Metabolic

Activity tab in model data under Occupancy header

Select the level of activity by selecting a metabolic rate component based on the level of activity of people using the space.

The metabolic rate determines the amount of heat gain per person in the zone under design conditions. This value is modified during simulations based on a correlation to account for variations in space temperature.  This should be borne in mind when analysing occupant sensible heat output in the Cooling design and Simulation results screens. Metabolic rate has units Watts per person and represents the total heat gain per person including convective, radiant, and latent heat. An internal algorithm is used to determine what fraction of the total is sensible and what fraction is latent. Then, the sensible gain is divided into radiant and convective portions.

Metabolic rate data can be found in the ASHRAE Handbook of Fundamentals and in CIBSE Guide A.

DesignBuilder default metabolic data is derived from the ASHRAE values and is for adult males having typical surface area of 1.8m2. For women multiply the adult male value by 0.85 and for children multiply by 0.75.

The metabolic factor accounts for people of various sizes.  Enter 1.00 for men, 0.85 for women, 0.75 for children or you can use an average value if there is a mix of sizes.

Background

Heat is generated in the human body by oxidation at a rate called the metabolic rate.  This heat is dissipated from the body surface and respiratory tract by a combination of radiation, convection and evaporation.  The relative proportions of sensible and latent heat from people is a complex function of the metabolic rate and the environmental conditions.

EnergyPlus uses a polynomial function to divide the heat gain into sensible and latent portions. More details can be found in the EnergyPlus EngineeringDoc.pdf documentation.

Note: If the Occupancy latent gains model option is set to Dynamic calculation then the sensible/latent split for occupancy gains is affected by the internal temperature and relative humidity.  With high internal temperatures, people cool themselves largely by evaporation (sweating) and sensible occupancy gains can be very low or even zero as the internal temperature approaches that of the human body.

Clothing

You can define the clothing levels of the occupants for summer and winter periods.  This data is used when generating comfort output.

Clothing reduces the body's heat loss and is classified according to its insulation value. The unit normally used for measuring clothing's insulation is the Clo unit. The more technical unit is m²°C/W is also used frequently (1 Clo = 0.155 m2°C/W). The Clo value can be calculated by adding the Clo value of each individual garment. The insulation value for individual garments can be found in ISO 7730.

Clo-Values for Different Items of Clothing and Ensembles

Note 1: Clo-values are additive, so one can calculate the clo-value for a person wearing a T-shirt and light socks (0.09 + 0.04) = 0.13. (Adapted from ASHRAE Fundamentals and "Technical Review of Thermal Comfort," Bruel and Kjaer, No. 2, 1982.)

Note 2: for equatorial regions where there is no clear 'summer/winter' weather pattern you should generally use a 'summer' value for both summer and winter clo factors.

CO2 generation rate

Enter the carbon dioxide generation rate per person in m3/s-W or (ft3/min)/(Btu/hr). The total carbon dioxide generation rate for the zone is:

Number of People * People Schedule * People Activity * Carbon Dioxide Generation Rate.

The default value is 3.82E-8 m3/s-W (obtained from ASHRAE Standard 62.1-2007 value at 0.0084 cfm/met/person over the general adult population). The maximum value can be 10 times the default value.