ENVI
®
Control
21
1.6.4
DHW Modes
The DHW system designs that can be accommodated by this control include:
DHW mode 1- a storage tank with temperature sensor
DHW mode 2- a storage tank with thermostat
DHW mode 3- a plate heat exchanger
Mach boilers, N Series Modufire boilers, and P-K Sonic Boilers can
NOT
be used for direct fire DHW
applications. These boilers require an isolating heat exchanger between the potable water and the non-
potable boiler loop.
D series Modufire
boilers and Mach ‘n Roll™ boiler packages can be used for direct potable water contact in
the DHW mode.
1.6.4.1
DHW Mode 1 (Storage & Sensor) Storage Tank with Temperature Sensor
Tank Sensor required.
A list of accessory choices for different applications is shown in section 1.0 on page 3.
Description
A storage tank equipped with a temperature sensor is connected to the boiler. The 12K ohm NTC sensor must be
wired into the boiler at the DHW sensor terminals (Typically terminals 7 & 8 on TB-1). When the temperature sensor
reads that the tank temperature is below the TANK SET parameter by the TANK ON DIFF, the DWH pump circuit is
energized and the boiler starts and supplies heat to the tank. The boiler modulates the firing rate to maintain the
DHW SETPOINT at the boiler outlet. When the temperature in the tank exceeds the TANK SET parameter by the
TANK OFF DIFF, the boiler shuts off the burner and the DHW pump continues to run for a pre-set time (POST PMP
TIME).
Note: Proper sizing of the storage tank is important to prevent short cycling of the boiler equipment. Check with your
authorized Patterson-Kelley Representative for assistance on tank sizing.
1.6.4.2
DHW Mode 2(Storage & Stat) Storage Tank with Thermostat
Installer needs to supply a closure device (aquastat, thermostat, flow switch, etc.) to close the DHW Enable circuit
(Typically terminals 7 & 8 on TB-1).
A list of accessory choices for different applications is shown in section 1.0
on page 3
Description
A storage tank equipped with a thermostat is connected to the boiler. When the closure device creates a closed state,
the DWH pump circuit is energized and the boiler starts and supplies heat to the tank. The boiler modulates the firing
rate to maintain the DHW SETPOINT at the boiler outlet. When the closure device opens, the boiler shuts off the
burner and the DHW pump continues to run for a pre-set time (POST PMP TIME).
1.6.4.3
DHW Mode 3 (Plate Heat Exchanger) Heat Exchanger without Storage
Installer needs to provide a flow-proving device (flow switch) and a temperature sensor. A list of accessory choices for
different applications is shown in section 1.0 on page 3.
Description
A plate heat exchanger equipped with a DHW flow proving device and a temperature sensor is connected to the
boiler. When the flow-proving device closes, it creates a call for heat and the boiler
’s DHW Pump Contactor terminals
close which starts the boiler DHW pump. If the DHW water temperature is below the DHW SETPOINT by the ON
DIFFERENTIAL, the boiler fires and supplies heat to the exchanger. The boiler modulates the firing rate to maintain
the DHW SETPOINT at the boiler outlet. When the temperature of the boiler water rises above the DHW SETPOINT
by the OFF DIFFERENTIAL, the boiler shuts off the burner and the boiler DHW pump continues to run for a pre-set
time (POST PMP TIME). When the demand is satisfied, the flow-proving device breaks the call for heat.
