# Fan Design Flow Source¶

The Design Flow Source option allows the user to choose how they wish to set the design flow rate for the fan components.

The design flow rate, along with the other design values, are used during the design flow calculation to fix the capacities of the flow components (fans, dampers and air-side economisers) without a fixed capacity.

When modelling a Constant Air Volume system, this design flow calculation will lead to the design flow rate being the flow rate of the air path the component is on.

When modelling a Variable Air Volume system, the design flow calculation will lead to the design flow rate tending to be the maximum allowed flow rate for the air path the component is on.

However, there can be instances, where the max flow rate will exceed the design flow rate.

Please note that it is recommended that all flow components (fans, dampers and air-side economisers) on the same air path have the same design flow rate, as setting different design flow rates will cause inconsistent design flow rate errors.

In TAS Systems, the user has the following options for the design flow source:

• None

• Value

• All Attached Zones Flow Rate

• All Attached Zones Fresh Air

• All Attached Zones Sized

• Nearest Zone Flow Rate

• Nearest Zone Fresh Air

• Nearest Zone Sized

## None¶

Upon choosing this option the user will be asked to enter the capacity of the fan.

## Value¶

Upon choosing this option the user will be asked to enter the design flow rate.

## All Attached Zones Flow Rate¶

With this option TAS will add up the flow rate of every zone in this system connected to the fan by ducts and use this as the design flow rate.

## All Attached Zones Fresh Air¶

With this option TAS will add up the fresh air rate of every zone in the system connected to the fan by ducts and use this as the design flow rate.

## All Attached Zones Sized¶

With this option, TAS will allow you to use sizing methods to calculate the design flow rate.

Each method below is run on every zone in this system connected to the fan by ducts.

The software then sums the sized flow rate for each zone to produce the design flow rate.

The seven sizing methods available are:

• Per Floor Area

• Per Volume

• Attached

• Peak Person

• Peak Person and Area

• Peak IC - Outside Air

• Peak IC - Ventilation

• Delta T

### Per Floor Area¶

Here TAS Systems asks the user to enter a value in l/s/m2 (cfm / ft2 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/m3 (cfm / ft3 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:

$\text{Sized Flow Rate} = \frac{\text{Peak OSG }+\text{Peak OLG}}{\text{Metabolic Rate}} \times \text{Area of Zone} \times \text{Value}$

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:

$\text{Max Temp of supply air} - \text{Zones thermostat lower limit}$

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:

$\text{Zones thermostat upper limit} - \text{Min Temp of supply air}$

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.

## Nearest Zone Flow Rate¶

With this option TAS will take the flow rate of the nearest zone to the component and use this as the design flow rate.

## Nearest Zone Fresh Air¶

With this option TAS takes the fresh air rate of the nearest zone to the component and uses this as its design flow rate.

## Nearest Zone Sized¶

With this option, TAS will allow you to use sizing methods to calculate the design flow rate.

The selected sizing method will be run on the zone nearest to the component and the resulting sized value will be the design flow rate.

Please note that the seven sizing methods available have already been discussed in the All Attached Zones Sized option above.