Add Occupants
Internal gains from occupants are accounted for in terms of heat and moisture contributions to the indoor environment. The human body generates heat due to metabolic processes, and a part of that heat is emitted into the environment, which affects the thermal balance inside a building. Furthermore, people release moisture into the environment due to respiration and perspiration.
The occupant density in a Space is typically defined by people per square meter (m²/person). This value is used to specify the number of people in a space and, consequently, the internal gains from people regarding heat and moisture output. For example, if you have a 100 square meter office and specify an occupant density of 10 m²/person, this equals 10 people in the office (100m² / 10 m²/person = 10 people). This occupancy density is then used in conjunction with occupancy schedules to define the variation of occupants (and thus internal gains from occupants) over the day, week or year.
Occupants
To define Occupant density, navigate to 'Spaces' and select the 'Default' Space. Then navigate to 'Occupants'. Next, use the Occupant slider to set the m²/person for the Space.
Activity
To define Activity, navigate to 'Spaces' and select the 'Default' Space. Then navigate to 'Occupants'. Next, use the Activity slider to set the W/Person for the Space.
The metabolic rate of people in a Space is defined as 'Activity' and is measured in watts per person (W/person). This value represents the energy produced by human metabolism, influencing thermal comfort and the energy balance of a building and influences HVAC load calculations. The metabolic rate varies with activity: for instance, a sleeping person has a lower metabolic rate than a person performing heavy physical work.
ASHRAE 55 standard and ISO 7730 define typical values based on different types of activities as follows:
Sleeping: around 70-80 W/person
Seated, quiet (e.g., office work, studying): around 100-120 W/person
Light work (e.g., standing, light manual labour): around 120-160 W/person
Moderate work (e.g., light industrial work, house cleaning): around 165-230 W/person
Heavy work (e.g., heavy industrial work, athletic activity): can exceed 400 W/person
Air Velocity
To define Air Velocity, navigate to 'Spaces' and select the 'Default' Space. Then navigate to 'Occupants'. Next, use the Air Velocity slider to set the m/s for the Space.
Air velocity is a parameter that influences thermal comfort calculations in the environment. This value is generally set as a fixed input and represents the speed of the indoor air in meters per second (m/s).
The air velocity is essential for thermal comfort because moving air can enhance heat loss from the human body through convection and evaporation, making people feel cooler. This effect is especially significant in warm or humid conditions.
In the context of a typical building simulation, the air velocity is often assumed to be relatively low (e.g., 0.1 m/s or less), reflecting the calm conditions inside most modern buildings. However, higher air velocities might be present in spaces with natural ventilation, ceiling fans, or other air movement forms, which can be modelled if necessary.
Clothing Method
To define a Clothing Method, navigate to 'Spaces' and select the 'Default' Space. Then navigate to 'Occupants'. Next, use the Clothing Method dropdown to nominate a method for the Space.
The method of defining clothing insulation will depend on the specifics of your project and the level of accuracy you require. While using a constant or scheduled value might be sufficient for many applications, using a calculated value can provide a more realistic representation of how people might adapt their clothing to changing conditions, potentially improving the accuracy of your thermal comfort predictions.
There are several ways to define the clothing insulation value:
Constant Value: Specify a constant clothing insulation value to be used throughout the simulation. For example, if you're modelling an office building, you might assume a constant clothing level of around 1 clo, which is typical for indoor office attire.
Scheduled Value: Create a schedule that changes the clothing insulation value over time. This allows you to represent seasonal changes in clothing, with higher values in the winter and lower values in the summer, for example.
Calculated Value: Adopt a dynamically calculated clothing insulation value based on indoor and/or outdoor environmental conditions. This is done using a clothing insulation model, such as the one proposed by the ASHRAE-55 standard, which adjusts the clothing level based on the mean monthly outdoor air temperature. According to the 2017 version of ASHRAE 55, the dynamic clothing insulation model is represented by the following formula:
where:
Icl is the clothing insulation in clo
Tavg is the average monthly outdoor air temperature in °C
Clothing
To define Clothing, navigate to 'Spaces' and select the 'Default' Space. Then navigate to 'Occupants'. Next, use the Clothing slider to set the Clo for the Space.
Clothing is the insulation value of occupants and is an important parameter that influences thermal comfort calculations. This value, typically measured in clo (where 1 clo = 0.155 m²K/W), represents the insulation provided by a person's clothing.
Typical values are as follows:
Naked: 0 clo
Underwear: 0.04 clo
T-shirt: 0.09 clo
Trousers: 0.15 clo
Sweater: 0.2 - 0.4 clo
Suit jacket: 0.2 - 0.4 clo
Light overcoat: 0.5 clo
Heavy overcoat: Up to 1 clo
Generally, for a person engaged in typical indoor activities (e.g., office work), the clothing insulation value is assumed to be around 0.5 to 1.0 clo. The exact value can depend on factors such as the outdoor climate, the indoor temperature, age, gender and personal preferences. As such, an actual value is challenging to determine.
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