16 DKDHR
VI.GP.N2.02
Danfoss District Energy
Instructions Water
Heaters
14.0 Maintenance
Maintenance work
Is only to be carried out by qualified and authorised personnel.
Visual control and heat meter reading is to be performed by the janitor or other
supervisor (the heat meter is not part of the delivery)
Inspection
The operator or other authorised personnel is obliged to perform inspections at
regular intervals and if necessary carry out maintenance work according to these
and other instructions. Within the scope of the above maintenance work all strain-
ers should be cleaned (see photo to the right), all connections should be tightened
and the operation of the safety valves should be checked by turning the valve head
in the indicated direction.
Rinsing / cleaning of plate heat exchanger
Brazed heat exchangers can be rinsed. For optimum cleaning the flow rate should
be a min. of 1.5 times normal flow rate, preferably in back-flush mode. This will
remove any deposits formed on the inside of the plate heat exchanger. In case of
more serious deposits, a cleaning liquid, approved by Danfoss (f.ex. Radiner FI)
can be pumped through the heat exchanger. Both are environmentally friendly
cleaning fluids and can be disposed of through the usual domestic sewerage
system. Afterwards rinse thoroughly with large amounts of water.
Deacidification of brazed plate heat exchanger
After long operation, because of the large variations in temperature and as
oxygenous water is used on the secondary side, the heat exchangers are expecially
subject to calification. Any deacidification of the plate heat exchanger is done as
shown on the drawing to the right. For brazed plate heat exchangers weak inhibited
acid solutions (e.g. 5% formic, acetic or phosphoric acid) may be used.
Deacidification of gasketed plate heat exhanger (Akva Lux II GW)
See page 16.
Measures after maintenance work
After maintenance work and before switching the system on again:
•
Check that all screwed connections are tight.
•
Check that all safety features, covers, that were removed, have been replaced
properly.
•
Clean the working area and remove any spilled materials.
•
Make sure that all tools, materials and other equipment that were used, have
been removed from the working area.
•
Connect to energy supply and check for leaks.
•
Vent the system.
•
If necessary adjust the system again.
•
Make sure that all safety features on the device and the system work properly.
Cooling / Return temperature reading
The cooling, i.e. the temperature difference between district heating supply and dis-
trict heating return is of great importance for the total heat economy. It is therefore
very important to observe the supply and return temperatures. Normal temperature
difference is 30-35 °C.
Please note,
that the lowest district heating return temperature is directly depend-
ent on the return temperature from the heating circuit and the recirculation circuit.
Therefore, please observe these return temperatures.
Cooling of the water heater alone
During the tapping process the cooling will typically be 30-35°C. During standby
the return temperature from the water heater will normally increase a little. The
heat meter will in this situation register only a very limited consumption, as the
water volume is very small.
On water heaters connected to the DHW recirculation system the calorimeter
measures the heat loss in the circulation pipe.
Tightening of connections
When reading the heat meter, all fittings and connections should be checked for
leaks. If leaks are detected, contact qualified and authorized personnel immediately.
