I’m studying the thermal comfort of a semi-exterior space, which I define as a transitional area between the outdoors and a conditioned interior space, such as a covered railway or airport hall. The goal of my research is to determine whether it’s more efficient to leave this space open or to enclose it, considering the implications of higher energy consumption and larger HVAC systems if enclosed. For this analysis, I’m assuming the worst-case scenario of low wind speeds (1 m/s), is primarily influenced by the ceiling fans.
I’m struggling to understand the differences between OUT_SET, SET, and PET, and when it’s appropriate to use each one. I know that SET is commonly used for indoor spaces when airspeed exceeds the PMV limits, but I’m unclear on how SET differs from OUT_SET. I assume it has something to do with how each responds to solar radiation in outdoor environments.
Additionally, I haven’t been able to pinpoint any major differences between SET and PET, but my results show significant variations in equivalent air temperature. Are the comfort classifications for SET and PET the same? I couldn’t find a comfort classification specifically for SET.
Any insight will be greatly appreciated.
The short answer is that it doesn’t. The way that SET is calculated is the same for the indoors as it is for the outdoors. It’s just that, when SET is calculated for outdoor conditions they call it OUT_SET (just to confuse us all).
If you are just tallying hours that are too hot vs. cold vs. neutral, you probably won’t find big disagreements between comfort models in general. But there are significant differences between PET and SET. PET is much newer than SET and the major advantage that PET has over SET is that PET allows you to customize several physiological aspects of the human subject, including age, sex, height, weight and posture. In Ladybug Tools, these customizations are done with the LB PET Body Parameters component.
The other advantage PET has over SET is that it’s the only model we have in Ladybug Tools, which can give you an estimate of the core body temperature of the human subject. So PET allows you to answer questions like “are these conditions for this type of human subject likely to cause hypothermia or hyperthermia?” Conversely, the SET model really isn’t equipped to give guidance about extreme cases like hypothermia or hyperthermia.
If you don’t have a case where you are studying a particular type of human subject (eg. children or the elderly) and you aren’t looking at extreme thermal conditions, then you’re probably fine just using SET. But, more often than not, I recommend PET for studying outdoor thermal comfort over SET because I think it’s better equipped to give guidance on the wide range of conditions that you tend to find in the outdoors.
