CMC · California Mechanical Code
When are variable‑flow pumps and controls required (energy provisions)?
If your building’s chilled‑ or hot‑water system has three or more modulating control valves, the California Mechanical Code requires the system be designed for variable flow and, for pumps above certain horsepower thresholds, fitted with controls (typically VFDs or equivalent) that reduce pump motor demand to no more than 30% of design wattage at 50% flow and can reduce flow to at least 25% of design flow (or the manufacturer minimum) — see § E503.5.7.2 for the full rules and Table E 503.5.7.2 for the hp thresholds.
Last reviewed: July 6, 2026
What the code requires — plain English (controlling §)
Hydronic chilled‑ and hot‑water distribution systems with three or more modulating control valves must be designed for variable fluid flow and be able to reduce pump flow to the larger of 25% of design flow or the minimum manufacturer required flow. In addition, individual or parallel pumps whose motor nameplate horsepower meets the thresholds in Table E 503.5.7.2 must have controls that limit pump motor demand to no more than 30% of design wattage at 50% of design flow; controls must modulate based on desired flow or to maintain a required differential pressure. See § E503.5.7.2 and related material in § E503.5.7.
The single most important rule: If your hydronic system has three or more modulating valves, design it for variable flow and install pump controls so the pumps can significantly reduce flow and motor demand (per § E503.5.7.2).
Requirements in detail
When the variable‑flow design is required
- Trigger: three or more control valves that modulate or step as a function of load. § E503.5.7.2 specifies this threshold and the variable‑flow requirement.
Required minimum turndown / minimum flow limits
- System must be capable of reducing pump flow to the larger of:
- 25% of design flow rate, or
- the minimum flow required by the heating/cooling equipment manufacturer for correct operation.
See § E503.5.7.2.
Pump control performance and measurement
- For pumps meeting the nameplate horsepower thresholds in the table, controls/devices must result in pump motor demand of ≤ 30% of design wattage at 50% design water flow. Controls must operate as a function of desired flow or to maintain a minimum required differential pressure. Differential pressure must be measured at or near the most remote heat exchanger (or the exchanger requiring the greatest differential pressure). The differential pressure setpoint must not exceed 110% of the pressure required to achieve design flow through the heat exchanger. Where DDC is used, the setpoint must be reset downward based on valve positions until one valve is nearly wide open. See § E503.5.7.2.
Nameplate horsepower thresholds (decision‑relevant)
- Table: climate‑zone / system type vs. minimum motor nameplate horsepower that triggers the motor‑control requirement. See Table E 503.5.7.2 and § E503.5.7.2.
| Decision dimension | Values / thresholds | Code reference |
|---|---|---|
| Number of control valves that trigger variable‑flow requirement | 3 or more modulating/step valves | § E503.5.7.2 |
| Minimum allowed reduced flow | Larger of 25% of design flow or manufacturer minimum | § E503.5.7.2 |
| Pump motor demand at 50% flow | ≤ 30% of design wattage | § E503.5.7.2 |
| Differential pressure setpoint limit | ≤ 110% of pressure required for design flow | § E503.5.7.2 |
| Where to measure differential pressure | At or near the most remote heat exchanger | § E503.5.7.2 |
| Nameplate hp thresholds (by climate/system) | See Table E 503.5.7.2 (e.g., chilled‑water and heating‑water thresholds vary by climate zone; values from 2 hp up to 200 hp in table) | Table E 503.5.7.2 / § E503.5.7.2 |
(Use the table above in design checks — Table E 503.5.7.2 in the code lists exact climate‑zone mappings and the corresponding hp thresholds.)
Control/legal language to note
- Controls may be variable‑speed drives (VFDs) or equivalent devices that accomplish the motor demand reduction. The code requires the controls to be driven by flow requirement or differential pressure control logic. DDC systems must implement setpoint reset based on valve positions when differential pressure control is used. § E503.5.7.2.
Exceptions & special cases
The Code provides specific exceptions to the variable‑pump flow control requirement (listed in § E503.5.7.2). Key exceptions include:
- Differential pressure set‑point reset is not required where valve position is used to comply with § E503.5.7.4.
- Variable‑pump flow control is not required on heating‑water pumps where >50% of annual heat is produced by an electric boiler.
- Primary pumps in primary/secondary systems are exempt from variable‑flow requirement.
- Coil pumps provided only for freeze protection are exempt.
- Heat‑recovery coil runaround loops do not require variable flow.
Note: Other related Code sections and the California Energy Code include parallel requirements and slightly different numeric triggers (for example, other sections reference a 50% flow reduction basis or different horsepower cutoffs for other system types). Use the CMC's § E503.5.7.2 and the linked tables first when the project is under the CMC Appendix E provisions.
