Raypak 5042004 operating instructions Operating Modes, Differential Graph

Deadband: Deadband is a band of temperature sens- ing where no action occurs. All temperature controllers have a deadband and the purpose is to prevent short- cycling of the heater. The on-board temperature controller has a deadband of 2ºF around the differen- tial.

Differential: A heat source must be operated with a temperature differential in order to prevent short- cycling. The temperature differential is divided around the “target” temperature or set-point. The Call For Heat (CFH) contact will close in the controller when the water temperature is below the target temperature by 1/2 of the differential setting, and will open when the water temperature is above the target temperature by 1/2 of the differential setting. See Fig. 30.

Fig. 30: Differential Graph

For systems with less than 4:1 turndown, the control should be placed in the system return, upstream of the inlet piping to the heater, as shown in Figs. 32, 34 and 35. This placement will avoid short cycling the heat source. Raypak recommends using a smaller differen- tial setting when controlling the water temperature on the return side. As a starting point, set the return differ- ential to 10ºF and this will allow the system return temperature to vary 5ºF above and 5ºF below the set- point.

For systems with more than 4:1 turndown, the recom- mended location of the system (target) sensor is in the system supply loop, downstream of the outlet piping from the heater. When controlling systems with more than 4:1 turndown; set the supply side differential to 20ºF and the temperature will vary ±10ºF around the setpoint.

In lieu of installing the target sensor in the system return, a properly-sized buffer tank can be installed as shown in Fig. 31. Consult factory for buffer tank sizing.

Operating Modes

Mode 1 (Not supported) – Setpoint operation using primary piping. The heater outlet water temperature is controlled to the boiler target setpoint.

Fig. 31: Buffer Tank Piping

Mode 2 – Setpoint operation using primary/secondary piping. The control operates the heater to satisfy a remote system sensor. The heater is turned off based on boiler target and boiler differential (factory default H7, P and WHP boilers). See Fig. 32.

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

Fig. 32: Mode 2 Primary/Secondary Piping

Mode 3 – Dedicated DHW operation using UniTemp 80 piping. A call for heat is determined by the DHW sensor and the DHW boiler target. The heater outlet water is also controlled to the boiler target temperature (factory default WH1 water heaters). See Fig. 33.

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