Jandy -Low NOx Installation And Operation Manual - page 31
LX and LT Low NOx Pool/Spa Heater
Page 29
7.6 Temperature Rise
The LX and LT Low NOx pool and spa heaters
have an internal bypass which accommodates a wide
range of water flow. The bypass is easily adjustable to
change the temperature rise for optimum performance
and length of heater life. The bypass assures constant
heat exchanger flow even though flow through the filter
system will vary depending on how dirty the filter is.
For most installations, an external bypass valve is
not needed in the heater water piping. This is due to the
large size of the heater's internal bypass valve. If the
pump flow rate is known to significantly exceed 125
gpm (7.9 l/s), an external bypass may be needed to
assure proper heater operation.
Water flow should be confirmed upon start-up of
the heater and in most servicing situations. If the flow is
not normal, corrections must be made to the pool
system. Flow is evaluated by determining the water
temperature rise through the heat exchanger.
Before checking the temperature rise, make sure
that the pool filter is clean and that gas supply and
manifold pressures are correct. If necessary, clean all
components of the filter system. Temperature rise is
measured in the outlet of the far-right tubes when
facing the inlet/outlet water heater. To measure the
temperature rise, turn off the filter pump and remove
the plastic plug to the right of, and just below the level
of the outlet water pipe. This is mounted flush with the
heater jacket (See Figure 29). With the plug removed,
install the special thread adapter and "Pete’s" plug
fitting and insert a pocket thermometer. A temperature
rise measurement kit is available through your Jandy
distributor. See Section 11 of this manual for the
correct kit number.
The internal bypass can be adjusted by means of a
screw on the right-hand side of the header. To adjust
the temperature rise to within the ranges specified in
Table 7, proceed as follows:
1.
If the piping system has an external bypass valve,
close it.
2.
Set the heater's control panel to the "Off" position.
3.
Start the filter pump.
4.
After three minutes, note and record the ther-
mometer reading. This is the pool water tempera-
ture.
5.
Start the heater by setting the control panel to
either "Pool" or "Spa". Allow the heater to operate
for five minutes or more. Note and record the
thermometer reading. Subtract pool water tem-
perature from this reading. This difference is the
temperature rise. Refer to Table 7. If your
measured temperature rise is within the range
designated for your heater, skip steps 6 through 8.
Figure 29. Temperature Rise Measurement
BYPASS
ADJUSTMENT
SCREW
THERMOMETER WITH
PETE'S PLUG
6.
Locate the bypass adjustment screw on the right-
hand side of the header (see Figure 29). Loosen
the nut so that the screw can be adjusted. A
slight water leak past the nut may be expected.
Turn the screw counterclockwise to decrease the
temperature rise, and clockwise to increase the
temperature rise as needed to achieve the ranges
in Table 7. After the adjustment, tighten the nut
so that no leaks occur.
7.
If the temperature rise is too low and cannot be
raised by means of the adjustment screw, the
flow is in excess of 125 GPM (7.9 l/s). An
external bypass will need to be installed, or if one
already exists, open the external bypass valve
gradually until the temperature range in Table 7 is
achieved.
8.
If it was necessary to adjust the external bypass
as outlined in step 7, scribe a line on the bypass
shaft and case to mark the correct adjustment
position. Wire or remove the valve handle to
prevent tampering.
Table 7. Water Temperature Rise and Flow Rates
(Measured at Input/Output Header)
Minimum
Maximum
Minimum System
Model Temp Rise, Temp Rise,
Flow
°F (C)
°F (C)
GPM (l/s)
250-L
24 (13)
28 (16)
30 (1.9)
400-L
36 (20)
40 (22)
30 (1.9)
In a system without external bypass, it may be
necessary to make changes. If temperature rise is too
low, a manual bypass must be installed. If temperature
rise is too high, there is inadequate flow, possibly
requiring a change to the piping system or a larger
pump. Before proceeding with either remedy, verify
proper heater operation. Low gas input results in low
temperature rise and vice-versa. A problem with the
heater internal bypass assembly also affects measured
temperature rise.