Overview Solar buffer top/bottom



This function block realizes a solar control for charging a stratified buffer at two heights (top and bottom). Depending on the available solar temperature, the buffer is charged either at the top (quickly usable heat) or at the bottom.

As long as the solar, the buffer-bottom and the buffer-top temperatures are below their maximum values, the block compares the solar temperature with the two buffer temperatures:
  • If the solar temperature is higher than Temp. buffer top by the Hysteresis solar on, the valve switches to buffer top (VP = 1) and the pump turns on – the buffer is charged at the top.
  • If the solar temperature is only higher than Temp. buffer bottom by the Hysteresis solar on, the valve switches to buffer bottom (VP = 0) and the pump turns on – the buffer is charged at the bottom.
  • If the solar temperature falls below Temp. buffer bottom + half the Hysteresis solar off, the pump is switched off.
With the pump switched on, the speed is controlled via a P controller (Gain) so that the respectively active buffer temperature (top or bottom) is held as setpoint; the result is present at the output Pump analog 0-100%. If the solar or one of the buffer temperatures reaches its maximum value, the pump is switched off immediately. The control is executed every 10 seconds.


Inputs

SO Temp. solar Temperature solar (collector).
PU
 Temp. buffer bottom
 Temperature buffer bottom.
PO
 Temp. buffer top
 Temperature buffer top.

Outputs
PU
 Pump digital
 Pump digital on/off.
PA
 Pump analog 0-100%
 Pump analog. As an alternative to control via switching hysteresis, a pump with analog control can be used at this output.
VP Valve buffer top Valve switchover buffer charging: 1 = buffer top, 0 = buffer bottom.

Parameters
Solar maximum
 Maximum temperature solar. If the temperature exceeds this value, the pump is switched off even if the buffer temperature has not been reached.
Buffer maximum Switch-off temperature buffer. If the temperature buffer top or bottom exceeds this value, the solar pump is switched off.
Hysteresis solar on
 Difference between solar and buffer at which the control becomes active.
Hysteresis solar off
 Difference between solar and buffer at which the control becomes inactive.
Gain Control setting; the higher the value, the faster the analog output changes with a change in temperature.

See also common parameters of all function blocks.