Environmental control

Heating Setpoint temperatures

Heating setpoint temperature

Defines the ideal temperature (i.e. the setting of the heating thermostat) in the space when heating is required. Its meaning depends on the Temperature control calculation option. When using 1-Air temperature control the Heating setpoint temperature corresponds to the air temperature in the space and when it is set to set to 2-Operative temperature it is the operative temperature (MAT+MRT)/2.

Heating setback setpoint temperature

Some buildings require a low level of heating during unoccupied periods to avoid condensation/frost damage or to prevent the building becoming too cold and to reduce peak heating requirements at startup.  Enter the setpoint temperature to be used at night-time, weekends and other holidays during the heating season. Its meaning depends on the Temperature control calculation option (above).

Note: when using the Typical workday timing option, this setback temperature set point is only applied during unoccupied periods such as night-time and holidays during the heating season. It is not applied during the summer (if heating is switched off during the summer.)

Note: if the setback temperature set does not appear to affect results when using a Compact schedule, this may be because the Zone setpoint heating schedule selected uses only 0 and 1, not the 0.5 required to access setback temperature. See Defining setpoint temperature schedules for more on this.

Cooling Setpoint temperatures

Cooling setpoint temperature

Defines the ideal temperature (i.e. the setting of the cooling thermostat) in the space when cooling is required. Its meaning depends on the Temperature control calculation option. When using 1-Air temperature control the Cooling setpoint temperature corresponds to the air temperature in the space and when it is set to set to 2-Operative temperature it is the operative temperature (MAT+MRT)/2.

 

Note: the cooling setpoint temperature must be higher than the heating setpoint temperature.

Cooling setback setpoint temperature

Some buildings require a low level of cooling during unoccupied periods to prevent the building becoming too hot and to reduce the startup cooling load the next morning.  Enter the setpoint temperature to be used at night-time, weekends and other holidays during the cooling season. Its meaning depends on the Temperature control calculation option (above).

Note: when using the Typical workday timing option, this setback temperature set point is only applied during unoccupied periods such as night-time and holidays during the cooling season. It is not applied during the winter (if cooling is switched off during the winter.)

Note: if the setback temperature set does not appear to affect results when using a Compact schedule, this may be because the Zone setpoint cooling schedule selected uses only 0 and 1, not the 0.5 required to access setback temperature. See Defining setpoint temperature schedules for more on this.

Humidity Setpoint Temperatures

When using some Simple and Detailed HVAC systems you can control humidity. In the case of AHU-type systems the humidity in a control zone is controlled. The zone humidification and dehumidification setpoints can be defined here. Note that for systems without humidity control these setpoints are ignored.

RH Humidification setpoint

The zone humidistat relative humidity setpoint for humidification (0 to 100%).

RH Dehumidification setpoint

The zone humidistat relative humidity setpoint for dehumidification (0 to 100%).

Comfort PMV Setpoints

When using Detailed HVAC and the Temperature control option is set to 4-Fanger comfort and the Detailed HVAC Activity data option is set to 1-Simple HVAC, the zones are heated and cooled using the Fanger PMV heating and cooling comfort setpoints defined below as setpoints. When using the 2-Detailed HVACDetailed HVAC Activity data option, schedules of Fanger PMV comfort are defined on the HVAC zone dialog instead.

 

The Thermal comfort calculator tool can be used to derive PMV values based on the known environmental conditions.

Heating PMV setpoint

The PMV used as the heating setpoint when the heating operation schedule on the HVAC tab has value 1.

Heating PMV setback

The PMV used as the heating setback when the heating operation schedule on the HVAC tab has value 0.5.

Cooling PMV setpoint

The PMV used as the cooling setpoint when the cooling operation schedule on the HVAC tab has value 1.

Cooling PMV setback

The PMV used as the cooling setback when the cooling operation schedule on the HVAC tab has value 0.5.

Ventilation Setpoint Temperatures

Natural ventilation indoor min temperature control

If you wish to use natural ventilation to cool the building/block/zone down to a particular setpoint temperature and then shut off when the temperature goes below that setpoint then check this box. This allows you to define the Natural ventilation cooling setpoint temperature described below.

 

Natural ventilation min temperature control applies to both Calculated and Scheduled natural ventilation.

