Siemens LMS14

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Building Technologies Division User Manual LMS14… CC1U7471en
6 The settings in detail 28.01.2015
With instantaneous water heaters, a distinction between 2 operating modes is made.
An open tap means DHW consumption. When the tap is opened, DHW should be
supplied at the preselected temperature as quickly as possible. In addition, the Keep
hot function is used. This function ensures that the water contained in the heat
exchanger is preheated. This means that next time DHW is drawn, it will be available
more quickly. The disadvantage in terms of convenience in comparison with a DHW
storage tank can thus be minimized
.
DHW consumption is detected either via a flow switch or via the water temperature
gradient in the heat exchanger (aqua booster). During DHW consumption, requests
from space heating are generally ignored. This means that the burner’s output is solely
used for DHW heating. During DHW consumption, the burner’s output is modulated in a
way that the water temperature at the outlet reaches the setpoint as quickly as possible,
even if the amount of water drawn varies.
If the heat exchanger is kept at a certain temperature level, comfort of instantaneous
water heating systems is enhanced. The water in the heat exchanger is heated up to
the Keep hot setpoint.
This means that next time DHW is drawn, it will be available
more quickly
.
The Keep hot function can be activated to have it either permanently On, or only for a
limited period of time after consumption. If confined to the point in time after
consumption, the minimum consumption time on completion of which the Keep hot
function shall be started can be set.
In the case of plants with diverting valve, the valve maintains the DHW position during
the Keep hot function, even if the heat exchanger reaches the Keep hot setpoint. If
DHW consumption follows, there is no need for the diverting valve to first travel to the
required position. As a result, requests from space heating cannot be fulfilled during the
time the Keep hot function is active. Nevertheless, to make certain that this situation will
not lead to a considerable reduction in room comfort, 2 values can be parameterized for
the period of time the Keep hot function is active: One value for the situation when there
is no request for heat from the space, and one value when the space calls for heat also.
Operating modes of
instantaneous water
heater
DHW consumption
Keep hot function