cooling load Diversity

[BECE]

Hi all
Im new here i just joined today after using the forum for years as a spectator.
I just wanted to find out if there a methodical way of calculating cooling load system diversity to keep the my condenser size within reasonable size.

Say the sum of peak loads is 100kW and i want to apply a 120-130% system diversity drop the size a little how do i go about it?.
If the load was dependent on facade orientation only then i guess it would be somewhat easier but the building is shortstays so people come and go randomly and i cant seam to think of a methodical way of justifying the system diversity that i want to apply.

I am worried that if guestimate it and thinks dont quite pan out as per my guestimate, the system will be undersized.
Thanks in advance for your help

 

[MintJulep]

the sum of peak loads is 100kW and i want to apply a 120-130% system diversity drop the size

This statement does not make sense.

Regardless, the generalize approach to load diversity is:
Characterize each load vs time.
Look at the sum of each load vs time.
Make an engineering judgement.

Although individual people often appear to behave randomly a sufficiently large population almost always behaves in a predicable way.

Businesses close at the same time every day, trains and airplanes operate on schedules, events usually start on the hour or half-hour, people have lunch at lunchtime, etc.

Your job is to find the stimuli that drive the pattern for your particular building.

 

[Ziggypump]

Utilizing "Sum of Peak Loads" will already over size your system. Depending on the number of spaces, exterior wall placements, space usage; peak loads will occur at differing times of the day. Lunch rooms would peak around noon, offices can peak anywhere between 1:00 and 4:00 typically (exterior forces really push this one) an office facing the east could peak at around 11:00 while an office on the West could peak around 4:00, and a classroom's peak will be affected by the school year (no school in summer).

The West vs. East frontages are the major player. a West facing office could peak at 11:00 am while the East facing office only requires 40% of its peak capacity at this time. While in reverse, the East office peaks at 4:00 while the West facing office only requires 60% of its peak capacity (all of these numbers are estimated). If utilizing Peak loads your system would be oversized by approximately 50% (assuming peak load numbers are the same, but they never are), and this is just a hypothetical condition.

I agree with MintJulep, you need to divine the buildings schedule - Ask questions. There are way too many variables to just throw a safety factor here.

PS.: Code calls for not over sizing the HVAC system, and while it's rare, code officials have been known to ask for calculations.

 

[Drazen]

For cooling load you don't apply diversity factor but you calculate it.

If you have peak loads that should mean you have hourly loads as well, and you should summarise your loads for each hour, find largest sum, and that would make your diversity.

 

[BECE]

Thanks guys, I appreciate your feedback.

 

[GT-EGR]

In addition to the solar load diversity, which it sounds like you know how to factor in - another somewhat mathematic way to come up with diversity is just by understanding how all your spaces will be used throughout a day, and then picking the busiest simultaneous point in time. If people are in their offices they probably aren’t in the breakroom, if people are in conference rooms they probably aren’t all in their offices, and then you can kindof look at the loads of the outlier spaces and how they compare to your total and from there you can kindof see a diversity factor. Another way is to look at the amount of chairs you factored into all your space loads, and compare it to the full time equivalent occupant count for the floor.

 

[willard3]

What the diversity is will also depend upon system choice, ie, heat pumps have no diversity on start up after set-back.