Shopping Malls have now become the best destination for office goers where they get everything at a single location. The comfort atmosphere within the shopping malls attracts more and more crowd. But it is seen that the while providing this comfort atmosphere, the developer ends up with huge electricity bill. Hence, the need to conserve power, its high cost and undependable supply in many parts of the country has made HVAC design engineers study each new building project carefully to evaluate the possibility of maximum power savings.
Background
Air conditioning system consumes 65% of the total electrical load but this load varies from time to time. The ambient factors and the floating occupancy are the basic reasons for this varying load profile.
Building Load Profile
A study was taken up to understand the daily and yearly load profile of shopping malls.
Selecting the AC System
As seen in the profile, HVAC load is changing throughout the day and the diversity comes nearly 30%. Now, we have to select equipment which can cater to peak requirement and should also not waster energy in off peak hours. Thermal Storage system is the option in this regard.
As shown in the figure, chillers are connected with low side system as in case of any chilled water system but instead of normal chillers, Brine chillers have used for the same. Secondly, the chilled water line has routed through some storage tanks, which converts the ice balls into ice during charging mode. In normal mode, the chilled water again passed through the tank, where the chilled water rejects heat to the ice ball and reduces its temperature.
Figure 1: Yearly and daily load profile of a shopping Mall.
The interesting part is that, the chillers are basically of dual mode. They work as normal chillers during off peak hours and works as sub zero chiller during night time, when the mall does not need cooling. Out of 12 hours of daily operation, peak load comes only for four hours, where the ice balls help in keeping the area cool by cooling the chilled water to the required temperature. Other time, chiller works on normal mode. Due to this, total connected chiller requirement goes down by 40%.
Advantages of Selecting the Thermal Storage Package
- Thermal storage system has the following advantages over the normal chilled water system.
- Total chiller load goes down by 40%.
- DG, transformer, cabling and panel cost goes down.
- Plant room sizes get reduced upto some extent.
- Electricity deposition amount reduces.
- Overall electricity cost reduces by 20%.
Figure 2: Thermal Storage system
Conclusion
All we know that the electricity distribution is not same in day and night time. Because of the industrial and agricultural requirement, day time load requirement is more as compared to night time, where offices and industries normally don’t work. Again, dual tariff is applicable in some states where there is a substantial cost difference between night time and day time. Night time cost is nearly 20% less than the day time unit cost. In that scenario, night time utilization of electricity and day time reduction of consumption will not only reduce the capital investment but also the running cost.
AUTHORS CREDIT & PHOTOGRAPH
Firoj Jena
Clancy Global Consulting Engineers,
Mumbai