Tip: To ensure that natural ventilation occurs regardless of internal temperature (e.g. to use nat vent provide fresh air) then uncheck this option.

Min temperature definition

There are 2 ways to define the Natural ventilation min temperature:

 

• 1-By value - use this option when the setpoint does not change with time in which case you can enter a fixed setpoint temperature.
• 2-By schedule - use this option when the setpoint changes with time in which case you can select a schedule of time-varying temperature setpoints.

Natural ventilation min temperature

This is the fixed indoor temperature (in °C or °F) below which ventilation is shut off. The control is visible when the 1-By value option is selected for Min temperature definition. It can be thought of as the cooling setpoint temperature which controls the activation of natural ventilation.  If the inside air temperature is greater than this setpoint temperature (and the natural ventilation operation schedule is on) then natural ventilation can take place. The way this works depends on the Natural ventilation model option.

 

Note that when using the Calculated natural ventilation model option windows and vents are only opened when:

 

• The inside air temperature is above this cooling setpoint temperature, and
• The inside air temperature is greater than the outside air temperature, and
• The operation schedule allows ventilation.

 

Also, the data under the Calculated Natural Ventilation header on the Advanced tab of the Model Options dialog can modify ventilation control behaviour.

 

When using the Scheduled natural ventilation model option the Natural ventilation delta T (below) can prevent natural ventilation from occurring if the outside air temperature is too high.

Natural ventilation min temperature schedule

The schedule which defines the time-varying indoor temperature (in °C) below which ventilation is shut off. The control is visible when the 2-By schedule option is selected for Min temperature definition. It can be thought of as the time-varying cooling setpoint temperature which controls the activation of natural ventilation.

 

See also Defining setpoint temperature schedules.

Natural ventilation indoor max temperature control

If there is a maximum zone air temperature above which the natural ventilation should shut off then check this option. This upper temperature limit is intended to avoid overheating a space and/or unnecessarily increasing cooling loads.

 

Normally when using natural ventilation for cooling this option will be left unchecked as it would be unusual to place an upper limit on the zone temperature for operation of such a system.

 

Indoor max temperature control option is used only with Scheduled natural ventilation and is not available for Calculated natural ventilation.

Max temperature definition

There are 2 ways to define the Natural ventilation max temperature:

 

• 1-By value - use this option when the setpoint does not change with time in which case you can enter a fixed setpoint temperature.
• 2-By schedule - use this option when the setpoint changes with time in which case you can select a schedule of time-varying temperature setpoints.

Natural ventilation max temperature

This is the fixed indoor temperature (in °C or °F) above which ventilation is shut off. The control is visible when the 1-By value option is selected for Max temperature definition.

Natural ventilation max temperature schedule

The schedule which defines the time-varying indoor temperature (in °C) above which ventilation is shut off. The control is visible when the 2-By schedule option is selected for Max temperature definition.

 

See also Defining setpoint temperature schedules.

Mechanical ventilation control

The mechanical ventilation cooling setpoint temperature and delta T values described below control the activation of mechanical ventilation when using Simple HVAC together with the 1-Room ventilation Mechanical ventilation method.

Mechanical ventilation cooling setpoint temperature

The mechanical ventilation cooling setpoint temperature controls the activation of mechanical ventilation when using Simple HVAC together with the 1-Room ventilation Mechanical ventilation method.  If the inside air temperature is greater than this setpoint temperature (and the mechanical ventilation operation schedule is on) then mechanical ventilation can take place.  

 

This data and the corresponding delta T data described below are not used in simulations when working with the Simple HVAC 2-Ideal loads option or with Detailed HVAC and are never used in Heating and Cooling design calculations.

Mechanical ventilation max natural ventilation in-out delta T

The mechanical ventilation Max int-out temp difference is used for Scheduled mechanical ventilationonly and is the temperature difference between the indoor and outdoor air dry bulb temperatures below which ventilation is shut off. This is to allow ventilation to be stopped if the temperature outside is too warm and could potentially heat the space. It is not related to preventing drafts.

