Notes to Table C407.5.1(3) state that hot water supply temperature shall be modeled at 180°F design supply temperature and 130°F return temperature. Piping losses shall not be modeled in either building model. Hot water supply water temperature shall be reset in accordance with Section C403.4.3.4 i.e.
Hydronic systems greater than or equal to 300,000 Btu/h (87 930 W) in design output capacity, supplying heated or chilled water to comfort conditioning systems shall include controls that have the capability to:
· Automatically reset the supply-water temperatures using zone-return water temperature, building-return water temperature, or outside air temperature as an indicator of building heating or cooling demand. The temperature shall be capable of being reset by at least 25 percent of the design supply-to-return water temperature difference; or
· Reduce system pump flow by at least 50 percent of design flow rate utilizing adjustable speed drive(s) on pump(s), or multiple-staged pumps where at least one-half of the total pump horsepower is capable of being automatically turned off or control valves designed to modulate or step down, and close, as a function of load, or other approved means.
For applicable IECC standard reference systems, the hot water supply temperature shall be reset based on the outdoor dry-bulb temperature. When the outdoor temperature is 20°F and below, the supply temperature shall be a constant 180°F. When the outdoor temperature is 50°F and above, the supply temperature shall be 150°F. When the outdoor temperature is between 20°F and 50°F, the supply temperature shall be ramped in a proportional manner between 180°F and 150°F.
Figure 6: Default hot water loop supply water temperature control settings
