UM / UM PLUS
Chillers and inverter air / water heat pumps with axial fans
31
17
OPERATING LIMITS
17.1
EVAPORATOR WATER FLOW RATE
The nominal water flow rate is referred to a
∆
T equal to 5°C, between the evaporator’s inlet and outlet temperatures. The allowed
maximum flow rate is corresponding to
∆
T=3°C; higher values may cause too high pressure drops. The allowed minimum water
flow rate is corresponding to
∆
T=8°C (except for the models UM / UM Plus 06 for which
a maximum temperature difference of
∆
T=
6,25°C is allowed
). Insufficient values may cause too low evaporating temperatures with the intervention of safety devices
which would stop the unit and, in some particular cases, the water can freeze in the evaporator coil causing the refrigeration
circuit to break down.
We enclosed below a most accurate table showing the minimum flow rates that to ensure for the plate heat exchanger for a the
proper operation of unit according to the model (
note:
the water flow switch is used for preventing the freezing sensor from
failure in the case of insufficient water flow but it does not ensure the minimum flow rate required in order the unit can work
properly)
Models
UM / UM Plus
06
08
12
16
Cooling capacity for reference [kW]
5,09
8,31
11,57
13,17
Minimum water flow rate that to ensure
[m3/h]
0,70 0,89 1,24 1,42
As a first approach, and in the absence of other detection systems, the proper flow rate for getting the best performance from
your unit can be found at maximum speed of the circulator, using the pressure gauges for controlling the pressure difference
between the return and the delivery water on the outside water connections of the unit and make sure that such value is equal or
less than the static pressure indicated on the curves shown in paragraph 14 for the respective models.
17.2
COLD WATER TEMPERATURE (SUMMER OPERATION)
The allowed minimum temperature at the evaporator’s outlet is 5°C; for more lower temperatures please contact us. In this case
contact our company for the feasibility study and evaluation of changes to be made according to your requests. The maximum
temperature that can be maintained at the outlet of the evaporator is 25°C. Higher temperatures (up to a maximum of 40°C) can
anyway be tolerated during transitions and start-up phases of the system.
In all cases, the maximum electrical input occurs for the heat pump operating mode at a water outlet temperature of 58°C and
with outdoor temperature of -15°C.
17.3
HOT WATER TEMPERATURE (WINTER OPERATION)
Once the system is working at the right temperature, the inlet hot water temperature should not to be lower than 25°C; the
lowest values that are not related to transitional or start-up stages may cause system’s malfunction and possible compressor
breakdowns. The maximum outlet water temperature have not to exceed 58°C. At this temperature, the power consumption and
performance in terms of C.O.P. are enhanced if the outdoor temperature is higher than 5°C, even if the unit is still able to work up
to the limit of -15°C.
For higher temperatures than those pointed out, especially if have a concomitant with the reduction of the water flow rate, it may
cause abnormalities to the normal operating of the unit, or the safety devices act in critical cases.
17.4
AMBIENT AIR TEMPERATURE
The units are designed and manufactured to operate, in summer operation, with the condensate control, with outdoor air
temperatures ranging between -10°C and 46°C. While operating as a heat pump, the allowed range of the outdoor temperature
goes from -15°C to 40°C as a function of the water outlet temperature as indicated in the below table.
Operation limits
Water chiller mode
Ambient temperature
Minimum -10°C M46°C
Water outlet temperature
M5°C M25°C
Heat pump mode
Ambient temperature
Minimum -15°C M30°C
Water outlet temperature
M25°C M58°C/+63°C
Heat pump mode for sanitary hot water
Ambient temperature with maximum water temperature 48°C
Minimum -15°C M40°C
Ambient temperature with maximum water temperature 55°C
Minimum -15°C M35°C
Water outlet temperature
M20°C M58°C/+63°C*
(*) with a supplementary electric heater (optional)
Below the operation limits are graphed, in the case of air conditioning and sanitary hot water production.