Common mistakes
- Treating “variable‑flow required” as equivalent to “use VFD on every pump.” The code requires controls adequate to meet the specified performance (≤30% motor demand at 50% flow) for pumps that meet the hp thresholds — that can be VFDs or other devices and control strategies. See § E503.5.7.2.
- Failing to check the nameplate horsepower threshold in Table E 503.5.7.2 for the system’s climate zone and system type — a pump that is just below the table threshold may not require the same controls.
- Measuring differential pressure in the wrong location. The code requires measurement at or near the most remote heat exchanger (or the one needing the greatest differential). Placing sensors upstream or at the pump discharge can defeat the required control behavior.
- Not implementing setpoint reset logic with DDC. If differential pressure control is used and DDC is installed, the static pressure setpoint must be reset downward based on valve positions until one valve is nearly wide open. This prevents excessive fixed setpoints. § E503.5.7.2.
Worked example — concrete scenario
Scenario: A chilled‑water distribution system in Climate Zone 4A has 5 two‑way modulating control valves (so ≥3). The serving pump is an individual pump with a 10 hp motor nameplate.
Step 1 — Is variable‑flow design required?
- Yes. There are 3 or more modulating valves, so the system must be designed for variable fluid flow per § E503.5.7.2.
Step 2 — Does the pump meet the hp threshold that triggers motor‑control performance?
- Table E 503.5.7.2 lists the minimum motor hp for chilled‑water pumps by climate zone (for many zones the threshold is ≥5 hp for chilled‑water pumps in similar zones). A 10 hp pump exceeds that threshold, so the motor‑control performance requirement applies. Table E 503.5.7.2 / § E503.5.7.2.
Step 3 — Compute required motor demand at 50% flow
- Convert nameplate hp to watts: 10 hp × 746 W/hp = 7,460 W (design wattage).
- The control must result in motor demand ≤ 30% of design wattage at 50% design flow: 0.30 × 7,460 W = 2,238 W.
- So the selected control (e.g., a VFD and pump controls) must be capable of driving the pump so motor input is at or below ~2.24 kW when system flow is 50% of design. § E503.5.7.2.
Step 4 — Minimum flow capability
- The system must be able to reduce flow to the larger of 25% design flow or the equipment manufacturer’s minimum. If the coil manufacturer requires 20% design flow, the code’s 25% value controls (system must reach 25%). § E503.5.7.2.
Step 5 — Differential pressure measurement and setpoint
- Locate DP sensor at or near the most remote heat exchanger, set the DP setpoint not to exceed 110% of the pressure needed for design flow, and if DDC is present implement setpoint reset tied to valve positions until one valve is nearly wide open. § E503.5.7.2.
Related provisions (other CMC sections you will commonly use)
- § E503.5.7.2 — Hydronic Variable Flow Systems (primary controlling text for this topic).
- § E503.5.7 — Boiler turndown/table and other hydronic system measures referenced nearby in App. E.
- Table E 503.5.7.2 — Pump flow control requirements and nameplate‑hp thresholds by climate zone.
- Related test/acceptance sections (functional testing for variable‑flow hydronic systems): E805.10 (hydronic system variable flow controls — testing and acceptance).
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 503.5.7.2 High relevance — show source text
Individual or parallel pumps serving variable-flow heating-water or chilledwater systems, where the nameplate horsepower of the motor or combined parallel motors is not less than the power shown in Table E 503.5.7.2, shall have controls or devices that will result in pump motor demand of not more than 30 percent of design wattage at 50 percent 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 setpoint shall not exceed 110 percent 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 setpoint shall be reset downward based on valve positions until one valve is nearly wide open.
Exceptions:
(1) Differential pressure set-point reset is not required where valve position is used to comply with Section E 503.5.7.4.
(2) Variable-pump flow control is not required on heating-water pumps where more than 50 percent of annual heat is generated by an electric boiler.
(3) Variable flow is not required for primary pumps in a primary/secondary system.
(4) Variable flow is not required for a coil pump provided for freeze protection.
