Lochinvar 500, 90 Additional Temperature Controls, 5Electrical connections, Shutdown, Ratio

Installation & Service Manual

5Electrical connections

Shutdown

The Shutdown knob specifies the outdoor air lockout temperature at which the control would prevent the unit from operating.

Outdoor Air Max (O.A. Max)

The O.A. Max knob allows a reset up to the maximum outdoor air temperature specified by this knob setting. When the outdoor air temperature is above the specified setting, the unit will not function in the O.A. Reset Mode, but will continue to run at the selected set point temperature.

Note that the set point knob will now indicate the “minimum” boiler temperature. Target temperature is determined by the ratio and outdoor air temperature below the O.A. Max setting.

Ratio

The Ratio knob allows control over the reset ratio to be used during Outdoor Air Reset. The allowable ratios are as low as 0.5:1 or as high as 1.5:1.

Selecting the 0.5:1 ratio will increase the set point 0.5° for every 1.0° drop in outdoor air temperature up to the maximum set point temperature.

Selecting the 1.5:1 ratio will increase the set point 1.5° for every 1.0° drop in outdoor air temperature up to the maximum set point temperature.

If the outdoor design and boiler design temperatures are known, the Ratio setting can be calculated using the following formula:

Ratio = (boiler design temperature - operator set point)

(O.A. Max. setting - outdoor design temperature)

Note that the reset set point cannot exceed the maximum set point of the boiler thermostat.

These settings are illustrated graphically in FIG. 5-7.

Figure 5-7_Outdoor Air Control Example Chart

Outdoor Air Shutdown Enable/Disable Switch

The Outdoor Air Shutdown Enable/Disable switch turns the outdoor air shutdown feature On and Off. Disabling the Outdoor Air Shutdown feature allows the unit to operate regardless of the outdoor air temperature. This is needed for indirect domestic hot water systems for example.

Additional Temperature Controls

High Water Temperature Limit Control

The appliance is supplied with a fixed setting, auto-reset high water temperature limit control. The setting of this control limits maximum discharge water temperature. If water temperature exceeds the setting, the limit will break the control circuit and shut down the appliance. The limit control will only be reset after the water temperature has cooled well below the setting of the limit. The auto-reset high water temperature limit control is mounted in the outlet side of the front header.

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