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

Detailed HVAC Activity data set to 2-Detailed HVAC

 

If the 2-Detailed HVAC Detailed HVAC Activity data model option is set then you can select schedules defining zone heating and cooling setpoint temperatures on this dialog. Otherwise, if the 1-Simple HVAC option is selected then zone setpoint temperatures and schedules are defined on the Activity and HVAC model data tabs respectively and the Thermostat schedule data is not displayed on this dialog.

Note: The temperatures defined in these schedules must be in °C regardless of whether you are using IP or SI units in the interface.

Thermostat heating setpoint schedule

This is the zone heating temperature schedule. Values in the schedule are temperatures (in °C).

Thermostat cooling setpoint schedule

This is the zone cooling temperature schedule. Values in the schedule are temperatures (in °C).

Comfort PMV Setpoint Schedules

Detailed HVAC Activity data set to 2-Detailed HVAC

 

If the 2-Detailed HVAC Detailed HVAC Activity data model option is set then you can select schedules which define zone heating and cooling setpoint PMV values on this dialog. Otherwise, if the 1-Simple HVAC option is selected then zone setpoint PMV values and schedules are defined on the Activity and HVAC model data tabs respectively and the Thermostat schedule data is not displayed on this dialog.

 

The Thermal comfort calculator tool can be used to derive PMV values based on perhaps more familiar parameters.

Heating PMV setpoint schedule

This is the zone heating PMV schedule. Values in the schedule are PMV indices, typically in the range -3 to 3.

Cooling PMV setpoint schedule

This is the zone cooling PMV schedule. Values in the schedule are PMV indices, typically in the range -3 to 3.

Humidistat Control

Humidistat control

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

Detailed HVAC Activity data is 1-Simple HVAC

If the 1-Simple HVAC option is selected then zone RH setpoints on the Activity tab are used and the demand schedule data on this dialog defines the times when these setpoints operate.

Humidifying demand schedule

This is a schedule that defines the times when humidification may be required. The schedule should have only values of 0 (for times when no humidification is required) or 1 (when humidification to the humidification setpoint defined on the Activity tab is required).

Dehumidifying demand schedule

This is a schedule that defines the times when dehumidification may be required. The schedule should have only values of 0 (for times when no dehumidification is required) or 1 (when dehumidification to the dehumidification setpoint defined on the Activity tab is required).

Detailed HVAC Activity data is 2-Detailed HVAC

If the 2-Detailed HVAC Detailed HVAC Activity data model option is set then you can select schedules defining zone relative humidity setpoints on this dialog.

Humidifying RH setpoint schedule

This is a schedule that defines the humidifying relative humidity setpoint, expressed as a percentage (0-100), for each timestep of the simulation.

Dehumidifying RH setpoint schedule

This is a schedule that defines the dehumidifying relative humidity setpoint, expressed as a percentage (0-100), for each timestep of the simulation.

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: When the DCV System outdoor air method is either 1-Zone sum or 2-Ventilation Rate Procedure (VRP) then this option does not need to be selected.

Note: When one of the proportional DCV System outdoor air methods is selected on the AHU dialog (4-Proportional control based on occupancy schedule or 5-Proportional control based on design occupancy) then selection of the CO2 and contaminant control checkbox on this dialog is optional. If you wish to specify zone minimum CO2 concentration settings for proportional control then you should check this checkbox, otherwise leave it unchecked, in which case outdoor air CO2 concentration will be used as the minimum instead. You can find details of the calculations used to calculate the target indoor CO2 concentration in the Engineering reference under Proportional Control.

Note: When one of the IAQP DCV System outdoor air methods are selected (3-Indoor Air Quality Procedure (IAQP) or 6-Indoor Air Quality Procedure (IAQP) generic contaminant) then the CO2 and contaminant option must be selected for at least one HVAC zone connected to the AHU.

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

Detailed HVAC Activity data is 1-Simple HVAC

If the 1-Simple HVAC option is selected then fixed contaminant setpoints from the Activity tab are used and no further data needs to be entered here.

Detailed HVAC Activity data is 2-Detailed HVAC

If the 2-Detailed HVAC Detailed HVAC Activity data model option is set then you can select schedules defining time-varying CO2 and contaminant setpoints on this dialog.

CO2 control availability schedule

This is a schedule that defines the availability of CO2 control for each timestep of the simulation.

CO2 setpoint schedule

This is a schedule that defines the CO2 setpoint in ppm, for each timestep of the simulation.

Minimum CO2 concentration schedule

This is a schedule that defines the minimum concentration of CO2 in ppm, for each timestep of the simulation.

Generic contaminant control availability schedule

This is a schedule that defines the availability of Generic contaminant control for each timestep of the simulation.

Generic contaminant setpoint schedule

This is a schedule that defines the Generic contaminant setpoint in ppm, for each timestep of the simulation. Enter values between 0 and 1.

