ASHRAE-90.1-2022- - Page 101
Extracted Content
6.5.5.2.2 Multicell heat-rejection equipment with variable-speed fan drives shall
a. operate the maximum number of fans allowed that comply with the manufacturer ’s requirements for all
system components and b. control all fans to the same fan speed required for the instantaneous cooling duty, as opposed to staged
(on/off) operation. Minimum fan speed shall comply with the minimum allowable speed of the fan drive system per the manufacturer ’s recommendations.
6.5.5.3 Limitation on Centrifugal Fan Open-Circuit Cooling Towers. Centrifugal fan open-circuit cooling towers with a combined rated capacity of 1100 gpm or greater at 95°F condenser water return, 85°F condenser water supply, and 75°F outdoor air wet-bulb temperature shall meet the energy efficiency requirement for axial fan open-circuit cooling towers listed in Table 6.8.1-7.
Exception to 6.5.5.3: Centrifugal open-circuit cooling towers that are ducted (inlet or discharge) or
require external sound attenuation. 6.5.5.4 Tower Flow Turndown. Open-circuit cooling towers used on water-cooled chiller systems that are configured with multiple- or variable-speed condenser water pumps shall be designed so that all opencircuit cooling tower cells can be run in parallel with the larger of
a. the flow that is produced by the smallest pump at its minimum expected flow rate or b. 50% of the design flow for the cell.
6.5.6 Energy Recovery 6.5.6.1 Exhaust Air Energy Recovery 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 the cooling design condition.
At the heating design condition, energy recovery performance shall be as follows:
a. Where active humidification is provided to spaces served by the system, energy recovery systems shall
result in an enthalpy recovery ratio of at least 60%. b. Where active humidification is not provided to spaces served by the system, energy recovery systems
shall result in a sensible energy recovery ratio of at least 60%.
The energy recovery system shall provide the required enthalpy recovery ratio or sensible energy recov- ery 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 ft [2] of gross conditioned floor area in Climate Zone 0, 1, 2, 3, 4C, and 5C.
- Energy recovery performance 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 6.5.6.1.2-2 shall be used for all ventilation systems that operate 8000 or more hours per year.
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 on-site renewable 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 a. used for another energy recovery system,
ANSI/ASHRAE/IES Standard 90.1-2022 (I-P) 99