in our blog Why Office Thermostat Wars Will Never End (But Here’s How to Survive Them)
Acceptable Comfort Ranges
The standard defines specific comfort zones that are considered acceptable for the majority of occupants, typically falling within a range of 20°C to 26°C (68°F to 79°F) for temperature, with relative humidity between 30% and 60%. It also specifies limits on air movement and radiant temperature asymmetry to avoid localized discomfort.
Measurement and Verification
To ensure compliance with the standard, ASHRAE 55 outlines methods for measuring and verifying thermal comfort. This includes on-site evaluations and the use of instruments to monitor air temperature, humidity, and air velocity, among other factors. Regular monitoring ensures that spaces consistently meet the comfort criteria, adapting as needed to maintain optimal conditions.
Importance of Long-Term Comfort
Finally, ASHRAE 55 highlights the significance of maintaining thermal comfort over time. It’s not just about meeting comfort criteria at one point in time but ensuring that these conditions are sustained throughout various seasons and usage patterns. This long-term approach ensures that spaces remain conducive to productivity, wellbeing, and overall satisfaction.
Comparing ASHRAE Standard 55, DIN 1960, and EN ISO 7730: A Unified Approach to Thermal Comfort
When it comes to creating thermally comfortable indoor environments, three major standards—ASHRAE Standard 55, DIN 1960, and EN ISO 7730—serve as the cornerstones of HVAC design and building operations. Although they originate from different regions and have their own unique features, these standards share a common goal: ensuring the thermal comfort of occupants. Let’s explore the similarities and differences between these standards, particularly from the perspective of enhancing thermal comfort in various indoor settings.
Commonalities
Focus on Occupant Comfort:
All three standards—ASHRAE 55 (U.S.), DIN 1960 (Germany), and EN ISO 7730 (International)—are fundamentally centered on the concept of thermal comfort for building occupants. They provide guidelines for creating indoor environments that promote comfort and well-being, emphasizing the need to balance multiple environmental factors such as temperature, humidity, air movement, and radiant heat.
Comprehensive Approach to Comfort:
Each standard takes a holistic approach to thermal comfort, recognizing that it is influenced by a combination of environmental and personal factors. These include air temperature, humidity, radiant temperature, air velocity, clothing insulation, and metabolic rate. By addressing these factors collectively, the standards aim to create environments that are not just functionally efficient but also pleasant and supportive of human health.
Comfort Zones:
All three standards define specific comfort zones that are deemed acceptable for the majority of occupants. These zones typically fall within a similar range of temperature and humidity, ensuring that indoor environments are conducive to comfort in various climates and building types. This shared focus on defining acceptable comfort ranges helps in designing HVAC systems that meet the needs of diverse populations.
Differences
Geographical and Cultural Context:
ASHRAE 55 is primarily used in North America, while DIN 1960 is rooted in German standards, and EN ISO 7730 is recognized internationally. These geographical differences reflect regional variations in climate, building design, and cultural expectations regarding comfort. For example, EN ISO 7730 incorporates adaptive comfort models that take into account regional climatic conditions and occupant behaviors, while ASHRAE 55 also includes adaptive models specifically for naturally ventilated buildings.
Adaptive Comfort Models:
While both ASHRAE 55 and EN ISO 7730 include adaptive comfort models that adjust comfort expectations based on outdoor conditions and occupant adaptation, DIN 1960 focuses more on defined comfort zones without explicitly incorporating adaptive strategies. This makes ASHRAE 55 and EN ISO 7730 more flexible in addressing comfort in naturally ventilated buildings and varying climates, whereas DIN 1960 adheres more closely to fixed parameters.
Measurement and Compliance:
EN ISO 7730 and ASHRAE 55 provide detailed methodologies for measuring and verifying thermal comfort, including the use of indices like Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD). These indices help quantify comfort and dissatisfaction levels within a space, offering precise tools for compliance and monitoring. DIN 1960, while also focused on comfort, does not emphasize these indices as heavily, instead relying on broader comfort zone definitions.
Specificity and Scope:
EN ISO 7730 tends to be more specific and technically detailed in its guidelines, making it highly suitable for complex building projects that require rigorous compliance with international standards. ASHRAE 55, while also detailed, offers a broader scope with flexibility in interpretation, especially in naturally ventilated spaces. DIN 1960 is more straightforward, focusing on clearly defined thermal comfort ranges, making it easier to apply in standard residential or commercial buildings.
Conclusion
While ASHRAE Standard 55, DIN 1960, and EN ISO 7730 each have their own unique characteristics and regional applications, they all converge on the importance of creating thermally comfortable indoor environments for occupants. Their shared emphasis on a holistic approach to comfort, alongside their specific regional adaptations and technical methodologies, make them indispensable tools in the HVAC industry. Understanding the nuances of these standards allows HVAC professionals to design and operate systems that not only meet compliance requirements but also enhance occupant well-being across different climates and building types.
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This article was conceptualized by Danijel Mursic, a mechanical engineer and thermodynamics expert with over 30 years of experience in the AHU and HVAC sector and former CEO of Menerga Slovenija.