INSTANT DHW PRODUCTION MANAGEMENT

Owned by Marco Serpelloni
Last updated: Feb 08, 2024
6 min read

This function is available from REG and RegConfig firmware version 4.32 onward within the ELETTRA/SOLAR page of RegConfig.

The function selectable from the System Type drop-down menu is number 5 (FLACS) and allows you to manage up to 8 Instant Domestic Hot Water Producers in cascade using dry contacts and a flow meter.

image-20240208-111055.png

In order to use this function, it is necessary to install, besides the Instant DHW Producers:

  • A REG-DIN-8 regulator;

  • Two-way ON/OFF valves on the input DHW pipe to each Producer (numbers 1, 2 and 3 in the following diagram);

  • A flow meter (number 5 in the following diagram);

  • A REG2VFS interface to enable communication between the REG and the flow meter:

image-20240208-112302.png

Currently, the REG2VFS interface communicates with the Grundfos VFS sensor, the interface is provided with cable and connector to precisely connect to the Grundfos VFS. For further information about the REG2VFS, please refer to the data sheet.

Operating Logic

Since there is no bypass valve, it is necessary that one of the ON/OFF valves is always open to allow water to flow at the moment of the first water withdrawal. As the withdrawal rate gradually increases, exceeding a threshold to define case-by-case, a second valve (and accordingly another producer) will be switched on to satisfy the demand and so on.

When the request drops the valves will be closed one by one (and consequently the producers will be switched off). The last producer will stop when the flow rate drops to zero, but its valve will remain open to allow the system to restart to satisfy a new request from the consumers. Therefore, the first producer to start will be the last one that shut down during the previous cycle. The rotation allows to evenly distribute the working hours over all installed producers.

Setting Parameters

The parameters to be set are:

  • Water flow sensor and water Outlet Temperature that are both detected by the Grundfos VFS meter via the REG2VFS interface (for installation and configuration see the REG2VFS data sheet)

  • DHW Producers Number: indicate the number of producers installed

  • P07 Minimum Active generator number: indicated the minimum number of valves that are always left open and consequently the minimum number of generators that will be switched on as soon as the flow rate detected will be greater than zero. Setting this value > 1 could be useful in the case of large system where the activation of only 1 producer on departure could lengthen response time.

  • P08 Maximum Active generator number: indicated the maximum number of generators that can be activated simultaneously. If 5 generators are enabled, but the maximum number is 3, this means that at most the algorithm can switch on 3 generators even though 4 would be needed. This choice could be useful in the case you have calculated, for example, 3 producers are sufficient, but you have decided to install more to have redundancy and therefore give reliability to the system.

  • P09 Excluded generators: if maintenance is being carried out on a producer or a producer is faulty and awaiting repair, it can be excluded from the cascade by simply flagging the relative box. This function of excluding generators could also be useful in the case of diagnostic or ignition, if only 1 specific producer is to be switched on at a time.

  • P01 New generator threshold [l/min]: this is the threshold above which the next valve is opened. Therefore, if the threshold is 15 l/min, up to this flow rate value only one valve will be opened, above 15 l/min at least for time P03, a second valve will be opened, above 30 l/min (for P03 time) a third valve will be opened and so on.

  • P02 Hysteresis shut off generator [l/min]: if the flow rate, instead of increasing decreases, the valves will be shut down. This parameter allows a hysteresis to be considered as to have as little pendulum as possible. Let's take the example from the previous point assuming P02 is 3 l/min: if flow rate drops below 30-3 l/min for time P04, valve number 1 (the one that was open at the start of the cycle) will be shut down. When flow rate drops below 15 - 3 l/min for time P04 then the second valve will also be closed. When the flow rate goes to zero, the last producer still running will stop, but its valve will remain open.

  • P03 New generator counter [s]: this is the time for which the flow rate must remain over the threshold before one more valve is opened

  • P04 Shut off generator counter [s]: this is the time for which the rate flow must remain below the threshold minus hysteresis value before a valve is closed.

A diagram is shown to better explain parameters P01, P02, P03, and P04; in red the flow rate trend over time, in blue the thresholds (multiples of P01) and in yellow the hysteresis referring to each threshold (always equal to P02):

Instant DHW Producers cascade status and output setting

To the right of the set parameters, it is possible to visualize the status of the system status:

  • Active generators number: is the number of producers whose valve is open;

  • First active generator: is the number of the producer whose valve is open first, in the image below it is the sixth producer;

  • Current flow rate and Current temperature: are the values read by the VFS in l/min and °C respectively;

  • Generator activation Threshold [l/min]: shows the threshold value that must be exceeded for another producer to be added. This value depends on how many generators are already active. Assuming that P01 is 15 l/min: if only a producer is active, the threshold will be 15 l/min, if 2 producers are active the threshold will be 30 l/min etc.

  • Generator deactivation Threshold [l/min]: shows the threshold value that must be exceeded (downwards) before removing a producer. This value depends on how many generators are active: if 3 generators are active, the threshold will be 27 l/min [P01*(number of active producer - 1) - P02], if 2 generators are active the threshold will be 12 l/min [P01*(number of active producer - 1) - P02], etc. If only one producer is active, this value will be negative if P02 is greater than zero.

  • Add/Removal Filter Timer [s]: reports the countdown (if started) of parameters P03 and P04;

Within the REGDIN OUTPUT page (or IOA / IOB OUTPUT in case expansions are needed as the REG system also manages other actuators within the heating/cooling system), it is possible to set the outputs to be assigned to the 8 DHW producers valves:

The outputs are configured as follows:

  • Output 98 and 99 → producer valve number 1 and 2

  • Output 102 and 103 → producer valve number 3 and 4

  • Output 106 and 107 → producer valve number 5 and 6

  • Output 110 and 111 → producer valve number 7 and 8