6.5.4 Hydronic System Design and Control
Boiler systems with design input of at least 1,000,000 Btu/h shall comply with the turndown ratio specified in Table 22.214.171.124.
|Boiler System Design Input, Btu/h||Minimum Turndown Ratio|
|≥1,000,000 and ≤5,000,000||3 to 1|
|>5,000,000 and ≤10,000,000||4 to 1|
|>10,000,000||5 to 1|
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 no more than the larger of 25% 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 chilled-water systems, where the nameplate horsepower of the motor or combined parallel motors is at least the power shown in Table 126.96.36.199, 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.
|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|
|4A, 4C, 5B||≥10 hp|
|7, 8||4B||≥15 hp|
|2A, 2B, 3A, 3B||≥25 hp|
|0A, 0B, 1A||≥200 hp|
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.
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 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.
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.
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.
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 188.8.131.52 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.
|Operating Hours/Year||≤2000 Hours/Year||>2000 and ≤4400 Hours/Year||>4400 Hours/Year|
|Nominal Pipe Size, in.||Other||Variable Flow/Variable Speed||Other||Variable Flow/Variable Speed||Other||Variable Flow/Variable Speed|
|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|