# Boundary Conditions¶

## Surface Temperatures¶

To specify the temperature of a segment of wall, click on the select button and then double click on the surface. Enter the value and then click on “OK”. All of the segments in the section should have their temperatures specified. The default temperature is 18C. Temperatures should be kept within the range -30C to 130C.

Multiple surface temperatures can be set at the same time. To do this left click on the “select” button, left click on multiple surfaces while holding down the control button. Right click and select “properties” from the pop-up menu. The surface parameters dialog box will then appear.

## Inlets and Outlets¶

Double click on the inlet segment will bring up a dialog box with the following parameters:

• Air Temperature: the temperature of the air coming through the inlet. The value is in centigrade and should be set to a value to -30 and 130 degrees

• Velocity: the speed of the air coming through the inlet. This value is in metres per second and should be set to a value within the range of 0.0m/s to 15.0m/s

• Humidity: the relative humidity of the air coming through the inlet. This value is entered as percentage and should be between 0% and 100%

Outlets have only their velocity specified in m/s.

Let us assume that the rate at which air enters a 6m by 4m room through a small 0.15m inlet is equivalent of 2.7 ach (air changes per hour). For the 1m deep section this is $$6m \times 4m \times 1m =24 m^3$$ multiply this value by the air change per hour. This gives $$24m^3 \times 2.7ach = 64.8m^3$$ per hour or 64.8 $$\frac{m^3} {3600} = 0.018 m^3/sec$$ .

The area of the inlet is 3 cells (at 0.05m per cell) high by effectively 1m deep, i.e. $$0.15m \times 1m = 0.15 m^2$$. The inlet velocity must therefore be $$\frac{0.018m^3/s} {0.15m^2}$$ = 0.12m/s. So, to achieve the equivalent of 6ach through the inlet its air velocity must be set to 0.12m/s. The outlet must be set to the same velocity to conserve mass within the section. If there are a number of inlets and outlets the above procedure should be followed for each of them and the overall volume of air entering the section must be matched by the volume of air leaving the section.

The flow rate is constant throughout the simulation period.

## Gain Regions¶

Double clicking on a gain while the “select” option has been chosen will bring up the gain parameters dialog box. It has the following parameters:

• Sensible gain: the amount of sensible gain in watts for the whole region. The sensible gain can be specified between -9999 watts and 9999 watts

• Latent gain: the amount of latent gain in watts for the whole region. The latent gain can be specified between -999 watts and 999 watts

• Radiant proportion: the radiant proportion indicates how much of the sensible gain is in the form of radiant energy. For a purely convective heat gain the radiant proportion should be set to 0 (zero). If 50% of the gain is radiant the proportion should be set to 0.5.

What follows is an example of how to determine the correct level of gains to be placed in a region:

The section can be thought of as a 1m slice through a space. Gains placed in the regions are representative of the level of gains in the subject space per square metre of floor area. Let us assume that the occupant gain in the subject building is 26.7 $$W/m^2$$ (a teaching space for example). The effective floor area of the section is 6m (the length of the floor) times the section thickness of 1m, i.e. $$6m^2$$. The total occupant gain in the section will therefore be $$26.7W/m^2 \times 6m^2 ~ 160W$$. This is represented in the section by two regions of gain, so each should be given 80W as input. The radiant proportion of this is about 0.3 (30%). The same principle applies to latent gains.

## Domain Parameters¶

Double clicking on anywhere other than a surface or a gain, will bring up the domain dialog box. It has the following parameters:

• Start Temperature: this is the initial air temperature. It is measure in degrees centigrade

• External Work: this value is used in the PPD calculation. It is measured in $$W/m^2$$. The value should be between 0 and 200. The default value is 0, which is correct for most activities.

• Metabolic Rate: this value is measured on a scale from 0 to 4. The default value is 1, which is the value for “seating, relaxed” activities.

• Clothing Value: this value is measured on a scale from 0 to 2. The default value is 0.7 which is the value for a “lighting working ensemble”.

Please check the Appendix for more details on PPD, external work, metabolic rate and clothing value.