When parallel fan powered boxes are required for the baseline building, fans shall run as the first stage of heating before the reheat coil is energized. Fans in parallel VAV fan-powered boxes shall be sized for 50% of the peak design primary air (from the VAV air-handling unit) flow rate and shall be modeled with 0.35 W/cfm fan power. Minimum volume setpoints for fan-powered boxes shall be equal to 30% of peak design primary airflow rate or the rate required to meet the minimum outdoor air ventilation requirement, whichever is larger. The supply air temperature setpoint shall be constant at the design condition.
|
Fan Powered Box Type |
|
|---|---|
|
Applicability |
HVAC zones that have fan powered boxes |
|
Definition |
Defines the type of fan-powered induction box. This is either:
|
|
Units |
List (see above) |
|
Input Restrictions |
As designed |
|
Baseline Rules |
Applicable for baseline building systems 6 and 8 and the fan powered box type is parallel. |
|
Fan Power |
|
|---|---|
|
Applicability |
HVAC zones that have fan powered boxes |
|
Definition |
The rated power input of the fan in a fan-powered box. |
|
Units |
W or W/cfm |
|
Input Restrictions |
As designed |
|
Baseline Rules |
For baseline building systems 6 and 8, power is prescribed at 0.35 W/cfm. |
|
Fan Powered Box Induced Air Zone |
|
|---|---|
|
Applicability |
HVAC zones that have fan powered boxes |
|
Definition |
Zone from which a series or parallel fan-powered box draws its air |
|
Units |
List (of zones) |
|
Input Restrictions |
As designed |
|
Baseline Rules |
If the proposed design has a plenum, then induced air will be drawn from that plenum. If the proposed design does not have a plenum, then induced air will be drawn from the space. |
|
Parallel PIU Induction Ratio |
|
|---|---|
|
Applicability |
HVAC zones that have fan powered boxes |
|
Definition |
The ratio of induction-side airflow of a fan-powered box at design heating conditions to the primary airflow |
|
Units |
Ratio |
|
Input Restrictions |
As designed |
|
Baseline Rules |
50% |
|
Parallel Fan Box Thermostat Setpoint |
|
|---|---|
|
Applicability |
HVAC zones that have parallel fan powered boxes |
|
Definition |
The temperature difference above the heating setpoint at which the parallel fan is turned on |
|
Units |
Degrees Fahrenheit (°F) |
|
Input Restrictions |
2°F above the heating setpoint schedule |
|
Baseline Rules |
2°F above the heating setpoint schedule |
|
Terminal Heating Control Type |
|
|---|---|
|
Applicability |
HVAC zones that have parallel fan powered boxes |
|
Definition |
Single Maximum VAV Box Fan Control: With parallel style fan powered VAV boxes, the terminal unit fan is only on when the zone is in heating mode. When the fan is running, the box mixes plenum air with primary air.
Figure 3.6.5-3: Single Maximum VAV Box Control |
|
Units |
List |
|
Input Restrictions |
As designed |
|
Baseline Rules |
Single Maximum with minimum air flow rate set to 30% of peak design primary air flow rate or the outside air ventilation rate, whichever is larger. Systems serving laboratory spaces shall reduce the exhaust and makeup air volume during unoccupied periods to the largest of 50% of zone peak airflow, the minimum outdoor airflow rate, or the airflow rate required to comply with applicable codes or accreditation standards. For baseline system 11, minimum volume setpoint shall be 50% of the maximum design airflow rate, the minimum ventilation outdoor airflow rate, or the airflow rate required to comply with applicable codes or accreditation standards, whichever is larger. Fan volume shall be reset from 100% airflow at 100% cooling load to minimum airflow at 50% cooling load. Supply air temperature setpoint shall be reset from minimum supply air temperature at 50% cooling load and above to space temperature at 0% cooling load. In heating mode supply air temperature shall be modulated to maintain space temperature, and fan volume shall be fixed at the minimum airflow. |
