Overview Heat request

This function block collects the heat requests of several consumers - heating circuits, domestic hot water, screed programme, pool heating - and reports a single request to the generator. It forms the maximum of the desired temperatures and decides who has priority.

Every request consists of two values: a bit "I need heat" and the desired flow temperature at the generator. This is exactly the form that Heating circuit and Boiler charging deliver at their outputs, and exactly the form the Heat generator expects at its inputs.

A consumer that only delivers a temperature can still be connected directly. If the bit input of a request is left unconnected, a temperature greater than 0 counts as a request. That is how the Heating+cooling curve, which has exactly one output, is connected without a comparator in front of it. The curve sets its output to 0 as soon as its enable drops - which ends the request as well.

The number of requests can be set from 2 to 8; each request creates two inputs. If eight are not enough, one collector may feed another collector - cascading is expressly permitted.

There is no dedicated control element. For the visualisation a text display on output ST and value displays on AT, AP and VR are sufficient. The variable for the status text must be of the string data type.

Note: the status text is issued by the controller in German plain text, like all blocks of the heating group.

Operation
Does the request count? If the bit input is connected, only the bit decides - a temperature without the bit set does not trigger anything. If the bit input is not connected, a connected temperature greater than 0 counts as a request; that is how a consumer with only one output gets by without a comparator. If both inputs are unconnected, the request never counts - an unconnected input delivers 0 and could otherwise not be told apart from a real value. If a switch-on delay is set, the bit has to be present for that long without interruption before the request counts. If it drops in between, the delay starts again.
Priority. Every request carries a priority mode. No priority means it counts like any other. Report only means it appears on output VR and in the status text, but does not displace anyone. Suppressing means that while it is present only it counts - which is exactly what domestic hot water charging needs. If several requests report a suppressing priority at the same time, the one with the lowest number wins.
Maximum priority duration. A suppressing priority blocks the other requests for at most this time. After that all requests are served again, until the priority request has dropped once. This is not a luxury: without that limit a faulty hot water sensor blocks the heating for days in January. As long as a priority request is suspended in this way, the status text reads "Vorrang abgelaufen" (priority expired).
Request temperature. Each valid request gets its offset added; the maximum of all counting requests is formed and limited to request minimum and maximum. The result is available on output AT. If nobody requests heat, the request minimum is applied.
Run-on. Output AN is 1 as long as at least one request counts. When the last one drops, AN stays on for the run-on time and AT holds its last value - if AT fell to the minimum right away, the generator would cool down during the run-on. The run-on belongs here on purpose and not in the generator, otherwise it would also run when the generator is switched off by hand. Locking ends the run-on immediately.
Percentage output. Some devices expect the request as a percentage. Output AP converts the request temperature linearly between two supporting points: the temperature that corresponds to 0 % and the temperature that corresponds to 100 %. Outside that range it is limited to 0 and 100 %; without a request AP is 0.
Restart. The block does not remember anything across a restart - this is intentional. The requests are rebuilt within one cycle, running delays and a running run-on start again.

Example
A house with two heating circuits and one hot water charging. The number of requests is set to 3.

Request 1 is named "Heizkreis EG" (ground floor), offset 0 K, no priority. Request 2 is named "Heizkreis OG" (upper floor), likewise. Request 3 is named "Warmwasser" (hot water), offset 5 K, suppressing priority, maximum duration 120 min. Request minimum 20 °, maximum 75 °, run-on time 120 s.

Both heating circuits request heat, the ground floor 38 °, the upper floor 42 °. AN is 1, AT is 42, VR is 0, ST reports "Heizkreis OG 42.0 C".

The hot water charging starts and requests 60 °. The priority takes effect: AT jumps to 65 ° (60 plus 5 K offset), VR is 3, ST reports "Warmwasser 65.0 C (Vorrang)". The two heating circuits no longer count.

The cylinder sensor fails, the charging never ends. After 120 minutes the block suspends the priority: AT stays at 65 °, but now the heating circuits count again, and ST additionally reports "Vorrang abgelaufen". The house keeps being heated.

