With outdoor reset, the system does not run at one fixed water temperature. It is called outdoor reset because the water temperature is changed (or reset) based on a change in the outdoor temperature. This is used to match the heating system’s output to the heat loss of the structure. As the outside temperature lowers, the rate of heat loss increases; therefore the water temperature has to be increased to match the load. Outdoor reset manages this.
For example, a reset schedule could be configured to supply 120°F hot water at 10°F outdoor air temperature, and 90°F water at 60°F outdoor air temperature. If it were 35°F outdoors, what would the heating system water supply temperature be?
This topic was part of our highly-attended October 2015 Coffee with Caleffi webinar entitled Designing for Condensing Boiler Performance with Jody Samuell, our manager of Engineer Education. Check out our Coffee with Caleffi archives and get signed up for our future webinars!