Mode 2: Central Heating with Outdoor Reset
This mode will only function when an outdoor sensor is
connected. The set point is calculated depending on the
outdoor temperature. The central heating set point is
calculated as follows:
ch_setpoint = t_day_ref + [(68 – T_outdoor) * Slope]
t_day_ref is the reference temperature for central heating set
point when T_outdoor is 68
o
F (20
o
C). T_day_ref is a user
settable parameter.
The Slope can be set via the menu between 0.1 to 5.0 with
steps of 0.1.
The calculated central heating set point is limited between
41
o
F (5
o
C) and 194
o
F (90
o
C).
Burner On:
Supply Temp < CH Setpoint – CH Hysterese
Burner Modulation:
CH Setpoint
Burner Off:
Supply Temp > CH Setpoint + CH Hysterese
Overnight an input signal from a room thermostat (RT) can
lower the ch_setpoint. When the RT input closes the
ch_setpoint will also be lowered by t_night_reduction.
The anti-freeze monitor on each boiler will monitor the inlet
water temperature and when it drops below 50
o
F (10
o
C) it
will bring on the pump to prevent freezing of the heat
exchanger.
Mode 3: Central Heating with Constant Temperature Loop
No outdoor sensor is needed. The supply temperature is
kept constantly at the set point temperature. The burner is
controlled in a similar way as Mode 0. When the room
thermostat contact closes the ch_setpoint will be decreased
with t_night_reduction. The pump is always on in this
condition.
Burner On:
Supply Temp < CH Setpoint – CH Hysterese
Burner Modulation:
CH Setpoint
Burner Off:
Supply Temp > CH Setpoint + CH Hysterese
6.4 DOMESTIC HOT WATER MODES
Mode 0: Disables Domestic Hot Water
No domestic hot water is available; therefore the DHW
sensor is not supplied.
Mode 1: Direct/Indirect DHW Storage Tank with 10kΩ
Temperature Sensor
The DHW temperature in the tank is measured with a
storage tank sensor and set with parameter DHW_setpoint.
DHW Demand:
DHW Temp < DHW Setpoint – DHW Store hyst down
Burner Start:
DHW Temp < DHW Setpoint + DHW store supply extra –
DHW supp hyst down
Burner Modulation:
Supply Temp = DHW Setpoint + DHW store supply extra
Burner Stop:
DHW Temp > DHW Setpoint + DHW store supply extra +
DHW supp hyst up
The anti-freeze monitor on each boiler will monitor the inlet
water temperature and when it drops below 50
o
F (10
o
C) it
will bring on the pump to prevent freezing of the heat
exchanger.
Mode 2: Direct/Indirect DHW Storage Tank with Aguastat
When the aquastat closes the control detects a demand for
the storage tank and starts the pump. Operation of Mode 2 is
identical to the operation of Mode 1, but an aquastat
replaces the use of a sensor in the storage tank.
Burner Start:
Supply Temp < DHW Setpoint – DHW supp hyst down
Burner Modulation:
DHW Setpoint
Burner Stop:
Supply Temp > DHW Setpoint + DHW supp hyst up
Mode 4: Combination Boiler using Plate Heat Exchanger and
10kΩ DHW Temperature Sensor
In this configuration the boiler can be used for space heating
and indirect domestic hot water. Camus supplies an on-
board brazed plate heat exchanger, a pump and a 3-way
diverter valve.
When a heat demand is detected the pump will run and the
3-way diverter valve switches over to the hydronic heating
loop. The pump continues to run until the ‘post pump CH
period’ is complete after cycling through a heat demand
cycle. When there is no heat demand the pump will turn off
individually controlled zone pumps will draw hot water from
the manifold and return from the zone to the manifold.
The temperature of the water leaving the plate heat
exchanger is constantly monitored and when it drops below
‘dhw_setpoint – dhw_hyst_down’, the on-board pump
activates to satisfy a demand for DHW and the 3-way
diverter valve switches over to DHW demand. If a central
heating demand is present when a DHW demand occurs,
the heating demand will be interrupted resulting in domestic
hot water priority. The 3-way valve shall switch over from
hydronic heating to DHW demand and the boiler will
continue to function in this state until DHW demand ends. If
hydronic demand is still present after DHW demand ends the
3-way valve switches over to hydronic heating. This results
in zero lag, as the burner does not restart when switching
between hydronic heating and DHW demand.
Due to the use of a plate heat exchanger a Pre-Heat function
is implemented in the algorithm. This ensures the plate is
always warm and prevents the user from receiving an initial
blast of cold water when they first turn on the tap. The Pre-
Heat function is enabled after 2 minutes of burner shut off. If
the DHW sensor detects that the temperature is below ‘Pre
Heat set point – pre heat hyst down’ the boiler will initiate the
ignition sequence and the burner will fire at minimum fire
until the DHW sensor temperature is equal to the Pre Heat
Setpoint. The Pre Heat function will only activate when a
DHW demand is non-existent.
The anti-freeze monitor on each boiler will monitor the inlet
water temperature and when it drops below 50
o
F (10
o
C) the
pump will be activated to prevent the heat exchanger from
freezing.
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