Domestic hot water (dhw) & setpoint, Section c: dhw, Pg 10 – tekmar 262 Boiler Control Installation User Manual

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2) as described in Section B1. With the RTU connected, the 262 measures the actual ROOM temperature. Indoor temperature feedback
fine tunes the supply water temperature in the system to prevent over heating or under heating. The RTU allows the user to adjust the
desired room temperature at the RTU. Remote sensor capability is also available through an RTU. See the Data brochure for the RTU
you are connecting.

Section C1 —General Domestic Hot Water (DHW) Operation (Mode = —1—)

DHW DEMAND

DHW demand is generated on the 262 by using one of two methods: either an external DHW

demand from an aquastat or an internal demand from a 10K tekmar sensor. If an external and
internal demand is present simultaneously, the control stops operation of the DHW.

External Demand (DHW SENS = NONE)

The 262 registers an external demand for DHW when a voltage between 24 and 240 V (ac)
is applied across the

Com Dem and the DHW Dem terminals (3 and 4). A DHW aquastat

or setpoint control is used as a switch in the DHW demand circuit. Once the 262 detects a
DHW demand, the

DHW Demand pointer turns on in the LCD and the control operates as

described below.

Internal Demand (DHW SENS = DHW)

The 262 registers an internal demand for DHW when a sensor is connected across the

Com

and the

DHW terminals (19 and 20). The DHW TANK setting is used to set the desired

indirect DHW tank temperature. When MODE –1– is selected, if 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 and record the highest and lowest DHW TANK temperatures. Also, the 262 can
control the DHW temperature with more accuracy than when using an aquastat.

DHW DEVICE (DHW THRU)

Once the 262 receives 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 Pump (DHW THRU = PUMP)

If PUMP is selected as the DHW device, the 262 assumes that the DHW pump provides
adequate flow through both the DHW tank heat exchanger and the boiler(s). To provide heat
to the DHW tank, the 262 closes the

DHW Pmp / Vlv contact (9 and 10) and operates the

boiler(s) to provide a sufficient boil supply temperature to the DHW tank. If using a primary
loop with the DHW tank piped in primary / secondary, select DHW VALV.

DHW Valve (DHW THRU = VALV)

If VALV is selected as the DHW device and there is a

DHW Demand, the 262 closes the DHW Pmp / Vlv contact (9 and 10) and the

Boil P1 contact (7 and 8). The boiler pump provides flow through the DHW tank’s heat exchanger once the DHW valve is opened.
The 262 operates the boiler(s) to provide a sufficient boiler supply temperature to the DHW tank.

BOILER TARGET DURING DHW GENERATION (Boil TRG)

The Boil TRG temperature during DHW operation depends on whether an external or internal demand is present. The DHW demand
overrides the reset water temperature.

External Demand (DHW SENS = NONE)

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).

Com

Dem

DHW

Dem

24 to 240 V (ac)

Aquastat

Com DHW

DHW

Storage Tank

Valve

Pump

Section C —Domestic Hot Water (DHW) and Setpoint (Mode = —1—)

Section C1

General Domestic

Hot Water (DHW)

Operation

Section C2

DHW Priority

Section C3

DHW with Low

Temperature

Boilers

Section C4

Dedicated

DHW