Mechanical Ventilation

Modified on Wed, 7 May at 11:02 AM

Mechanical Ventilation Library Help

If you don't know the manufacturers specifications for ventilation systems, you can check the Home Ventilating Institute's Certified Products Directory.

Type

Options include:

Exhaust Only - One or more exhaust fans (commonly located in bathrooms and/or kitchens) that either continuously or intermittently remove air from the home.
Supply Only - An indoor fan that brings in air from outside and distributes it throughout the home.
Balanced - A combination of exhaust and supply ventilation that simultaneously balances air flowing into and out of the home, keeping the indoor pressure constant.
ERV - Energy-Recovery Ventilators utilize a balanced ventilation strategy, and recover both sensible and latent heat during air exchange.
HRV - Heat-Recovery Ventilators are a simpler sub-type of ERVs, that recover only sensible heat during air exchange.
Air Cycler - Supply-duct integrated ventilation using the central air handler with electronically controlled dampers. Also known as Central Fan Integrated Supply (CFIS) systems. Ekotrope will only account for fan energy beyond what would normally be consumed by the air handler.
Air Cycler w/ Supp. Fan - This is similar to a traditional Air Cycler system, but when ventilation is necessary at times that the air handler is not already on, ventilation is provided by a supplemental fan (e.g. a bathroom exhaust fan) that is wired to the Air Cycler control system rather than by the air handler itself. For these systems, the Fan Watts specified should be the Watts for the supplemental fan, not for the air handler.

Note: when rating a system where a supplementary fan is used in addition to the air handler fan and both fans are used when ventilation is called for, it should be modeled as an Air Cycler and the sum of the watts of the air handler and supplementary fans should be entered into the Fan Watts field.

Can flow rate be measured?

If ventilation can be measured, it must be measured. Mark "Yes" if ventilation can be measured, otherwise mark "No." If ventilation is unmeasured, the HERS Rated home will not get credit for low infiltration measurements, and a default fan ventilation will be used for the HERS Rated home. Please see ANSI/RESNET Standard 301-2014 Addendum 39 or ANSI/RESNET Standard 301 - 2019 Table 4.2.2(1) - Specifications for the Energy Rating Reference and Rated Homes - Air exchange rate for further details. Other codes and standards will still use the user entered unmeasured ventilation rate.

Ventilation Rate

Enter the mechanical ventilation rate in [Cubic Feet / Minute]. Reference ASHRAE Standard 62.2 for recommended ventilation rates.

Ventilation Rate

Enter the mechanical ventilation rate in [Cubic Feet / Minute]. Reference ASHRAE Standard 62.2 for recommended ventilation rates.

For CFIS systems, this is the rate of outdoor airflow provided through the return side outdoor air intake.

For mechanical ventilation systems that provide fresh air to multiple dwelling units in a multifamily building, please see guidance here.

Use Default Fan Watts

If ventilation wattage is not known, mark this checkbox to use default wattage. Defaults will be chosen based on ANSI/RESNET Standard 301-2014 Addendum 39 or ANSI/RESNET Standard 301 - 2019. Default Watts/CFM can be found in ANSI 301 - 2019 Table 4.2.2(1b).

Fan Watts

If the rated or measured wattage of the ventilation fan is known specify it here. If it isn't known, you may select the "Use Default Fan Watts" checkbox, which will satisfy RESNET Addendum 39.

For Central Fan Integrated Supply systems (CFIS, aka Air Cyclers) without a supplemental fan, enter the wattage consumed by the air handler when running for the design ventilation rate, which is the rate of controlled outside air for Indoor Air Quality. If the air handler does not have a dedicated ventilation speed, this is the full wattage when running in heating or cooling.

For systems that consume energy beyond what is needed to operate the ventilation fan (such as dehumidifiers), fan watts shall be the value observed either per OEM specifications or through direct measurement in the Rated Home for the highest airflow setting in ventilation-only mode.

