Installation

7 of 36 © 2001 D 364 - 07/01
Internal Demand (tekmar Sensor)
If the DHW SENS item is set to DHW, the 364 looks for a DHW sensor connected to
the DHW and the Com terminals (28 and 27). The DHW TANK setting is used to set
the desired indirect DHW tank temperature.
When the temperature at the DHW sensor drops 3°F (1.5°C) below the DHW TANK
setting, The DHW Demand pointer turns on in the LCD and the control operates
as described below. An advantage to using the DHW sensor is that the control can
display the current DHW TANK temperature. Also, the 364 can control the DHW tem-
perature with more accuracy than when using an aquastat.
DHW DEVICE (DHW THRU)
Once the 364 has received a DHW demand, the sequence of operation depends on the
type of DHW device selected. The DHW device is selected using the DHW THRU item
in the Adjust menu.
DHW Valve (VALV)
If VALV is selected as the DHW device and there is a DHW demand, the 364 closes
the DHW Pmp / Vlv contact (13 and 14) and the Prim P1 contact (7 and 8). The
primary pump provides flow through the DHW tank’s heat exchanger once the DHW
valve is opened. If the Boil SENS item is set to SUP, the 364 operates the Boiler
contact to provide a sufficient boiler supply temperature to the DHW tank. If the Boil
SENS item is set to RET or NONE, the 364 closes the Boiler contact to provide heat
to the DHW tank.
DHW Pump (PUMP)
If PUMP is selected as the DHW device, the 364 assumes that the DHW pump pro-
vides adequate flow through both the DHW tank heat exchanger and the boiler. To
provide heat to the DHW tank, the 364 closes the DHW Pmp / Vlv contact (13 and 14).
If the Boil SENS item is set to SUP, the 364 operates the Boiler contact to provide suf-
ficient boiler supply temperature to the DHW tank. If the Boil SENS item is set to RET
or NONE, the 364 closes the Boiler contact to provide heat to the DHW tank. If using
a primary loop with the DHW tank piped in primary / secondary, select DHW valve.
BOILER TARGET DURING DHW GENERATION (Boil TRG)
A boiler target temperature is calculated only if the Boil SENS item is set to SUP. The Boil TRG temperature during DHW operation
depends on whether an external or internal demand is occurring. The DHW demand overrides the reset water temperature. If the
Boil SENS item is set to RET or NONE, the boiler is simply enabled during a call for DHW. In this case, the boiler temperature is
limited by the boiler’s operating aquastat.
External Demand (Aquastat)
If the control receives a DHW demand through an external device such as an aquastat, the Boil TRG temperature is at least as
hot as the DHW heat exchanger setting (DHW XCHG).
Internal Demand (tekmar Sensor)
If the control receives a DHW demand from a DHW sensor connected to the DHW and the Com terminals (28 and 27), the Boil
TRG temperature is at least as hot as the DHW TANK setting plus 40°F (22°C).
DHW PRIORITY
It is often desirable to limit or even stop the flow of heat to the heating system when the DHW tank calls for heat. This allows for
faster recovery of the DHW tank. The 364 has a number of features that it can use when dealing with DHW priority. The features
available depend on the type of DHW device that is being used and the type of DHW demand the control receives.
Mixing Priority (DHW PRI = MIX)
It can be selected that the DHW tank has priority over the mixing
zones. If this option is chosen, the mixing device is throttled back
on a call for DHW. The mixing system pump (P3) continues to
operate based on the mix demand. By reducing the mixing device
output, more heat is directed to the DHW tank. The boiler zones
continue to operate without change.
Section C2: DHW PRIORITY
Com
27
DHW
28
DHW
Storage
Tank