(5) Variable flow is not required for heat recovery coil runaround loops. [ASHRAE 90.1:6.5.4.2]
CHILLED WATER PUMPS
IN THESE
CLIMATE ZONESHEATING WATER
PUMPS IN THESE
CLIMATE ZONESMOTOR
NAMEPLATE
HORSEPOWER
0A, 0B, 1A, 1B, 2BNR ≥2 hp
2A, 3BNR ≥3 hp
3A, 3C, 4A, 4B7, 8 ≥5 hp
4C, 5A, 5B, 5C, 6A, 6B3C, 5A, 5C, 6A, 6B ≥7.5 hp
─4A, 4C, 5B ≥10 hp 7, 8 4B ≥15 hp
─2A, 2B, 3A, 3B ≥25 hp
─1B ≥100 hp
─0A, 0B, 1A ≥200 hp For SI units: 1 horsepower = 0.746 kW
CMC § 90.1 High relevance — show source text
[ASHRAE 90.1:6.5.4.1]
2025 CALIFORNIA MECHANICAL CODE 439
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
APPENDIX E
TABLE E 503.5.7.2
PUMP FLOW CONTROL REQUIREMENTS
[ASHRAE 90.1: TABLE 6.5.4.2]
BOILER SYSTEM DESIGN INPUT, Btu/h MINIMUM TURNDOWN RATIO
≥1 000 000 and≤5 000 0003 to 1
>5 000 000 and≤10 000 0004 to 1
>10 000 0005 to 1 »
TABLE E 503.5.7
BOILER TURNDOWN
[ASHRAE 90.1: TABLE 6.5.4.1]
For SI units: 1000 British thermal units per hour = 0.293 kW
E 503.5.7.2 Hydronic Variable Flow Systems. Chilled- and hot-water distribution systems that include three or more control valves designed to modulate or step open and close as a function of load shall be designed for variable fluid flow and shall be capable of and configured to reduce pump flow rates to not more than the larger of 25 percent of the design flow rate or the minimum flow required by the heating/cooling equipment manufacturer for the proper operation of equipment. Individual or parallel pumps serving variable-flow heating-water or chilledwater systems, where the nameplate horsepower of the motor or combined parallel motors is not less than the power shown in Table E 503.5.7.2, shall have controls or devices that will result in pump motor demand of not more than 30 percent of design wattage at 50 percent 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 setpoint shall not exceed 110 percent 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 setpoint shall be reset downward based on valve positions until one valve is nearly wide open.
Exceptions:
(1) Differential pressure set-point reset is not required where valve position is used to comply with Section E 503.5.7.4.
(2) Variable-pump flow control is not required on heating-water pumps where more than 50 percent of annual heat is generated by an electric boiler.
(3) Variable flow is not required for primary pumps in a primary/secondary system.
(4) Variable flow is not required for a coil pump provided for freeze protection.
(5) Variable flow is not required for heat recovery coil runaround loops. [ASHRAE 90.1:6.5.4.2]
CMC § 90.1 High relevance — show source text
Exception: Units employing fluid economizers.
[ASHRAE 90.1:6.5.4.5.1]
E 503.5.7.5.1 Controls. Hydronic heat pumps and water-cooled unitary air-conditioners having a total pump system power exceeding 5 hp (3.7 kW) shall have controls, devices, or both (such as variable speed control) that will result in pump motor demand of not more than 30 percent of design wattage at 50 percent of design water flow. [ASHRAE 90.1:6.5.4.5.2]
E 503.5.7.6 Pipe Sizing. 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 E 503.5.7.6 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 shall be permitted to be made from the “Variable Flow/Variable Speed” columns. All others shall be made from the “Other” columns.
Exceptions:
(1) Design flow rates exceeding the values in Table E 503.5.7.6 shall be permitted 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 percent of operating hours.
TABLE E 503.5.7.6 PIPING SYSTEM DESIGN MAXIMUM FLOW RATE (gallons per minute)
[ASHRAE 90.1: TABLE 6.5.4.6]
OPERATING HOURS/YEAR ≤2000 HOURS/YEAR Col3 >2000 AND ≤4400 HOURS/YEAR Col5 >4400 HOURS/YEAR Col7 NOMINAL PIPE SIZE,
(inches)OTHER VARIABLE FLOW/
VARIABLE SPEEDOTHER VARIABLE FLOW/
VARIABLE SPEEDOTHER VARIABLE FLOW/
VARIABLE SPEED21⁄2 120 180 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
14-24 inches in size8.5 ft/s 13.0 ft/s 6.5 ft/s 9.5 ft/s 5.0 ft/s 7.5 ft/s For SI units: 1 gallon per minute = 0.06 L/s, 1 foot per second = 0.3048 m/s, 1 inch = 25.4 mm
2025 CALIFORNIA MECHANICAL CODE 441
«
CMC § 140.4 High relevance — show source text
Exception 1 to Section 140.4(k)4: Hydronic systems that use variable flow to reduce pumping energy in accordance with 140.4(k)1.
Exception 2 to Section 140.4(k)4: Systems serving healthcare facilities. 5. Water-cooled air conditioner and hydronic heat pump systems. Water circulation systems serving water-cooled air conditioners, hydronic heat pumps, or both that have total pump system power exceeding 5 hp shall have flow controls that meet the requirements of Section 140.4(k)6. Each such air conditioner or heat pump shall have a two-position automatic valve interlocked to shut off water flow when the compressor is off.
- Variable flow controls.
