RE: [EnergyPlus_Support] Re: Shading Mask

Very good description. However, I would like to add a little more details.

1) Bare wooden table top increased surface and cool by room air convection.

2) Table covered with glass, convection is not so effective, and the table surface may remain hot for a longer time, zone mean radiation temperature (ZMRT) may be higher.

3) Metal top table. heat is conducted to other part of the table and then removed by convection.

4) Highly reflective The beam is reflected to heat other surfaces in the zone. A concaved reflecting surface may cause a fire in the zone.

Becareful with small thermal plastic objects. They may melt and distort in shape.

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With a table, the bean would be blocked from heating the floor directly. The effect may be small, because the aborption coefficient of the table may be small, and the rest of the radiation is diffused and convected onto all the surfaces, including the floor. The colour of the table is related to the absorbtion amount of the visible spectrum.

Even if the beam hit the floor directly, the floor surface temperature will stay a while at the ZMRT and then settle to ZMAT by convection. On the ground floor, the floor is also cooled from below at the same time.

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Dr. Li

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: jeannieboef@xxxxxxxxx
Date: Mon, 14 Nov 2011 18:23:28 +0000
Subject: [EnergyPlus_Support] Re: Shading Mask

First a little background...Solar radiation has a large spectrum of different wave lengths. Most of the total energy of all the wave lengths lay in a small band around the infrared range. This means that most of the solar energy hitting a window does not pass through, but is reflected or absorbed by the glass which then heats up and reradiats at a different frequency. Of the solar energy that can pass directly through the glass (such as the visual spectrums), those would hit a surface like a desk and be mostly absorbed together with the reradiated (now diffuse) radiation from windows and other sources. Wood, having little mass, and low conductivity, will heat up almost instantaniously only on its very outer surface and inturn reradiate this energy difusely to surroundings which due to it's geometric relation (form factor) would be mostly to the ceiling. All things being equal, the room surfaces will transfer some of this energy to the room air through convection.

The point is that the heated desk will almost instantaniously heat up either the walls, ceiling and or floor, which will then heat the air. Furniture increases the conduction surfaces in a room as well as the internal mass. There is an object for internal mass that you could use to approximate this effect. If I am correct, you could even insert an internal surface into your zone to do the same. If it would shade the floor is a good question, which I've seen answered in the io ref, but I can't remember, sorry.

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