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 |
| Baseline Rules |
Baseline building is not modeled with natural ventilation. |
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. |
| 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. |
