Rating System

LEED BD+C: New Construction

Rating System Version

v2 - LEED 2.2

Inquiry

The design for our building includes ventilation shafts that provide a pathway for warm air to rise out of the building using only buoyancy forces to overcome the small amount of friction from the air passing through the shafts. Our analysis of local hourly weather data indicates that conditions would be favorable for natural ventilation via buoyancy during about 170 occupied hours per year. We predict that no fan energy, or mechanical cooling will be required during those times when outside conditions are favorable. Our control strategy also includes mechanical-assisted ventilation to provide space comfort and ventilation by drawing outside air through open windows, into the occupied rooms, and out through the ventilation shafts. This mode uses 25% of the fan energy that would be required by economizer operation which uses the HVAC system fans to overcome all of the pressure drop in the ductwork. The system will be in this mode when outside air conditions are favorable to provide occupant comfort, but there is not enough temperature differential for buoyancy forces alone to be effective. We predict that outside air conditions will be favorable for this mode approximately 300 occupied hours per year. This is a demonstration that occupants can be comfortable without air conditioning in a modern building that has been designed for that purpose. The building is located in a high humidity climate. It is equipped with air conditioning that will be in operation when the outdoor dew point is above 64 F, which includes all of the hours when the dry bulb temperature exceeds 85 F. We propose to demonstrate the reduction of energy consumption and cost from the use of ventilation shafts that allow for natural ventilation and mechanical-assist ventilation using the exceptional calculation method. Our proposed building energy model will include controls that shut off the HVAC system during specified weather conditions and utilize exhaust fans only during specified weather conditions. The occupants retain control over their environment through the use of operable windows. The occupants will not have the ability to over-ride the control system to enable mechanical cooling when conditions are suitable to use outside air. We are defining those conditions as 68-85 F dry bulb temperature and dew point of 64 F or less. The budget building model will include air conditioning throughout the cooling season. The budget building model will not include economizer operation because the building is in a humid climate that does not require economizer by ASHRAE 90.1. We assert that these strategies to optimize energy performance meet the intent of this credit and we request permission to take credit for energy saved through natural and mechanically assisted mechanical ventilation in our modeling process.