Siemens LMU64 Series - Summer; Winter (S; W) Changeover

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Siemens Building Technologies Basic Documentation LMU54... / LMU64... CC1P7494en
HVAC Products 3 Functions 07.11.2002
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:
1)
• Summer operation: All heating circuits locked
• Winter operation: All heating circuits released
• Automatic operation: The heating circuits are controlled via automatic S / W
changeover
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 S / Wauto = 0 at TaGed > THG + 1K
(from winter to summer)
Releasing the demand for heat S / Wauto = 1 at TaGed < THG - 1K
(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
Automatic S / W
changeover LMU
Impact on RU
HC(s)
Impact on LMU
HC(s)
Impact on the
zone
Summer Summer Locked Locked Locked
Winter Summer Locked Locked Locked
Summer Winter Locked Released Released
Winter Winter Released Released Released
Summer / winter
(S / W) changeover