Thermal comfort refers to a person's subjective satisfaction with the thermal environment. In this state, an individual feels comfortable – not too hot or too cold – whilst wearing normal clothing. Considering the thermal comfort of occupants is crucial when designing a building, particularly offices and warehouses, as it impacts well-being and productivity. At Jet Black Fan Systems, we work alongside engineers to provide a solution that enhances thermal comfort.
Environmental factors such as air temperature, humidity, radiant temperature, and air velocity influence thermal comfort, as well as personal factors including metabolic rate, activity level and clothing insulation. The heat experienced by a person is not solely determined by air temperature, but rather by the temperature of the skin. Fans are an effective method of improving thermal comfort, as the cooling breezes passing over the skin can make occupants feel up to 6°C cooler, without lowering room temperature.
Thermal Comfort Indices: PMV and PPD
PMV
PMV or ‘Predicted Mean Vote’, predicts the mean response of a large group of people on a 7-point thermal sensation scale, from +3 (hot) to –3 (cold) with 0 being neutral. The metric is designed for fully mechanically ventilated buildings and is determined in accordance with ANSI/ASHRAE Standard 55. PMV can be significantly influenced by strategic fan placement, as air velocity affects both convective and evaporative heat transfer – both of which play a role in thermal comfort.
PPD
In the context of thermal comfort, PPD stands for ‘Predicted Percentage of Dissatisfied’ and is an index to predict the percentage of people likely to be uncomfortable with the thermal conditions of a space. This is calculated based on the PMV, with higher PPD values indicating that a greater number of occupants would experience discomfort related to excessive heat or cold.
SpecLab
At Jet Black Fan Systems, we work with specifiers using a proprietary tool called SpecLab – a form of Computational Fluid Dynamics or CFD – to ensure delivery of a solution that positively impacts the PMV and PPD of buildings. While most fan companies require substantial investment to produce a CFD, SpecLab allows us to provide rapid, complimentary assessment of thermal comfort – so specifiers can make informed decisions.
How Fans Improve Thermal Comfort:
High Volume, Low Speed (HVLS) fans can provide perceived cooling up to 6°C without lowering ambient temperature. This effect occurs through convective heat transfer and evaporative cooling of the skin, enhancing the body’s thermoregulatory processes.
HVLS fans are particularly effective at managing vapour pressure differentials in hot and humid climates. As people sweat, they release sensible and latent heat, and if the vapour pressure of the humidity is higher than the body, the body loses its ability to shed heat via evaporation. HVLS fans increase air speeds, leading to increased evaporative cooling effectiveness.
In conjunction with HVAC systems, fans allow for raising thermostat settings to reduce energy consumption without sacrificing comfort. For year-round efficiency, HVLS fans can be set at slow speeds to direct warm air from ceiling height down to occupant level, creating an even temperature throughout the space. Directional fans allow staff to adjust fan speed and direction, based on their comfort needs, without significant impact on energy consumption (unlike adjusting thermostats).
Final Thoughts
Considering thermal comfort is essential for designing productive, comfortable spaces. Strategic fan placement can create spaces that maintain optimal comfort while minimising energy consumption.
At Jet Black Fan Systems, we work closely with specifiers to provide data-driven solutions using computational tools like SpecLab. This ensures that your comfort solutions are not just theoretical but practically effective for your specific application.
Request a SpecLab here, or get in touch with our experts by calling 09 217 6801 or emailing us at customerservice@jetblackfans.co.nz
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