INDOOR DESIGN CONDITIONS

[Adnan86]

Hi, I have been looking for the answer of one basic question for so long and I hope I will find some interesting answers here. My question is related to Indoor design conditions. In summer, we generally keep indoor temperature 24C. But in winter why the indoor temperature is set to 21C. Irrespective of the season, the human comfort remains the same within the building. Please explain.

 

[Zesti]

People dress differently in summer and winter.

When it is cold outside (winter) people will wear warmer clothing which they will also wear when going indoors. Therefore, 21 degrees inside is more than enough.

In summer, people dress lightly and 24 degrees is considered comfortable.

 

[Adnan86]

Zesti, that sounds something logical. Does that mean that in order to save energy, the indoor temperature in winter is maintained at 21C rather than 24C? Does humidity play any role in this case?

 

[Zesti]

It is not energy saving that is the main reason, it is the comfort of the people.
In winter, higher than 21 degrees is not needed. And, depending on the outdoor climate you are in, 24 degrees inside in summer might also be too low.

Cold winter air is very dry. Bringing this into the building can cause problems for people with contact lenses, for instance.
So, humidity does have some comfort issues attached to it. But, having humidification in an office HVAC system is a bit of a luxury. For hospitals, it is more necessary.

 

[Noway2]

There are several aspects to human comfort with regards to air temperature. As Zesti mentioned, humidity is a big factor. Human comfort is related more to the wet bulb temperature than the dry bulb temperature, the former accounts for humidity. In dry air, it takes less energy to make the air feel warmer. Other factors include thermal radiation (heat transferring from warmer to colder sources), convection heating caused by sunlight, and air movement.

 

[urgross]

ASHRAE 55 might provide a suitable explanation.

 

[Adnan86]

Thanks guys for all your good responses. Zesti and Noway2, your explanation helped me a lot. Urgross I will look into ASHRAE 55. Thanx once again.