Inputs
FR
 Enable
 Other than 0 enables the block, 0 locks it. Optional. Not connected: the block is considered enabled.
SP
 Lock
 Other than 0 locks the block, 0 enables it. While locked AN, AP and VR are 0 and AT is the request minimum; a running run-on ends immediately. Optional. Not connected: never locked.
A1 - A8
 Request 1 - 8
 Heat request of the consumer as a bit. Other than 0 requests heat, 0 does not. How many of these inputs exist is determined by the parameter number of requests. Optional. Not connected: the matching temperature input decides instead, a value greater than 0 counts as a request. If both inputs are unconnected, this request never counts.
T1 - T8
 Request 1 - 8 temperature
 Desired flow temperature of this consumer in °C. The offset of the request is added to it. If the matching bit is connected, the value is only evaluated while that bit is set; if the bit is not connected, a value greater than 0 counts as a request by itself. Optional. Not connected: 0 applies, the request then only takes effect through its offset and the lower limit.

Outputs
AN
 Request
 1 as long as at least one request counts or the run-on is active, otherwise 0. Belongs on input AN of the heat generator.
AT
 Request temperature
 Maximum of the counting requests including their offset in °C, limited to request minimum and maximum. During the run-on the last value is held, without a request the request minimum is applied.
AP
 Request percent
 Request temperature as a percentage between the two supporting points, 0 to 100. Without a request 0.
VR
 Priority active
 Number of the request that currently has priority - 1 to 8. 0 means that no request with priority is present.
ST
 Status text
 Plain text stating who requests heat right now and at which temperature - for example "Warmwasser 65.0 C (Vorrang)", "Heizkreis OG 42.0 C", "kein Bedarf, Nachlauf 120 s" or "Gesperrt". Needs a variable of the string data type.
WW
 Hot water request
 1 as soon as at least one valid request of the kind hot water is present, otherwise 0. Belongs on the input WW of the heat generator, which carries the same short name: it lifts the generator's outdoor shutdown limit so that hot water is not left cold in summer. During the run-on time the signal stays, just like the request temperature. A suppressing priority changes nothing here - what is reported is that a hot water request exists, not whether it is being served right now.

Parameters
Number of requests
 How many consumers report their request, 2 to 8. Each request creates two inputs. If the number is reduced, the inputs of the trailing requests are removed together with their connections. Default 4.
Switch-on delay
 A request has to be present for that long without interruption before it counts. Default 0 s, so the request counts immediately.
Run-on time
 The collected request stays on for that long after the last individual request has dropped. Default 0 s, so no run-on.
Request minimum
 Lower limit of the request temperature. It also applies when nobody requests heat. Default 0 °.
Request maximum
 Upper limit of the request temperature. Protects the generator against an excessive request. A value lower than or equal to the lower limit does not limit at all. Default 80 °.
Maximum priority duration
 A suppressing priority may block the other requests for at most this time. 0 switches the limit off - a faulty sensor then blocks the heating indefinitely. Default 120 min.
Temperature for 0 %
 Request temperature that results in 0 % on output AP. Default 20 °.
Temperature for 100 %
 Request temperature that results in 100 % on output AP. In between the value is calculated linearly. If both supporting points are equal, AP stays 0. Default 80 °.
Request 1 - 8 name
 Name of the consumer as it shall appear in the status text - for example "Warmwasser" or "Heizkreis EG". Without an entry the status text shows "Anforderung" and the number.
Request 1 - 8 offset
 Added to the temperature reported by this request. Covers heat exchanger losses and mixing valve reserve of this consumer. Default 0 K.
Request 1 - 8 priority
 No priority: the request counts like any other. Report only: it appears on output VR and in the status text, but does not displace anyone. Suppressing: while it is present, only it counts. Default no priority.
Request 1 - 8 kind
 What the generator is to run for. Heating: the request only counts towards the heat demand. Hot water: it additionally appears at output WW. Default heating.

See also: Heat generator, Heating+cooling curve, Heating circuit, Boiler charging, Maximum

See also general parameters of all function blocks.