Edit HVAC Zone Data - General Tab

Data on this tab is used for controlling the zone internal conditions during the simulation and also for autosizing heating, cooling and outside air equipment related to the zone.

General

Name

This is the name of the building zone with which the current HVAC zone is linked.

Thermostat Schedules

Comfort PMV Setpoint Schedules

Humidistat Control

Humidistat control

This check-box is used to specify whether or not the zone has humidity control.

 

 

 

More information on controlling humidity is available in the Humidity control section.

 

The rest of the General tab of the HVAC Zone dialog is related to Detailed HVAC autosizing calculations only.

CO2 and Contaminant Control

CO2 and contaminant control

This check-box is used to specify whether or not the zone has CO2 or contaminant control. This must be selected if the zone is to have maximum CO2 or generic contaminant concentration controlled through one of the IAQP DCV methods.

 

Note: This option must not be selected for zones connected to an AHU with System outdoor air method set to 1-Zone sum or 2-Ventilation Rate Procedure (VRP).

Note: For AHUs with IAQP control at least one connected HVAC zone must have this option selected.

 

 

 

More information on DCV is available in the DCV control section of the AHU help page.

 

The rest of the General tab of the HVAC Zone dialog is related to Detailed HVAC autosizing calculations only.

Zone Air Distribution Effectiveness

Method

You can choose to either define fixed zone air distribution effectiveness values for heating and cooling or select a schedule with time-varying values to cover both heating and cooling together. Select from:

 

Effectiveness in cooling mode

Enter the fixed zone air distribution effectiveness when the zone is in cooling mode. ASHRAE Standard 62.1-2010 provides typical values (see table below). The default value 1.0.

Effectiveness in heating mode

Enter the fixed zone air distribution effectiveness when the zone is in heating mode. ASHRAE Standard 62.1-2010 provides typical values (see table below). The default value 1.0.

 

Zone Air Distribution Effectiveness (TABLE 6-2 ASHRAE 62.1)  
Air Distribution Configuration Ez

Ceiling supply of cool air.

1.0

Ceiling supply of warm air and floor return.

1.0

Ceiling supply of warm air 15°F (8°C) or more above space temperature and ceiling return.

0.8

Ceiling supply of warm air less than 15°F (8°C) above space temperature and ceiling return provided that the 150 fpm (0.8 m/s) supply air jet reaches to within 4.5 ft (1.4 m) of floor level. Note: For lower velocity supply air, Ez = 0.8.

1.0

Floor supply of cool air and ceiling return provided that the 150 fpm (0.8 m/s) supply jet reaches 4.5 ft (1.4 m) or more above the floor. Note: Most underfloor air distribution systems comply with this proviso.

1.0

Floor supply of cool air and ceiling return, provided low-velocity displacement ventilation achieves unidirectional flow and thermal stratification.

1.2

Floor supply of warm air and floor return.

1.0

Floor supply of warm air and ceiling return.

0.7

Make-up supply drawn in on the opposite side of the room from the exhaust and/or return.

0.8

Make-up supply drawn in near to the exhaust and/or return location.

0.5

1. “Cool air” is air cooler than space temperature.

2. “Warm air” is air warmer than space temperature.

3. “Ceiling” includes any point above the breathing zone.

4. “Floor” includes any point below the breathing zone.

5. As an alternative to using the above values, Ez may be regarded as equal to air change effectiveness determined in accordance with ANSI/ASHRAE Standard

 

Recirculation fraction

The non-negative numeric input for this field is the fraction of a zone’s recirculation air that does not directly mix with the outdoor air. The zone secondary recirculation fraction Er is determined by the designer based on system configuration. For plenum return systems with secondary recirculation (e.g., fan-powered VAV with plenum return) Er is usually less than 1.0, although values may range from 0.1 to 1.2 depending upon the location of the ventilation zone relative to other zones and the air handler. For ducted return systems with secondary recirculation (e.g., fan-powered VAV with ducted return), Er is typically 0.0, while for those with system-level recirculation (e.g, dual-fan dual-duct systems with ducted return) Er is typically 1.0. For other system types, Er is typically 0.75. Minimum is 0.0, and default is 0.0 for single-path systems (also to maintain backward compatibility). For parallel fan-powered VAV systems, the secondary ventilation path only functions (Er > 0.0) when the fans in the VAV boxes operate, which is during heating. The local ventilation path and the benefits of secondary recirculation disappear during cooling, when

the local parallel fans are off (Er = 0.0).

