VAV with Package Rooftop

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

Click to see 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

Click to see curve

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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