164/238
Building Technologies Modular Heating Controller RMH760B CE1P3133en
HVAC Products 10 DHW heating 05.02.2007
Main menu >Commissioning > Extra configuration > DHW > Inputs > Flow signal Assign
terminal
Main menu > Commissioning > Settings > … or
Main menu > Settings > DHW > Controller primary circuit
Operating line Range Factory setting
Min stroke with flow signal
0…100 % 25 %
When DHW consumption starts, the flow switch will open the primary valve up to the
set "Min stroke with flow signal“, independent of the flow temperature. The setting is to
be made in % of the maximum stroke.
When DHW consumption is finished, the valve will close fully and immediately.
Normally, in summer operation, the valve opening required for 100 % load is about 80
%. This percentage is called the
design point and must be included in the calculations.
The “Min stroke with flow signal” can be calculated as follows:
Heat exchanger volume
secondary
Minimum stroke with flow signal =
∅ DHW consumption × opening time × design point
Example of calculating the load limit to be set for a heat exchanger with the following
characteristics:
Water content on the secondary side = 1.0 liter
Average DHW consumption
= 0.33 liters / second
Opening time of DHW actuator
= 15 seconds
Design point = 80 % (0.8)
1.0
Minimum stroke with flow signal =
0.33 × 15 × 0.8
× 100 = 25 %
This value is used as a guide value and can vary depending on the plant’s hydraulic
layout. It is recommended to start with the calculated minimum stroke and then proceed
as follows:
• Decrease the value if the DHW flow temperature significantly overshoots after
consumption
• Increase the value if the DHW flow temperature significantly undershoots
The impact of flow switch and PID controller is matched in a way that the actuator
travels to the new position as quickly as possible. After the flow switch has responded,
the control system will resume control of the actuator on the primary side.
The end of DHW consumption is also detected by the flow switch, and actuator Y1 on
the primary side will be driven to the fully closed position.
In contrast to plant types with storage tank, the circulation losses cannot be compen-
sated here via the storage tank, but must be continuously drawn from the heating
network.
When the flow switch indicates the end of DHW consumption, the primary valve will not
be fully closed for this reason. If the valve’s position exceeds the set ”Min stroke with
flow signal”, it will start to close until the minimum stroke is reached. From this position,
valve control is started. For this reason, the controller must be aware of externally
operated circulating pumps:
Main menu > Commissioning > Settings > … or
Main menu > Settings > DHW > DHW
Operating line Range Factory setting
External circulating pump Yes / No No
The assumption is made that the external circulating pump operates 24 hours a day.
Setting
Mode of operation
Calculation of the mini-
mum stroke
Example
Flow switch with circu-
lating pump
Setting
To Next Page
Loading...
