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06617645-02
27
(QLAC / FC FREE COOLING VERSION)
FREE COOLING SYSTEMS MUST ALWAYS BE FILLED WITH GLYCOL SOLUTION
The free cooling versions can operate in 3 different operating modes. The free-cooling coil is installed in
series with the water chiller evaporator; the 3 way valve controls the water flow through the coil. When the
ambient temperature is lower than the return water temperature, the microprocessor allows the water flow to
pass through the free-cooling coil first, then through the evaporator.
Cooling mode (Summer operation) Ambient temperature is higher than the
return water temperature. In
this case, the ambient conditions are not suitable to allow Free Cooling operation; the 3 way valve is closed
and the water flows to the evaporator, where it is cooled. The compressors, fans, and the water pump are
activated; the unit operates like a normal liquid cooler.
Free cooling mode (Winter operation) Ambient temperature is much lower than the return water
temperature. In this case, the ambient conditions are suitable to allow Free Cooling operation; the 3 way
valve opens and the water flows into the free cooling coil, where the ambient conditions are sufficient to give
the total required load. In this case the pump and the fans are in operation, while the compressors are
stopped. In this case, the free cooling system works in substitution of the water chiller.
Cooling mode + Free cooling (Mid-season operation) Ambient temperature is lower than the return water
temperature. In this case, the ambient conditions are suitable to allow Free Cooling operation; the 3 way
valve opens and water flow passes into the free cooling coil although the ambient conditions are not
sufficiently low to give the total required load. The microprocessor control activates the compressors (pump
and fans are already in operation) to satisfy the required load. In this case the free cooling system works in
conjunction with the water chiller. In these circumstances the head pressure control device is activated.
CONDENSING PRESSURE CONTROL (optional)
If unit operation below 20°C is expected, a condensing pressure control must be fitted in the unit. This
device will allow unit operation under low ambient temperature, by reducing condenser air flow and
obtaining acceptable operating parameters. This device modulates the fan speed in proportion to the
condensing pressure measured by the pressure transducer.
This device is factory pre-set. The values must never be modified.
OPERATIONAL LIMITS
Evaporator water flow rate
The nominal water flow rates are based on a delta T (W
in
- W
out
) of 5 °C. The maximum flow rate allowed is
that achieved with a delta T of 3 °C: higher values may cause too high pressure drop. The minimum water
flow rate allowed is that achieved with a delta T of 8 °C. Insufficient values cause too low evaporating
temperatures, tripping safety devices which stop the unit.
Chilled water temperature (summer operation)
The minimum temperature allowed at the evaporator outlet is 5 °C. To work below this limit, the unit
requires modification - please contact TEV Ltd. The maximum temperature allowed at the evaporator inlet is
20 °C.
Hot water temperature (winter operation)
Once the system is at temperature, the water temperature at the condenser inlet should not be less than 23
°C: lower values could cause incorrect working operation of the compressor and compressor failure may
occur. The maximum water temperature at the condenser outlet should not exceed 48 °C: higher values will
cause safety devices to trip and stop operation.
Ambient air temperature
The units are designed and manufactured to operate, in cooling, with ambient air temperature between 20°C
to 42 °C If a fan speed control is installed then the minimum ambient air temperature is -10°C. In winter
operation (heat pump cycle) operates from -5°C to 20°C.