Combined AHU and Fan Coil system for a zone?

[scythe13]

Hi,
I have seen in some buildings for a zone there are fan coils as well as AHU system.
My question is what percent each system (fan coil and AHU)shares the cooling/heating load of the zone. How do you size fan coil and AHU?

Thanks

 

[Drazen]

it is up to designer to decide on it, based on load calculations and systems scenarios.

one thing is sure, if you are designer who wants to optimize solutions for your client, you will certainly not use "rule of thumb" for that.

i would say the most influencing factors are: relative load characteristics according to local climate magnitude of cooling and heating loads), ventilation loads relative to space loads, internal load sources.

 

[TamHD]

Hello,

The AHU should be large enough to deliver the correct amount of fresh/recirc air for the building/zone as per countries own fresh air requirements regulations, (UK is about 10 litres per person per second on average). The AHU tempers,(heats/cools depending on internal sensors, BMS set up, Energy strategies) and filters this air and it is delivered to the fan coil units in the building/zone. The extract from the building/zone is via the AHU and the heat is recovered from the space and either reused,(recirc with 10% fresh air), or discarded out of the building. These FCU's then further temper the air as to local requirements and deliver into local space, eg AHU 1 supplies filtered fresh air to Floors 1 - 3 at a temperature of 17c. Floor 1 office space west FCU 3 is being told to increase this air to 21c by the variable thermostat positioned in this area. Sizing is carried out by qualified design engineers and varies greatly from building to buidling. Mech vent is an art form.

 

[willard3]

There is no general answer to your general question.