FCU change to VAV, space cooling increase 30%?

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Hi all,

Lately I am modelling an office & hotel complex through
eQUEST with energy conservative strategies added one by one to test the energy
saving effect. The project location is a city in China with hot summer and warm

Base case:

Water side

Central water cooled chiller loop for office and hotel;

Air cooled heat pump for hotel guest room heating;

Air side

FCU + SZR (OA ventilator) for both office and hotel;

FCU ( fan power 0.0003kW/cfm) /SZR ( fan power 0.0009kW/cfm) 

When I switch the office air side system from FCU to VAV
(fan power 0.0011kW/cfm), it is found that though the office fan power
consumption decreased roughly 35%, the office space cooling power consumption
increased for 32% as well as the cooling tower and chilled water pumps. As a
result, the office equipped with VAV consumes overall 4% more electricity than
the office with FCU.

I suspected before that higher fan power of VAV results in
more temperature increase through fan and hence more space cooling requirement.
But after manually change the delta T through fan, the effect is not very
obvious that the space cooling increase proportion drops from 32% to around
28%.seems it is not the main cause.

Before this I thought VAV is generally more energy
efficient than Fan coil especially for office building but am confused now.
Hope to get your advice in this issue. Many thanks!

ALLISON's picture
Joined: 2015-07-09
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