Manual No. 4801- 2997 Rev 1-15
Secondary Sensing System
23 of 42
7.2.2 Minimum Ventilation Protection
As explained earlier, this Back-Up System contains a back-up minimum ventilation timer. This timer is
normally off but is triggered upon an alarm occurring on the Control System auxiliary input. There are two
situations that can cause an alarm on the Control
System auxiliary that depends on the setting in P62
(See Section 6.3). Whether P62 is set to be a Cycle
Pressure Alarm or a normal control system alarm, if
the alarm is triggered the S3 will enable the 5
minute timer clock. Then Cool1 will operate based
on the setting in P3. This process will continue as
long as the Control System auxiliary alarm is
present.
7.2.3 Fail-Safe Relay Strip
The stand-alone system will be equipped with a fail-
safe relay strip. This relay strip has four output
relays. Each relay is capable of driving up to 1 h.p.
Also, each relay has a stage jumper. These stage
jumpers can be used to assign each relay to a back-
up stage, Heat, Cool1, Cool2, Cool3. Therefore, the
end user can select what stages that he would like to
back up. For example, you may not care to back up
your heat stages; therefore, you could use one relay
for Cool1, one relay for Cool2, and two relays for
Cool3.
Any combination will be acceptable but it is important that you understand the operation of each output so
that you back up your main control system appropriately. For example, minimum ventilation protection is
provided by Cool1. If you do not assign a relay output to Cool1, you will not have back up protection for
minimum ventilation. It is also important to choose the correct fans to back up. For example, choose a fan
that is not your typical minimum ventilation fan to run off of Cool1, such as one of your initial tunnel fans.
This will help you two ways. First, it will protect against fan mechanical failure. Secondly, by choosing a
tunnel fan it will not affect tunnel ventilation if the back up kicks in on a hot day. The graph in
Section
7.2.1
helps to show how the stages operate but it is also important to understand how the inlet overrides
operate in conjunction with the Cool outputs (
See Section 7.2.4
). The following table helps associate the
Back-Up stage outputs with the type of equipment that you are trying to operate.
Type of Stage Operation
Jumper Assignment
Cool Negative Tunnel Fan
COOL 1 *
Cool Negative Tunnel Fan
COOL 2
Cool Tunnel Fan/Evap.
COOL 3
Heat Stage
HEAT
Stage not on Back-Up
No Jumper Installed
* IMPORTANT NOTE:
Cool1
controls your minimum ventilation Back-Up Stage.
7.2.4 Vent/Tunnel Inlet Override Operation
The S
3
contains override relays to operate your
Vent
or
Tunnel
inlets during Back-Up situations. It is
intelligent enough to understand how it needs to operate these overrides in a manner that will not disrupt
what the main control system is trying to do.
Typical operation results in the
Tunnel
inlet being overridden open anytime the Back-Up stage
Cool3
is
on. Otherwise, if
Cool1
or
Cool2
is on, the S
3
will override the
Vent
inlets open. This is the correct
assumption most of the time but there are exceptions.
STAGE RELAY BOARD
Stage Relay
COOL 3
COOL 2
COOL 1
HEAT
Stage
Jumpers
