tekmar 422 Universal Reset Module - Manual (Page 24)

© 2007 D 422 - 08/07 24 of 32
DHW Mode and Priority Operation
The control has four different settings available for DHW
Mode that affect pump operation. The required DHW Mode
setting will depend on the piping arrangement of the DHW
tank and whether or not priority for DHW is necessary. DHW
Priority stops or limits the delivery of heat to the building
heating system while the DHW tank calls for heat. This
allows for quick recovery of the DHW tank.
•
• Locate the DHW Mode setting in the Adjust menu.
DHW MODE 1 - DHW in Parallel no Priority
When a DHW Demand is present, the DHW Pump contact
closes. The primary pump (P1) does not turn on, but may
operate based on either Boiler or Mixing requirements or
a Setpoint Demand.
It is assumed that the DHW pump will provide adequate
flow through the heat exchanger and the boiler.
DHW MODE 3 - DHW in Primary / Secondary no Priority
When a DHW Demand is present, the DHW Pump contact
is closed and the primary pump (P1) is operated.
DHW Priority Override Time
Increasing Time
Decreasing Outdoor Air Temperature
Mode = 1
DHW
Pump
Primary
Pump
Mode = 2
DHW
Pump
Primary
Pump
OFF
Mode = 3
DHW
Pump
Primary
Pump
Mode = 4
OFF
DHW
Pump
Primary
Pump
DHW MODE 2 - DHW in Parallel with Priority
When a DHW Demand is present, the DHW Pump contact
closes. The primary pump (P1) can operate when a boiler
demand is present. If the boiler is unable to maintain the
boiler target temperature, space heating zones are shut
off sequentially using tN4 communication in order to
provide priority to the DHW tank. This is known as zone
load shedding.
It is assumed that the DHW pump will provide adequate
flow through the heat exchanger and the boiler.
DHW MODE 4 - DHW in Primary / Secondary with
Priority
When a DHW Demand is present, the DHW Pump contact
is closed and the primary pump (P1) is operated. Priority
over space heating zones is achieved by shutting off the
zone pumps or zone valves through tN4 communication.
This is known as zone load shedding.
DHW Priority Override
DHW Priority Override applies to DHW MODE 2 and 4.
To prevent the building from cooling off too much or the
possibility of a potential freeze up during DHW priority, the
control limits the amount of time for DHW priority. As the
outdoor air temperature becomes colder, the length of time
that the control provides DHW priority is reduced. Once the
allowed time for priority has elapsed, the control overrides
the DHW priority and resumes space heating.