DRAFT – your comments are welcome.

3.3.6 Natural Ventilation

Natural ventilation may be modeled for a thermal block in the proposed design when the following conditions are met:

  • The thermal block does not have an air conditioning system.
  • The temperature of the thermal block does not exceed the cooling setpoint temperature for more than 300 hours for the year of the simulation with just the natural ventilation system operating.

Under these circumstances, the thermal block in the proposed design is modeled with no air conditioning when the natural ventilation system maintains temperature. For periods when the space temperature is greater than the cooling setpoint, an air conditioner like the one for the baseline building is assumed to operate to maintain temperature. The fans in this simulated system cycle with loads. The corresponding thermal block in the baseline building is modeled with air conditioning and the fans operate continuously.

Natural Ventilation Method

Applicability

All thermal blocks with natural ventilation

Definition

The method used to model natural ventilation. The choices will depend to some extent on the capabilities of the energy simulation  program. One procedure that could be used with most energy simulation programs would be to approximate the effect of natural ventilation by scheduling a high rate of infiltration when conditions are right. The schedule would typically be developed through computational fluid dynamic software or with other software that is capable of estimating the cooling benefit of natural ventilation and relating it to climate so that the schedule can be developed.

Units

List: choices depend on the capabilities of the energy simulation program.

Input Restrictions

None. If natural ventilation is modeled as an increased infiltration rate, two inputs will be specified: 'Infiltration through building envelope' and 'Infiltration as a result of Automatically Controlled Natural Ventilation System'.

Baseline Rules

Baseline building is not modeled with natural ventilation. If natural ventilation is modeled as an increased infiltration rate in the proposed design, the component ‘Infiltration as a result of Automatically Controlled Natural Ventilation' is not modeled for the baseline building. 

 

Air Flow Rate

Applicability

All projects with natural ventilation that use a method that require the specification of an air flow rate

Definition

The rate of air flow through the thermal block when the natural ventilation system is operating

Units

Air changes per hour or cfm

Input Restrictions

The air flow rate for the proposed design shall be determined using sound engineering methods and supporting documentation shall be provided. If not modeled directly by the simulation program, an exceptional calculation method shall be used, with proper documentation submitted.

Baseline Rules

Baseline building is not modeled with natural ventilation.

 

Natural Ventilation Schedule

Applicability

All projects with natural ventilation that use a method that requires a schedule

Definition

A schedule that modifies the airflow rate through the thermal block dictates when windows can be opened to provide natural ventilation.

Units

Data structure: schedule, fractional

Input Restrictions

The schedule for the proposed design shall be determined using sound engineering methods and keyed to outdoor temperature and perhaps other conditions on the weather file used for the simulation.

Baseline Rules

The baseline building is not modeled with natural ventilation.

 

Minimum Indoor Temperature

Applicability

All projects with natural ventilation or mixed mode ventilation with automatic controls

Definition

The minimum indoor temperature below which natural ventilation is disabled

Units

Degrees, F

Input Restrictions

As designed

Baseline Rules

Not applicable

 

Maximum Indoor Temperature

Applicability

All projects with natural ventilation or mixed mode ventilation with automatic controls

Definition

The maximum indoor temperature above which natural ventilation is disabled

Units

Degrees, F

Input Restrictions

As designed

Baseline Rules

Not applicable

 

Minimum Outdoor Temperature

Applicability

All projects with natural ventilation or mixed mode ventilation with automatic controls

Definition

The minimum outdoor temperature below which natural ventilation is disabled

Units

Degrees, F

Input Restrictions

As designed

Baseline Rules

Not applicable

 

Maximum Indoor Temperature

Applicability

All projects with natural ventilation or mixed mode ventilation with automatic controls

Definition

The maximum outdoor temperature above which natural ventilation is disabled

Units

Degrees, F

Input Restrictions

As designed

Baseline Rules

Not applicable

Building EQ


 

Energy Star