Hello all,
I have a question about occupancy schedules for energy models.
Generally the owner will provide peak occupancy numbers on a room-by-room basis; and a peak overall occupancy number for the entire building. Inevitably the room-by-room numbers will add up to significantly more than the overall building number.
Which numbers should be used for the energy model? Would you use the room-by-room number and scale them down with the occupancy schedule based on the overall occupancy?
Obviously, this has a significant impact on the results.
Thanks,
Brian Tysoe M.A.Sc., P.Eng., LEED AP
I typically apply an hourly fraction to each space occupancy whereby space
peak values would not coincide at the same hour, and if they do, they should
match the building overall count for the building. Similar to how you would
calculate external gains by exposure.
Arpan Bakshi
This is a very important point that is often forgotten in simulation
modeling. The computer is a strange object and if you tell the computer
to put one occupant for every 100ft2, then is does just that and the
related ventilation air and cooling (or heating).
I usually request the architect provide me with the occupation
calculations for the elevators and cafeteria and also the Fire Marshall
rating for building occupancy. These numbers are typically around 70% of
the simulation program occupants. The occupancy density in the program
and therefore be adjusted to match this.
How this could be interpreted in 90.1 I will leave up to any following
discussions?
Peter Simmonds, Ph.D.
The topic is kind of broad but I'll take a swing:
- The ideal "100% occupied" figures and scheduling to use are
those describing actual occupancy in an existing/future building. In
the real world, energy modelers generally can't get ahold of this
information for new construction. Real-world scheduling may be readily
available for schools and the like, however.
- The best "100% occupied" occupancy numbers in lieu of "real
world" would be those already used to develop the HVAC design loads - at
the minimum you know the modeled equipment capacities/airflows will be
sufficient for the resultant interior/ventilation loads. Your architect
may or may not be the person to talk to to get this information.
- When the mechanical designer's ventilation/occupancy figures
aren't handy either... a fire plan's space/exit capacity figures, while
inflated to a worst case for life safety purposes, might be okay in a
pinch if you don't have time to develop your own figures, but given
time...
- ...I would sooner develop my own numbers (play the part of
the missing ME) using the furniture plans and occupancy density figures
(P/1000SF) per ASHRAE Std 62/62.1. Such figures are often built into
load calc and energy modeling programs for the user's convenience, and
those are a good starting point to refine/round using other resources at
hand.
90.1 Appendix G is (thankfully) fairly simple and "hands-off" when it
comes to how occupancy/scheduling should be handled. As long as
everything is identical between baseline and proposed, everyone on the
reviewer side should be happy, so the means by which we approximate
maximum occupancies and hourly fractional scheduling is pretty much up
to the modelers. This is one of those "self-policing" approaches within
90.1: Skewing the occupancy/scheduling too far in either direction is
not in the best interest for a LEED model, as you will either (A) have
an overly-vacant building with fewer loads for your more-efficient
systems to handle, decreasing the building performance %, or (B) have an
over-occupied building resulting in loads that cause unmet hours the
proposed equipment capacities can't handle.
NICK CATON, E.I.T.
Hello all,
The ?best case scenario? is to match the room-by-room peak occupancy numbers
with the total building ones by adjusting hourly schedules which would be
fairly complicated to ensure the total building occupants can be distributed
in different rooms but remain the same all the time.
In reality, the objectives of estimating either room-by-room peak numbers or
overall building numbers vary according to disciplines. Architects may have
concerns over spatial constrain while mechanical engineers will worry about
system size, peak loads and energy requirements. When it comes to modeling,
my understanding is to see the issue mainly from mechanical design point of
view:
- The room-by-room peak occupancy numbers govern ventilation rate and
size of cooling system. Managing to ask mechanical designers to verify the
numbers provided by architects and running the load calculation with respect
to these numbers.
- On the other hand, the overall building numbers, as one of internal
heat sources, have impact on the overall building energy requirements.
Architects or building owners may have better idea of how many they would be
and there is little room to change the figures by engineers. Running energy
simulation with respect to these numbers. Scale the room-by-room numbers
down to match the overall building numbers is acceptable at this point.
Regards,
Cheney