Solar Plant / RWD32S
Basic application # 2
/ Solar storage system with additional heat source
Hot water storage tank with solar heating, charging pump and non-return valve. Additional heat source to be used as alternative to solar source
Use / Differential temperature control of a storage tank with changeover to a separate heat producer (typically a boiler or an electric immersion heater) when the solar energy is not sufficient
Options /
- Minimum temperature at the collector is required before charging can take place
- Maximum limitation of the storage tank temperature
- Frost protection of solar collector
- Periodic pump start to ensure reliability of sensors values
Plant diagram /
Function diagrams / Storage temperature control / Heat source pump control
/
Maximum limitation / Minimum charging temperature / Frost protection
/ /
B1 / Tank temperature sensor / SD2 / Pump or command M2 switching differential
B2 / Solar collector temperature sensor / Tsol / Solar collector temperature
B3 / Immersion temperature sensor / Tsto / Storage tank temperature
E1 / Hot water storage tank / WB2lim / Minimum charging collector temperature setpoint
E2 / Solar collector / WB3lim / Maximum tank temparetaure setpoint
E3 / Additional heat source / Wsp_3 / Additional heat source setpoint
M1 / Charging pump / ΔtK1 / Differential temperature [K]
M2 / Boiler pump or heat source command / ΔtWsp / Differential temperature setpoint
SD1 / Pump M1 switching differential
Description
of Functions / Basic functions / Options
The differential temperature controller (N1) acquires the temperature in the hot water storage tank (E1) via temperature sensor (B1), and the temperature in the solar collector (E2) by sensor (B2). The measured temperature difference (ΔtK1) is compared to the desired setpoint (ΔtWsp) set on the controller.
If the measured difference exceeds the setpoint by ½ the switching differential (SD1), the controller switches on charging pump (M1) to charge the storage tank with hot water.
The charging pump is switched off when the measured differential falls below the setpoint by ½ the switching differential.
Charging the tank via additional heat source (E3)
This application requires an optional sensor (B3 or B1 instead) in the upper part of the storage tank to maintain a fixed temperature. This allows the hot water storage tank to be charged by a secondary heat source according to demand, when solar energy is not sufficient.
If the storage tank temperature, measured by the immersion sensor (B3 or B1) falls below the absolute temperature setpoint (Wsp_3), the pump (M2) is activated. The charging pump is switched off when the temperature exceeds the setpoint by the switching differential set value. / Minimum charging temperature
If required, a minimum charging temperature can be set on the controller to ensure charging takes place only when sufficient heat is available in the solar collector. The temperature measured by the solar collector sensor (B2) is compared to the minimum value (WB2lim). The charging pump (M1) is disabled until the desired temperature + 4 K is reached.
Maximum limitation
In order to prevent too high temperatures causing damage to the storage tank, the temperature can be limited
If the tank temperature (B1 or B3) exceeds the set value (WB3lim), the controller switches off the charging pump (M1). The pump is switched on again when the storage tank temperature falls 10 K below the set value.
Frost protection
The collector temperature (B2) is monitored to avoid freezing. If the temperature drops down to 5°C, the pump is switched on.
Gradient function
The pump can periodically be switched on, as the temperature at the collector (primarily vacuum pipes) cannot be measured reliably when the pump is off.
Device list / Legend / Type of unit / Data sheet / Product No. / Qty.
N1 / Differential temperature controller / N3344 / RWD32S / 1
B1 / Cable temperature sensor silicone 1.5 m, LG-Ni1000 / N1831 / QAP21.3 / 1
B2 / Cable temperature sensor for high-temperature applications (180°C) / N1833 / QAP21.2 / 1
Optional / Legend / Type of unit / Data sheet / Product No. / Qty.
B3 / Immersion temperature sensor LG-Ni1000 with protection pocket / * / QAE2120.. / 1
Variants / Legend / Type of unit / Data sheet / Product No. / Qty.
B3a / Strap-on temperature sensor LG-Ni 1000 / N1801 / QAD22
* For selection of the sensors, refer to the Product Catalog or HIT Selection Tool
Connection
diagram /
Parameter settings / Parameter / Setting / Function / Remarks
Path: ... > PS1 Level
APPL / 2 / Select application / Standard application # 2
Path: ... > PS2 Level
B3 / On or OFF / Display B3 in normal mode / If B3 is not connected to controller, this parameter disables B3 display in normal mode to avoid “out of range” display
Path: ... > PS4 Level
Q1 SD / 2 K / Relay output Q1 differential
Q1 OFF / 120 sec. / Relay output Q1 delay time
Q2 SD / 2 K / Relay output Q2 differential
Q2 OFF / 120 sec. / Relay output Q2 delay time
B2 / 30 °C / Minimum charging temperature for solar collector
B3 / 60 °C / Maximum tank temperature / If B3 is not connected, maximum tank temperature function will be controlled by sensor B1
FROST / On or OFF / Frost protection
GRAD / On or OFF / Gradient function / Periodic start of the pump
SP_3 / 60 °C / Temperature setpoint for loop 2
ΔSP / 5 K / Differential temperature setpoint / Difference between solar collector and tank to charge
Only parameters necessary for commissioning are mentioned above. For the complete parameter list, please refer to the installation instructions.
Application notes / General
For this type of control, the default values preconfigured within the controller will normally offer good control.
All default values shown must be checked and / or amended to suit the exact requirements of the plant.
Commissioning
During first commissioning or when the application type is modified, the plant control is stopped until end of commissioning.
Connections
The function provided by the optional sensor (B3) is automatically enabled, when the input is connected at the controller. If no sensor is connected to B3 controller input, maximum limitation function remains active and based on B1 sensor.
Schematics
The wiring diagram only shows the HVAC control functions. Not included are safety devices and interlocks, which are the responsibility of the installer.
The hydraulic circuits shown are to be used as a guideline only and should be modified to suit the application.
Controller notes / Operating voltage
An operating voltage of AC 230 V (±10 %) is necessary for this control loop and frost protection function.
When installing mains power and low voltage, please ensure local electrical regulations are observed.
This document provides general application information and should be used as a guideline only, and remains subject to change without prior notice.
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Technical information in this document might not be up to date and are subject to change. Drawings serveillustration purposes only. Siemens is not responsible for the content and any manual modifications. / 06.10.2008
CE1A3344en02