Sequence Of Operation - Bradford White S-SW2-60R6DS Service Manual

Solar water heater with electric backup

Specification sheet (2 pages)

Table of Contents

Non-Simultaneous Operation

Non-Simultaneous Mode: Allows only one heating element to operate at a time. For example, when the tank is cold,

the upper element is energized first, heating the top of the tank. Only when the upper thermostat is satisfied, the upper

element is de-energized and power is directed to the lower thermostat, energizing the lower element and heating the

bottom portion of the tank until the lower thermostat is satisfied. As hot water is drawn off the tank, it is replaced with

cold water delivered through the dip tube to the bottom of the tank. When the tank cools at the lower thermostat level,

the thermostat will call for heat energizing the lower element. If enough hot water is drawn from the tank, the top portion

of the tank cools and the upper thermostat will call for heat, de-energizing the lower element and allowing only the top

element to energize until the upper thermostat is satisfied.

The lower thermostat in the solar water heater is located above the internal heat exchanger. This design allows the heat

exchanger to be in cooler water during short draws, providing more heat transfer from the solar heating system.

Solar water heaters with double electric element backup are designed to operate using a single operating mode detailed

as follows:

Sequence of Operation- Double Element, Non-Simultaneous Operation, Single Phase.

Line voltage is applied across terminals

L1 & L3 of the upper thermostat. ECO is

closed, so there is voltage at terminal L4

and to one side of the upper and lower

elements.

Tank is cold. Therefore, the thermostats are closed

at terminals T2 & 2 (calling for heat). The circuit is

complete through the upper thermostat only,

allowing current to flow through the upper element.

When the upper thermostat is satisfied, it opens at

terminal T2, interrupting current flow through the

upper element. Terminal T4 closes, allowing voltage

to pass to terminal 1 of the lower thermostat. This

completes the circuit through the lower thermostat

and allows current flow through the lower element.

When the lower thermostat is satisfied, it opens at

terminal 2, interrupting current flow through the

lower element. The system is now in stand-by mode

waiting for the next call for heat

The lower thermostat/element

combination will generally

cycle on and off more often

then the upper. In some cases,

such as a cold tank or in high

demand periods, the

upper thermostat will

call for heat (opening at

terminal T4 and closing at

terminal T2) prior to the lower

thermostat being satisfied. This

will interrupt current flow

through the lower thermostat

and element and allow current

to flow through the upper

element only. When the upper

thermostat is satisfied, it

resumes operation as

described in sequence #3

above.

Thermostat closed

at terminal T4

Upper

T'stat

Upper

Element

Lower

T'stat

Lower

Element

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