A. Variable speed drives. Individual pumps serving variable flow systems and having a motor horsepower exceeding 5 hp shall have controls or devices (such as variable speed control) that will result in pump motor demand of no more than 30 percent of design wattage at 50 percent of design water flow. The pumps shall be controlled as a function of required differential pressure. B. Pressure sensor location and setpoint. i. For systems without direct digital control of individual coils reporting to the central control panel, differential pressure shall be measured at the most remote heat exchanger or the heat exchanger requiring the greatest differential pressure. ii. For systems with direct digital control of individual coils with a central control panel, the static pressure setpoint shall be reset based on the valve requiring the most pressure, and the setpoint shall be no less than 80 percent open. Pressure sensors may be mounted anywhere.
Exception 1 to Section 140.4(k)6: Heating hot water systems.
Exception 2 to Section 140.4(k)6: Condenser water systems serving only water-cooled chillers.
2025 CALIFORNIA ENERGY CODE 125
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
NONRESIDENTIAL AND HOTEL/MOTEL OCCUPANCIES—PERFORMANCE AND PRESCRIPTIVE
COMPLIANCE APPROACHES FOR ACHIEVING ENERGY EFFICIENCY
- Hydronic heat pump (WLHP) controls. Hydronic heat pumps connected to a common heat pump water loop with central devices for heat rejection and heat addition shall have controls that are capable of providing a heat pump water supply temperature dead band of at least 20°F between initiation of heat rejection and heat addition by the central devices.
Exception to Section 140.4(k)7: Where a system loop temperature optimization controller is used to determine the most efficient operating temperature based on real-time conditions of demand and capacity, dead bands of less than 20°F shall be allowed. 8. High capacity space heating gas boiler systems. In Climate Zones 1 through 6, 9 through 14, and 16, gas hot water boiler systems for space heating with a total system input of at least 1 MMBtu/h but no more than 10 MMBtu/h shall meet all of the following requirements. A. Boiler system efficiency. Gas hot water boilers shall have a minimum thermal efficiency of 90 percent. Systems with multiple boilers can meet this requirement if the space-heating input provided by equipment with thermal efficiencies above and below 90 percent has an input capacity-weighted average thermal efficiency of at least 90 percent. For boilers federally regulated by combustion efficiency, the calculation for the input capacity-weighted average thermal efficiency shall use the combustion efficiency value. B. **Hot water distribution design.
CMC § 170.2 High relevance — show source text
Chillers that are piped in series for the purpose of increased temperature differential shall be considered as one chiller.
iii. Boiler isolation. When a hot water plant includes more than one boiler, provisions shall be made so that flow through any boiler is automatically shut off when that boiler is shut off while still maintaining flow through other operating boiler(s). iv. Chilled and hot water temperature reset controls. Systems with a design capacity exceeding 500,000 Btu/hr supplying chilled or heated water shall include controls that automatically reset supply water temperatures as a function of representative building loads or outside air temperature. Exception to Section 170.2(c)4Iiv: Hydronic systems that use variable flow to reduce pumping energy in accordance with Section 170.2(c)4Ii.
v. Water-cooled air conditioner and hydronic heat pump systems. Water circulation systems serving watercooled air conditioners, hydronic heat pumps or both, that have total pump system power exceeding 5 hp, shall have flow controls that meet the requirements of Section 170.2(c)4Ivi. Each such air conditioner or heat pump shall have a two-position automatic valve interlocked to shut off water flow when the compressor is off.
vi. Variable flow controls.
a. Variable speed drives. Individual pumps serving variable flow systems and having a motor horsepower exceeding 5 hp shall have controls or devices (such as variable speed control) that will result in pump motor demand of no more than 30 percent of design wattage at 50 percent of design water flow. The pumps shall be controlled as a function of required differential pressure. b. Pressure sensor location and setpoint. I. For systems without direct digital control of individual coils reporting to the central control panel, differential pressure shall be measured at the most remote heat exchanger or the heat exchanger requiring the greatest differential pressure. II. For systems with direct digital control of individual coils with a central control panel, the static pressure setpoint shall be reset based on the valve requiring the most pressure, and the setpoint shall be no less than 80 percent open. Pressure sensors may be mounted anywhere. Exception 1 to Section 170.2(c)4Ivi: Heating hot water systems. Exception 2 to Section 170.2(c)4Ivi: Condenser water systems serving only water-cooled chillers. vii. Hydronic heat pump (WLHP) controls. Hydronic heat pumps connected to a common heat pump water loop with central devices for heat rejection and heat addition shall have controls that are capable of providing a heat pump water supply temperature deadband of at least 20°F between initiation of heat rejection and heat addition by the central devices.
