Bradford-White Corp BWCV Internet Version for Reference Only, Bradford White, Differential

Internet Version for Reference Only

Page 26 Bradford White

6.3.1 Differential

Differential has an abbreviated name of DIFF. An on/off heat source must be operated with a differential in order to prevent short cycling. The differential

is divided around the boiler target temperature (see Figure 13). The first stage contact will close when the water temperature at the operating sensor is one-half of the differential setting below the target temperature. It will open when the water temperature at the operating sensor is one-half of the differential setting above the target temperature. The remaining stages will operate sequentially, based on the staging mode selected.

6.3.2 Staging Mode

The Copper Brute II 500 and 750 control operates two stages. The Copper Brute II 1000 control operates three stages. The Copper Brute II control for models 1250-2000 operates four stages. The method of staging used by the control is either P (proportional) or PID (proportional & integral & derivative), and

is selected using the STGMODE item in the Adjust menu.

Proportional (P) – Proportional staging, also known as step staging, is based on manually adjusted settings which determine when the next stage is required to turn on. These manual settings are based on temperature and time. The interstage differential sets the temperature drop at which the next stage turns on. However, in order for a stage to fire, the interstage delay on and minimum off times must first elapse.

Interstage Differential (STG DIFF) – The interstage differential is the temperature drop at which the next stage will turn on. Once a stage turns on, the next stage cannot turn on until the temperature drops the interstage differential below the temperature at which the previous stage turned on. The interstage differential is adjustable through the STG DIFF setting in the Adjust menu. See Figure 13.

Interstage Delay On (ON DLY) – The

interstage delay on is the amount of time that must elapse before turning on the next stage. Once a stage turns on, the next stage cannot turn on until the interstage delay on time elapses. The interstage delay on is adjustable through the ON DLY setting in the Adjust menu.

Interstage Delay Off (OFF DLY) – The interstage delay off is the amount of time that must elapse before turning off the next stage. Once a stage turns off, the next stage cannot turn off until the interstage delay off time elapses. The interstage delay off is adjustable through the OFF DLY setting in the Adjust menu.

Minimum On Time (MIN ON) – The minimum on time is the minimum amount time that a stage must be on before it is allowed to turn off. Once a stage turns on, it cannot turn off until a minimum on time elapses. The minimum on time is adjustable through the MIN ON setting in the Adjust menu.

Minimum Off Time (MIN OFF) – The minimum off time is the minimum amount time that a stage must be off before it is allowed to turn on. Once a stage turns off, it cannot turn on until a minimum off time elapses. The minimum off time is adjustable through the MIN OFF setting in the Adjust menu.

Proportional & Integral & Derivative (PID)

–PID staging allows the control to determine when the next stage is required to turn on. The control automatically determines the settings that are manually selected in proportional staging mode. After each stage is turned on in the firing sequence, the control waits a minimum amount of time before turning on the next stage. After the minimum time delay between stages has expired, the control examines the control error to determine when the next stage is to fire. The control error is determined using PID logic.

Proportional compares the actual operating sensor temperature to the heater target temperature. The colder the temperature, the sooner the next stage is turned on.

Integral compares the actual operating sensor temperature to the heater target temperature over a period of time.

Derivative determines how fast or slow the operating sensor temperature is changing. If the temperature is increasing slowly, the next stage is turned on sooner. If the temperature is increasing quickly, the next stage is turned on later, if at all.

Boiler Mass (BOIL MASS) – The boiler mass setting allows the installer to adjust the control to the thermal mass of different types of heat sources used. The boiler mass setting automatically determines the interstage differential, interstage delay on, interstage delay off, minimum on time and minimum off time of the stages when PID staging is used. A higher thermal mass setting provides slower staging, while a lower thermal mass setting provides faster staging. Copper Brute II water heaters are low-mass appliances, and therefore, should be used with the lower thermal mass setting. Set BOIL MASS to “1”.

6.3.3 Boiler Minimum (BOIL MIN)

The minimum boiler setting (BOIL MIN) is the lowest water temperature that the control is allowed to use as a target temperature. During mild conditions, if the control calculates a target temperature that is below this setting, the target temperature is adjusted to at least the minimum setting. During this condition, if the unit is operating, the MIN segment turns on in the LCD while the target temperature or operating sensor temperature is viewed. For Copper Brute II units, this must be set no lower than 120°F (49°C) to protect the unit from condensing on the heat exchanger (see Figure 14).