Whole-building mechanical systems designed to provide
intermittent ventilation shall be in accordance with
Section E 605.1.7.1 and Section E 605.1.7.2. [ASHRAE
62.2:4.5]

Where
mechanical ventilation is provided at least once
every three hours by a system of one or more fans,
the intermittent mechanical ventilation rate shall be
calculated as the larger of the time average supply or
exhaust airflow rate and shall be not less than specified
in Section E 605.1.3. [ASHRAE 62.2:4.5.1]

Where mechanical ventilation is not
provided at least once every three hours by a single
fan system, the intermittent fan airflow rate (

Where:

Table E 605.1.7.2 also requires the calculation of the required turnover,

Where:

For SI units: 1 cubic foot per minute = 0.00047 m

For values not listed in Table 605.1.7.2, use the next higher value for

*Q*) shall be calculated in accordance with Equation E 605.1.7.2(1). Fan cycle time (_{on}*T*) shall not exceed 24 hours. Where the fan airflow rate during the on-cycle varies with time, the time average airflow rate during each hour shall meet or exceed the intermittent mechanical ventilation requirement in accordance with Equation E 605.1.7.2(1)._{cyc}*Q*≥

_{on}*Q*[Equation E 605.1.7.2(1)]

_{fan}/(ε•f)Q_{on} |
= | intermittent fan airflow rate during the on-cycle |

Q_{fan} |
= | continuous mechanical ventilation air requirement (from Table E 605.1.3.1 or Equation E 605.1.3.1) |

ε |
= | mechanical ventilation effectiveness (from Table E 605.1.7.2) |

f |
= | fractional on-time. defined as the on time for one cycle divided by the cycle time. |

Table E 605.1.7.2 also requires the calculation of the required turnover,

*N*, in accordance with the following:*N*= 12.8•

*Q*[Equation E 605.1.7.2(2)]

_{fan}•*T*/_{cyc}*A*_{floor}Q_{fan} |
= | mechanical ventilation air requirement (from Table E 605.1.3.1 or Equation E 605.1.3.1), ft ^{3}/min |

T_{cyc} |
= | fan cycle time, defined as the total time for one off-cycle and one on cycle, hours |

A_{floor} |
= | floor area of residence, ft^{2} |

For SI units: 1 cubic foot per minute = 0.00047 m

^{3}/s, 1 square foot =0.0929 m^{2}For values not listed in Table 605.1.7.2, use the next higher value for

*N*or the next lower value for*f*. Linear interpolation shall be permitted. [ASHRAE 62.2:4.5.2]**TABLE E 605.1.7.2**

MECHANICAL VENTILATION EFFECTIVENESS (

[ASHRAE 62.2:TABLE 4.2]

MECHANICAL VENTILATION EFFECTIVENESS (

*ε*) FOR INTERMITTENNT FANS[ASHRAE 62.2:TABLE 4.2]