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Diversity Factor and Peak Load Vs Block Load

Diversity Factor and Peak Load Vs Block Load

(OP)
Hi All,

I am aware of the definitions of PEAK load and BLOCK load. Would anyone please suggest me when to use peak load and when to use block load?

I am designing a commercial office building. The office has 16 systems. Each system has 12 zones and each zone has 2 space associated with it. I have also calculated the individual SPACE PEAK LOADS for the office with the following scheme:

No of spaces/zone: 2;
No. of zones/system: 12;
Total no. of spaces: 192;
Total no. of zones: 96;
Total no. of systems: 16; (All 16 are similar)

System Type: Chilled Water AHU;
Zone: VAV w/ local thermostat control (NO REHEAT);

Central Plant: Air-Cooled Chillers;

Now, to calculate the total load of the office area/to size the chillers, should I go with the sum of peak load estimate or with the block load estimate?

Would there be any DIVERSITY FACTORS to be considered? If so, please advice me on how to choose the DIVERSITY FACTORS?

Please do guide me on this regard. Please do reply for any clarifications.

Thanks in advance for the support.

RE: Diversity Factor and Peak Load Vs Block Load

2
Here's the thing to remember, the earth rotates.

I know this is basic knowledge, but what it means for a large office building is that while one side/area is getting a lot of sun, another is not. This is something that you need to take into account when sizing HVAC equipment, especially VAV systems. Each zone will have different Peak times, east zones will reach peak conditions before west zones.

Beacause you have zones that peak at different times, there is no need for the AHU to be sized to handle ALL zone peak conditions. Your AHU need only handle the peak of the zones that when summed provide the greatest AHU peak load. Same thing goes for chillers with multiple AHU's.

I only ever do a block load at the start of a project when I need a ballpark estimate of AHU/Chiller sizes.

On the issue of Diversity; Use for space load calculations, i.e. the number of people in the office. Some people get to the office early while others stay late. Using Diversity for AHU/Chiller sizing is mute due to the above.

Programs like Carrier HAP and Trane Trace take this into account and will give you the needed sizes of AHUs and chillers.

RE: Diversity Factor and Peak Load Vs Block Load

(OP)
Thank you @dbill74.

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