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Thermal Comfort in Buildings: How to Better Control and Predict

thermal comfort

Controlling and predicting thermal comfort in buildings is essential when designing HVAC systems. The operation schedules of ventilation systems often don’t consider the diurnal fluctuations of either the ambient temperature or the exposure of windows to direct sunlight. Poorly designed and installed ventilation systems can directly affect productivity, particularly in office buildings.

Why is Thermal Comfort in Buildings Important?

Buildings Thermal Comfort SimScale

It’s simple: working in optimal conditions enables us to think and work better. Eliminating potential health hazards is also a very important aspect of maintaining ideal thermal comfort. The lack of both individual and group comfort is detrimental to the overall well-being and productivity of the building’s occupants. Furthermore, it is relatively simple to understand and design adequate HVAC systems from the inception stages, particularly when it comes to individual rooms or single office spaces. Things become somewhat more complicated when considering the design of complete office buildings, where each room and floor have quite different thermal comfort parameters: different number of people, different sizes, placing of windows may differ, diversity of the electronic equipment or the vicinity of special areas such as server rooms, central heating systems, staircases, and other service premises may alter the thermal requirements.

The design and construction of buildings that fit all thermal comfort standards and requirements is a delicate process. For the final design to be energy efficient, we need the essential contribution of the HVAC systems simulation algorithms, which allows us to predict the ventilation and air conditioning systems’ performance.

What is Thermal Comfort?

According to international standard EN ISO 7730, thermal comfort is: “that condition of mind which expresses satisfaction with the thermal environment”. In simple words, is the comfortable condition where a person is not feeling too hot or too cold. [1]

Human thermal comfort cannot be expressed in degrees and can’t be defined by an average range of temperatures. It is a very personal experience and a function of many criteria, which differs from person to person in the same environmental space. The Health and Safety Executive estimates that reasonable comfort can be established when a minimum of 80% indoor occupants are feeling comfortable with the thermal environment. [3]

What Influences Thermal Comfort?

Thermal comfort is a cumulative effect resulting from a series of environmental and personal factors. Environmental factors include [1]:

  • Air temperature — The air contact temperature measured by the dry bulb temperature (DBT)
  • Air velocity (AV) — The air contact velocity measured in m/s
  • Radiant temperature (RT) — The temperature of a person’s surroundings; generally expressed as mean radiant temperature (MRT) which is a weighted average of the temperature of the surfaces surrounding a person and any strong mono-directional radiation, such as the solar radiation
  • Relative humidity (RH) —The ratio between the current amount of vapor in the air and the maximum amount of water vapor that the air can hold at that air temperature, expressed as a percentage.

Personal factors are also important and are independent of the environment:

  • Clothing — Clothes insulate a person from exchanging heat with the surrounding air and surfaces
  • Metabolic heat — The heat produced through physical activity. Usually, a person who stays still feels cooler than those who are moving.

There are other contributing factors that could be considered such as the availability of drinks and food, acclimatization device, or health status of the individual.

How to Control Thermal Comfort with Simulation Software

Buildings Thermal Comfort SimScale

Comparison of velocity streamlines for variation in placements of inlets/outlets. The inlet is on top (and outlet on bottom) is shown on left while the opposite on right.

Whether you are an architect, a civil engineer or an HVAC designer, engineering simulation software can be used to simulate optimal thermal conditions. Inlet and outlet vanes sizes and positions can be optimized to minimize energy costs. Moreover, SimScale can be used for preliminary virtual testing of innovative smart building systems, such as underfloor heating or passive ventilation systems.

The optimization of HVAC systems is based on multiple thermodynamics analyses. Airflow distribution and dynamics can be simulated in any building space, starting from basic aspects such as the infusion of fresh air and removal of stale air, the heating produced by electronic devices, walls insulation, office cubicles or windows/doors exposure to external factors.

You can find more details about the simulation of optimal thermal comfort, the factors that influence it and other practical aspects related to HVAC system design in this article: “How to Improve Thermal Comfort in an Office Environment”.

Moreover, in the SimScale Public Project library, you can find many freely available templates that you could use as starting point to better understand thermal comfort and HVAC systems optimization for different rooms, office spaces, and special building configurations.

White Paper: How to Ensure Thermal Comfort in Buildings with CFD


References

1. “Thermal comfort in buildings”, Designing Buildings Wiki, 2016

2. ISO 7730:2005 – Ergonomics of the thermal environment – Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria, 2005

3. “Health and Safety Executive HSE“, Designing Buildings Wiki, 2016

4. Fabbri, K. – “Indoor Thermal Comfort Perception”, A Brief History of Thermal Comfort: From Effective Temperature to Adaptive Thermal Comfort, Springer International Publishing Switzerland, 2015.

5. Harish, A. – “How to Improve Thermal Comfort in an Office Environment”, SimScale Blog, July 2016.

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