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

Zone Air Distribution Effectiveness

ASHRAE Standard 62.1 defines Zone air distribution effectiveness (Ez) as a measure of how effectively the zone air distribution system uses the supply air to maintain acceptable air quality in the occupied zone (also known as the breathing zone). In an imperfect system the fresh air introduced through supply diffusers may not mix fully with the rest of the room air before being extracted. These settings allow the distribution effectiveness to be defined separately for heating and cooling operation modes.

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:

• 1-Separate heating and cooling where fixed zone air distribution effectiveness values are entered separately for heating and cooling.
• 2-Scheduled where a schedule is selected which defines how the zone air distribution effectiveness for both heating and cooling varies with time.

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.

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:

 

• 1- Supply air temperature means that the Zone cooling design supply air temperature (below) will be used to determine the zone cooling design air flow rate.
• 2-Temperature difference where the Zone cooling design supply air temperature difference (below) is used to determine the zone cooling design air flow rate.

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:

 

• 1‑Design day means the program will calculate the zone design cooling air flow rate using the zone cooling sizing information and a design day simulation without imposing any limits other than those set by the minimum outside air requirements.
• 2‑Flow/zone means that the program will use the Cooling design air flow rate as the zone design cooling air flow rate.
• 3‑Design day with limit means that the maximum from Cooling minimum flow per zone floor area and Cooling minimum air flow will set a lower limit on the design maximum cooling air flow rate.

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:

 

• 1- Supply air temperature means that the Zone heating design supply air temperature (below) will be used to determine the zone heating design air flow rate.
• 2-Temperature difference where the Zone heating design supply air temperature difference (below) is used to determine the zone heating design air flow rate.

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:

 

• 1‑Design day means the program will calculate the zone design heating air flow rate using the zone heating sizing information and a design day simulation without imposing any limits other than those set by the minimum outside air requirements.
• 2‑Flow/zone means that the program will use the Heating design air flow rate as the zone design heating air flow rate.
• 3‑Design day with limit means that the maximum from Heating maximum flow per zone floor area and Heating maximum air flow will set a lower limit on the design maximum heating air flow rate.

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:

 

• 1‑Flow/Zone, means that the program will use the Outdoor air flow per zone as the zone design outdoor air flow rate.
• 2‑Flow/Person, means the program will use the input from the field Outdoor air flow per person and the maximum occupancy to calculate a zone design outdoor air flow rate.
• 3‑Flow/Area, means that the flows calculated from the fields Outdoor air flow per zone floor area used to obtain the zone design outdoor air flow rate.
• 4‑Sum, means that the flows calculated from the fields Outdoor air flow per person, Outdoor air flow per zone floor area and Outdoor air flow per zone will be added to obtain the zone design outdoor air flow rate.
• 5‑Maximum means that the maximum flow derived from Outdoor air flow per person, Outdoor air flow per zone floor area and Outdoor air flow per zone will be used for the zone design outdoor air flow rate.

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

Account for Dedicated Outdoor Air System

Checking this option means that the zone sizing calculation will use the inputs below to calculate the heat gain or loss imposed on the zone by a Dedicated Outdoor Air System (DOAS). This heat gain/loss is 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

Select from three control strategies for the outdoor air system. The choices are:

 

• 1-Neutral supply air, the default option in which ventilation air supplied to the zone will cause little heating or cooling. The air will be heated or cooled to keep it between the low and high temperature setpoints specified in the subsequent two fields. A good choice for these fields might be 21.1 and 23.9°C.
• 2-Neutral dehumidified supply air, where the ventilation air will be cooled and dehumidified and then reheated to a neutral temperature. The ventilation air is cooled to the lower setpoint temperature (if necessary) and reheated to the upper setpoint temperature. A good choice for the setpoints would be 14.4 and 22.2°C, or
• 3-Cold supply air where the ventilation air will be used to supply cooling to the zone. Cold outside air is heated to the upper setpoint; warm outside air is cooled to the lower setpoint. A good choice for the setpoints would be 12.2 and 14.4°C.

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.

Load Outdoor Air Model Data

When using the Detailed HVAC Activity data model option, 2 links are displayed on the Info panel to facilitate the copying of relevant outdoor air data from the HVAC and Activity model data tabs to the Outdoor air sizing section of the HVAC zone dialog.

 

Load outdoor air data to this HVAC zone only

When the Load outdoor air data to this HVAC zone only Info panel link is clicked, model data from the associated building zone is copied from the Activity and HVAC tabs to this dialog.

 

For example, if the Mechanical Ventilation > Outside air definition method on the HVAC tab is set to 4-Min fresh air (Sum per person + per area), DesignBuilder will make the following settings under the Outside Air Sizing header of this dialog.

 

• Outside air method is set to 4-Sum.

• Outside air flow per person is set based on the setting on the Minimum fresh air per person setting on the Activity tab.

• Outside air flow per zone floor area is set based on the setting on the Mech vent per area setting on the Activity tab.

Load outdoor air data to all HVAC zones

When the Load outdoor air data to all HVAC zones Info panel link is clicked, model data from the associated building zone is copied from the Activity and HVAC tabs to this dialog. Then if/when you press the OK button to confirm settings for this HVAC zone, the Outside Air Sizing data on this dialog is also copied to all other HVAC zones in the model.