Room heat loss to open door? - Program Idea

[mkjt88]

Hello all. I've been teaching myself C++ programming and had an idea for a project. I am building a calculator for the heat loss of a room when an outside door/window is open. I'm currently writing out the functions I need to make this happen... Now what I need help with is this. I can't seem to stumble upon a formula I can use to test ambient air to outside air temps through the means of wind or just exposing the two through the door. I guess it's not the best explanation but do you get what I mean?? I plan to add in three variables if necessary to match if higher wind speeds were forcing more cold air in. Anyway any help on how to solve this would be much appreciated.

 

[CWatters]

That's a tricky problem. Consider.. How does any air get in if there is no way for the air to get out? I can think of two mechanisims...

1) Turbulence - allowing air to enter one part of the door opening and exit via another.
2) Convection - cold air enters at the bottom and warm air leaves at the top.

I can see a host of factors altering the amount of ventilation an open door provides. I doubt it's going to be possible to calculate all this from first principles. Probably best see if you can google up data on energy lost from real world trials. Perhaps it's been done for retail stores that have open doors?

If you can find data on typical air flow rates through an open door its possible to caculate the implied heat loss..

The power lost to ventilation is given by:

Power = Temperature delta * Volumetric heat capacity of air * flow rate

If air conditioning is involved it's probably more complicated due to the water content to the air.

 

[CWatters]

I haven't read it but a quick scan might give you an idea of the complexity...

http://www.ecbcs.org/docs/annex_20_air_flow_through_large.pdf

Selected quotes..

Airflow Through Large Openings on Buildings

New studies of interzonal airflow and single sided ventilation at seven laboratories in Europe and Canada, have then been canied out in this project's framework and have led to improved models.

The single sided ventilation studies (chapter 4) were designed to determine the effect of wind on the ventilation and/or heat loss rates through openings in one external wall only. Collaboration between four european laboratories led to the following conuibutions :

- CSTB test house at Bouin, France, with horizontal slit, to measure internal pressures and the effect of air compressibility
- BBRI attic test room at Gent, Belgium, with open window, to monitor long term ventilation rates and assess possible correlations with measured parameters including wind, temperature and surface pressures
- BRE office at Garston, England, with open window, to assess the time dependence of
ventilation rates following the opening of the window, due to the combined effect of the wind and the thermal properties of the room.
- EPFL offices at Lausanne, Switzerland, with open window, to study the energy consequences of user behaviour by measuring the time dependence of cooling induced by natural ventilation for rooms of different thermal mass.

 

[Naty1]

Heat loss is a factor of conduction, convection, radiation. As noted already, with an open door it is VERY complicated.

You can find formulas for calculating heat losses in a closed room...In those, an air exchange flow with the outside, as through window and door frames is assumed.
And they have formulas for various temperature differences and outside wind speed.