FREE COOLING OPERATION
The operation of the free cooling system uses finned coil heat exchangers placed in front of the condensing coils. The air passes through the free cooling coils before reaching the refrigerant condensers.
When the external temperature is lower than the temperature of the fluid returning to the system, the free cooling system is activated. The efficiency of free cooling (EER) depends on the temperature difference between the ambient temperature and the refrigerated fluid: the greater the gap of fluid/air temperature, the higher the EER level.
The chiller can operate under three main conditions:
- mechanical cooling
- partial free cooling
- 100% free cooling
The ambient temperature is higher than the inlet fluid temperature.
In this case the free cooling system is completely excluded and the cooling of the fluid is obtained only by the action of the compressor.
The ambient temperature is lower than the inlet fluid temperature (about 2.5 ° C or 4/5 °F).
In this case, the cooling of the fluid is guaranteed by the combined action of the free cooling system and the compressor.
The ambient temperature is lower than the inlet fluid temperature.
The compressor is off. The cooling and the cooling capacity are solely dependent on free cooling.
Total free cooling is guaranteed with a temperature gap between air and fluid of about 5 °C (10/15 °F).
The abovementioned types of operation are automatically managed by a microprocessor control system designed to optimise energy consumption keeping to the pre-set working conditions.
The microprocessor receives four temperature inputs from sensors reading the following parameters:
- ambient temperature TAE
- returning water temperature from user’s plant TFC
- evaporator entering water temperature RWT
- evaporator leaving water temperature LWT
When the ambient air is at least 2 °C (5 °F) lower than the returning water temperature, the microprocessor allows the free cooling system to operate. Thanks to the three-way valve opening, water flows into the water coils before crossing the evaporator.
Through the sensor monitoring the evaporator entering water temperature, the microprocessor accordingly reduces the compressor action (multistep capacity control) until they are completely excluded if total free cooling operation is reached.
If the free cooling efficiency is too high (as the ambient or required cooling load is very low) to keep a constant leaving water temperature, the microprocessor proportionally reduces the air flow through the coils and if this is not sufficient, it controls the water flow in the coils by means of the three-way valve opening.
EER of FC units compared to standard units at the same conditions.
The free cooling system works when the ambient temperatures are low enough to cool the heat transfer fluid without the use of refrigeration compressors.
With high temperatures of the heat transfer fluid, the system is even more effective.
These units are therefore the optimal solution in the air conditioning systems of data processing centers, for the refrigeration of industrial machining centers or industrial processes.
The greater the temperature gap between the circulating water and the outside air, the better the system performance will be.
Condensing coils consisting of self-spacing high-efficiency aluminum fins to ensure perfect spacing (distance between the fins) and perfect contact with copper or stainless steel pipes (on request).
FC coils are made with copper tubes and aluminum fins. The supporting frame is in aluminum or stainless steel; the manifolds are equipped with air bleed valves and water drain valves.
The main features of the fans are compactness, low noise and exceptional efficiency.
The variable speed EC fans react continuously to load variations ensuring maximum efficiency especially at partial loads.
Compared to conventional fans, energy savings of 30% can be achieved.
Assuming continuous operation, the additional cost of these high efficiency fans can easily be recovered within the first year of operation.
This includes the three-way proportional mixing valve for the insertion the Free Cooling system, for constant control of the water temperature, and all the hydraulic connections between the evaporator and the finned exchangers. The whole unit is insulated with closed cell insulation, suitable for outdoor installation.
The regulation is developed to meet the most common needs regarding the operation of the chiller with free cooling during the winter period.
The software is optimized to achieve maximum results in terms of energy savings.
The software controls the temperature of the water leaving the evaporator, interacting optimally between the 3-way valve, the fan speed regulator and the compressors.