DHW METHODS HeatNet Control V3
Page 42
This method will control a tank temperature when the tank
temperature setpoint needs to be maintained for extended
periods with minimal cycling. Multiple boilers can be used
via the H-Net, as this method employs the same PID
algorithm as for space heating. SETTINGS:
DISTRIBUTED CONTROL: MASTER TYPE: AUTO.
1. JPS1 must be cut on all boilers providing DHW
to ensure the maximum output temperature of all
boilers is limited to 200F for DHW operation.
This Method is very similar to the DHW only
method, but:
A. The display will not indicate that it is a
DHW heating boiler.
B. The DHW Heating band will also not be
displayed.
C. The heating band will use the space
heating band and not the UPPER and
LOWER DHW heating band limits.
D. DHW settings are not used.
E. Set the SETTINGS: DISTRIBUTED
CONTROL: MASTER TYPE: to
AUTO.
F. This method is for backwards
compatibility.
2. Use the Heat Demand Control Method 1
located in the CONTROL METHODS section.
Instead of placing the Header sensor in the
Header pipe, place it in a well, in the tank, or a
DHW loop.
The temperature at which boilers are staged ON,
and then OFF is controlled by the SETTINGS:
SETPOINTS: HEAT BAND differential. This
can be understood by referring to the
INTRODUCTION section on the MASTER in
the beginning of this manual.
This differential has the added effect of heating
the tank above the tank’s setpoint temperature. If
the tank setpoint is set to 140F and the heat band
is set to 10F, then the tank temperature will rise
to 145F before the first boiler turns off (setpoint
=140F +/- heat band/2). With (2) boilers running,
the SHED BOILER DELAY time could add to
the tank temperature. So, to ensure that all boilers
are shut off at the upper point of the heat band,
set the SHED BOILER DELAY time to 0 or
other small value. This will effectively turn off
all boilers at the upper heat band point of:
(example) 145F.
Now, there is one more thing to consider, the
pump’s post purge time. Dumping the heat from
all boilers (that were running) using a pump post
purge cycle will have an effect on the tank’s
water temperature. Consider this when
establishing the local pump’s POST PURGE
TIME.
3. Connect to the Local Pump relay contact on J13
to enable the DHW pump. Set its post purge time
to dump the boiler’s heat into the tank when the
boiler shuts off.
4. Enable the system by placing the
LOCAL/REMOTE switch on the MASTER to
the LOCAL position.
JPS1 MUST be cut on all boilers
providing DHW.
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