254 2025 CALIFORNIA ENERGY CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
MULTIFAMILY BUILDINGS—PERFORMANCE AND PRESCRIPTIVE COMPLIANCE APPROACHES
Exception to Section 170.2(c)4Ivii: Where a system loop temperature optimization controller is used to determine the most efficient operating temperature based on real-time conditions of demand and capacity, deadbands of less than 20°F shall be allowed .
J. Reserved.
K. **Fan control.
CMC § 503.5.7. High relevance — show source text
(3) Water temperature reset is not required where valve position is used to comply with Section E 503.5.7. [ASHRAE 90.1:6.5.4.4]
E 503.5.7.5 Hydronic (Water Loop) Heat Pump and Water-Cooled Unitary Air Condi- tioners. Hydronic heat pumps and water-cooled unitary air-conditioners shall have a two-position automatic valve interlocked to shut off water flow
when the compressor is off.
Exception: Units employing fluid economizers.
[ASHRAE 90.1:6.5.4.5.1]
E 503.5.7.5.1 Controls. Hydronic heat pumps and water-cooled unitary air-conditioners having a total pump system power exceeding 5 hp (3.7 kW) shall have controls, devices, or both (such as variable speed control) that will result in pump motor demand of not more than 30 percent of design wattage at 50 percent of design water flow. [ASHRAE 90.1:6.5.4.5.2]
E 503.5.7.6 Pipe Sizing. 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 E 503.5.7.6 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 shall be permitted to be made from the “Variable Flow/Variable Speed” columns. All others shall be made from the “Other” columns.
Exceptions:
(1) Design flow rates exceeding the values in Table E 503.5.7.6 shall be permitted 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 percent of operating hours.
TABLE E 503.5.7.6 PIPING SYSTEM DESIGN MAXIMUM FLOW RATE (gallons per minute)
[ASHRAE 90.1: TABLE 6.5.4.6]
CMC § 207.2.4.1. High relevance — show source text
Exception: Hydronic systems that use variable flow to reduce pumping energy in accordance with Section A6.207.2.4.1.
A6.207.2.4.5 Water-cooled air conditioner and hydronic heat pump systems. Water circulation systems serving watercooled air conditioners, hydronic heat pumps or both that have total pump system power exceeding 5 hp shall have flow controls that meet the requirements of Section A6.207.2.4.6. Each air conditioner or heat pump shall have a two-position automatic valve interlocked to shut off water flow when the compressor is off.
A6.207.2.4.6 Variable flow controls.
A6.207.2.4.6.1 Variable speed drives. Individual pumps serving variable flow systems and having a motor horsepower 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 percent of design wattage at 50 percent of design water flow. The pumps shall be controlled as a function of required differential pressure.
A6.207.2.4.6.2 Pressure sensor location and setpoint.
- For systems without direct digital control of individual coils reporting to the central control panel, differential pressure shall be measured at or near the most remote heat exchanger or the heat exchanger requiring the greatest differential pressure.
- For systems with direct digital control of individual coils with central control panel, the static pressure set point shall be reset based on the valve requiring the most pressure and the set- point shall be no less than 80 percent open. The pressure sensor(s) may be mounted anywhere.
Exceptions:
- Heating hot water systems.
- Condenser water systems serving only water-cooled chillers.
A6.207.2.4.7 Hydronic heat pump (WLHP) controls. Hydronic heat pumps connected to a common heat pump water loop with central devices for heat rejection and heat addition shall have controls that are capable of providing a heat pump water supply temperature dead band of at least 20°F between initiation of heat rejection and heat addition by the central devices.
Exception: Where a system loop temperature optimization controller is used to determine the most efficient operating temperature based on real-time conditions of demand and capacity, dead bands of less than 20°F shall be allowed.
A6.207.2.5 Air distribution system duct leakage sealing. All duct systems shall be sealed to a leakage rate not to exceed 6 percent of the fan flow if the duct system:
A6.207.2.5.1 Is connected to a constant volume, single zone, air conditioners, heat pumps or furnaces; and
A6.207.2.5.2 Serves less than 5,000 square feet of floor area; and
A6.207.2.5.3 Has more than 25 percent duct surface area located in one or more of the following spaces:
Outdoors; or
In a space directly under a roof where the U -factor of the roof is greater than the U -factor of the ceiling; or Exception: Where the roof meets the requirements of Section 143(a)1C of Title 24, Part 6.
In a space directly under a roof with fixed vents or openings to the outside or unconditioned spaces; or
In an unconditioned crawlspace; or
In other unconditioned spaces.
CMC § 140.4 Medium relevance — show source text
Exception 4 to Section 140.4(i): In buildings with more than three chillers, only three chillers are required to meet the Path B efficiencies.
(j) Limitation of air-cooled chillers. Chilled water plants shall not have more than 300 tons provided by air-cooled chillers.
