ASHRAE-90.1-2022- - Page 098
Extracted Content
| Table 6.5.4.1 Boiler Turndown | Col2 |
|---|---|
| Boiler System Design Input, Btu/h | Minimum Turndown Ratio |
| 1,000,000 and5,000,000 | 3 to 1 |
| >5,000,000 and10,000,000 | 4 to 1 |
| >10,000,000 | 5 to 1 |
Table 6.5.4.2 Pump Flow Control Requirements
| Chilled-Water Pumps in These Climate Zones | Heating Water Pumps in These Climate Zones | Motor Nameplate Horsepower |
|---|---|---|
| 0A, 0B, 1A, 1B, 2B | NR | 2 hp |
| 2A, 3B | NR | 3 hp |
| 3A, 3C, 4A, 4B | 7, 8 | 5 hp |
| 4C, 5A, 5B, 5C, 6A, 6B | 3C, 5A, 5C, 6A, 6B | 7.5 hp |
| 4C, 5A, 5B, 5C, 6A, 6B | 4A, 4C, 5B | 10 hp |
| 7, 8 | 4B | 15 hp |
| 7, 8 | 2A, 2B, 3A, 3B | 25 hp |
| 7, 8 | 1B | 100 hp |
| 7, 8 | 0A, 0B, 1A | 200 hp |
ment manufacturer for the proper operation of equipment . Individual or parallel pumps serving variable-flow heating-water or chilled-water systems, where the nameplate horsepower of the motor or combined parallel motors is at least the power shown in Table 6.5.4.2, shall have controls or devices that will result in pump motor demand of no more than 30% of design wattage at 50% of design water flow The controls or devices shall be controlled as a function of desired flow or to maintain a minimum required differential pressure. Differential pressure shall be measured at or near the most remote heat exchanger or the heat exchanger requiring the greatest differential pressure. The differential pressure set point shall be no more than 110% of that required to achieve design flow through the heat exchanger. Where differential pressure control is used to comply with this section and DDC systems are used, the set point shall be reset downward based on valve positions until one valve is nearly wide open.
Exceptions to 6.5.4.2:
- Differential pressure set-point reset is not required where valve position is used to comply with Section 6.5.4.4.
- Variable- pump flow control is not required on heating-water pumps where more than 50% of annual heat is generated by an electric boiler .
- Variable flow is not required for primary pumps in a primary/secondary system .
- Variable flow is not required for a coil pump provided for freeze protection.
- Variable flow is not required for heat recovery coil runaround loops.
Informative Note: ASHRAE Guideline 36 includes detailed sequences of control of variable flow hydronic systems, including resetting differential pressure set point based on control valve position.
6.5.4.3 Chiller and Boiler Isolation Informative Note: ASHRAE Guideline 36 includes detailed sequences of control for chiller and boiler flow isolation and staging.
6.5.4.3.1 When a chilled-water plant includes more than one chiller, provisions shall be made so that all fluid flow through the chiller is automatically shut off when the chiller is shut down. Chillers piped in series for the purpose of increased temperature differential shall be considered as one chiller. Where constant-speed chilled-water or condenser water pumps are used to serve multiple chillers, the number of pumps shall be no less than the number of chillers and staged on and off with the chillers.
6.5.4.3.2 When a boiler plant includes more than one boiler, provisions shall be made so that the flow through the boiler is automatically shut off when the boiler is shut down. Where constant-speed hot-water
96 ANSI/ASHRAE/IES Standard 90.1-2022 (I-P)