From ANSI/RESNET Standard 301-2014 Addendum 39
To determine fan energy in the Rated Home, ventilation fan watts shall be based on the table below for the given system or the value observed in the Rated Home, for the highest airflow setting. Where needed to calculate fan watts, for systems other than Central Fan Integrated Supply (CFIS), the Whole-House Mechanical Ventilation System rate shall be assumed to be equal to Qfan, as calculated in accordance with Section 4.1.2 of ASHRAE Standard 62.2. For CFIS systems, the cfm used to determine fan watts shall be the larger of 400 cfm per 12 kBtu/h cooling capacity or 240 cfm per 12 kBtu/h heating capacity.

Default Ventilation Fan Watts
Equipment Type	Watts/CFM
Exhaust ventilation fans	0.35
Supply ventilation fans	0.35
Balanced ventilation fans	0.70
HRV/ERV fans	1.00
CFIS fans	0.50
Range hoods	0.70

Operational Hours per Day

Enter the number of hours the fan is running per day.

For CFIS systems, enter the number of hours that the system will be running the blower fan or supplemental fan for ventilation per day when there are no heating or cooling operational hours. This, along with the ventilation rate, is used to set the target outdoor air volume that the CFIS system will meet every hour independent of ventilation occurring during heating or cooling modes on the air handler.

Runs Once Every Three Hours

This box should be checked if intermittent ventilation runs at least once every three hours. This will not affect the energy consumption or HERS Index of the home, but it will affect the ASHRAE 62.2 required ventilation calculation. ASHRAE 62.2 specifies a different ventilation effectiveness for fans that run at least once every 3 hours.

Fan Efficacy Override

Use this override if the ventilation system meets efficacy threshold for IECC Ventilation Requirement at a different rating point.

Fan Efficacy
[CFM / W]

Enter the value of the rated fan efficacy in CFM / W

Is this an inline fan?

This selection will show only for certain ventilation types. It was added to Ekotrope in September 2021 in order to support the IECC 2021 code, which has different efficacy requirements for inline fans. If left as "Unspecified," which is the default value, Ekotrope will indicate that the home does not meet IECC 2021.

For CFIS systems with supplemental fan type "Supply ventilation fan", if the supply fan is an inline fan Ekotrope will assume the supply fan is inline with the return side outdoor air intake and feeds the ventilation air to the duct system. If not it is assumed that the supplemental supply fan operates as a separate fan in the dwelling.

New in Version 5.1.0 and later for CFIS / Air Cycler ventilation types

Distribution System Assigned

The forced air distribution system that the CFIS controller is attached to.

Has automatic flow control of outdoor air?

If the CFIS system has a mechanical damper to automatically control the flow of outdoor air.

Blower fan control strategy

Choose whether the CFIS system operates on a control strategy to run the blower fan at fixed time intervals (irrespective of the heating and cooling runtime) or only uses heating and cooling runtime to meet the hourly ventilation target.

Has a strategy to meet the ventilation remainder?

If checked the blower fan will always be run at minimum, long enough to meet the hourly ventilation target., or if unchecked the blower fan will only run during heating and cooling calls.

Supplemental Fan Type

If the supplemental fan for the ventilation type Air Cycler w/ Supplemental Fan (CFIS) is an exhaust fan or a supply fan.

Does supplemental fan run simultaneously with blower fan?

If the supplemental fan runs at the same time as the blower fan.

For exhaust supplemental fans, this potentially creates a possibly temporarily "balanced" system. For supply supplemental fans this will mean that extra supplemental fan air flow will be supplied during times the blower fan is running and already supplying outdoor air.

If ERV or HRV are selected for type then the following field will also be available:

Energy Recovery Percent

Specify the Adjusted Sensible Recovery Efficiency (ASRE) of the ERV or HRV. If using the HVI directory, this will be in a row listed HEATING. If there are multiple rows, please select the ASRE with the corresponding temperature and fan flow that most closely reflects the climate and fan speed that will be present.

For more details on modeling CFIS / Air Cycler ventilation systems see here.