 

For example, if you specify a maximum delta temperature of 2°C, ventilation is assumed to be available if the outside air temperature is at least 2°C cooler than the zone air temperature. If the outside air dry bulb temperature is less than 2°C cooler or warmer than the indoor dry bulb temperature, then ventilation is automatically turned off. The values for this field can include negative numbers. This allows ventilation to occur even if the outdoor temperature is above the indoor temperature. The Delta Temperature control works in the code in the following way:

 

if (IndoorTemp - OutdoorTemp) < Max ventilation in-out delta T then ventilation is not allowed.

 

For example:

 

Value of Mechanical ventilation Max in-out delta T	Effect
0	Mechanical ventilation only operates when OutdoorTemp < IndoorTemp
-50	Mechanical ventilation unrestricted by Inside-Outside delta T
2	Mechanical ventilation only operates when OutdoorTemp + 2 < IndoorTemp

Tip: Enter a large negative number to allow ventilation even if the outdoor temperature is greater than the indoor temperature. This useful for uncontrolled mechanical ventilation or as a way to estimate the effect of required ventilation air for load calculations.

See also Defining setpoint temperature schedules.

Minimum Fresh Air

Minimum fresh air data is defined on the Activity tab because the fresh air requirement of the people in the zone depends on the activity (use) of the space.

Fresh air

The Minimum fresh air per person defines the fresh air requirements of each person in the zone and is used to generate appropriate mechanical outside air distribution rates when the mechanical ventilation Outside air definition methods on the HVAC tab  is set to any of:

 

• 2-Min fresh air per person where the fresh air flow rate is calculated as the Fresh air (l/s//person) x People / m2 x Zone floor area (m2)
• 4-Min fresh air (Sum per person + per area) where the fresh air flow rate is the sum of 'per person' and 'per area' fresh air requirements
• 5-Min fresh air (Max per person and per area) where the fresh air flow rate based on 'per person' is compared with 'per area' and the maximum is used.

 

This data is also used to calculate natural ventilation outside air flow rates into the zone when the natural ventilation Flow type on the HVAC tab is set to 2-Min fresh air per person.

Mech vent per area

The Mech vent per area data defines the fresh air requirements of the zone per floor area and is used to calculate mechanical outside air distribution rates when the mechanical ventilation Outside air definition methods on the HVAC tab is set to any of:

 

• 3-Min fresh air (Per area), where the fresh air flow rate is calculated as the Mech vent per floor area (l/s/m2) x Zone floor area (m2)
• 4-Min fresh air (Sum per person + per area),
• 5-Min fresh air (Max per person and per area).

 

This data is not currently used for natural ventilation and is only used if one of the above mechanical ventilation Outside air definition methods has been used.

CO2/Contaminant Setpoints

If the zone has its fresh air delivery controlled using the 3-IAQP DCV method and the 1-Simple HVAC Detailed HVAC Activity data model option is set then you must enter the CO2 setpoint and minimum setting here on the Activity tab. Likewise if the 5-IAQP generic contaminant option is selected then the generic contaminant setpoint and minimum setting must be entered here.

 

If the 2-Detailed HVAC Detailed HVAC Activity data model option is set then this data is entered on the HVAC Zone dialog using schedules.

CO2 concentration Setpoint

Enter the constant CO2 concentration setpoint in ppm.

Min CO2 concentration

Enter the minimum allowed CO2 concentration in ppm.

Generic contaminant concentration setpoint

Enter the constant generic contaminant concentration setpoint in ppm. The value should be between 0 and 1.

Lighting

Target illuminance

The desired lighting level (in lux) at the first daylighting sensor. This is also the lighting level that would be produced at this sensor position at night if the overhead electric General lighting were operating at full input power. Recommended values depend on type of activity; they may be found, for example, in the Lighting Handbook of the Illuminating Engineering Society of North America and in CIBSE A Guide. A typical value for general office work (excluding computer terminals) is 500 lux.

Default display lighting density

This data allows you to define the typical density of display lighting for the activity. The value is used as a default on the Lighting tab for the Task and Display lighting density to ensure that the display lighting density is appropriate for the activity of the zone.

 

When the Lighting gain units model option is set to 1-Power density and a lighting template is loaded, this value is copied directly from the Activity tab to the corresponding Task and Display Gain value on the Lighting tab.

 

The Default display lighting density comes from the activity rather than from the lighting template because the gain is more likely to be a function of the activity than of the type of lighting system installed.