Summer / Winter (S / W) Changeover - Siemens LMU54 Series Basic Documentation

Summer / winter
(S / W) changeover
Automatic S / W
Siemens Building Technologies
HVAC Products
S / W changeover can be accomplished in 2 different ways:
1. With the manual switch on the HMI.
2. Through automatic S / W changeover via the outside sensor.
Notes on 1.: S / W switch
Depending on the type of HMI, a S / W switch is integrated. That switch causes central
locking of the heat demands of all heating circuits and a change to automatic S / W
changeover. The following states are possible:
• Summer operation:
• Winter operation:
• Automatic operation: The heating circuits are controlled via automatic S / W
1) Also refer to CC1 B7494 / Operation / HMI
Notes on 2.: Automatic S / W changeover (can be accomplished in several ways):
a) Via the RU (refer to Basic Documentation QAA73):
When an RU is used, that RU ensures automatic S / W changeover with regard to the
heating circuits connected to it (HC1 / HC2).
The LMU... has no information about the the RU's S / W changeover state. In other
words, if the RU locks the heating circuits based on automatic S / W changeover, the
LMU... cannot release them again.
(If this is not desired, automatic S / W changeover of the RU must be deactivated by
setting a higher changeover temperature).
b) Via the LMU...:
The LMU... performs automatic S / W changeover of its active heating circuits
(heating circuits not controlled via the RU).
If the system uses an outside sensor (connected to the LMU... or to the RVA...), and
if a valid S / W changeover temperature was parameterized, automatic S / W
changeover becomes active.
Locking the demand for heat
(from winter to summer)
Releasing the demand for heat
(from summer to winter)
Automatic S / W changeover of the LMU... can be locked via parameterization:
At THG = 30 °C, automatic changeover is inactive and releases the demand for heat
in that case.
The current state of automatic LMU... S / W changeover is indicated on the HMI by an
LED.
The following table shows the correlation between the 2 automatic S / W changeover
facilities in the «Automatic» position of the HMI:
Automatic S / W
changeover RU changeover LMU
Summer Summer
Winter Summer
Summer Winter
Winter Winter
Basic Documentation LMU54... / LMU64...
3 Functions
1)
All heating circuits locked
All heating circuits released
changeover
S / Wauto = 0 at TaGed > THG + 1K
S / Wauto = 1 at TaGed < THG - 1K
Impact on RU
HC(s)
Locked
Locked
Locked
Released
Impact on LMU Impact on the
HC(s) zone
Locked Locked
Locked Locked
Released Released
Released Released
CC1P7494en
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07.11.2002