Air systems consists of various components such as air handling units, zone components, central components, zone terminal units, economizers, and energy recovery wheels. These systems can be configured on Air System page. Once simulations are completed, Air System results can be accessed by navigating to Air System tab of the Results Page. An overview of the air system results is provided below.
Air System Details
Area Served [ft² (IP) | m² (SI)]: The total area of the building served by this air system
Number of Zones: The total number of zones assigned to this air system
Number of People: the total number of occupants in thermal zones connected to the Air System
Template: This is the source template for the Air System.
Primary Cooling Coincident Load Details
Total Cooling Load [Btu/h (IP) | Watts (SI)]: Actual peak cooling load for the air system taking into account the dynamic nature of individual zone loads that make up the total.
Sensible Cooling Load[Btu/h (IP) | Watts (SI)]: The component of the total cooling load that is sensible.
Latent Cooling Load [Btu/h (IP) | Watts (SI)]: The component of the total cooling load that is latent.
Time of Peak: The day and hour of the year when air system experience the peak cooling load.
Outside Air Temperature [°F (IP) | °C (SI)]: Dry bulb and wet bulb outside air temperature at the time of peak.
Supply Air Setpoint [°F (IP) | °C (SI)]: Dry bulb and wet bulb temperature of the supplied air
System Cooling Sensible Load Breakdown: Cooling sensible load is divided into contributing factors to envelope gains and losses as well as internal gains.
Envelope Gains/Losses [Btu/h (IP) | Watts (SI)]: The sensible portion of total cooling load that was gained or lost through building envelope.
External Walls: Cooling load gains and losses through external walls.
Ground Walls : Cooling load gains and losses through ground contact walls.
Roofs: Cooling load gains and losses through the roof.
Ground Floor: Cooling load gains and losses through the ground contact floors.
Exposed Floor: Cooling load gains and losses through floors exposed to outside air.
Glazing Conduction and Solar Radiation: Cooling load gains and losses through glazing conduction and radiation. Typically the heat gains are divided into two components, the Conduction related to the U-value and the Radiation related to the SHGC. Dividing the heat gains in this fashion is helpful because it allows key characteristics of the glazing, U-value and SHGC, to be considered in regard to their impact on cooling loads. More detail on the glazing calculations can be found here.
Doors: Cooling load gains and losses through the doors associated with the air system.
Infiltration: Cooling load gains and losses through infiltration between inside and outside of the building
Internal Gains [Btu/h (IP) | Watts (SI)]: The sensible portion of total cooling load that was gained through internal loads such as occupant, light, equipment and adjacent spaces.
Internal Walls: Internal load gains from the adjacent spaces through internal walls
Internal Floors: Internal load gains from the adjacent spaces through internal floors
Lights: Internal load gains from lights in the space
People: Internal load gains from the occupants
Equipment: Internal load gains from the adjacent spaces through electrical equipment
Ventilation: Internal load gains through ventilation, note these are only reported when the Ideal Air Load system is used.
Latent Gains/Losses [Btu/h (IP) | Watts (SI)]: The latent portion of cooling load gained or lost representing the amount of energy that is necessary to dehumidify the air in a building.
Infiltration: Latent load gains and losses through infiltration between building and outside environment.
People: Latent load gains and losses caused by occupants
Equipment: Latent load gains and losses generated by operating equipment
Simulation Factors [Btu/h (IP) | Watts (SI)]:
Breakdown estimate: EnergyPlus calculations peak loads via the Heat Balance method. This method reports a single combined value for all gains and losses at time of peak. In order to report components EnergyPlus runs a secondary method to estimate the gain and losses from each component at that time of peak. The difference between sum of these estimates and the actual peak is reported here.
Safety factor represent the added value to the total load to account for the safety factor assigned on the Setting page.
Primary Heating Coincident Load Details
Total Heating Load [Btu/h (IP) | Watts (SI)]: Actual peak heating load for the air system taking into account the dynamic nature of individual zone loads that make up the total.
Sensible Cooling Load[Btu/h (IP) | Watts (SI)]: The component of the total heating load that is sensible.
Latent Cooling Load [Btu/h (IP) | Watts (SI)]: The component of the total heating load that is latent.
Time of Peak: the day and hour of the year when air system experience the peak heating load.
Outside Air Temperature [°F (IP) | °C (SI)]: Dry bulb and wet bulb outside air temperature at the time of peak.
