Overview
This template generates a multi-zone VAV system served by a rooftop Air Handling Unit that provides ventilation and cooling. Each zone contains a VAV box which varies the flow of air for zone-level cooling and/or heats the air to provide heating.
Air Handling Unit (AHU)
The table below describes the key properties of the AHU for this system:
AHU Feature |
Default |
Extent of user-control |
Supply Air Temperature |
Constant (13C/55F) |
Can change constant value |
Supply Air Temperature Reset Controls |
None |
None |
Supply Air Pressure Reset Controls |
None |
None |
Peak Fan Power |
3.5 W/(L/s) or 1.65 W/cfm |
Can control peak load |
Fan Curve |
Standard ASHRAE. Click to see fan curve |
No control |
Economiser Cycle |
Dry-bulb Control with 19C threshold |
Can disable or change to enthalpy control (xx) |
Minimum Outside Air |
Sum of all zones minimum ventilation air |
Can change ventilation requirements in internal conditions |
Heating Coil |
Hot water from gas boiler |
Can change to electric coil or direct gas |
Heat Recovery |
Via return air only (not indirect) |
None |
DX Efficiency |
COP 3.5 |
Adjustable |
DX Efficiency Curve |
Click to see curve |
No control |
Zone VAV boxes
The table below describes the key properties of the zone level VAV boxes for this system:
VAV Box Feature |
Default |
Extent of user-control |
Heating Coil Type |
Hot water (from Gas Boiler) |
Can change to electric coil or direct gas |
Minimum Turndown Ratio |
Constant for all zones - 0.3 |
Constant rate is variable. No individual zone control |
VAV Box type |
Standard (damper only) |
User can choose fan powered terminal unit instead |
Peak Fan Power (Fan Powered Terminal Unit) |
0.10 W/(L/s) or 0.05 W/cfm |
Can control peak load |
Fan Curve |
Constant Volume Fan |
No control |
Supply Air Temperature |
Constant for all zones (36C / 95F) |
User can change constant |
Demand Control Ventilation |
None |
None |
Central Plant
The base case option is assumed to have a central plant that provides heating hot water to the AHU and VAV boxes. This only appears if the user chooses hot water as the source of heating for one of the heating types.
Central Plant Feature |
Default |
Extent of user-control |
Heating Hot Water Source |
Natural Gas |
Can change to electric boiler |
Boiler Peak Efficiency |
Assumed to be 0.9 |
Value can be changed |
Boiler Performance Curve |
No Control |
|
Supply and Return Temperatures |
80/70 C or 176/158 F |
User can control |
System losses |
Constant loss rate at 15% |
User can control loss rate only. |
Peak Pumping Energy |
1.32 W/(L/s) or 21 W/gpm |
No control |
Pump Efficiency Controls |
Variable Speed Drives |
No control |
Efficiency Curve for Variable Pumping |
No control |
|
Pumping Configuration |
Primary Only |
No control |
Additional modifications to the template
Sefaira has not made any additional modifications to the template other than the settings described above. The above modifications are all changed before the “expand object” script is run and applied to the building.
Notes about VAV
If a user selects single zone per floor (or manually adds very large perimeter zones) then there will be a visible reduction in heating energy.
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