Problems Of Start Up - Danfoss EKC 316A Reference Manual

Max SH – The maximum limit of SH ref.
Min SH – The minimum limit of SH ref. Care should be taken not to
set value too low in order to avoid flooding back in the
compressor.
Stability – This factor determines how much instability can be
accepted. Small values will cause the SH ref to increase
if the slightest instability in SH is detected. Conversely,
higher values will accept a higher degree of instability.
SH mode = 2
SH ref follows a defined curve as shown below. This curve is defi-
ned by three values: SH close SH max and SH min.
This form of regulation is similar to the thermostatic valve where
the spring force can be adjusted to keep the SH (superheat) in the
stable region to the right of the curve.
The advantage over the thermostatic valve is that there are three
settings to define the operating curve.

Problems of start up

Sometimes in one to one applications, the valve does not open
sufficiently on start-up, and troublesome low pressure trips hap-
pen. This problem is typical when using the single loop control
where the only the SH controls the opening of valve.
The force opening of valve function has been implemented in the
EKC 316A controller. This is not stated in the controller manual,
but please be aware that this function will give after start up, a
constant set minimum opening degree during a set time period,
without any regard to the superheat value. The setting parameters
are called Start OD% (n17) and StartUp time (n15), and are found
in the For Danfoss only menu in AKM and also in the EKC 316A
controller.
Please observe that the Start OD% is a minimum value after start
up and if the measured superheat (u21) produces a value greater
than Start OD% then this value will be valve opening degree (u24)
- see diagram.
EKC 316A Reference manual RS8ED102 © Danfoss 03-2006 7