Function Block "Heat Demand; Purpose; Heat Demand Relay - Siemens RMB795B Basic Documentation

"Control action"
Request evaluation
Note
Heat demand signal
generation
Purpose and function
Configuration
Siemens
Building Technologies
The maximum flow temperature readjustment can be parameterized.
With valve positions ≤ 90 %, the current flow temperature is:
"Heating flow setpoint" – "Flow temperature reduction max".
To adapt the control system to the plant, the control action of the flow temperature
can be adjusted to the setpoint shifts in 3 steps (fast, medium, slow).
Setting "Request evaluation" is used to determine if the max value or the average
of the requests is to be used.
• When using the "Maximum" setting, the flow temperature will be readjusted in a
way that the valve position of the consumer with the greatest heat demand is
90 %
• When using the "Average setting, the flow temperature will be readjusted in a
way that the valve positions of the 4 largest consumers will be 90 % on average
This setting does not ensure that all consumers are covered. It makes certain,
however, that an individual consumer cannot force the flow temperature to high
levels (e.g. because a window was left open).
11.3

Function block "Heat demand"

11.3.1 Purpose

The function block generates a "Heat demand" signal that can be used by other
devices. The heat demand is provided in the form of the following signals:
• Digital signal at output Q ("Heat demand relay")
• Analog signal at output Y ("Heat demand modulating")
• Bus signal ("Communication")
The 3 variants are described below.

11.3.2 Heat demand relay

The heat demand relay must be configured to a relay output N.Qx of the RMB795B
central control unit. Release for an external refrigeration source, for example, can
be connected to this output.
The heat demand relay responds as soon as the bus calls for heat.
Meaning:
• Contact open
=
• Contact closed
=
Main menu > Commissioning > Extra configuration > Heat demand
Operating line
Heat demand relay
Central control unit RMB795B
Distribution zones
No heat demand.
Heat demand
Adjustable values / remarks
---, N.Q1, N.Q3, ... /
activation of output
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CE1P3122en
18.01.2012