Watts Tekmar Zone Control 368 User Manual Download

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Common Blocks

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The 368 has 2 common blocks for both the RTU inputs and the relay outputs. Each
common block has a terminal starting with

Com (Eg. Com Sen or Com 1-2 ). Each

common block can be used for either two One Stage zones or one Two Stage zone.

One Stage Common Blocks

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If an RTU is connected to the lowest number in the common block, a One Stage common
block is created.

Example An RTU connected between the terminals

Com Sen — RTU 1 is used to control

the output relay

1, and an RTU connected between the terminals Com Sen —

RTU 2 is used to control the output relay 2.

Note If only one RTU is used, it must be placed on the lower number in the common

block. In the above example this would be

Com Sen — RTU 1 controlling output

relay

Com 1-2 — 1.

PID Zoning Logic

The 368 operation is based on a 15 minute cycle. During each cycle,
the control turns on the zone relay for a specific on time. This zone
on time is calculated based on the PID response of the zone during
the previous 15 minute period. If the zone needs more heat, the on
time is increased and if the zone needs less heat, the on time is
reduced. In order to prevent short cycling, the 368 ensures that the
zone relays remain on or off for at least 3 minutes.

Two Stage Common Blocks

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When a single RTU is connected to the highest terminal number in the common block,
a Two Stage common block is created. The single RTU therefore controls two output
relays: a

Lo stage relay and a Hi stage relay.

Example An RTU connected between the terminals

Com Sen — RTU 2 is used to

control the output relays

1 and 2. Relay 1 is the Lo stage output relay and relay

2 is the Hi stage output relay.

PID Zoning logic

The temperature within each Two Stage zone is controlled by
varying the on time of the output relays over a 15 minute period.
During light loads, the 368 cycles the

Lo stage relay on and off. As

the load increases, the

Lo stage relay on time increases until it

reaches a maximum of 15 minutes. The

Hi stage relay is then turned

on and its on time is increased as the load increases. When the
heating load decreases again, the on time of the

Hi stage relay is

reduced until the

Hi stage relay is turned off completely. The control

then starts to reduce the on time of the

Lo stage relay.

Zone Control Load Staggering and Synchronization

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The 368 staggers the operation of the zones in order to achieve a steady load on the boiler while minimizing boiler running time and
preventing boiler short cycling. Multiple Zone Controls can be connected together to increase the number of zones. Each of the Zone
Controls synchronizes its zone operating cycles based on the

Zo In input from the other Zone Controls. This results in a more stable

system flow rate and improved boiler operation.

Zone Control Operation with a tekmar House Control

The 368 can communicate with a tekmar House Control in order to
provide indoor temperature feedback, turn on the system pump and
operate the boiler. When multiple Zone Controls are used, each Zone
Control sequentially passes the information to the tekmar House
Control. This ensures that the heat requirements of all zones are
satisfied. When the 368 is requesting heat from the House Control, the
Heat Required light is turned on.

Fast Acting Zone Valves or Zone Pumps

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If the

Thermal Motor DIP switch is set to Off, the 368 assumes that fast acting (electric

motor) zone valves or zone pumps are connected to the zone relays. The

Heat Required

light is therefore turned on as soon as the first zone relay is turned on. One minute before
the last zone relay is turned off, the 368 purges the boiler by signaling to the House Control
to turn off the boiler and keep the system pump operating.

LR 58233

E150539

LR 58233

E150539

tekmar Zone Control

15 minute Cycle

Lo Stage

Hi Stage

Lo Stage

Hi Stage

Lo Stage

Off