MEWAH-OILS SDN. BHD. TO : Ms. Agnes LimWESTPORT PROJECT

ADVANTAGES OF CENTRIFUGAL CHILLERS OVER SCREW TYPE CHILLERS

Mewah-Oils Sdn. Bhd. decided to buy two units of 625TR new centrifugal chillers for their new project at Westport as their analysis of specification and performance data proves that centrifugal chillers are much more superior especially for high capacity service.

Following are the distinct advantages of using a centrifugal chiller over screw type chillers.

1. Screw type chillers are inefficient due to higher mechanical friction losses. This is indicated by the higher power consumption in screw type chillers as compared to centrifugal chillers.Power consumption per ton of refrigerant :Screw type : 0.619 kWHCentrifugal Type : 0.550 kWHDifference : 0.069 kWH- Extra power consumption per day (636 TR screw chiller as offered by Durham Bush) : 44kWH- Extra power consumption per year : 379,123kWH- Extra cost incurred on power consumption : RM 87,128 @ RM0.23/kWH

Which comes to 16% of the cost of the new Durham Bush screw type chiller (RM 535,000).Hence we have to pay extra power cost of RM 87,128 per year which is very substantial amount.

2. Maintenance cost is high on screw type chillers as compared to centrifugal chillers. - Screw type chillers supplied by Durham Bush has 3 units of compressors on each chiller and

wear and tear would be high due to screw type of rotating mechanism. Any mechanical deficiency will result in the replacement of the complete compressor. Hence maintenance cost is high and not advisable to buy screw type chillers.

3. R-22 refrigerant used in screw type chillers is not safe to use.-R-22 refrigerant chillers normally operates at higher pressure (200psig) as compared to chillers with R-123 which operates at 8 psig (max)In the event of leakages more refrigerant quantities are drawn into the surroundings and hence pollution of the environment occurs. It is safe to use R-123 refrigerant which is normally used in centrifugal chillers.

4. Centrifugal chillers’ lubrication system is more reliable.-Centrifugal chillers operate with external oil pump lubrication. Hence pressure and lubrication rate can be controlled whereas screw type chiller operates with differential pressure lubrication between condenser and evaporator. Any differential pressure change would affect lubrication rate, hence it is very risky.

5. Centrifugal chillers are designed and tested as per ARI (American Air Conditioning and Refrigeration Institute) whereas locally made screw chillers do not conform to these standards.

6. Centrifugal chillers have higher reliability and higher life span - Life span of centrifugal chillers : 23-24 years- Life span of screw chillers : Less than 20 years

To summarise the above, Mewah-Oils Sdn. Bhd. feels that screw chillers result in high cost of ownership for the users in the form of higher maintenance, higher operation and not user friendly design features, thus making the screw chiller operation non-competitive.

16/6/2001