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ANTICIPATION
The operation
of a low
voltage thermostat
based solely
on
mechanical means,
generally results
in
wide
varia-
tions in
temperature
in
the
conditioned
area
whether
the
application
is
for
heating
or
cooling.
To
insure
a
more
precise
control of
area
temperature,
low
voltage thermo-
stats
contain heating and cooling anticipators.
In addition to
improved
room
temperature
control,
heat
anticipation contributes
to
better
air
circulation.
The
burner may cycle
on and
off
several
times during
one
cycle
of
the fan. Since heat anticipators are
powered
and effective
only
during
the
heating cycle,
they
are
placed
in
series
with the control
contacts. When
the
contacts
are
closed, power
is
supplied
to
the
heat
anticipator
resistor.
MANUAL SWITCHING
OPERATIONS
Generally,
a
sub-base used
to
control both
heating
and
cooling equipment
will
contain
two
switches,
one
marked
"FAN"
and
one
marked
"SYSTEM."
FAN SWITCH
ON
Constant
fan. The fan
will
run continuously
re-
gardless
of
the thermostat
demand.
AUTO
The fan runs only
as
required by the
system
operatlon.
SYSTEM SWITCH
HEAT
-
Heating
system
only,
operates
in
response
to
the
thermostat.
OFF
Heating
system
and cooling
system
both
off.
COOL
-
Cooling
system
only,
operates
in
response
to
the
thermostat.
CAL/TION: Care should always be taken
in
the
align-
ment
of
the thermostat attaching
screws,
as they
may
also
serve
as
terminal
connectors.
If
threads
are
stripped,
a
poor
electrical connection
will
result.
INSTALLATION AND
SERVICE
l.
A
low
voltage thermostat
is a
precision
instru-
ment and should be treated as one. Care must
be
used
to
insure
a
level installation
with
thermostats
using mercury
bulbs.
2. Mount
on a solid
wall.
3. Locate
the
thermostat
on an
inside
wall four
to
five
feet above
the
floor in
an
area
free
from
drafts
and direct sunlight.
Do not
locate where
directly
affected
by
lamps,
fireplaces,
appliances,
or
on
walls
containing
hot or
cold
pipes, ducts,
chimneys.
4.
Be
sure anticipator matches
or is
adjusted
to
match current (amp)
draw
of
equipment
being
controlled.
5.
Make
all
wiring
connections
clean
and
tight'
lf
a
heating
system
has
an improperly
sized
anticipator
and
excessive
heat
is
generated
in
the thermostat,
the
result
is a short "on"
cycle.
During
periods when
the
system
is running
close
to its full
capacity,
more
of
the
heat
sensed
by the
bi-metal
is from
the
anticipator
than
from room air; and the
controlled area
tempera-
ture
will
progressively
decrease.
THERMOSTATS
Insufficient
heat
anticipation
in
a
heating
system results
in
the bi-metal
lagging behind
the room
temperature
change.
This
will
cause
longer
"on" and
longer
"ofl'
periods
with a
resultant larger
room
temperature
varlatlon.
A
common heating valve current
draw is 0.4
amps,
and this should
be
matched
on
any adjustable
antici-
pator.
If
the
adjustable anticipator
is
set
appreciably
higher,
for
example rJ.1 amps,
it will
increase
the
room
temperature
variations by 3oF. or 4oF. and
cause
longer running
cycles.
For
longer
"on"
periods,
set
the heat anticipation
ad-
justment pointer
at
slightly higher amp value.
For
shorter
"on"
periods, set
the pointer
at
slightly
lower
amp value.
Move only
t/q
to
/z
scale
division
at a
time.
(Never set
the pointer
at
more
than
I
%
scale
divisions
below the amp rating
of
the valve
or
relay
current
rating.)
The
anticipation function in a cooling thermostat is
the
reverse
of
its
heating application.
The cooling
antici-
pator is
powered
during the
"ofl'
cycle.
As the
room
temperature
increases,
heat
is
applied
to
the
bi-metal
decreasing
the time
necessary
for
the bi-metal
to
close
the
contacts.
Excessive
cool
anticipator
temperature
results
in
shorter
"offl'
periods, consequently,
more
frequent cycling
of
the cooling equipment.
Insufficient
anticipation
in
a cooling
thermostat
causes
long
"ofl'
and
cycles resulting
in
larger
temperature
variations
in
the
room.
ANTICIPATION PROBLEMS
HEATING
SETTING
TOO
LOW
l.
Excess
anticipation "on"
cycles
too
short.
2.
Rapid
cycling.
3.
Small temperature swings
from the
setting
with
a tendency
to
drop.
SETTING
TOO
HIGH
l.
Insufficient
anticipation
cycles
too
long.
2.
lnfrequent
cycling.
3.
Wide
temperature swings
from the
set
point
with
a
tendencl to
lag.
COOI,ING
RESISTOR
TOO
SMALL
L
Voltage
too
low.
2.
Short
"ofl'
time.
3.
Short "on"
time.
4.
Rapid
cycling.
5.
Temperature maintained closer
to
the set
point
with
a
tendency
to
rise.
R'.S/.STOR TOO
IARGE
l.
Voltage
roo
high.
2.
"Off'time
too
long.
3.
"On"
time
too
long.
4.
Fewer
"on"
cycles.
5.
Wide
temperature swings
from the
set
point
with
a
tendency
to
lag.
l7
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