Solar Plant / RWD32S
Basic application # 6
/ Solar storage system with layered storage tank
Hot water storage tank with solar heating, charging pump, bypass valve and non-return valve. Storage tank with two heat exchangers
Use / Differential temperature control of a storage tank with two heat exchangers. During periods of low solar energy, this application maximizes the heat available by charging the lower part of the storage tank only. As the solar energy increases, the bypass valve closes and the upper part of the tank is charged.
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 / Bypass valve control
/
Maximum limitation / Minimum charging temperature / Frost protection
/ /
B1 / Tank temperature sensor / Tsol / Solar collector temperature
B2 / Solar collector temperature sensor / Tsto / Storage tank temperature
B3 / Immersion temperature sensor / WB2lim / Minimum charging collector temperature setpoint
E1 / Hot water storage tank / WB3lim / Maximum tank temparetaure setpoint
E2 / Solar collector / Y1 / Bypass valve
M1 / Charging pump / ΔtK1 / Differential temperature B2–B3 [K]
SD1 / Pump and valve switching differential / ΔtK2 / Differential temperature B2–B1 [K]
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.
Bypass valve control (Y1)
The temperature in the upper part of the tank will always be higher than the lower part.
The bypass valve (Y1) is opened when the set temperature differential (ΔtK2) between solar collector (B2) and the upper part of the tank (B3) exceeds the setpoint (ΔtWsp) by ½ the switching differential, and the storage tank is now charged via the upper heat exchanger only. / 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 temperature causing damage to the storage tank, temperature can be limited
If the tank temperature (B3) exceeds the set value (WB3lim), the controller switches off charging pump (M1). The pump is switched on again when the storage tank temperature falls 10 K below the set value.
Frost protection
Solar collector temperature (B2) is monitor to avoid freezing. If temperature drops down to 5°C, pump is switched on.
Gradient function
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
B3 / Cable temperature sensor silicone 1.5 m, LG-Ni1000 / N1831 / QAP21.3 / 1
Y1 / 3-port valve / * / VX... / 1
3-position valve actuator, AC 230 V / * / S..3... / 1
* For selection of the sensors and valves, refer to the Product Catalog or HIT Selection Tool
Connection
diagram /
Parameter settings / Parameter / Setting / Function / Remarks
Path: ... > PS1 Level
APPL / 7 / Select application / Standard application # 7
Path: ... > PS4 Level
Q1 / Q2 SD / 2 K / Relay output Q1 / Q2 differential
Q1 OFF / 120 sec. / Relay output Q1 delay time
Q2 OFF / 120 sec. / Relay output Q2 delay time
B2 / 30 °C / Minimum charging temperature for solar collector
B1 / 60 °C / Maximum tank E1 temperature
B3 / 60 °C / Maximum tank E3 temperature
FROST / On or OFF / Frost protection
GRAD / On or OFF / Gradient function / Periodic start of the pump
ΔSP / 5 K / Differential temperature setpoint / Difference between solar panel collector and tank to charge
Only parameters necessary for commissioning are mentioned above. For the complete parameter list, please refer to the 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.
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. / 25.11.2008
CE1A3344en06