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 the temperature of the buffer section currently being charged + Hysteresis solar off, the pump and the analog output are switched off. The reference is therefore Temp. buffer top while the top is being charged, otherwise Temp. buffer bottom.
With the pump switched on, the speed is set proportional to the temperature difference: speed in per cent = Gain x (solar temperature - temperature of the buffer section being charged), limited to 0 to 100 %. The value is present at the output Pump analog 0-100%; with the pump switched off it is 0. 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, the shutdown at maximum temperature acts immediately.


System diagram

Collector Buffer SO PO PU PD PA VP top bottom Input (sensor) Output

Inputs

SO Temp. solar Temperature solar (collector). Not linked: the block calculates with 0 °C, the pump stays off.
PU
 Temp. buffer bottom
 Temperature buffer bottom. Not linked: the block calculates with 0 °C and charges the bottom permanently. This sensor must be linked.
PO
 Temp. buffer top
 Temperature buffer top. Not linked: the block calculates with 0 °C and then always charges the top. This sensor must be linked.

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.