Midea Aqua Tempo Super MC-SP25-RN1L, Technical & Service Manual, Page: 103 / 153

Aqua Tempo Super Series air cooled scroll chiller unit (50Hz) MCAC-ATSM-201606
101
13.2.13 Design of expansion tank
If a closed expansion tank with its filled volume of air is too small, the system pressure will easily exceed the
maximum allowable pressure and cause water to discharge from the pressure relief valve, thus wasting
water. If the closed tank is too large, when the water temperature drops, the system pressure may decrease
to a level below the minimum allowable value and cause trouble in the air vent. Therefore, accurate sizing of
a closed expansion tank is essential.
For diaphragm expansion tanks, the minimum volume of the water tank, Vt, gal(m3),can be calculated by the
following formula, recommended by ASHRAE Handbook 1996, HVAC Systems and Equipment:
V
t
=V
s
v
2
/v
1
-1-3
α
(T
2
-T
1
)
1-p
1
/p
2
T
1
=lower temperature,
o
F (
℃
)
T
2
=higher temperature,
o
F (
℃
)
V
s
=volume of water in system, gal(m
3
)
p
1
=absolute pressure at lower temperature,psia(kPa abs.)
p
2
=absolute pressure at higher temperature,paia(kPa abs.)
v
1
,v
2
=specific volume of water at lower and higher temperature, respectively, ft
3
/lb(m
3
/kg)
α
=linear coefficient of thermal expansion; for steel,
α
=6.5x10
-6
in./in
·
o
F(1.2x10
-5
per
℃
); for copper,
α
=9.5x10
-6
in./in
·
o
F(1.7x10
-5
per
℃
)
In a chilled water system, the higher temperature T2 is the highest anticipated ambient temperature when
the chilled water system shuts down during summer. The lower temperature in a heating system is often the
ambient temperature at fill conditions(for example, 50
o
F or 10
℃
).
13.2.14 Selection and installation of the pump
(1)Select the pump
a. Select the water-flow of the pump
The rated water-flow must no less than the unit rated water-flow; in terms of multi-connect the units, that
water-
flow must no less than total units’ rated water-flow.
b. Select the left of the pump.
H=h1+h2+h3+h4
H: The lift of the pump.
h1: Main unit water resistance.
h2: Pump water resistance.
h3: Water resistance of the longest water-
loop distance, includes: pipe resistance, different valve’s
resistance, flexible pipe resistance, pipe elbow and three-way resistance, two-way resistance or three-way
resistance, as well as filter resistance.
H4: the longest terminal resistance.
(2) Installation the pump
a. The pump should be installed at the water inlet pipe, both of which sides must mount the soft connectors
for vibration-proof.
b. The backup pump for the system (recommended).