Honeywell DHC, Service Manual

Page: 212 / 262

Hydraulic Components SDC / DHC
212 EN2H-0221GE51 R0812
Whenever the buffer tank is not being loaded by the heat
generator (buffer setpoint reached) the differential between the
heat generator temperature and the buffer tank temperature is
measured continuously if configured to do so. The buffer loading
pump is switched on as soon as the temperature differential rises
above the set extended running switch-on differential. The buffer
loading pump is switched off immediately when the temperature
differential drops to the extended running switch-off differential.
This siphon function ensures that excess energy in the heat
generator (e.g. due to extended heating) will not be lost.
When operating a heating system without buffers, boiler start-up
protection is generally implemented via temporary separation of
the energy consumers from the heat generator (switch-off of
pumps, close mixed heating circuits).
With buffer operation, there is no start-up protection for the heat
generator acting on the heating circuits. The start-up protection
only acts on the buffer loading pump. If the buffer minimum
temperature is undershot when the buffer start-up protection is
switched on, all consumer circuits (heating circuits, hot water) are
separated on the water side (pumps switch off). The buffer start-
up protection is disabled (pumps are switched on again) when the
buffer temperature exceeds the buffer minimum temperature plus
half of the buffer switching differential. All consumer circuits
remain in operation when buffer start-up protection is switched off.
With operation in conjunction with buffer tanks, the hydraulic
conditions for each buffer control mode deviate from this. Special
considerations must be made regarding boiler start-up protection
for this reason.
Buffer start-up protection can be switched off.
Buffer discharge protection disables the buffer loading pump until
the heat generator temperature has risen to more than 5 K above
the buffer setpoint temperature.
This function helps prevent rear buffer discharge though the heat
generator. The buffer loading pump is disabled again as soon as
the temperature differential between the heat generator and the
buffer tank has dropped to less than 2 K.
For operation without buffer tanks, tank discharge protection ("Hot
Water" menu, parameter 08) acts on the heat generator. The heat
generator sensor and the hot-water circuit sensor are compared.
Buffer siphon
function
Buffer start-up
protection
Buffer discharge
protection