Raypak MVB TYPE B 504-2004 Betriebsanleitung PDF herunterladen (Seite 31)

maintain near 160ºF system supply temperature, and

if the system ΔT is 10ºF, then the system return (target)

set-point is 160-10=150ºF.

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. 27.

For systems with less then 4:1 turndown, the control

should be placed on the system return, as shown in

Fig. 29, to avoid short cycling the heat source. Raypak

recommends using a smaller differential setting when

controlling the water temperature on the return side.

As a starting point, set the return differential 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. When controlling systems with

more than 4:1 turndown; set the supply side differen-

tial to 20ºF and the temperature will vary ±10ºF around

the set-point.

In lieu of installing the target sensor in the system

return, a properly-sized buffer tank can be installed as

shown in Fig. 28. Consult factory for buffer tank sizing.

Operating Modes

Mode 1 – Not recommended.

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. 29.

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

Fig. 29: Mode 2 Primary/Secondary Piping

Fig. 27: Differential Graph

Fig. 28: Buffer Tank Piping

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

California Hot Water Supply, Inc.

(800) 249-7244

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