ASHRAE-90.1-2022- - Page 100
Extracted Content
6.5.4.7 Chilled-Water Coil Selection. Chilled-water cooling coils shall be selected to provide a 15°F or higher temperature difference between leaving and entering water temperatures and a minimum of 57°F leaving water temperature at design conditions .
Exceptions to 6.5.4.7:
- Chilled-water cooling coils that have an air-side pressure drop exceeding 0.70 in. of water when rated at 500 fpm face velocity and dry conditions (no condensation).
- Individual fan-cooling units with a design supply airflow rate 5000 cfm and less.
- Constant-air-volume systems .
- Coils selected at the maximum temperature difference allowed by the chiller.
- Passive coils (no mechanically supplied airflow).
- Coils with design entering chilled-water temperatures of 50°F and higher.
- Coils with design entering air dry-bulb temperatures of 65°F and lower.
6.5.4.8 Buildings with High-Capacity Space-Heating Gas Boiler Systems. New buildings with gas hot-water boiler systems for space heating with a total system input of at least 1,000,000 Btu/h but not more than 10,000,000 Btu/h shall comply with Sections 6.5.4.8.1 and 6.5.4.8.2.
Exceptions to 6.5.4.8:
- Where 25% of the annual space heating requirement is provided by on-site renewable energy, site-recovered energy, or heat recovery chillers.
- Space heating boilers installed in individual dwelling units .
- Where 50% or more of the design heating load is served using perimeter convective heating, radiant ceiling panels, or both.
- Individual gas boilers with input capacity less than 300,000 Btu/h shall not be included in the calculations of the total system input or total system efficiency .
6.5.4.8.1 Boiler Efficiency. Gas hot-water boilers shall have a minimum thermal efficiency ( Et ) of 90% when rated in accordance with the test procedures in Table 6.8.1-6. Systems with multiple boilers are allowed to meet this requirement if the space heating input provided by equipment with thermal efficiency ( Et ) above and below 90% provides an input capacity-weighted average thermal efficiency of at least 90%. For boilers rated only for combustion efficiency, the calculation for the input capacity-weighted average thermal efficiency shall use the combustion efficiency value.
6.5.4.8.2 Hot-Water Distribution System Design. The hot-water distribution system shall be designed to meet all of the following:
a. Coils and other heat exchangers shall be selected so that at design conditions the hot-water return tem perature entering the boilers is 120°F or less. b. Under all operating conditions, the water temperature entering the boiler is 120°F or less, or the flow rate
of supply hot water that recirculates directly into the return system, such as by three-way valves or minimum flow bypass controls, shall be no greater than 20% of the design flow of the operating boilers .
6.5.5 Heat-Rejection Equipment 6.5.5.1 General. Section 6.5.5 applies to heat-rejection equipment used in comfort cooling systems, such as air-cooled condensers, dry coolers, open-circuit cooling towers, closed-circuit cooling towers, and evaporative condensers.
Exception to 6.5.5.1: Heat-rejection devices whose energy use is included in the equipment efficiency
ratings listed in Tables 6.8.1-1 through 6.8.1-4, Tables 6.8.1-8 through 6.8.1-14, and Tables 6.8.1-16, 6.8.1-17, and 6.8.1-20. 6.5.5.2 Fan Speed Control Informative Note: ASHRAE Guideline 36 includes detailed sequences of control for staging and controlling variable-speed cooling tower cells and fans.
6.5.5.2.1 The fan system on a heat-rejection device powered by an individual motor or an array of motors with a connected power, including the motor service factor, totaling 5 hp or more shall have controls and/or devices (such as variable-speed control) that shall result in fan motor demand of no more than 30% of design wattage at 50% of the design airflow and that shall automatically modulate the fan speed to control the leaving fluid temperature or condensing temperature/pressure of the heat-rejection device.
Exceptions to 6.5.5.2.1:
- Condenser fans serving multiple refrigerant or fluid cooling circuits.
- Condenser fans serving flooded condensers.
98 ANSI/ASHRAE/IES Standard 90.1-2022 (I-P)