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# Ventilation Rate - ASHRAE 62.2   # General

Number of Bedrooms:  You may leave this value as zero in order to use the default value shown in the gray box to the right.Otherwise, enter the number of bedrooms if different from the value shown in the gray box to the right.  The number of bedrooms is used in the following formula:

Qtot = 0.03 * Afloor + 7.5 * (Nbr + 1)

Where:

Qtot = total required ventilation rate

Afloor = dwelling unit floor area

Nbr = number of bedrooms (not to be less than 1)

Number of People:  You may leave this value as zero in order to use the default value shown in the gray box to the right.Otherwise, enter the number of people if different from the value shown in the gray box to the right.  The number of people is used only if the number of people is more than the number of bedrooms plus one.  When that happens the total ventilation rate is increased by 7.5 cfm for each additional person.

Low to High Point Distance:  You may leave this value as zero in order to use the default value shown in the gray box to the right.Otherwise, enter the vertical distance between the lowest and highest above-grade points within the pressure boundary if different from the value shown in the gray box to the right.  This value is used to calculate the normalized leakage using the following formula:

NL = 1000 * ELA / Afloor * (H / Hr) ^ z

Where:

NL = normalized leakage

ELA = effective leakage area

Afloor = floor area of residence

H = vertical distance between the lowest and highest above-grade points within the pressure boundary

Hr = reference height, 8.2 ft.

z = 0.4 for the purpose of calculating the Effective Annual Infiltration Rate

Normalized Leakage Area:  This gray box shows the normalized leakage area that takes into account the vertical low to high point difference.  The normalized leakage is calculated using the following formula:

NL = 1000 * ELA / Afloor * (H / Hr) ^ z

Where:

NL = normalized leakage

ELA = effective leakage area

Afloor = floor area of residence

H = vertical distance between the lowest and highest above-grade points within the pressure boundary

Hr = reference height, 8.2 ft.

z = 0.4 for the purpose of calculating the Effective Annual Infiltration Rate

Weather and Shielding Factor:  You may leave this value as zero in order to use the default value shown in the gray box to the right.Otherwise, enter the value you want if different from the value shown in the gray box to the right.

The weather and shielding factor (wsf) is from Appendix B in ANSI/ASHRAE Standard 62.2-2016.  It is used by the ASHRAE 62.2 ventilation calculations to determine the Effective Annual Infiltration Rate.

This value is only non-zero for those cities that are listed in the above publication.

Conditioned Floor Area:  You may leave this value as zero in order to use the default value shown in the gray box to the right.Otherwise, enter the conditioned floor area if different from the value shown in the gray box to the right.

This value is for the entire conditioned floor area of the building, unless you have set the system to be isolated.  For an isolated system use the floor area of the system.

The floor area is used to determine the Total Ventilation Rate, the Normalized Leakage, and the Effective Annual Average Infiltration Rate

Total Ventilation Rate (Unadjusted):  The total ventilation rate is calculated using the following formula:

Qtot = 0.03 * Afloor + 7.5 * (Nbr + 1)

Where:

Qtot = total required ventilation rate

Afloor = dwelling unit floor area

Nbr = number of bedrooms (not to be less than 1)

Provide Infiltration Credit:  Select whether you want to provide infiltration credit to reduce the required amount of ventilation.  If you select Yes, then click the General tab and enter the required blower door infiltration inputs.

Effective Annual Average Infiltration Rate (Unadjusted):  This box shows the Effective Average Infiltration Rate (unadjusted) calculated using the following formula:

Qinf = (NL * wsf * Afloor) / 7.3

Where:

Qinf = effective annual infiltration rate

NL = normalized leakage

wsf = weather and shielding factor

Afloor = floor area of residence

Effective Annual Infiltration Rate (Adjusted):  This box shows the infiltration credit used to determine the Required Mechanical Ventilation Rate.  It is equal to the smaller of the non-adjusted effective annual infiltration rate and 2/3 of the Total Ventilation Rate.

Exterior Envelope Surface Area Ratio:  This value is 1 for single family detached homes.  This value is the ratio of exterior envelope surface area that is not attached to garages or other dwelling units to total envelope surface area for single-family attached homes.

# Result

Required Mechanical Ventilation Rate:  The required mechanical ventilation rate is the final result of all of these inputs.  It is calculated using the following formula:

Qfan = Qtot - (Qinf x Aext)

where:

Qfan = required mechanical ventilation rate

Qtot = total required ventilation rate

Qinf = effective annual infiltration rate, but not greater than 2/3 x Qtot

Aext = exterior envelope surface area ratio, which is 1 for single family detached homes, or the ratio of exterior envelope surface area that is not attached to garages or other dwelling units to total envelope surface area for the single-family attached homes

Insert Winter, Insert Summer Buttons:  These buttons let you copy the results shown in "Required mechanical ventilation rate" boxes above into the winter or summer ventilation input at the bottom of the window.

Ventilation Rate, Winter and Summer:  Specifies the amount of ventilation to use for this system.  The amount you enter for ventilation and exhaust will affect the amount of infiltration you entered for this system.  If ventilation is greater than exhaust, the system will be under positive pressure and the infiltration will be reduced.  If exhaust is greater than infiltration, the system will have negative pressure and the amount of infiltration will be increased above the amount that you specified.

# Infiltration Credit

Building Volume:  This box shows the building volume used for certain infiltration calculations.  The volume shown here is based on the Building Volume Option on the General Project Data window.

If the current system is set to be isolated using the System Is Isolated input on the System Data window then this value shows the current system's volume.

Wind Shielding Class:  Select the wind shielding class from the list in the dropdown help.  These options are from Manual J's Table 5D, on page 177.  The higher the wind shielding class, the lower the infiltration.

Stories in Building:  Select the number of stories in the building from the list below.  This input sets the value called the Stack Coefficient from Manual J's table 5D, page 177.  The more stories, the higher the infiltration.

Assumed n (Single-Point Assumed Value of "n" Parameter):  When using single-point blower test results, the value of the flow exponent "n" parameter is usually assumed to be 0.65.  If you want to use a different value for the "n" parameter enter it here.  The value here will be used along with the pressure difference and flow you enter to calculate the effective leakage area.  Then from the effective leakage area the infiltration CFM will be calculated.

Pressure Difference of 4 Pa:  For the purpose of determining infiltration credit the pressure is fixed at 4 Pa.

Test Flow or AC/hr Option:  Select whether you want to enter a test flow or a test air changes per hour value.  Once you select an option the corresponding input below will become enabled.

Test Flow:  Enter the airflow used for the blower door test single-point data, in CFM.  The value you enter here will be used along with the flow exponent "n" and test pressure difference you enter to calculate the effective leakage area.  Then from the effective leakage area the infiltration CFM will be calculated.

Test AC/hr:  Enter the test air changes per hour of infiltration while the blower door test is being performed.  In the dropdown help are some typical air changes per hour values, but you may enter a different value if you like.

Effective Leakage Area (in²):  This box shows the calculated leakage area (sq. in.) calculated from the inputs above.

Effective Leakage Area (ft²):  This box shows the leakage area converted to square feet, which is then used in the formula for calculating the Normalized Leakage Area, which is given earlier on this page.

Recalculate Button:  Click this button if you want to immediately see the new results after having edited the inputs on this page.