Secondary Supply Temperature Control

The DHW heat exchanger controls the secondary supply temperature. The domestic hot water temperature setpoint is defined as shown in the table below.

Table 1.   DHW Heat Exchanger Configurations

Configuration

Connection

Comments

single domestic hot water heat exchanger

connect the output "CalcDHWTempSp" of a "DHA_DWH" segment to the input "DHW_TempSp".

a single DHW heat exchanger receives its DHW setpoint by connecting it to the heat demand output of a DHW segment

continuous-flow or tankless heaters

connect a datapoint assigned to a time schedule to the input "DHW_TempSp"

the default setpoint in the time program must be 60 °C during workdays and weekends.

If a flow switch is connected, the DHW setpoint is equal to the value defined in the time schedule. If there is no flow (= 0) the setpoint is equal to "0".

If you do not connect a flow switch, enter the default value "1" to the flow switch input


Configuration Schematics


Single Domestic Hot Water Heat Exchanger

Continuous-flow or Tank less Heaters

The heat exchanger reduces the charging temperature for the domestic hot water storage tank. In this configuration, use the macros BOD_HeatExch_DHW and DHA_DHW. Connect the storage tank heat demand output to the heat demand input of the heat exchanger macro

Connect a time schedule for DHW setpoint to the heat demand input of the heat exchanger

In all configurations, the maximum a primary supply temperature limitation can be configured to protect the heat exchanger against calcification

Fig. 1.   Domestic Hot Water Configurations

Depending on the setpoint value the DHW heat exchanger is in occupied or un-occupied period.

Table 2.   DHW Control Setpoint

DHW setpoint

Condition

DHW_TempSp

Auto operation - time schedule

DHW_TempSp >= SYS-01: occupied setpoint

DHW_TempSp < SYS-01: un-occupied setpoint


According to the currently-valid Drinking Water Guidelines, the DHW setpoint must be at least 60 °C, to guarantee a minimum circulation temperature of 55 °C. In both configurations, the setpoint can be overridden using the extended operation or anti-legionella setpoints.

Table 3.   DHW Control Setpoint

DHW setpoint

Condition

DHW_TempSp

Auto operation - time schedule

DHW_TempSp >= SYS-01: occupied setpoint.

DHW_TempSp < SYS-01: un-occupied setpoint

parameter DEX-01

DHW setpoint during extended operation

parameter LEG-01

DHW setpoint during anti-legionella operation


This secondary supply setpoint is increased by the value of the parameter SST-04 (setpoint increase to compensate losses),
e.g. 5 K. The setpoint is ramped up by a setpoint increase (SST-05).

The setpoint is limited between the minimum and maximum supply temperature limits, which are defined by the parameters SST-02 (minimum supply temperature) and SST-01 (maximum supply temperature) as shown in the next figure.

Fig. 2.   SST Setpoint Ramp

Depending on the calculated P-band, the integral action time, the D-time, and the calculated system supply temperature setpoint, the control signal varies from 0...100% as shown in the next figure.

During un-occupied periods the domestic hot water minimum setpoint is equal to SST-02 based on the assumption that occupied setpoints are higher than SST-02.


Fig. 3.   SST Control


Table 4.   Parameter List

Description

Value Range

Default Value

Unit

SST-01: maximum supply temperature

50...200

90

°C

SST-02: minimum supply temperature

0...90

10

°C

SST-03: occupied / un-occupied changeover; 0 = disable

0...50

40

°C

SST-04: setpoint increase to compensate losses

0...20

5

K

SST-05: maximum setpoint increase per minute

1...100

25

K

SST-06: P-band SST control

1...1000

20

K

SST-07: I-time system supply temperature control

0...3600

300

sec

SST-08: D-time system supply temperature control

0...1000

0

sec