QUESTION:

I am simulating the lighting in two rooms -- one on the ground floor and one above it on level 1. When I change the internal reflectance of the floor in the first room and change nothing in the second room, it changes the result of the lighting analysis in the second room !

What could be causing this error ?

ANSWER:

Firstly I have done a couple of models to help explain this situation, they are:

DFavg-notright.eco & DFavg-right.eco

In DFavg-notright.eco although you would consider the two rooms as separate, ECOTECT does not understand this as they haven't been modelled as two separate Zones.

This is very important when you are looking at any Zone based calc. or numbers as you were -- that is, the "average" value for the Zone.

Because all the geometry is on the same Zone, according to ECOTECT they are the same space. Thus any change you make to a material (whether it be thermal or lighting etc.) is going to have an effect on the whole Zone.

ECOTECT is just a dumb computer program, and as such cannot understand that just because you put the right amount of geometry in and call it the right thing, that a complete separate space will result. The Zone definition is fundamental to the idea of separate spaces/rooms/volumes of air etc.

In DFavg-right.eco I have modelled the geometry correctly as two separate Zones. This is the correct way to go about things given that the only way ECOTECT can understand "rooms" is by the user modelling them as separate Zones.

Finally, I have also added some extra geometry to this correct model in the form of window reveals, and adjusted the material reflectance’s slightly. We have found that DF calcs tend to be a lot more accurate with this extra bit of geometry, and reflectance’s as follows:

ceiling = 0.7
floor = 0.2
wall = 0.5

So after that we are pretty happy with the Avg. value of 1.64% for both.

Note: Having said that ECOTECT is a dumb computer program, I should be fair and add; that if you had done an inter-zonal adjacency calc. ECOTECT would have told you that there were errors in your model relating to the Zone geometry.

So it does try to help out as best it can...