Overview Buffer storage



A buffer storage sits between generator and consumers and decouples both. It is the reason why a heat pump does not cycle. This function block knows how full the buffer is, whether it covers the consumers' request by itself and when it has to be reloaded. It requests heat from the generator only if the buffer cannot supply it itself.

The block sits in the request chain: the requests of the consumers (heating circuits, hot water) arrive via the Heat request block at AN and AT, the request to the generator leaves at the outputs AN and AT towards the Heat generator block.

Does the buffer cover the request?

The consumers request, for example, 45 °C. Charge level and energy. The charge level LZ is the mean of the connected sensors (each stands for the same share of the volume, with three sensors one third each), mapped linearly between the two reference temperatures to 0 to 100 %. A sensor that is not connected does not count as 0 °C. The usable energy EN is volume times 1.163 Wh/(l*K) times the difference to the reference temperature 0 %. This is an estimate: it ignores the stratification within a sensor range and the heat loss. Accurate enough for a display and for the decision whether reloading pays off, but not a meter. For billing use a calibrated heat meter. The charge level is not saved, it is recalculated within one cycle.

Layered charging. With layered charging a diverter valve (output UO) charges at the top when the buffer is cold and at the bottom when it is warm. The bottom sensor decides, without it the mean. The valve switches only after the switching delay, otherwise it hunts in the transition range. At the start of a reload the choice applies at once.

Foreign heat source. If another source supplies heat at the moment (solar, solid fuel boiler), input FQ is 1. Depending on the setting the reload is then blocked or the switch-on threshold is lowered. After it ends the source counts as active for the run-on time: a solar pump that pauses briefly does not start the boiler at once.

Excess heat removal. If the buffer gets too hot at the top, UW reports a 1. It is a separate output for a relay or a message: the block forces no consumer to heat, a heating circuit stays off in summer.

Discharge enable. If the top temperature falls below the set minimum temperature, EF goes to 0 and blocks the consumers (for example at input SP of a heating circuit). The default 0 switches the function off. If the top sensor is missing, EF stays open - a missing sensor must not shut the heating off.

Example

1000 litre buffer with three sensors and a heat pump. The Heat request block reports 45 °C at AN and AT. The buffer is at 60 °C at the top: it covers, the heat pump stays off and EF is 1. If the buffer falls to 42 °C at the top, the reload starts and requests 50 °C (45 plus 5 K charge offset). It ends when the middle sensor has reached 51 °C and the minimum charge time is over.

Inputs

TO Buffer temperature top Mandatory input. Not connected or outside -50 to 150 °C: fault, no reload.
TM Buffer temperature middle Optional. Counts into the charge level and, depending on the setting, into reload and end of charging. Not connected: the sensor is ignored.
TU Buffer temperature bottom Optional. Like TM; also the reference of layered charging. Not connected: the sensor is ignored.
AN Request consumers Optional. Bit of the heat request. Not 0 requests. Not connected: only AT counts - a temperature above 0 counts as a request.
AT Request consumers temperature Optional. Wanted temperature. Not connected or 0: the parameter request without temperature applies.
FQ Foreign heat source active Optional. Not 0: another source is charging. Not connected: there is no foreign source.
FR Enable Optional. 0 blocks the reload, not 0 enables. Not connected: the block counts as enabled.
SP Lock Optional. Not 0 blocks the reload, 0 enables. Not connected: never locked.

Outputs
AN Request to the generator 1 during the reload.
AT Request to the generator temperature Request plus charge offset during the reload, otherwise 0.
LP Charge pump generator 1 during the reload.
UO Diverter valve layered charging top 1: charge at the top. Only with layered charging and during the reload.
EF Discharge enable 1: the consumers may draw from the buffer.
LZ Charge level in % 0 to 100 %, from the available sensors.
EN Usable energy in kWh Estimate, see above.
UW Excess heat removal active 1 as long as the buffer top is above the limit temperature.
ST Status text State in plain text (German, ASCII, written by the runtime), for example "Puffer 44 %, deckt die Anforderung". For a text address.
SR Fault 1 with a missing or implausible top sensor.

Parameters
Volume, reference temperature 0 % and 100 % Default 1000 l, 25 ° and 70 °.
Sensor for reload, sensor for end of charging Default top and middle. A sensor that is not connected is replaced by the top one or the reload sensor.
Switch-on difference, switch-off difference, charge offset Default 2 K, 6 K and 5 K. The switch-off difference must be larger than the switch-on difference.
Request without temperature Default 45 °C.
Minimum charge time, minimum pause Default 5 min each.
Layered charging, top below, switching delay Default off, 40 ° and 60 s.
With foreign source, lowering of switch-on threshold, run-on Default "block reload", 5 K and 10 min.
Excess heat removal, from, reset difference Default off, 90 ° and 5 K.
Discharge enable minimum temperature Default 0 = off.

See also general parameters of all function blocks.