Supply Air Setpoint [°F (IP) | °C (SI)]: Dry bulb temperature of the supplied air
System Cooling Sensible Load Breakdown: Heating sensible load is divided into contributing factors to envelope gains and losses as well as internal gains.
Envelope Gains/Losses [Btu/h (IP) | Watts (SI)]: The portion of total heating load that was gained or lost through building envelope.
External Walls: Heating load gains and losses through external walls.
Ground Walls : Heating load gains and losses through ground contact walls.
Roofs: Heating load gains and losses through the roof
Ground Floor: Heating load gains and losses through the ground contact floors.
Exposed Floor: Heating load gains and losses through floors exposed to outside air.
Glazing Conduction and Solar Radiation: Heating load gains and losses through glazing conduction and radiation. Typically the heat gains are divided into two components, the Conduction related to the U-value and the Radiation related to the SHGC. Dividing the heat gains in this fashion is helpful because it allows key characteristics of the glazing, U-value and SHGC, to be considered in regard to their impact on cooling loads. More detail on the glazing calculations can be found here.
Doors: Heating load gains and losses through the doors associated with the air system.
Infiltration: Heating load gains and losses through infiltration between inside and outside of the building
Internal Gains [Btu/h (IP) | Watts (SI)]: The portion of total heating load that was gained through internal loads such as occupant, light, equipment and adjacent spaces.Internal Walls: Internal load gains from the adjacent spaces through internal walls
Internal Floors: Internal load gains from the adjacent spaces through internal floors
Ventilation: Internal load gains through ventilation, note these are only reported when the Ideal Air Load system is used.
Latent Gains/Losses [Btu/h (IP) | Watts (SI)]: The portion of heating load gained or lost representing the amount of energy that is necessary to dehumidify the air in a building.
Infiltration: Latent load gains and losses through infiltration between building and outside environment.
Simulation Factors [Btu/h (IP) | Watts (SI)]:
Breakdown estimate EnergyPlus calculations peak loads via the Heat Balance method. This method reports a single combined value for all gains and losses at time of peak. In order to report components EnergyPlus runs a secondary method to estimate the gain and losses from each component at that time of peak. The difference between sum of these estimates and the actual peak is reported here.
Safety factor represent the added value to the total load to account for the safety factor assigned on the Setting page.
System Airflows
Supply Air [CFM (IP) | L/S (SI)]: Air volume supplied by the air system into the connected zones
Outside Air [CFM (IP) | L/S (SI)]: Air volume of the outside air brought in and distributed by the air system
Return Air [CFM (IP) | L/S (SI)]: Air volume that gets recirculated into the air system
Exhaust Air [CFM (IP) | L/S (SI)]: Air volume of the air that gets released into the atmosphere after circulating through the air system
Pressurization [CFM (IP) | L/S (SI)]: This value reports how much the building is positively or negatively pressured. This value is calculated by subtracting system exhaust air flow from system outside air flow
Outside Air Percent: The fraction of the outside air that gets mixed with the return air
Cooling Min [CFM (IP) | L/S (SI)]: The minimum volume of air required to during unoccupied or turn-down conditions.
Heating Min [CFM (IP) | L/S (SI)]: The minimum volume of air required to meet the heating load of a space system is connected to.
System Checks
Total Cooling [Btu/h/ft²(IP) | W/m² (SI)]: This check provides the total cooling load per served area for the air system and is calculated by dividing total cooling peak load to the area served by the air system.
Sensible Cooling [Btu/h/ft²(IP) | W/m² (SI)]:This check provides the sensible cooling load per served area for the air system and is calculated by dividing sensible cooling peak load to the area served by the air system.
Heating [Btu/h/ft²(IP) | W/m² (SI)]: This check provides the heating load value per square foot area served by the air system.
Cooling [CFM/ft²(IP) | L/s/m² (SI)]: This check provides the cooling air volume flowing into the space per square foot area served by the air system.
Heating [CFM/ft²(IP) | L/s/m² (SI)]: This check provides the heating air volume flowing into the space per square foot area served by the air system.
Outside Air [CFM/ft²(IP) | L/s/m² (SI)]: This check provides the outside air volume per served area for the air system and is calculated by dividing outside air flow volume to the area served by the air system.
Primary Cooling Coil Sizing (Hydronic)
Total Capacity [Btu/h (IP) | Watts (SI)]: This is a measure of cooling coil's ability to remove heat from the space.
