Zone Flow Rate¶
This section contains supplementary information for the Flow Rate property of the Zone Component in the component guide.
The Flow Rate field of a Zone component is a parameter that can be used by flow components (fans, dampers and air-side economisers) to set the flow rate around the system.
Please note that just entering a flow rate here does not mean that this will be the flow rate through the zone. Instead, it will depend on the design flow rate of the nearest flow component, which can be set up to read the value specified in this field.
There are 3 options on setting the flow rate target of a zone. The first one, not used, indicates that the target flow rate is not used in the simulation.
The second option, value, allows the user to type in the flow rate into this field.
The final option is sized. Upon choosing this option, the user is asked to choose from the following seven sizing methods:
Per Floor Area
Per Volume
ACH
Peak Person
Peak Person and Area
Peak IC
Delta T
Per Floor Area¶
TAS Systems asks the user to enter a value in \(l/s/m^2\) (\(\text{cfm}/\text{ft}^2\) in U.S. customary units). This value is then multiplied by the area of the zone to give the flow rate in l/s (cfm in U.S. customary units). Please note that the user can use the size fraction field to over-size or under-size this value.
Per Volume¶
Here TAS Systems asks the user to enter a value in \(l/s/m^3\) (\(\text{cfm}/\text{ft}^2\) in U.S. customary units). The value is then multiplied by the volume of the zone to give the flow rate. Please note that the user can use the size fraction field to over-size or under-size this value.
ACH¶
The Value field here stands for how many air changes per hour the user wishes to size the flow rate on. Please note that the user can use the size fraction field to over-size or under-size this value.
Peak Person¶
TAS Systems asks the user to enter an air rate per person. TAS then uses the following formula to give the sized flow rate:
Where \(OSG\) is the occupancy sensible gain and \(OLG\) is the occupancy latent gain. Both of these values, along with the metabolic rate are read from the zones internal condition.
\(Value\) is the value entered in Systems for the air rate per person.
Please note that the user can use the size fraction field to over-size or under-size this value.
Peak Person and Area¶
The Peak Person and Area method allows the user to size the flow rate on both the Peak Person and Per Floor Area methods.
The user is asked to enter in their flow rates per person and per floor area.
TAS then uses the value entered into the Per Person field in the Peak Person method and the value entered into the Per Area field in the Per Floor Area method.
TAS will then add the results of both of these methods together and report the sum as the flow rate.
Peak IC - Outside Air¶
The Peak Internal Condition method works like the Peak Person method, but instead of asking the user for the air rate per person it uses the Outside Air rate from the zone’s Internal Condition instead.
Please note that the user can use the size fraction field to over-size or under-size this value.
Peak IC - Ventilation¶
The air rate is sized using the maximum value from the Ventilation gain in the zone’s Internal Condition.
Delta T¶
The Delta T method is the default method for sizing the flow rate for a zone.
Upon choosing this method, the user is asked to enter a heating delta T and a cooling delta T. The heating delta T value entered should be:
where the zone’s thermostat is read from the Internal Condition of the zone.
TAS Systems will then work out what is the maximum flow rate required with the supply air heated to this maximum temperature to keep the zone’s temperature above the lower limit.
Please note that this is done using the heating loads from the TSD file, as this sizing is done before the simulation.
The cooling delta T works in a similar way with the zone’s thermostat upper limit. The cooling delta T value entered should be equal to:
where the zone’s thermostat is read from the internal condition of the zone.
TAS Systems will then work out what is the maximum flow rate required with the supply air cooled to this minimum temperature to keep the zone’s temperature below the upper limit.
Please note that this is done using the cooling loads from the TSD file, as this sizing is done before the simulation.
Upon working out the flow rate needed for the heating delta T and the cooling delta T, TAS will take the max of the two as the flow rate for the zone.
Note
The values entered here do not impact the supply air temperatures. It is just used to work out the sized flow rate.
After entering the delta T values, the user will be asked to choose the design condition (or just the simulation data) to choose which days to size the flow rate on.
Please note that the user can use the size fraction field to over-size or under-size this value.