Overview Solar 2 collectors exchanger/buffer



This function block controls a solar system with two collector fields (e.g. east and west, or two buildings) that charge a stratified buffer through a common heat exchanger. Each field has its own speed-controlled pump; the exchanger's secondary pump runs as soon as one of the fields is running. A diverter valve charges the buffer at the top as long as the exchanger flow is warm enough for that, otherwise at the bottom.

The block corresponds to scheme 13 of the HMI-Master and is executed every second.
  • Collector pumps P1/P2: Each field is compared with the colder of the two buffer sensors. The pump starts when the collector is warmer by the switch-on difference, and switches off when the difference falls below the switch-off difference. Above collector maximum, or if both buffer sensors are above buffer maximum, the pump stays off. An unlinked field (S2) always stays off.
  • Exchanger pump PT: runs as long as P1 or P2 is running.
  • Diverter valve VU: If the exchanger flow (WP) is warmer than the buffer top by the switch-on difference, the top is charged immediately (VU = 0). If it no longer is, the valve switches to the bottom after the switch-over delay (VU = 1).
  • Speed A1/A2: Gain x (collector - temperature of the charging zone), limited to minimum speed up to 100 %. The charging zone is buffer top or bottom, depending on the valve.
  • Speed AT: Gain x (exchanger flow - charging zone). If a collector field is running at more than 78 %, or the exchanger flow is more than 30 K warmer than the charging zone, the exchanger pump runs at 100 % so that heat does not build up in the exchanger.
  • Lock SP (manual/automatic): When set, all outputs go to 0 once. After that the block sends nothing more - not even cyclically - so that the pumps can be operated manually. When reset, the block re-evaluates immediately.
The analog outputs deliver 0-100. Linked to an address of type 1 byte percent (DPT 5.001), the actuator sends 0-255.

System diagram

Collector 1 Collector 2 Exchanger Buffer top bottom S1 S2 WP WS PO PU P1 A1 P2 A2 PT AT VU Input (sensor) Output

Inputs

S1 Temp. collector 1 Temperature collector field 1. Must be linked.
S2 Temp. collector 2 Optional. Temperature of collector array 2. Not linked: pump P2 stays off, the block works with one array.
WP Temp. exchanger primary Flow of the heat exchanger (solar side). Determines the diverter valve and the speed of the exchanger pump. Must be linked.
WS Temp. exchanger secondary Optional. Exchanger flow (buffer side), only shown in the status text. Not linked: the status text shows the primary flow only.
PU Temp. buffer bottom Must be linked.
PO Temp. buffer top Must be linked.
SP Lock (manual) Optional. Not equal to 0 locks: all outputs go to 0 once, then the block sends nothing more (manual mode). Changing to 0 releases, the block evaluates immediately. Not linked: never locked.

Outputs
P1 / A1 Pump collector 1 On/off or speed 0-100 %.
P2 / A2 Pump collector 2 On/off or speed 0-100 %.
PT / AT Pump exchanger/buffer Secondary pump on/off or speed 0-100 %.
VU Diverter valve 0 = buffer top, 1 = buffer bottom.
ST Status text State as plain text, e.g. "laedt oben: K1 64%, K2 0%, Tauscher 70% (58.2/52.0 C)" (German text). For a text address (14 byte).

Parameters
Collector maximum Above this temperature the pump of the field stays off (stagnation protection). Default 120 °C.
Buffer maximum If both buffer sensors are above this, charging stops. Default 85 °C.
Switch-on difference Collector versus the colder buffer sensor, above which the pump starts; also the threshold of the diverter valve. Default 10 K.
Switch-off difference Below this the pump switches off. Limited to the switch-on difference. Default 5 K.
Gain Speed in % per Kelvin of difference. Default 4 %/K.
Minimum speed Lower limit of a running pump. Default 12 %.
Switch-over delay bottom How long the exchanger flow must be too cold for the top before the valve switches to the bottom. Default 15 s.

See also general parameters of all function blocks.