Sizing

Cooling Sizing

Cooling design supply air temperature input method

This option determines how the cooling design air flow rate is calculated in the system autosizing calculations:

 

Cooling design supply air temperature

This is the supply air temperature (in °C or °F) for the zone cooling air flow rate calculation. Air is supplied to the zone at this temperature during the cooling design day simulation and the zone load is met by varying the zone air flow rate. The maximum zone flow rate is used as the zone cooling design air flow rate.

 

This data is only available when the Cooling design supply air temperature input method (above) is 1-Supply air temperature.

Cooling design supply air temperature difference

The temperature difference between cooling design supply air temperature and room air temperature (in delta°C or delta°F) for the zone cooling design air flow

rate calculation. Air is supplied to the zone with this temperature difference during the cooling design day autosizing simulation. The zone load is met by varying the zone air flow rate. The maximum zone flow rate is used as the zone cooling design air flow rate.

 

This data is only available when the Cooling design supply air temperature input method (above) is 2-Temperature difference.

Cooling design supply air humidity ratio

This is the humidity ratio in kilograms of water per kilogram of dry air of the supply air in the zone cooling autosizing air flow rate calculation.

Cooling minimum air flow fraction

This is the minimum zone design cooling volumetric flow rate expressed as a fraction of the zone design cooling volumetric flow rate for VAV systems only. In all cases the maximum flow derived from Cooling minimum flow per zone floor area, Cooling minimum air flow, and Cooling minimum air flow fraction is used to set a minimum supply air flow rate for the zone for VAV systems. The default is zero. This input is currently used in sizing the fan minimum flow rate. It does not affect other component auto-sizing.

 

Note: This value is only used when the zone is connected to a VAV Air loop, in which case this data is used for sizing and not for the simulation itself.

Zone cooling sizing factor

This is the zone level cooling sizing ratio. The zone design cooling air flow rates and loads will be multiplied by the number input in this field. The default value comes from the Zone group dialog whose default Zone cooling sizing factor is the ASHRAE recommended cooling oversizing factor of 1.15.

Cooling design air flow method

There are 3 options:

 

Cooling design air flow rate

This is the design zone cooling air flow rate (in m3/s or ft3/min). This setting is only required if Cooling design air flow method is specified as 2‑Flow/zone. This value will be multiplied by the global or zone sizing factor and by zone multipliers.

Cooling minimum flow per zone floor area

This is the minimum zone cooling volumetric flow rate per square meter (units are m3/s-m2). This setting is only required if the Cooling design air flow method is specified as 3‑Design day with limit. In this case it sets a lower bound on the zone design cooling air flow rate. In all cases the maximum flow derived from Cooling minimum flow per zone floor area, Cooling minimum air flow, and Cooling minimum air flow fraction is used to set a minimum supply air flow rate for the zone for VAV systems. The default is 0.000762 m3/s-m2, corresponding to 0.15 cfm/ft2. The applicable sizing factor is not applied to this value.

Cooling minimum air flow

This is the minimum zone cooling volumetric flow rate (in m3/s). This field is used when Cooling design air flow method is specified as 3‑Design day with limit. In this case it sets a lower bound on the zone design cooling air flow rate. In all cases the maximum flow derived from Cooling minimum flow per zone floor area, Cooling minimum air flow, and Cooling minimum air flow fraction is used to set a minimum supply air flow rate for the zone for VAV systems. The default is zero. The applicable sizing factor is not applied to this value.

Heating Sizing

Heating design supply air temperature input method

This option determines how the heating design air flow rate is calculated in the system autosizing calculations:

 

Heating design supply air temperature

This is the supply air temperature (in °C or °F) for the zone heating design air flow rate calculation. Air is supplied to the zone at this temperature during the heating design day simulation, The zone load is met by varying the zone air flow rate. The maximum zone flow rate is used as the zone heating design air flow rate.

Heating design supply air temperature difference

The temperature difference between heating design supply air temperature and room air temperature (in delta°C or delta°F) for the zone heating design air flow

rate calculation. Air is supplied to the zone with this temperature difference during the heating design day autosizing simulation. The zone load is met by varying the zone air flow rate. The maximum zone flow rate is used as the zone heating design air flow rate.

Heating design supply air humidity ratio

This is the humidity ratio in kilograms of water per kilogram of dry air of the supply air in the zone heating design air flow rate calculation.

Zone heating sizing factor

This is the zone level heating sizing ratio. The zone design heating air flow rates and loads will be multiplied by the number input in this field. The default value comes from the Zone group dialog whose default Zone heating sizing factor is the ASHRAE recommended heating oversizing factor of 1.25.

