tekmar 257 User Manual
- Data Brochure
DHW Control 257
D 257
03/09
The DHW Control 257 is used for dedicated domestic hot water systems. The control operates two on/off boilers, or one
two-stage boiler to maintain the DHW Target temperature at the DHW Sensor. The control can operate in Proportional (P)
mode, or Proportional, Integral, Derivative (PID) mode.
Additional functions include:
Boiler rotation
•
Cumulative boiler run time hours
•
P or PID staging modes of operation
•
CSA and UL certified for use in the USA and Canada
•
Input
24 V (ac)
Power Supply
Meets Class B:
Canadian ICES
FCC Part 15
Made in Canada
tektra 906-11
Stage Mode Delay
Item
DHW Control 257
Two Sta ge
Rotate
1234
On
Power Heat 1
CR
Off
Power: 24 V ±10% 50/60 Hz 3 VA
Relays: 240 V (ac) 10 A 1/3 hp
DifferentialDHW
Tar get DHW
Signal wiring
must be rated
at least 300V
56
Heat 2
No Power
7
Com
DHW
Sen
Sen
H3014B
Date Code
8
Input
Universal Sensor
Included
Output
Boiler
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Output
Boiler
How to Use the Data Brochure
This brochure is organized into three main sections.
They are: 1) Sequence of Operation, 2) Installation, and
3) Control Settings.
Table of Contents
User Interface ............................................................... 2
Display and Symbol Description ............................... 3
Sequence of Operation ................................................. 4
Powering up the Control ........................................... 4
Staging Operation .................................................... 4
Rotation ...................................................................5
Delay ........................................................................ 5
Installation ...................................................................6
Getting Ready .......................................................... 6
Mounting .................................................................. 6
Rough-in Wiring .......................................................6
The Control Settings section of this brochure describes
the various items that are adjusted and displayed by the
control. The control functions of each adjustable item are
described in the Sequence of Operation.
Testing the Wiring .................................................... 6
Electrical Connections to the Control ....................... 7
Control Settings ............................................................ 8
DIP Switch Settings .................................................. 8
Default Menu ............................................................9
Program Menu ....................................................... 10
Field Test .................................................................... 11
Error Messages .......................................................... 11
Technical Data ............................................................ 12
Limited Warranty ....................................................... 12
User Interface
The 257 uses a Liquid Crystal Display (LCD) to display
information. Use the LCD to set up and monitor the
operation of the system. The 257 has three push buttons
(Item, ▲, ▼) for selecting, viewing, and adjusting settings.
As you program the control, record the settings in the
ADJUST menu table which is found in the second half of
this brochure.
Item
The selected item will be displayed using a pointer in the
display. To view the next available item, press the Item
button. Once you have reached the last available item,
pressing the Item button again will return the display to
the first item.
Item
Adjust
To make an adjustment to a setting in the control, press and
hold simultaneously for 1 second all three (3) buttons. The
display will then show the word PRGM. Select the desired
item using the Item button. Finally, use the ▲ or ▼ button
to make the adjustment.
Item
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°
Display
Menu Field
Displays the
current menu
Item Field
Displays the current
item selected.
Stage Mode Delay
Item
Target DHW
Number Field
Displays the current value
of the selected item
Status Field
Displays the current status
of the control’s inputs,
DifferentialDHW
outputs and operation
Buttons
Selects Menus, Items
and adjusts settings
Symbol Description
POINTER
▼
Displays the control operation as indicated
by the text.
HEAT RELAY
Displays when the HEAT 1 relay is closed.
HEAT RELAY
Displays when the HEAT 2 relay is closed.
°F °°C
PRGM
°F, °C
Units of measurement
PROGRAM MENU
Program the control settings.
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Sequence of Operation
Powering Up the Control
When the DHW Control 257 is powered up all LCD segments
are displayed for 2 seconds followed by the version number
being displayed for 2 seconds. The control then enters
Staging Operation
Proportional Staging Mode (P)
When the Stage Mode is set to P, the on/off points of the
HEAT 1 and HEAT 2 relays are determined by the Target
DHW setpoint, the Differential 1 and the Differential 2
settings. This is a manual way of staging the boilers. See
figure 1 for a visual representation.
Target
DHW
Increasing
Temperature
Increasing Time
OFF
Stage 1
Stage 1
Stage 1 & 2
into the normal operating mode and the LCD defaults to
displaying the current DHW temperature.
Differential 1 & Differential 2 (P Mode)
Manually adjust Differential 1 and 2 to set the on points
of stage 1 and 2. Stage 1 will fire when the temperature
falls below Target DHW minus Differential 1. Stage 2 will
fire when the temperature falls below Target DHW minus
differential 1 minus differential 2.
OFF
Differential 1
Stage 1
Stage 1 & 2
Differential 2
Proportional, Integral, Derivative Staging Mode (PID)
To provide proper boiler staging and accurate DHW
Target temperatures, PID mode should be used. When
the Stage Mode is set to PID, the on and off points of
the HEAT 1 and HEAT 2 relays are determined by PID
logic and the differential setting.
What is PID?
Proportional Error - How far is the temperature from theTarget?
•
Integral Error - How long has the temperature been there?
•
Derivative Error - How fast it is the temperature changing?
•
By considering these three errors, the control can better
decide when to turn on a boiler stage. This function provides
greater boiler plant efficiency and also prevents water
temperature drop that is commonly seen on proportional
staged systems.
Figure 1 - Staging operation for proportional logic
Differential (PID Mode)
If Differential is set to Auto, the control will calculate an
appropriate differential to reduce boiler short cycling.
If a boiler short cycles, the differential is automatically
increased. If auto differential is not desirable, the installer
may select a manual differential.
Minimum On and Off Times
The minimum on and off time for each boiler is 30
seconds.
DHW Maximum
If the DHW temperature rises 2°F above the Target DHW
setpoint due to minimum boiler on times, the control will
open both the Heat 1 and Heat 2 relays.
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