Circuit For Heat Recovery Or Hot Tap Water - Danfoss AK-PC 781A User Manual

Circuit for heat recovery or hot tap water

Application
This regulation can only be carried out when the selected refriger-
ant is CO 2 , which makes it possible to supply hot gas for heating a
receiver vessel.
Reference
Regulation is done for a tap water temperature of typically 55°C,
where the value is adjustable. A temperature sensor Stw8 is
installed in the hot water receiver, and the temperature is held in a
band around the adjusted value.
If Stw8 or Stw4 is selected as the controller sensor, the reference
can be displaced based on an external 0-10 V signal. 0 V results in
no displacement. 10 V results in a displacement indicated by the
set value.
Reference
Band
Valve - V3tw
When tap water heating is required, the gas valve changes over
and routes the gas in through the heat exchanger.
When the temperature goes above the reference plus half the
band, the gas will be routed outside of the heat exchanger.
Regulation
Regulation can be done using one of the following principles:
• Only Stw8. The temperature here is regulated using an on/off
thermostat. The pump can be controlled on/off or variably.
• Only Stw4. The temperature is regulated using an on/off thermo-
stat. The pump has to be variably controlled.
• Stw4 - Stw3. Here "Delta T" over the heat exchanger is used for
regulation. Here the pump must be controlled using variable
speed. When the Stw8 temperature has been achieved, the gas is
routed outside of the heat exchanger.
(With a Delta T controller, the reference cannot be displaced
using an external signal.)
• Stw8 and Stw8a. Here regulation is done using the two tempera-
ture sensors in the receiver. Stw8 is placed at the top and Stw8a
further down.
AK-PC 781A Capacity controller RS8HE202 © Danfoss 2017-07
Reference
Band
The pump is controlled via on/off and is connected when Stw8
is below the reference plus half the difference. It is disconnected
when Stw8a is above the reference plus half the difference.
The pump - Pump tw
It is recommended to use a pump with variable speed, so that the
regulation flows and does not display great fluctuations in the
condensing pressure.
Flow switch - FStw
A flow switch should be installed for safety reasons, in case of
pump failure. The controller will then disconnect the entire recov-
ery circuit.
Sensors - Stw2, Stw3, Stw4 and Stw8
All sensors must be installed due to safety reasons:
Stw2: The controller must know the temperature of the gas that is
sent for condensation
Stw3:Heat exchanger cold access. Used for temperature regulation
Stw4: Heat exchanger hot outlet Used for temperature regulation
Stw8: Receiver temperature and in relation to the reference.
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