Exception 1 to Section 140.4(j): Where the water quality at the building site fails to meet manufacturer’s specifications for the use of water-cooled chillers.
Exception 2 to Section 140.4(j): Chillers that are used to charge a thermal energy storage system with a design temperature of less than 40°F (4°C).
Exception 3 to Section 140.4(j): Systems serving healthcare facilities.
(k) Hydronic system measures.
- Hydronic variable flow systems. HVAC chilled and hot water pumping shall be designed for variable fluid flow and shall be capable of reducing pump flow rates to no more than the larger of: a) 50 percent or less of the design flow rate; or b) the minimum flow required by the equipment manufacturer for the proper operation of equipment served by the system.
Exception 1 to Section 140.4(k)1: Systems that include no more than three control valves.
Exception 2 to Section 140.4(k)1: Systems having a total pump system power less than or equal to 1.5 hp. 2. Chiller isolation. When a chilled water system includes more than one chiller, provisions shall be made so that flow through any chiller is automatically shut off when that chiller is shut off while still maintaining flow through other operating chiller(s). Chillers that are piped in series for the purpose of increased temperature differential shall be considered as one chiller.
- Boiler isolation. When a hot water plant includes more than one boiler, provisions shall be made so that flow through any boiler is automatically shut off when that boiler is shut off while still maintaining flow through other operating boiler(s).
- Chilled and hot water temperature reset controls. Systems with a design capacity exceeding 500,000 Btu/hr supplying chilled or heated water shall include controls that automatically reset supply water temperatures as a function of representative building loads or outside air temperature.
Exception 1 to Section 140.4(k)4: Hydronic systems that use variable flow to reduce pumping energy in accordance with 140.4(k)1.
Exception 2 to Section 140.4(k)4: Systems serving healthcare facilities. 5. Water-cooled air conditioner and hydronic heat pump systems. Water circulation systems serving water-cooled air conditioners, hydronic heat pumps, or both that have total pump system power exceeding 5 hp shall have flow controls that meet the requirements of Section 140.4(k)6. Each such air conditioner or heat pump shall have a two-position automatic valve interlocked to shut off water flow when the compressor is off.
- Variable flow controls.
A. Variable speed drives. Individual pumps serving variable flow systems and having a motor horsepower exceeding 5 hp shall have controls or devices (such as variable speed control) that will result in pump motor demand of no more than 30 percent of design wattage at 50 percent of design water flow. The pumps shall be controlled as a function of required differential pressure. B. Pressure sensor location and setpoint. i. For systems without direct digital control of individual coils reporting to the central control panel, differential pressure shall be measured at the most remote heat exchanger or the heat exchanger requiring the greatest differential pressure. ii.
CMC § 207.2.4 Medium relevance — show source text
A6.207.2.4 Hydronic system measures.
A6.207.2.4.1 Hydronic variable flow systems. HVAC chilled and hot water pumping shall be designed for variable fluid flow and shall be capable of reducing pump flow rates to no more than the larger of: a) 50 percent or less of the design flow rate; or b) the minimum flow required by the equipment manufacturer for the proper operation of equipment served by the system.
Exceptions:
- Systems that include no more than three control valves.
- Systems having a total pump system power less than or equal to 1 [1] / 2 HP.
A6.207.2.4.2 Chiller isolation. When a chilled water plant includes more than one chiller, provisions shall be made so that flow through any chiller is automatically shut off when that chiller is shut off while still maintaining flow through other operating chiller(s). Chillers that are piped in series for the purpose of increased temperature differential shall be considered as one chiller.
A6.207.2.4.3 Boiler isolation. When a hot water plant includes more than one boiler, provisions shall be made so that flow through any boiler is automatically shut off when that boiler is shut off while still maintaining flow through other operating boiler(s).
A6.207.2.4.4 Chilled and hot water temperature reset controls. Chilled and hot water systems with a design capacity exceeding 500,000 Btu/hr supplying chilled or heated water (or both) shall include controls that automatically reset supply water temperatures as a function of representative building loads or outside air temperature.
Exception: Hydronic systems that use variable flow to reduce pumping energy in accordance with Section A6.207.2.4.1.
A6.207.2.4.5 Water-cooled air conditioner and hydronic heat pump systems. Water circulation systems serving watercooled air conditioners, hydronic heat pumps or both that have total pump system power exceeding 5 hp shall have flow controls that meet the requirements of Section A6.207.2.4.6. Each air conditioner or heat pump shall have a two-position automatic valve interlocked to shut off water flow when the compressor is off.
A6.207.2.4.6 Variable flow controls.
A6.207.2.4.6.1 Variable speed drives. Individual pumps serving variable flow systems and having a motor horsepower 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 percent of design wattage at 50 percent of design water flow. The pumps shall be controlled as a function of required differential pressure.
