The automatic bypass system allows part of the boiler discharge water to be mixed with the inlet water to the primary heat exchanger to increase the boiler inlet temperature above 130°F (55°C). This will prevent the products of combustion from condensing on the primary heat exchanger. Avalve must also be provided on the boiler discharge, after the bypass. Closing this discharge valve sets the maximum flow through the appliance. (See
A minimum water temperature of 50°F (10°C) has been established for each boiler based on the Btu/hr input at 100% of rated burner input. The temperature set point for the Excel 10 controller sensing system must not be set lower than the specified minimum for each model. Maintaining inlet water temperatures to the boiler equal to or higher than the specified minimum set point ensures proper operation of the bypass and allows all condensate formation to occur on the secondary heat exchanger. A boiler allowed to sustain operation at water temperatures lower than the specified minimum set point may not provide enough heat from the burner to maintain water temperatures in the primary heat exchanger above the 130°F (55°C) dew point of flue products. Operation of a boiler at a temperature below the specified minimum set point will result in
TABLE - CC
Minimum Inlet Water Temperatures
THREE WAY VALVES
The installation of a three way valve on this boiler is not recommended because most piping methods allow the three way valve to vary flow to the boiler. This boiler is a low mass, high efficiency unit which requires a constant water flow rate for proper operation. Low flow rates can result in overheating of the boiler water which can cause short burner cycles, system noise, relief valve discharge and in extreme cases, a knocking flash to steam. These conditions can cause operational problems and non- warrantable failures of the boiler.
MAXIMUM FLOW FOR
HEATING BOILER
CAUTION
The maximum flow rate through the boiler with a copper heat exchanger must not exceed the following:
Btu/hr Input | Maximum Flow |
|
|
1,500,000 - 2,000,000 | 90 GPM |
|
|
If higher flow rates are required through the boiler, an optional
Input |
| Minimum Return |
Btu/hr |
| Temperature |
|
|
|
1,500,000 |
| 50°F (10°C) |
_________ |
| __________________ |
1,700,000 |
| 50°F (10°C) |
_________ |
| __________________ |
2,000,000 |
| 50°F (10°C) |
|
|
|
Minimum Setpoint
105°F (40.6°C)
______________
90°F (32.2°C)
______________
70°F (23.9°C)
The heat exchanger is capable of operating within the design flow rates for the boiler secondary loop requirements. Erosion of the finned copper tubes may occur if the flow rate exceeds the maximum allowable flow rate through the boiler. The maximum flow through the boiler must be adjusted with the bypass valve in the full closed position. Maximum flow is 90 GPM. Flow rate can be determined by measuring the temperature rise through the boiler when it is firing at full rate input. See
CAUTION
A boiler allowed to operate at set point temperatures below the specified minimum settings may experience operational problems with the operating controls and safety switches, obstruction of the flue gas passages on the primary heat exchanger, incomplete combustion and possible flue gas spillage. Operation at lower than specified water temperatures may cause hazardous conditions that result in
BOILER TEMPERATURE
RISE CHART
TABLE - DD
Temperature Rise at Full Rate Fire
Bypass Fully Closed and 90 GPM Flow
Btu/hr Input |
| Temperature Rise |
|
|
|
1,500,000 |
| 31.5°F (17.5°C) |
_______________________ |
| ________________________ |
1,700,000 |
| 35.7°F (19.8°C) |
_______________________ |
| ________________________ |
2,000,000 |
| 42.0°F (23.3°C) |
|
|
|
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