Heating design air flow method

There are three options:

 

Heating design air flow rate

This is the design zone heating air flow rate (in m3/s or ft3/min). This setting is only required if Heating design air flow method is specified as 2‑Flow/zone. This value will be multiplied by the global or zone sizing factor and by zone multipliers.

Heating maximum flow per zone floor area

This is the maximum zone heating volumetric flow rate per square metre (units are m3/s-m2). This setting is only required if the Heating design air flow method is specified as 3‑DesignDayWithLimit. In this case it sets an upper bound on the zone design heating air flow rate. In all cases the maximum flow derived from Heating maximum flow per zone floor area, Heating maximum air flow, and Heating maximum air flow fraction is used to set a maximum heating supply air flow rate for the zone for VAV systems. The default is 0.002032 m3/s-m2, corresponding to .40 cfm/ft2. This input is not currently used for auto-sizing any of the components.

Heating maximum air flow

This is the maximum zone heating volumetric flow rate in m3/s. This setting is only required if the Heating design air flow method is specified as 3‑Design day with limit. In this case it sets an upper bound on the zone design heating air flow rate. In all cases the maximum flow derived from Heating maximum flow per zone floor area, Heating maximum air flow, and Heating maximum air flow fraction is used to set a maximum heating supply air flow rate for the zone for VAV systems. The default is 0.14158 m3/s, corresponding to 300 cfm. This input is not currently used for auto-sizing any of the components.

Outdoor Air Sizing

When the Detailed HVAC Activity data is set to 1-Simple HVAC then all data under the Outdoor Air Sizing header is disabled and the outdoor air requirement settings are copied from the corresponding building zones' Activity and/or HVAC model data as described below.

 

When the Detailed HVAC Activity data is set to 2-Detailed HVAC then the outdoor air requirement is defined here on the HVAC zone dialog.

Outdoor air method

There are five options:

 

 

Note: If the Detailed HVAC Activity data is set to 1-Simple HVAC then this option is disabled and the Outdoor air method is copied from the corresponding building zones' HVAC model data.

Outdoor air flow per person

This is the design outdoor air flow rate per person for this zone (in m3/s or ft3/min). This setting is only required if either one of the 2‑Flow/person, 4‑Sum, or 5‑Maximum options have been selected for the Outdoor air method. The default is 0.00944 m3/s (20 cfm per person). An outdoor air flow rate is calculated based on the total number of people assigned to the zone. Occupancy schedule values are not applied.

 

Note: If the Detailed HVAC Activity data is set to 1-Simple HVAC then this option is disabled and the Outdoor air flow per person is copied from Outdoor air flow per person from the corresponding building zones' Activity model data.

Outdoor air flow per zone floor area

This is the design outside air volumetric flow rate per square meter of floor area (in m3/s-m2). This setting is only required if either one of the 3‑Flow/area, 4‑Sum, or 5‑Maximum options have been selected for the Outdoor air method. This value is multiplied by the zone floor area to obtain a flow rate.

 

Note: If the Detailed HVAC Activity data is set to 1-Simple HVAC then this option is disabled and the Outdoor air flow per zone floor area data is copied from the corresponding building zones' Activity model data.

Outdoor air flow per zone

This is the design outdoor air flow rate for this zone (in m3/s or ft3/min). This setting is only used if either one of the 1‑Flow/zone, 4‑Sum, or 5‑Maximum options have been selected for the Outdoor air method.

 

Note: If the Detailed HVAC Activity data is set to 1-Simple HVAC then this option is disabled and the flow per zone is calculated from the ac/h value set on the HVAC model data tab and displayed here.

Dedicated Outdoor Air System Sizing

The DOAS sizing settings below are available in v5.1 and later only

Account for Dedicated Outdoor Air System

This is a choice field with choices Yes or No. The default is No. Choosing Yes means that the zone sizing calculation will use the subsequent inputs to calculate the heat gain or loss (heat gains are positive, heat loss is negative) imposed on the zone by a Dedicated Outdoor Air System (DOAS). This heat gain is then added to the zone design heat gain for the zone and the zone design air flow rate is adjusted to meet the DOAS heat gain plus the zone design heat gain.

Field: Dedicated Outdoor Air System Control Strategy

This is a choice field with a choice of three ideal control strategies for the DOA system. The choices are:

 

Low temperature setpoint for design

The lower setpoint temperature to be used with the DOAS design control strategy (in °C or °F). The default is autosized to the values given above for the three design control strategies.

High temperature setpoint for design

The higher setpoint temperature to be used with the DOAS design control strategy (in °C or °F). The default is autosized to the values given above for the three design control strategies.