Failure to exceed 105ºF (41ºC) within 7 minutes may result in the premature failure of the hot surface ignit- er, remote flame sensor, burners and heat exchanger. It can cause operational problems, bad combustion, sooting, flue gas spillage and reduced service life of the vent system. The bypass allows part of the heater discharge water to be mixed with the cooler heater return water to increase the heater inlet temperature above 105ºF (41ºC). This precautionary measure should prevent the products of combustion from con- densing in most installations. Warranty claims will be denied when condensation occurs.
Cold water operation issues are applicable to both cold water start and cold water run applications. Cold water operation for 7 minutes or less on
Cold Water Starts
Frequent (more than once a week) cold water starts, wherein the inlet water temperature remains below 105ºF (41ºC) for more than 7 minutes, must have cold water start protection. Known protection methods con- sist of mixing heated outlet water with the inlet water with a bypass to raise the inlet to 105ºF (41ºC) or high- er. Once the system is heated up and has return water temperatures of 105ºF (41ºC) or higher, the mixing of outlet water with inlet water is no longer needed and the bypass can be shut off. If the bypass is not shut off as the system heats up, the outlet temperature may continue to climb and actuate the high limit, thereby shutting down the heater. Thus an automatic valve system, such as a
NOTE: Individual and
Cold Water Run
Cold water run differs from cold water start in that the system water entering the heater remains below 105ºF (41ºC) continuously. Typically, this is the case in swim- ming pool heating and water source heat pump applications as well as some others. If the system water is kept in a narrow temperature range, a perma- nent manual bypass can be employed and manually adjusted to achieve an inlet temperature of 105ºF (41ºC) or higher. An injector pump arrangement may also be utilized to keep the heater loop at or above 105ºF (41ºC). An injector pump approach has the added value of being able to adjust to changes in the system water coming back to the heater
NOTE: To ensure proper operation, use 20°F ∆T boiler flow rates when designing the heating system loop pump.
Temperature & Pressure Gauge
The temperature and pressure gauge is factory- mounted in the in/out header.
Hydronic Heating
Pump Selection
In order to ensure proper performance of your heater system, you must install a correctly sized pump. Ray- pak recommends using a 20°F ∆T as design ∆T. (∆T is the temperature difference between the inlet and out- let water when the heater is firing at full rate). If a ∆T of larger than 20°F is necessary, see Table H and Table I for flow rate requirements.
Model | 10°F | T | 20°F | T | 30°F | T | 40°F | T | Min. Flow |
| Max Flow |
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No. | gpm |
| P (ft) | gpm |
| P (ft) | gpm |
| P (ft) | gpm |
| P (ft) | gpm | P (ft) | T | gpm | P (ft) | T |
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302B | 50 |
| 3.3 | 25 |
| 0.8 | N/A |
| N/A | N/A |
| N/A | 20 | 0.5 | 25 | 90 | 9.8 | 6 |
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402B | 67 |
| 5.8 | 34 |
| 1.4 | 22 |
| 0.6 | N/A |
| N/A | 20 | 0.5 | 34 | 90 | 10.0 | 7 |
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502B | 84 |
| 9.1 | 42 |
| 2.3 | 28 |
| 1.1 | 21 |
| 0.6 | 21 | 0.6 | 40 | 90 | 10.4 | 9 |
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652B | N/A |
| N/A | 55 |
| 4.1 | 36 |
| 1.8 | 27 |
| 1.1 | 27 | 1.1 | 40 | 90 | 10.8 | 12 |
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752B | N/A |
| N/A | 63 |
| 5.7 | 42 |
| 2.6 | 32 |
| 1.5 | 32 | 1.5 | 40 | 90 | 11.3 | 14 |
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902B | N/A |
| N/A | 76 |
| 8.3 | 50 |
| 3.8 | 38 |
| 2.2 | 38 | 2.2 | 40 | 90 | 11.7 | 17 |
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Notes: 1. Basis for minimum flow is 20 gpm or 40°F ∆T. Basis for maximum flow is 90 gpm. Flow switch will not operate if flow is less than 20 gpm.
2.
Table H: Heater Rates of Flow and Pressure Drops
16
