Boiler reset – tekmar 262 Boiler Control Installation User Manual

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External Unoccupied

An external signal can place the 262 into an UnOccupied mode. Any time the

UnO Sw (18)

and the

Com Sen (19) terminals are shorted together, the control operates in the UnOccupied

mode. When in the UnOccupied mode, the

UnOcc segment is displayed in the LCD. The

262 adjusts the supply water temperature based on the

UnOcc setting made in the control.

Internal Overrides (OVERRIDE)

The 262 has a number of setback overrides that are selected through the

Schedule (Schd)

Menu. These setback overrides have priority over any external setback signal. Any time an
override is in effect, the

Ovr segment is displayed in the LCD.

Temporary (TMPY)

If a temporary OVERRIDE is selected, the 262 operates in the selected override mode for
3 hours. Once over, the control reverts to the previous operation.

Permanent (PERM)

If a permanent OVERRIDE is selected, the 262 operates in the selected override mode
until a new OVERRIDE is selected.

Away (AWAY)

If the AWAY override is selected, the 262 operates with a fixed WWSD of 62˚F (17˚C) and a fixed room temperature of 62˚F (17˚C).
Any DHW demand is ignored. The setpoint operation is not affected by the AWAY override.

EXERCISING (EXERCISE)

The 262 has a built in pump exercising function. The exercising period setting is adjustable and is factory set at 70 hours. If a pump output
on the control has not been operated at least once during every exercising period, the control turns on the output for 10 seconds. This
minimizes the possibility of the pump seizing during a long period of inactivity.

Note: The exercising function does not work if power to the control or pump(s) is disconnected.

Section B —Boiler Reset (Mode = —1—)

Section B1 —General Boiler Operation

BOILER DEMAND

A boiler demand is generated by applying a voltage between 24 and 240 V (ac) across the

Boil Dem (1&2) terminals. Once voltage is

applied, the

Boiler Demand pointer is displayed in the LCD. If the 262 is not in WWSD, it closes the Boil P1 contact, which starts the

boiler pump and the control turns on the boiler pump segment in the LCD. The 262 calculates a Boil TRG supply temperature based
on the outdoor air temperature and settings. The 262 then fires the boiler(s), if required, to maintain the target supply temperature.

CHARACTERIZED HEATING CURVE OR RESET RATIO

The 262 has two methods of varying the supply water temperature based on the outdoor air temperature. The installer can select either
a

Characterized Heating Curve or a Reset Ratio.

Characterized Heating Curve

The

Characterized Heating Curve is the most accurate method of controlling the supply water temperature based on outdoor air

temperature and optionally indoor temperature. The control takes into account the type of terminal unit that the system is using. Since
different types of terminal units transfer heat to a space using different proportions of radiation, convection and conduction, the supply
water temperature must be controlled differently. Once the control is told what type of terminal unit is used, the control varies the supply
water temperature according to the type of terminal unit. This improves the control of the air temperature in the building.

Reset Ratio

The

Reset Ratio method of controlling the supply water temperature is based solely on the outdoor air temperature. This method does

not take into account the type of terminal unit that the heating system is using and therefore is not as accurate as a

Characterized

Heating Curve.

Section B2

Alternate Boiler

Demands

Section B1

General Boiler

Operation

18 19

Com

UnO

Timer Switch

UnOcc

Schd

Ovr