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.
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 |