SUNCHILL POWER LTD

www.sunchill.net

Advance Refrigeration Technology

● Optimization of Head Pressure● Liquid Sub­Cooling● Glycol or Hot Gas Defrost● Liquid Overfeed● Optimization of Evaporating Pressures● Optimization of TXV● Heat recovery● Compressors Capacity Control

Head Pressure Control

How we control head pressure in a refrigeration system?

Our company's technical team will monitor your refrigeration system with the latest control instruments and evaluate the working conditions of your system and optimizeIt at its most efficient and smooth running parameter to maximize the cooling capacityand power consumption.

From the table above we can see the cooling capacities and power consumption indifferent condensing temperatures.

As a result by optimize the head pressure (condensing temperature) we can increasecooling capacity,depending on the solution we will follow up to 35% and reduce powerconsumption by 15%.

Conclusion:● An increase in cooling capacity means that our system will work less time

thus an extra energy will be saved increasing the total savings.● Lower head pressures means extent of compressors life● Fewer possibilities of leaks

Liquid Sub-CoolingAs we sub-cool liquid refrigerant, we reduce the level of energy content and create higher potentialfor the refrigerant to absorb heat, therefore a lower Mass Flow Rate (Mass Flow Rate is definedas the molecular measurement of the gas flow rate expressed by units of mass per unit of time)is required for sub-cooled 10˚C liquid than 32˚C liquid to absorb the same quantity of watts.

Basically we have three methods under which liquid sub-cooling can occur that we need to consider.

● Mechanical Sub Cooling● Sub-Cooling Circuits and Heat Exchangers● Ambient Sub-Cooling

Finally, another widespread application of subcooling is boosting and economising. Inversely tosuperheating, subcooling, or the amount of heat withdrawn from the liquid refrigerant on thesubcooling process, manifests itself as an increase on the refrigeration capacity of the system.This means that any extra heat removal after the condensation (subcooling) allows a higher ratioof heat absorption on further stages of the cycle.

Glycol or Hot gas defrost

The two most popular words in the HVAC&R industry today are energy savings

Depending on what defrosting technology is used, between five per cent and65 per cent of daily power consumption required within an evaporator can befrom defrosting.

Evaporator providing 34.2kW of cooling on R404A at 6kTD in a -18°C freezer room:

� Within the evaporator, electric resistance heater elements are installed.These get very hot during the defrosting cycle and can reach temperatures over 200°C.They radiate heat to the locations they are fitted and over time conducts/spreads to meltthe frost from the whole evaporator.This is a proven technology that is very effective. It is easy to install, and simple toimplement and maintain.On the downside, there is high power consumption. If heaters fail, sections of theevaporator become covered in frost, triggering alarms and requiring replacement.The high temperatures cause evaporation of water and moisture can build on freezerroom ceilings, resulting in icy floors and wet product.

� During normal operation, a tank of glycol is warmed to 50°Cusing the system's discharge gas and standard heat recovery.The evaporator is specially circuited with separate glycol tubes and drain pan glycol tubes.During defrost a separate circulation pump is activated and the warm glycol from the tankis pumped through the evaporator.In parallel systems heat can continuously be added to the tank and a relatively small tankcan be used.In standalone systems the tank is sized so the thermal mass is sufficient to perform one defrost.The glycol is warmed from 100 per cent waste heat.On the upside, its installation and implementation, while new to the industry, is relatively simple.It only requires a small pump and low power consumption, defrost occurs at 50°C and doesn�tcause steam around the evaporator, and there is reduced risk of frost formation within the room.On the downside, installation costs are higher than other types of defrosting.

The liquid overfeed systems are normally used for low temperature applications, where there aremultiple evaporators operating at the same temperature or at different temperatures. Of late, liquidoverfeed or liquid recirculation systems are becoming more and more popular. Basically, these areflooded evaporator operation with higher than required liquid feed to the evaporator.In pump circulation system design, the advantage is one effectively decouples refrigeration systemwith load allowing more efficient operation and lot of flexibility for design and operation.The overfeed means much more liquid is fed to evaporator than the liquid actually vaporizes.Excess liquid is called overfeed, which returns to low pressure side accumulator or L.P.receiver. By over feeding the evaporator, the inner surface is kept thoroughly wetted and thusachieves optimum heat transfer.For small number of low temperature evaporators, flooded coil evaporators is bestoption.As the number of evaporators increases and as the temperature requirement gets lowerand lower, liquid recirculation/overfeed systems are the choice systems. Normally formore than 3 to 5 evaporators, liquid recirculation is the best option. At lowtemperatures, achieving good heat transfer in the evaporator is crucial since the plantoperates with high compression ratios, where quantities of flash gas are appreciableaffecting proper wetting of the surface. The fundamentally liquid overfeed systemcauses more wetting of tubes associated with high velocity of refrigerant results inhigher heat transfer rate.

Variable Refrigerant Capacity Control

The Refrigeration Cycle.The condensing temperature is lowered.The evaporating temperature is raised.Decreasing the temperature lift by 1°C will improve efficiency and reduce operating costs by 2%to 4%. Temperature lift can be reduced by increasing the evaporator temperature or by decreasing the condenser temperature.

Performance Optimization of Refrigeration Equipmentand Opportunity Strategies

For optimal evaporator efficiency, the evaporating temperature should be as high as possible.Oil should not be allowed to build up within the evaporator, and the tubes in a shell and tubeevaporator should be cleaned regularly so as to prevent corrosion and fouling.Moreover, refrigerant flow through the evaporator should be correctly controlled to make fulluse of its capacity with minimum amount of superheat.

Evaporators, Condensers and Expansion Valves

Lowering the condensing temperature generally results in lower overall energy consumption.

Condensing temperature can be lowered by improving the heat transfer capability, which includes

the following:

Keeping air-cooled condenser fin blocks free of debris.Not using water-cooled condenser tubes that are fouled, corroded or scaled.Keeping air and other non-condensables out of the system.Allowing the condensing pressure to float with ambient temperature to take advantage of the lowerambient temperatures overnight and during winter.

Refrigeration systems are designed to have a maximum duty to balance a calculated maximum load.For most of its operational life, the system may work at some lower load level. Capacity control canbe achieved by many means.Speed control is the most obvious method, but this requires an inverter drive. Rotational speed canbe reduced by two-speed electric motors or by use of a variable speed drive to control the motorspeed. The lowest permitted speed is generally dictated by the in-built lubrication system.Multi-cylinder machines permit reduction of the working swept volume by removing cylindersfrom service with blocked suction or valve-lifting mechanisms.