ASHRAE-90.1-2022- - Page 099
Extracted Content
Table 6.5.4.6 Piping System Design Maximum Flow Rate in GPM
| Operating Hours/Year | 2000 Hours/Year | Col3 | >2000 and 4400 Hours/Year | Col5 | >4400 Hours/Year | Col7 |
|---|---|---|---|---|---|---|
| Nominal Pipe Size, in. | Other | Variable Flow/ Variable Speed | Other | Variable Flow/ Variable Speed | Other | Variable Flow/ Variable Speed |
| 2 1/2 | 120 | 180 | 85 | 130 | 68 | 110 |
| 3 | 180 | 270 | 140 | 210 | 110 | 170 |
| 4 | 350 | 530 | 260 | 400 | 210 | 320 |
| 5 | 410 | 620 | 310 | 470 | 250 | 370 |
| 6 | 740 | 1100 | 570 | 860 | 440 | 680 |
| 8 | 1200 | 1800 | 900 | 1400 | 700 | 1100 |
| 10 | 1800 | 2700 | 1300 | 2000 | 1000 | 1600 |
| 12 | 2500 | 3800 | 1900 | 2900 | 1500 | 2300 |
| Maximum velocity for pipes over 14 to 24 in. in size | 8.5 ft/s | 13.0 ft/s | 6.5 ft/s | 9.5 ft/s | 5.0 ft/s | 7.5 ft/s |
pumps are used to serve multiple boilers, the number of pumps shall be no less than the number of boilers and staged on and off with the boilers .
6.5.4.4 Chilled- and Hot-Water Temperature Reset Controls. Chilled- and hot-water systems with a design capacity exceeding 300,000 Btu/h supplying chilled or heated water to comfort conditioning systems shall include controls that automatically reset supply water temperatures by representative building loads (including return water temperature) or by outdoor air temperature. Where DDC is used to control valves, the set point shall be reset based on valve positions until one valve is nearly wide open or set-point limits of the system equipment or application have been reached.
Exceptions to 6.5.4.4:
- Where chilled-water supply is already cold, such as chilled water supplied from a district cooling or thermal energy storage system, such that blending would be required to achieve the reset chilledwater supply temperature.
- Where a specific temperature is required for a process application .
- Water temperature reset is not required where valve position is used to comply with Section 6.5.4.2.
Informative Note: ASHRAE Guideline 36 includes detailed sequences of control for resetting chilledwater and hot-water system temperature set points based on control valve position.
6.5.4.5 Hydronic (Water Loop) Heat Pumps and Water-Cooled Unitary Air Conditioners
6.5.4.5.1 Each hydronic heat pump and water-cooled unitary air conditioner shall have a two-position automatic valve interlocked to shut off water flow when the compressor is off.
Exception to 6.5.4.5.1: Units employing a fluid economizer.
6.5.4.5.2 Hydronic heat pumps and water-cooled unitary air conditioners having a total pump system power exceeding 5 hp shall have controls and/or devices (such as variable-speed control) that will result in pump motor demand of no more than 30% of design wattage at 50% of design water flow.
6.5.4.6 Pipe Sizing. All chilled-water and condenser-water piping shall be designed such that the design flow rate in each piping segment shall not exceed the values listed in Table 6.5.4.6 for the appropriate total annual hours of operation. Piping size selections for systems that operate under variable flow conditions (e.g., modulating two-way control valves at coils) and that contain variable-speed pump motors are allowed to be made from the “Variable Flow/Variable Speed” columns. All others shall be made from the “Other” columns.
Exceptions to 6.5.4.6:
- Design flow rates exceeding the values in Table 6.5.4.6 are allowed in specific sections of piping if the piping in question is not in the critical circuit at design conditions and is not predicted to be in the critical circuit during more than 30% of operating hours.
- Piping systems that have equivalent or lower total pressure drop than the same system constructed with standard weight steel pipe with piping and fittings sized per Table 6.5.4.6.
ANSI/ASHRAE/IES Standard 90.1-2022 (I-P) 97