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6.5.6.1 Exhaust Air Energy Recovery
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6.5.6.1.1 Nontransient Dwelling Units
Nontransient dwelling units shall be provided with outdoor air energy recovery ventilation systems. For nontransient dwelling units, energy recovery systems shall result in an enthalpy recovery ratio of at least 50% at cooling design condition and at least 60% at heating design condition. The energy recovery system shall provide the required enthalpy recovery ratio at both heating and cooling design conditions, unless one mode is not required for the climate zone by the exceptions below.
Exceptions to 6.5.6.1.1
- Nontransient dwelling units in Climate Zone 3C.
- Nontransient dwelling units with no more than 500 ft2 of conditioned floor area in Climate Zone 0, 1, 2, 3, 4C, and 5C.
- Enthalpy recovery ratio requirements at heating design condition in Climate Zones 0, 1, and 2.
- Enthalpy recovery ratio requirements at cooling design condition in Climate Zones 4, 5, 6, 7, 8.
6.5.6.1.2 Spaces Other Than Nontransient Dwelling Units
Each fan system serving spaces other than nontransient dwelling units shall have an energy recovery system where the design supply fan airflow rate exceeds the value listed in Tables 6.5.6.1.2-1 and 6.5.6.1.2-2, based on the climate zone and percentage of outdoor air at design airflow conditions. Table 6.5.6.1.2-1 shall be used for all ventilation systems that operate less than 8000 hours per year, and Table 6.5.6.1.2-1 shall be used for all ventilation systems that operate 8000 or more hours per year.
For spaces other than nontransient dwelling units, energy recovery systems shall result in an enthalpy recovery ratio of at least 50%. The energy recovery system shall provide the required enthalpy recovery ratio at both heating and cooling design conditions, unless one mode is not required for the climate zone by the exceptions below. Provision shall be made to bypass or control the energy recovery system to permit air economizer operation as required by Section 6.5.1.1.
Exceptions to 6.5.6.1.2
- Laboratory systems meeting Section 6.5.7.3.
- Systems serving spaces that are not cooled and that are heated to less than 60°F.
- Heating energy recovery where more than 60% of the outdoor air heating energy is provided from site-recovered energy or site-solar energy in Climate Zones 5 through 8.
- Enthalpy recovery ratio requirements at heating design condition in Climate Zones 0, 1, and 2.
- Enthalpy recovery ratio requirements at cooling design condition in Climate Zones 3C, 4C, 5B, 5C, 6B, 7, and 8.
- Where the sum of the airflow rates exhausted and relieved within 20 ft of each other is less than 75% of the design outdoor airflow rate, excluding exhaust air that is
- Systems in Climate Zones 0 through 4 requiring dehumidification that employ series energy recovery and have a minimum SERR of 0.40.
- Systems expected to operate less than 20 hours per week at the outdoor air percentage covered by Table 6.5.6.1.2-1.
- Indoor pool dehumidifiers meeting Section 6.5.6.4.
Table 6.5.6.1.2-1 Exhaust Air Energy Recovery Requirements for Ventilation Systems Operating Less than 8000 Hours per Year
| Climate Zone | % Outdoor Air at Full Design Airflow Rate | |||||||
|---|---|---|---|---|---|---|---|---|
| ≥10% and <20% | ≥20% and <30% | ≥30% and < 40% | ≥40% and < 50% | ≥50% and < 60% | ≥60% and <70% | ≥70% and < 80% | ≥80% | |
| Design Supply Fan Airflow Rate, cfm | ||||||||
| 3B, 3C, 4B, 4C, 5B | NR | NR | NR | NR | NR | NR | NR | NR |
| 0B, 1B, 2B,5C | NR | NR | NR | NR | ≥26000 | ≥12000 | ≥5000 | ≥4000 |
| 6B | ≥28,000 | ≥26,500 | ≥11000 | ≥5500 | ≥4500 | ≥3500 | ≥ 2500 | ≥1500 |
| 0A, 1A, 2A, 3A, 4A, 5A, 6A | ≥26,000 | ≥16,000 | ≥5500 | ≥4500 | ≥3500 | ≥2000 | ≥1000 | >120 |
| 7,8 | ≥4500 | ≥4000 | ≥2500 | ≥1000 | ≥140 | ≥120 | ≥100 | ≥80 |
NR—Not required
Table 6.5.6.1.2-2 Exhaust Air Energy Recovery Requirements for Ventilation Systems Operating Greater than or Equal to 8000 Hours per Year
| Climate Zone | % Outdoor Air at Full Design Airflow Rate | |||||||
|---|---|---|---|---|---|---|---|---|
| ≥10% and <20% | ≥20% and <30% | ≥30% and < 40% | ≥40% and < 50% | ≥50% and < 60% | ≥60% and <70% | ≥70% and < 80% | ≥80% | |
| Design Supply Fan Airflow Rate, cfm | ||||||||
| 3C | NR | NR | NR | NR | NR | NR | NR | NR |
| 0B, 1B, 2B, 3B, 4C, 5C | NR | ≥19,500 | ≥9000 | ≥5000 | ≥4000 | ≥3000 | ≥1500 | ≥120 |
| 0A, 1A, 2A, 3A, 4B, 5B | ≥2500 | ≥2000 | ≥1000 | ≥500 | ≥140 | ≥120 | ≥100 | ≥80 |
| 4A, 5A, 6A, 6B, 7, 8 | ≥200 | ≥130 | ≥100 | ≥80 | ≥70 | ≥60 | ≥50 | ≥40 |
NR—Not required
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