Carrier Omnizone 50BVC Installation, Start-Up, Service And Controls Operation And Troubleshooting page 22

DUCT HIGH-STATIC (DHS) LIMIT SWITCH (VAV ONLY)
The duct high static limit switch is a field provided mechanical
safety that prevents duct over pressurization. The switch is option-
al and is field-provided.
IMPORTANT: Use tubing that complies with local codes. Im-
proper location or installation of the supply duct pressure tubing
will result in unsatisfactory unit operation and poor perfor-
mance.
Step 5 — Make Piping Connections
CONDENSER WATER PIPING
Always follow national and local codes when installing water pip-
ing to ensure a safe and proper installation. Connections to the unit
should incorporate vibration eliminators to reduce noise and vibra-
tion to the building, and shutoff valves to facilitate servicing.
Prior to connecting the unit(s) to the condenser water system, the
system should be flushed to remove foreign material that could
cause condenser fouling. Install a screen strainer with a minimum
of 20 mesh ahead of the condenser inlet to prevent condenser foul-
ing and internal condenser tube damage from foreign material.
Supply and return water piping must be at least as large as the
unit connections, and larger for long runs. Refer to the System
Design Manual, Part 3, and standard piping practice, when siz-
ing, planning, and routing water piping. See dimension drawings
(Fig. 7-15) for water connection sizes and locations.
Units are furnished standard with a copper heat exchanger. A
cupronickel heat exchanger is also available as a factory-installed
option. Copper is adequate for closed loop systems where good
quality water is available. In conditions where scale formation or
water treatment is questionable, the optional cupronickel heat ex-
changer should be used. Where the water is especially corrosive or
could lead to excessive fouling, intermediate plate frame heat ex-
changers are recommended.
CAUTION
Galvanized pipe or fittings are not recommended with 50BV
units due to the possibility of galvanic corrosion caused by dis-
similar metals. When selecting piping materials, use only ap-
proved piping materials that meet applicable codes and that
will handle the temperatures and pressures that may be experi-
enced in the application. Piping systems will sweat if low tem-
perature fluid is used in the system. For these applications,
supply and return water piping should be insulated to protect
from condensation damage. The minimum recommended en-
tering water temperature to the unit is 50°F.
The unit is capable of operating with entering water tempera-
tures as low as 55°F in cooling or heat pump heating mode,
without the need for head pressure control. If the entering water
temperature is expected to be lower, or more stable unit opera-
tion is desired, a field-supplied water-regulating valve may be
used. The extended range option or field provided coaxial coil
insulation should be supplied to prevent condensation, when the
entering water temperature can be below the dew point in the
unit installation location.
This unit has multiple independent refrigerant circuits with sepa-
rate condensers. The individual condensers are manifolded togeth-
er on the waterside to provide easy, single-point water connec-
tions. In order to achieve proper head pressure control when a wa-
ter-regulating valve is used, a temperature-actuated valve is
recommended. This allows any of the independent refrigerant cir-
cuits to operate while still modulating condenser water flow in re-
sponse to loop water temperature.
A glycol solution should be used if ambient temperatures are ex-
pected to fall below freezing or if the loop water temperature is
below 55°F while the unit is operating in heating mode. Refer to
Table 4, which lists freezing points of glycol at different concen-
trations. A minimum concentration of 20% is recommended.
Water pressure drop will increase and unit performance will de-
crease with increasing glycol concentrations.
Units with factory-installed waterside economizers have cooling
water passing through the economizer and condenser in series
while operating in the economizer mode. During normal opera-
tion, water bypasses the economizer coil.
Table 4 — Glycol Freezing Points
% GLYCOL
ETHYLENE GLYCOL
20
30
40
50
All manual flow valves used in the system should be of the ball
valve design. Globe or gate valves must not be used due to high
pressure drops and poor throttling characteristics.
Do not exceed recommended condenser fluid flow rates shown in
Tables 5 and 6. Serious damage or erosion of the heat exchanger
tubes could occur. Piping systems should not exceed 10 fps fluid
velocities to ensure quietness and tube wall integrity. Refer to
Tables 5 and 6 for condenser water pressure drop versus flow rate.
Flow rates outside of the published range should not be used.
Table 5 — Condenser Pressure Drop
50BVC,J,Q Units
SIZE 020
FLOW RATE
(GPM)
35 9.1
40 9.9
45 13.5
50 14.9
55 18.4
60 20.6
65 23.9
70 27.2
75 —
80 —
85 —
90 —
95 —
100 —
105 —
110 —
115 —
120 —
Table 6 — Condenser Pressure Drop
50BVT,V,W Units
SIZE 034
FLOW RATE
(GPM)
60 8.9
70 11.7
80 14.9
90 18.4
100 24.2
110 29.3
120 34.9
130 —
140 —
150 —
160 —
170 —
180 —
190 —
200 —
210 —
220 —
230 —
240 —
22
FREEZE POINT (° F)
PROPLYLENE GLYCOL
18 19
7 9
–7 –5
–28 –27
SIZE 024 SIZE 028
PRESSURE DROP (FT WG)
— —
6.2 —
7.5 —
9.3 9.3
10.9 10.9
12.9 12.9
14.8 14.9
17.0 17.2
19.2 19.2
21.7 22.2
— 24.1
— 27.8
— 30.8
— 34.0
— —
— —
— —
— —
SIZE 044 SIZE 054
PRESSURE DROP (FT WG)
— —
— —
6.3 —
8.6 —
10.4 6.0
12.3 7.3
14.4 8.8
16.7 10.2
19.4 11.7
22.3 13.2
25.3 15.5
— 17.4
— 19.6
— 21.8
— 24.2
— —
— —
— —
— —
SIZE 034
—
—
—
—
—
10.8
12.7
15.5
16.9
19.7
21.7
24.4
27.1
29.5
33.1
36.3
39.7
43.2
SIZE 064
—
—
—
—
—
—
8.7
10.2
11.8
13.2
14.8
16.6
18.3
21.8
24.2
26.6
29.2
31.9
34.8