5
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Operation
User reference guide
42
EWAA011~016DA + EWYA009~016DA
Packaged air-cooled water chillers
and packaged air to water heat pumps
4P620246-1 – 2020.06
5.8.3 Slope-offset curve
Slope and offset
Define the weather-dependent curve by its slope and offset:
▪
Change the
slope
to differently increase or decrease the temperature of the
leaving water for different ambient temperatures. For example, if leaving water
temperature is in general fine but at low ambient temperatures too cold, raise
the slope so that leaving water temperature is heated increasingly more at
decreasingly lower ambient temperatures.
▪
Change the
offset
to equally increase or decrease the temperature of the leaving
water for different ambient temperatures. For example, if leaving water
temperature is always a bit too cold at different ambient temperatures, shift the
offset up to equally increase the leaving water temperature for all ambient
temperatures.
Examples
Weather-dependent curve when slope is selected:
X1
X2
c
d
e
Y1
Y2
Y3
Y4
a
b
Weather-dependent curve when offset is selected:
Y1
Y2
Y3
Y4
X1
X2
a
b
c
d
e
Item
Description
a
WD curve before changes.
b
WD curve after changes (as example):
▪
When slope is changed, the new preferred temperature at X1 is
unequally higher than the preferred temperature at X2.
▪
When offset is changed, the new preferred temperature at X1 is
equally higher as the preferred temperature at X2.
c
Slope
d
Offset
e
Selected weather dependent zone:
▪
: Main zone or additional zone heating
▪
: Main zone or additional zone cooling
X1, X2
Examples of outdoor ambient temperature