Total Capacity (Tons): Cooling coil's capacity provided in tons.
Airflow [CFM (IP) | L/S (SI)]: The air flow rate passing through the cooling coil.
Sensible Capacity [Btu/h (IP) | Watts (SI)]: Sensible cooling capacity of the cooling coil.
Fluid Flow [GPM (IP) | L/S (SI)]: Fluid volume passing through the cooling coil.
Entering and Leaving Temperatures [°F (IP) | °C (SI)]:The entering and leaving fluid temperatures (depending on coil type) of the coil. The default Inlet temperature is assigned per the Heating Source Mechanical Plant for fluid temperature.
Primary Heating Coil Sizing (Hydronic)
Total Capacity [Btu/h (IP) | Watts (SI)]: This is a measure of cooling coil's ability to heat the space
Total Capacity (Tons): Heating coil's capacity provided in tons.
Airflow [CFM (IP) | L/S (SI)]: The air flow rate passing through the heating coil.
Sensible Capacity [Btu/h (IP) | Watts (SI)]: Sensible cooling capacity of the heating coil.
Fluid Flow [GPM (IP) | L/S (SI)]: Fluid volume passing through the heating coil.
Entering and Leaving Temperatures [°F (IP) | °C (SI)]:The entering and leaving fluid temperatures(depending on coil type) of the coil. The default Inlet temperature is assigned per the Heating Source Mechanical Plant for fluid temperature.
Primary Cooling Coil Sizing (DX)
Total Capacity [Btu/h (IP) | Watts (SI)]: This is a measure of cooling coil's ability to remove heat from the space.
Total Capacity (Tons): Cooling coil's capacity provided in tons.
Airflow [CFM (IP) | L/S (SI)]: The air flow rate passing through the cooling coil.
Sensible Capacity (Btu/h): Sensible cooling capacity of the cooling coil.
Entering and Leaving Temperatures [°F (IP) | °C (SI)]:The entering and leaving fluid temperatures of the coil. The default Inlet temperature is read from the Winter Design Day for air temperature.
Primary Heating Coil Sizing (DX)
Total Capacity [Btu/h (IP) | Watts (SI)]: This is a measure of heating coil's ability to add heat to the space.
Airflow [CFM (IP) | L/S (SI)]: The air flow rate passing through the heating coil.
Entering and Leaving Temperatures [°F (IP) | °C (SI)]: The entering and leaving air temperatures of the heating coil. The default Inlet temperature is read from the Winter Design Day for air temperature.
Primary Cooling Coil Sizing (Gas and Electric)
Total Capacity [Btu/h (IP) | Watts (SI)]: This is a measure of heating coil's ability to add heat to the space.
Airflow [CFM (IP) | L/S (SI)]: The air flow rate passing through the heating coil.
Entering and Leaving Temperatures [°F (IP) | °C (SI)]: The entering and leaving air temperatures of the heating coil. The default Inlet temperature is read from the Winter Design Day for air temperature.
Primary Heating Coil Sizing (Gas and Electric)
Total Capacity [Btu/h (IP) | Watts (SI)]: This is a measure of heating coil's ability to remove heat from the space.
Airflow [CFM (IP) | L/S (SI)]: The air flow rate passing through the heating coil.
Entering and Leaving Temperatures [°F (IP) | °C (SI)]: The entering and leaving air temperatures of the heating coil. The default Inlet temperature is read from the Winter Design Day for air temperature.
Preheat Coil Sizing
Total Capacity [Btu/h (IP) | Watts (SI)]: This is a measure of preheat coil's ability to remove heat from the air before entering primary heating coil
Airflow [CFM (IP) | L/S (SI)]: The air flow rate passing through the heating coil.
Entering and Leaving Temperatures [°F (IP) | °C (SI)]: The entering and leaving air temperatures of the heating coil. The default Inlet temperature is read from the Winter Design Day for air temperature.
Humidifier
Water Flow [GPM (IP) | L/S (SI)]: Volume of water passing through the humidifier.
Peak Capacity [Btu/h (IP) | Watts (SI)]: Maximum moisture output humidifier can produce
FAQ
Q: Why is there an option for mixed air temperature autosizing on the cooling side, but not the heating side?
A: Within EnergyPlus, the default behavior for heating coils ignores the heat recovery and reports a sizing based on the 100% outdoor air condition for the coil.