The simplest method to study the performance of a building without modeling a full HVAC system is by utilizing the Ideal Air Loads HVAC system. This piece of zone equipment is not connected to a central air system (no need to specify air loops, water loops, etc.) and instead supplies sufficient cooling or heating air to a zone to meet its load or up to its specified limits. The system has options for humidity control, outdoor air, economizer, demand-controlled ventilation, and heat recovery. It is 100% efficient, always available, and has infinite capacity. By default, all new Zones will be assigned to Ideal Air Loads. Zones can be manually assigned to Ideal Air Loads during the modeling process in the Project Data Editor.

Within the platform, the ideal air loads system is modeled as an ideal VAV terminal unit with variable supply temperature and humidity; the supply airflow ventilation rate is varied between zero and the maximum in order to satisfy the heating or cooling load, humidity controls, outdoor air requirements, and other specified constraints. This system acts as the default system for the building if no Zones or Air Systems are specified. If running the model without considering Zones, the Project Data Editor and Air System page can be skipped, and the model will run using the Ideal Air Load system assigned to every room of the model.

Airflow rates reported are based on a cooling supply air temperature of 57.4°F (14.1°C) and a heating supply air temperature of 104°F (40°C). Outdoor airflow is determined using an Air Distribution Effectiveness of 1.0 for both heating and cooling.

When running an ideal air loads system, the ventilation load is reported in the Peak Load Breakdown within the Detailed Cooling/Heating Load Results tab on the Results page, which is not the case for projects with zones supplied by non-ideal air systems.

Energy consumed by the ideal air load system for heating and cooling is attributed to the District Heating and District Cooling end uses respectively.

Note: The Ideal Air Load System is not designed to be used for energy performance estimation. Its core use is to help determine room-level heating and cooling loads. The energy reporting will not consider the HVAC system and may be inaccurate.

Q. How does the air balance work for an Ideal Air System? Which type of air flow values can be customized?

A. The airflow values for a thermal zone are always balanced with the Ideal Air System. Since the ideal air loads are a simplified piece of conditioning equipment, the outdoor air flow rates can be edited directly by users as it equals the supply air. And since the air is balanced, the exhaust airflow rates will be the same as well.