Raypak 503-2003 manual Hydronic Heating, Pump Selection, Feedwater Regulator, Cold Water Starts

longer than 7 minutes or where cold water operation is continuous, provisions must be made to mix higher temperature outlet water with the colder inlet water and thereby raise the inlet temperature to at least 120°F (49°C) within the 7-minute time limit.

Cold Water Starts

Cold water starts, where the inlet water temperature remains below 120°F (49°C) for more than 7 minutes, must have cold water start protection. Known pro- tection methods consist of mixing heated outlet water with the inlet water using a bypass to raise the inlet to 120°F (49°C) or higher. Once the system is heated up and has return water temperatures of 120°F (49°C) 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 out- let temperature may continue to climb and trip the high limit, thereby shutting down the heater. Thus an auto- matic valve system, such as a three-way proportional valve to control the bypass, should be used.

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*Maximum 4 times the pipe diameter or 12”, whichever is less.

Fig. 9: Cold Water Start

Cold Water Run

Cold water run differs from cold water start in that the system water entering the heater remains below 120°F (49°C) continuously. Typically, this is the case in swimming pool heating and water source heat pump applications as well as some others. If the system

water is kept in a narrow temperature range of no more than 10°F (5°C), a permanent manual bypass can be employed and manually adjusted to achieve an inlet temperature of 120°F (49°C) or higher as adjust- ed at the minimum temperature in this narrow temperature range (i.e. Range 75°F to 85°F, adjust bypass with temperature at 75°F (24°C)) so that when temperature is 85°F (29°C), minimum inlet tempera- ture would be 130°F (54°C). An injector pump arrangement may also be utilized to keep the heater loop at or above 120°F (49°C). An injector pump approach has the added value of being able to adjust to changes in the system water coming back to the heater take-off.

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*Maximum 4 times the pipe diameter or 12”, whichever is less.

Hydronic Heating

Pump Selection

In order to ensure proper performance of your heater system, you must install a correctly-sized pump. Ray- pak requires designing for a ∆T within the range of 10°F to 40°F (5°C to 20°C). See Table F for accept- able flow rates for each model (∆T is the temperature difference between the inlet and outlet water when the heater is firing at full rate).

Feedwater Regulator

Raypak recommends that a feedwater regulator be in- stalled and set at 12 psi minimum pressure at the highest point of the system. Install a check valve or back flow device upstream of the regulator, with a manual shut-off valve as required by local codes.

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