Conduction through external glazing

[adrianchong85]

I have to modelled an office building under a tropical climate (Singapore) and ran ApacheSim. However, the conductive heat gain through glazing is negative which does not seems to make any sense since I have set the indoor temperature at 25 deg C while outdoor temperatures varies between 27 and 32.
Upon a closer look, it seems that the negative values are mainly obtained when during night times during the absence of solar radiation even though outdoor temperatures may be a little higher (approx 26deg C) than the set point of 25 deg C. hence it would seem that conduction through external glazing depends more on solar radiation than the outdoor temperatures. In addition, upon varying the emissivity values, I realised that the conduction through fenestration is highly affected as well.
Hence I would like to ask how solar radiation plays a part in conduction in IES since I though conduction depends mainly on the outdoor and indoor temperatures as well as U values and not so much on solar radiation which is calculated under solar gain or is there something that I have modelled wrongly.

Hope that someone replies to this.

Cheers,
Adrian

[PCully]

Hi,

I've passed this feedback on to those above me as I'd quite like to be able to comment on this. Hopefully have some update for you with clarification quite soon.

Phil

[adrianchong85]

Hi,

I've passed this feedback on to those above me as I'd quite like to be able to comment on this. Hopefully have some update for you with clarification quite soon.

Phil

Hi Phil,

was wondering if there's any updates on this

Cheers,
Adrian

[PCully]

Hi,

Sorry for the delay, I asked one of the thermal team to review this and his conclusions below:

The likely cause of the negative conduction loss through glazing overnight is that the sky temperature is a degree or two below the ambient air temperature. This situation occurs on clear or partially cloudy nights. It affects glazing conduction via the long-wave radiant effect.

Phil