FCU v.s. VAV comparison and Modelling Heat Pump Heating in eQUEST

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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 winter.

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)

Q1: FCU v.s. VAV

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!

Q2: Modelling heat pump

To model the air cooled heat pump as heating source for hotel, I modelled 2-pipe heat pump loop at water-side and set it as the heating source at air-side (cooling source as chilled water loop). The loop operation is set as snap with the snap temp as mean temp of indoor heating and cooling design temperature (otherwise much unmet hour occur).

When I set the sub meter to measure the component performance, I found the heat pump loop is both heating and cooling the hotel instead of designed heating only, while the chilled water loop only cools the hotel during early morning. Since the heat pump cop (2.8) is lower than the chiller COP (5.1), the simulated results cannot reflect the design performance.

Now I am modelling the case twice every time, one with heat pump loop and one without hence to model the chiller energy consumption of hotel cooling part. I am wondering if anyone has this issue before and if there is any strategy I can use to solve this problem? Thanks a lot!

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