A6.207.2.4.6.2 Pressure sensor location and setpoint.
- For systems without direct digital control of individual coils reporting to the central control panel, differential pressure shall be measured at or near the most remote heat exchanger or the heat exchanger requiring the greatest differential pressure.
- For systems with direct digital control of individual coils with central control panel, the static pressure set point shall be reset based on the valve requiring the most pressure and the set- point shall be no less than 80 percent open. The pressure sensor(s) may be mounted anywhere.
Exceptions:
- Heating hot water systems.
- Condenser water systems serving only water-cooled chillers.
CMC § 170.2 Medium relevance — show source text
- 40 percent of the design chiller cooling capacity. Exception 3 to Section 170.2(c)4G: Chillers used to charge thermal energy storage systems where the charging temperature is < 40°F. Exception 4 to Section 170.2(c)4G: In buildings with more than three chillers, only three chillers are required to meet the Path B efficiencies.
H. Limitation of air-cooled chillers. Chilled water plants shall not have more than 300 tons provided by air-cooled chillers.
Exception 1 to Section 170.2(c)4H: Where the water quality at the building site fails to meet manufacturer’s specifications for the use of water-cooled chillers.
Exception 2 to Section 170.2(c)4H: Chillers that are used to charge a thermal energy storage system with a design temperature of less than 40°F (4°C). I. Hydronic system measures . i. Hydronic variable flow systems. HVAC chilled and hot water pumping shall be designed for variable fluid flow and shall be capable of reducing pump flow rates to no more than the larger of: a) 50 percent or less of the design flow rate; or b) the minimum flow required by the equipment manufacturer for the proper operation of equipment served by the system. Exception 1 to Section 170.2(c)4I: Systems that include no more than three control valves. Exception 2 to Section 170.2(c)4I: Systems having a total pump system power less than or equal to 1.5 hp. ii. Chiller isolation. When a chilled water system includes more than one chiller, provisions shall be made so that flow through any chiller is automatically shut off when that chiller is shut off while still maintaining flow through other operating chiller(s). Chillers that are piped in series for the purpose of increased temperature differential shall be considered as one chiller.
iii. Boiler isolation. When a hot water plant includes more than one boiler, provisions shall be made so that flow through any boiler is automatically shut off when that boiler is shut off while still maintaining flow through other operating boiler(s). iv. Chilled and hot water temperature reset controls. Systems with a design capacity exceeding 500,000 Btu/hr supplying chilled or heated water shall include controls that automatically reset supply water temperatures as a function of representative building loads or outside air temperature. Exception to Section 170.2(c)4Iiv: Hydronic systems that use variable flow to reduce pumping energy in accordance with Section 170.2(c)4Ii.
v. Water-cooled air conditioner and hydronic heat pump systems. Water circulation systems serving watercooled air conditioners, hydronic heat pumps or both, that have total pump system power exceeding 5 hp, shall have flow controls that meet the requirements of Section 170.2(c)4Ivi. Each such air conditioner or heat pump shall have a two-position automatic valve interlocked to shut off water flow when the compressor is off.
vi. Variable flow controls.
a. Variable speed drives. Individual pumps serving variable flow systems and having a motor horsepower exceeding 5 hp shall have controls or devices (such as variable speed control) that will result in pump motor demand of no more than 30 percent of design wattage at 50 percent of design water flow. The pumps shall be controlled as a function of required differential pressure. b. Pressure sensor location and setpoint.
CMC § 805.9.1 Medium relevance — show source text
This requirement applies to chilled and hot water systems that are not designed for variable flow, and that have a design capacity greater than or equal to 500 000 Btu/h (147 kW).
E 805.9.1 Test Procedure. The procedure for performing a functional test for supply water temperature reset controls shall be in accordance with Section E
805.9.1.1 and Section E 805.9.1.2.
E 805.9.1.1 Construction Inspection. Prior to functional testing, verify and document the supply water temperature sensors shall be either factory or field calibrated.
E 805.9.1.2 Functional Testing. The functional testing shall be in accordance with the following steps:
Step 1: Change reset control variable to its maximum value. Verify and document the following:
(1) Chilled or hot water temperature setpoint is reset to appropriate value.
(2) Actual supply temperature changes to meet setpoint.
(3) Verify that supply temperature is within 2 percent of the control setpoint.
Step 2: Change reset control variable to its minimum value. Verify and document the following:
(1) Chilled or hot water temperature setpoint is reset to appropriate value.
(2) Actual supply temperature changes to meet setpoint.
(3) Verify that supply temperature is within 2 percent of the control setpoint.
Step 3: Restore reset control variable to automatic control. Verify and document the following:
(1) Chilled or hot water temperature setpoint is reset to appropriate value.
