Smith Cast Iron Boilers GT Series manual Determining Reset Temperature HICalc, =140.6 F, 42C

Page 28 GT INSTALLATION AND OPERATION INSTRUCTIONS

Determining Reset Temperature HICalc

Once the Sentry 2100T control identifi es the presence of a good outdoor sensor, the control will automatically reduce the HI setting based upon the outdoor temperature. For example, if Hi = 200°F, 93°C, RES = 70°F, 21°C and the Air Temperature = 32°F, 0°C, the HI setpoint, HICalc, would be calculated as follows:

RESET RATIO

=(High Setting - RES)/RES

=(200°F, 93°C - 70°F, 21°C) /70°F, 21°C

=1.85

RESET TEMPERATURE HICalc =[(RES-Outdoor Air) x Reset Ratio] + RES =[(70°F, 21°C - 32°F, 0°C) x 1.85] + 70°F, 21°C =[70.6°F, 21°C] + 70°F, 21°C

=140.6 F, 42°C

NOTE: The design temperature is 0°F, -18°Coutside air, so at 0°F, -18°Cor less, the hi setting is used, and not surpassed.

Figures 39 & 40 are examples of reset temperatures based upon different set points and outdoor air temper- atures. The vertical axis is the water temperature that the boiler will maintain and is also the Hi setting of the Sentry 2100T control. The Horizontal axis is the outdoor air temperature.

Figures 39 - Reset Curve For Res = 85 °F, 29°C

Figures 40 - Reset Curve For Res = 70 °F, 21°C