Danfoss DHP-R 7Ua User Manual page 9

controls a shunt valve that shunts out as much heat as needed from the burner
subsystem.
The blocking of the burner is released when the integral reaches the limit for
starting the auxiliary heater. When the burner starts it may be full of fairly cold
water, and it will take a while for the burner to achieve the right water tempe-
rature. The shunt valve is therefore locked in the closed position for a period
of time defined by the setting Heat up delay. After that time the burner is as-
sumed to be able to deliver energy.
The shunt valve is controlled proportionally, so that it is fully open when the
integral has reached the limit for full auxiliary heat and is closed when at the
start limit.
When the shunt valve has been closed for a certain time it is reasonable to be-
lieve that the burner won't be needed for a while. It is turned of by the signal
Block. extra heater. How long the delay should be before the burner is turned
off is decided by the setting Burner off delay.
2�1�3�2 electrical heater
An auxiliary heater in the form of an electrical heater with only one power
setting is controlled using the signal Block. extra heater. The heater is started
when the integral passes the limit for starting the auxiliary heater, and is tur-
ned of when it rises above the limit for starting the last heat pump.
When the heater is started it is controlled not only by the integral, but also by
the controller error. If the difference between the primary supply temperature
and the set point is greater than the value Turn off limit, the heater is turned
off. As long as the integral value is not above the start limit for the last heat
pump it is turned on again if the controller error goes below Turn on limit.
2�1�3�3 0 to 10 V
If the auxiliary heat comes from a district heating network, the WM HPC con-
trols a shunt using the analogue signal Extra heater. This mode of auxiliary heat
can also be used for other types of heaters that can be controlled with a pro-
portional signal. One example is electrical heating with multiple power steps
controlled by an analogue input.
The signal Extra heater is at 100% (10 V) when the integral has reached the
auxiliary heater maximum limit and is zero at the auxiliary heater start limit.
A district heating system will usually not need the signal Block. extra heater,
but it is still available. The blocking is lifted when the integral passes the auxi-
liary heater start limit, and is blocked again when it rises above the start limit
for the last heat pump.
Danfoss – 9