(2) Actual supply temperature changes to meet setpoint.
(3) Verify that supply temperature is within 2 percent of the control setpoint.
E 805.9.2 Acceptance Criteria. The supply water temperature sensors are either factory calibrated (with calibration certificates) or field-calibrated. Sensor performance shall comply with the specifications. The supply water reset is operational.
E 805.10 Hydronic System Variable Flow Controls (Form MECH-10A). The purpose of this test is to ensure that hydronic variable flow chilled water and water-loop heat pump systems with circulating pumps larger than 5 hp (3.7 kW) vary system flow rate by modulating pump speed using a variable frequency drive (VFD) or equivalent. As the loads within the building fluctuate, control valves modulate the amount of water passing through each coil and add or remove the desired amount of energy from the air stream to satisfy the load. In the case of water-loop heat pumps, each two-way control valve associated with a heat pump will be closed where that unit is not operating. As each control valve modulates, the pump variable frequency drive (VFD) responds accordingly to meet system water flow requirements. This is not required on heating hot water systems with variable flow designs or for condensing water serving water cooled chillers. E 805.10.1 Test Procedure. The procedure for performing a functional test for hydronic system variable flow controls shall be in accordance with Section E
805.10.1.1 and Section E 805.10.1.2.
E 805.10.1.1 Construction Inspection. Prior to functional testing, verify and document the pressure sensors are either factory or field calibrated. E 805.10.1.2 Functional Testing. The functional testing shall comply with the following steps:
Step 1: Open control valves to increase water flow to not less than 90 percent design flow. Verify and document the following:
CMC § 90.1 Medium relevance — show source text
(3) Variable flow is not required for primary pumps in a primary/secondary system.
(4) Variable flow is not required for a coil pump provided for freeze protection.
(5) Variable flow is not required for heat recovery coil runaround loops. [ASHRAE 90.1:6.5.4.2]
CHILLED WATER PUMPS
IN THESE
CLIMATE ZONESHEATING WATER
PUMPS IN THESE
CLIMATE ZONESMOTOR
NAMEPLATE
HORSEPOWER
0A, 0B, 1A, 1B, 2BNR ≥2 hp
2A, 3BNR ≥3 hp
3A, 3C, 4A, 4B7, 8 ≥5 hp
4C, 5A, 5B, 5C, 6A, 6B3C, 5A, 5C, 6A, 6B ≥7.5 hp
─4A, 4C, 5B ≥10 hp 7, 8 4B ≥15 hp
─2A, 2B, 3A, 3B ≥25 hp
─1B ≥100 hp
─0A, 0B, 1A ≥200 hp For SI units: 1 horsepower = 0.746 kW
E 503.5.7.3 Chiller and Boiler Isolation. Where a chilled-water plant includes more than one chiller, provisions shall be made so that the fluid flow through the chiller is automatically shut off where 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 not less than the number of chillers and staged on and off with the chillers. [ASHRAE 90.1:6.5.4.3.1]
E 503.5.7.3.1 Boiler Isolation. Where a boiler plant includes more than one boiler, provisions shall be made so that the flow through the boiler is automatically shut off where the boiler is shut down. Where constant-speed hot-water pumps are used to serve multiple boilers, the number of pumps shall be not less than the number of boilers and staged on and off with the boilers.
[ASHRAE 90.1:6.5.4.3.2]
E 503.5.7.4 Chilled- and Hot-Water Tempera- ture Reset Controls. Chilled- and hot-water systems with a design capacity exceeding 300 000 Btu/h (88 kW) 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 setpoint limits of the system equipment or application have been reached.
Exceptions:
Frequently asked questions
Do systems with fewer than three control valves need variable flow?
No — the variable‑flow requirement in § E503.5.7.2 is triggered when the distribution system has three or more modulating/stepping control valves.
If I use a primary/secondary piping arrangement, do primary pumps need to be variable?
No — primary pumps in a primary/secondary system are explicitly exempt from the variable‑flow requirement in § E503.5.7.2.
Where must I measure differential pressure for the pump control?
Differential pressure must be measured at or near the most remote heat exchanger or the exchanger requiring the greatest differential pressure, per § E503.5.7.2.
What does “≤30% of design wattage at 50% flow” mean for VFD selection?
It means the control strategy and equipment (typically a VFD plus correct control logic) must reduce motor electrical input so that at 50% of design water flow the motor is consuming no more than 30% of its design electrical wattage. Designers convert nameplate hp to watts to size and verify controls. § E503.5.7.2.
Are there exceptions for small pumps or special loops?
Yes — the code lists several exceptions in § E503.5.7.2, including coils for freeze protection, heat‑recovery runaround loops, primary pumps in P/S systems, and heating pumps primarily served by electric boilers (see § E503.5.7.2).
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