Dhw Storage With Thermostat; Dhw Mode 2; Instantaneous Water Heating With Plated Heat Exchanger; Dhw Mode 3 - Slant/Fin VGH-299-CH Installation And Service Manual

12.9.3 DHW S
TORAGE WITH THERMOSTAT
In this mode DHW is prepared by warming up an indirect tank. Either a DHW circulator or 3-way valve can be
used to switch to DHW mode. The temperature of the DHW in the indirect tank is regulated by a
thermostat/aquastat (instead of a sensor), which must provide only an open/closed signal to the control.
When the thermostat/aquastat closes the control detects a demand from the DHW indirect tank and starts the
DHW circulator.
If the supply temperature T_Supply drops below DHW_Store_Setpoint
starts. When the boiler is ON the power is PID-controlled based on T_Supply toward DHW_Store_Setpoint.
The boiler is stopped when the supply temperature rises above DHW_Store_Setpoint
The demand for DHW ends when the indirect tank thermostat/aquastat opens. The circulator continues
DHW_Post_Circulator_Period after the DHW demand has stopped.
DHW priority
See paragraph 12.8.2 – DHW Mode 1 – Storage with sensor
Relevant variables
Specific Parameters
DHW_Mode
DHW_Store_Setpoint
Sets the supply temperature from the boiler to prepare
DHW in the indirect tank
DHW_Priority
DHW_Max_Priority_Time
Sets the maximum time for either DHW or CH priority.
DHW_Post_Circulator_Period
Table 12. 21
12.9.4 I
NSTANTANEOUS WATER HEATING WITH PLATED HEAT EXCHANGER
In DHW mode 3 the water flow through a plated heat exchanger is checked with a flow switch. If the switch
closes a water flow is detected, and either a DHW pump or a 3-way valve can be used to switch to DHW mode.
The temperature of the DHW is set with DHW_Setpoint.
If the T_DHW_Out sensor drops below DHW_Setpoint
burner is on, the power is PID-controlled based on T_DHW_Out toward DHW_Setpoint. The burner stops when
the T_DHW_Out temperature rises above DHW_Setpoint
demand for the tapping is ended and the burner stops. The pump continues DHW_Post_Pump_Period.
Based on a DHW temperature rise of
Boiler model Minimum flow (gpm)
VGH 299
VGH 399
VGH 500
Table 12. 20
Specific Parameters
DHW_Mode
DHW_Setpoint
Sets the desired DHW temperature
DHW_Post_Pump_Period
Table 12. 21
78
; DHW 2
MODE
Level
2: Installer
2: User
[-]
2: Installer
2: Installer
minus
100 °F following minimum and maximum DHW flows are advised:
Maximum flow (gpm)
1.1
1.4
1.8
Level
2: Installer
2: User
2: Installer
E93.1601EN032.C VGH installation manual
minus DHW_Supp_Hyst_Down the boiler
(Default) Value Range
0 0, 1, 2, 3, 4, 5, 6, 7, 8
149 ºF (65 ºC) 104...160 ºF
2 0=Time, 1=OFF, 2=ON
60 min.
120 sec. 10...900
; DHW
MODE
DHW_Hyst_Down the burner starts. When the
plus DHW_Hyst_Up. When the flow switch opens the
5.3
7.1
9.0
(Default) Value Range
0 0, 1, 2,3, 4, 5, 6, 7, 8
122 ºF (50 ºC) 86...176 ºF (30...80 ºC)
20 s 10...900 s
plus DHW_Supp_Hyst_Up.
(40...71 ºC)
3