Source: https://buildingscience.com/documents/information-sheets/information-sheet-ventilation-system
RESNET/ICC 301-2022 Addendum E-2022 was added in Ekotrope in Version 5.1.0 and adds a major update for modeling CFIS or Air Cycler systems which use the blower fan of the ducted distribution system to provide mechanical ventilation to the dwelling unit. The update states that the duct losses from running mechanical ventilation through the ducts must be accounted for.
What qualifies as mechanical ventilation in RESNET
Notably not all CFIS systems will qualify as dwelling unit mechanical ventilation systems, the RESNET definition is:
“Dwelling Unit Mechanical Ventilation System – A Ventilation system, operating continuously or through a programmed intermittent schedule, consisting of powered Ventilation equipment,[1] related mechanical components,[2] and automated control devices[3] that provides Dwelling Unit Ventilation at a known or measured airflow rate.”
CFIS systems in Ekotrope V5.1.0 and later that use a blower fan control strategy of “Heating and Cooling Runtime” without a strategy to meet the ventilation remainder will not qualify as a mechanical ventilation system as the ventilation will only occur when the blower fan is running for heating and cooling purposes.
How Inputs Determine CFIS Systems
For Ventilation Type: Air Cycler (CFIS)
To model these systems enter the inputs for “Fan Watts” and “Ventilation Rate” when the blower fan is running in a ventilation mode. The "Operational Hours per Day” should be input along with the ventilation rate to meet the ventilation target, this will be the operational hours per day of the blower fan if there are no heating or cooling calls for the entire day and it only operates for ventilation.
Has automatic flow control of outdoor air? | Blower fan control strategy | Has a strategy to meet the ventilation remainder? | System Description |
TRUE | Fixed Time Intervals | NA | CFIS with return side air intake with an automatic motorized damper, has a simple controller for ventilation based on a timer to operate the blower fan in order to meet the minimum ventilation requirement.
If the air handler is set up to run on a fixed time interval and does so regardless of the heating and cooling runtime. Any additional blower fan runtime energy modeled using the equation in Section 4.2.2.7.2.13.3.2 of Addendum E-2022. |
Heating and Cooling Runtime | TRUE | The standard CFIS system with a return side outdoor air intake with an automatic motorized damper. Has a controller to ensure hourly that the ventilation target is met, by first checking if the heating and cooling conditioning runtime meets the ventilation target, if not it will run the blower fan to meet the remainder of the ventilation target.
The blower fan will supply ventilation during heating and cooling calls, and will run at minimum the fraction of the hour needed as per the ventilation target. Furthermore the damper will prevent additional outside air ventilation if the heating and cooling calls require the air handler to run for longer than the ventilation target. |
Heating and Cooling Runtime | FALSE | CFIS with a return side outdoor air intake that only provides ventilation during heating and cooling calls. This does not qualify as dwelling unit mechanical ventilation per the definition in ANSI / RESNET / ICC 301
Will run ventilation only when there is a need for heating or cooling by the system. With the automatic damper it will not ventilate longer than required but without the ventilation strategy it will not always meet the ventilation target. |
FALSE | Fixed Time Intervals | NA | CFIS with return side air intake that does not have a qualified automatic damper, has a simple controller based on a timer to operate the blower fan in order to meet the minimum ventilation requirement.
If the air handler is set up to run on a fixed time interval and does so regardless of the heating and cooling runtime. Any additional blower fan runtime energy modeled using the equation in Section 4.2.2.7.2.13.3.2 of Addendum E-2022. Without a damper outdoor ventilation is modeled during all heating, cooling, and ventilation periods. |
Heating and Cooling Runtime | TRUE | A CFIS system with a return side outdoor air intake withOUT an automatic motorized damper. It has a controller to ensure hourly that the ventilation target is met, by first checking if the heating and cooling conditioning runtime meets the ventilation target, if not it will run the blower fan to meet the remainder of the ventilation target.
The air handler will supply ventilation during heating and cooling calls, and will run at minimum the fraction of the hour needed as per the ventilation target. As there is no automatic damper in this case, if the heating and cooling calls are longer than the runtime requirement for the ventilation target, the air handler will continue ventilation over its entire run time. |
Heating and Cooling Runtime | FALSE | CFIS with a return side outdoor air intake that only provides ventilation during heating and cooling calls. This does not qualify as dwelling unit mechanical ventilation per the definition in ANSI / RESNET / ICC 301
Will run ventilation only when there is a need for heating or cooling by the system. Without an automatic damper it can ventilate longer than required during some hours there is no guarantee for ventilation any hour. |
For Ventilation Type: Air Cycler w/ Supplemental Fan (CFIS)
To model these systems enter the inputs for “Fan Watts” and “Ventilation Rate” of the supplemental fan. The "Operational Hours per Day” will be used to set the ventilation target, here this will be the operational hours per day of the supplemental fan if there are no heating or cooling calls for the entire day and the blower fan does not run at all.
Here Ekotrope will assume that the ventilation rates of the supplemental fan and the return side outdoor air intake of the CFIS system are equal. And at no point will the blower fan run for ventilation only so the consumption of the blower fan is only accounted for in the heating or cooling consumption.
Has automatic flow control of outdoor air? | Blower fan control strategy | Does supplemental fan run simultaneously with blower fan? | System Description |
TRUE | Heating and Cooling Runtime | TRUE | A CFIS system with a return side outdoor air intake, a qualified automatic damper, and a supplemental supply or exhaust fan that is controlled to operate in unison with the blower fan when running in heating and cooling modes. The ventilation will run to meet the ventilation target, and the blower fan will run only during heating and cooling modes. |
FALSE | A CFIS system with a return side outdoor air intake, a qualified automatic damper, and a supplemental supply or exhaust fan. The controller will allow ventilation through the damper during heating and cooling calls, and then if the ventilation target is not met will run the supplemental fan until the target is met.
The ventilation target will always be met exactly, if heating or cooling mode is required to run longer than is needed for the ventilation target the damper will close and end ventilation. |
FALSE | TRUE | A CFIS system with a return side outdoor air intake, a qualified automatic damper, and a supplemental supply or exhaust fan that is controlled to operate in unison with the blower fan when running in heating and cooling modes. The ventilation will run to meet the ventilation target, and the blower fan will run only during heating and cooling modes.
Here there is potential for the blower fan to over ventilate as there is no control to stop ventilation when the target is met. |
FALSE | A CFIS system with a return side outdoor air intake, a qualified automatic damper, and a supplemental supply or exhaust fan. The controller will allow ventilation through the damper during heating and cooling calls, and then if the ventilation target is not met will run the supplemental fan until the target is met.
If heating or cooling mode is required to run longer than is needed for the ventilation target will be exceeded as there is no damper. |