63
Fig. 31: MODE 3
– Master/Slave with Indirect DHW on Water Heater Loop
Operation Notes:
•
Hydronic CFH and burner firing rate is determined by system sensor S3a (Master S3).
•
Indirect DHW CFH is determined by indirect DHW tank sensor S5a (Master S5), however burner
firing rate is controlled by indirect DHW flow line sensor S6a.
NOTE:
The target temperature is
boosted by 20 ~ 50% during an indirect DHW CFH (depending on Indirect DHW setpoint value) to
facilitate faster heating of the indirect DHW tank. e.g. for an Indirect DHW Setpoint of 65°C the
target temperature will be 88°C, and heating will continue until the indirect DHW tank sensor S5a
detects 65°C at which time the indrect DHW CFH will be satisfied.
The boosted target
temperature (not the Indirect DHW Setpoint parameter value) will be displayed as the Target
temperature in the view menus.
•
Heater pumps P1a, P1b, P1c and P1d operate during the relevant heaters CFH and are delayed
'OFF' (according to Post Purge parameter in BOILER menu) after the burner has shut down.
•
System pump P2a must be controlled by the Master to enable indirect DHW priority. P2a operates
whenever the enable/disable switch is closed (if fitted) or a switch bridging wire (default) is present
between field wiring terminal strip 'Enable/Disable' terminals 11 & 12. Note: indirect DHW priority
is always activated for operation mode 3 and system pump P2a will turn off whenever an indirect
DHW CFH is present for the programmed time period (Priority Ovr Timer parameter).
•
Indirect DHW pump P3a operates during an indirect DHW tank CFH and turns off after indirect
DHW CFH is satisfied (with no delay 'OFF').
•
Optional outdoor air compensation: Optional outdoor air sensor S4 can be utilised to automatically
adjust the target water temperature as the outdoor air temperature changes. For outdoor air
compensation to operate, Target Mode parameter must be set to RSET. The CFH target is then
calculated and determined according to Boiler Start and Boiler Design parameters and the outdoor
air temperature detected by outdoor air sensor S4.
Operational Settings
•
Operation Mode parameter in ADJUST menu must be set to 3 (refer to
on page 64 for parameter settings and
on page 88). Note: Indirect DHW has
priority and is not selectable for operation mode 3.
•
A bridging wire (or optional Aquastat) must be installed between field wiring terminal strip 'Indirect
DHW Override' terminals 10 & 12 to permit indirect DHW operation.
•
Heater A VERSA control board DIP switch 2 must be set to ON (Master). Heaters B, C and D VERSA
control board DIP switch 2 must be set to OFF (slave). Refer to Cascade System Connections on
page 77.
