The 5,000 [ft.sup.2] (465 [m.sup.2]) cafeteria had a design occupancy
of 200 students at the time of the study.
* Design occupancy
sensor network for real-time HVAC operation in real buildings;
"As carbon dioxide levels rise, it indicates that the ventilating system is malfunctioning or the design occupancy
of the room is being exceeded.
Since population contributes to ventilation demand, demand-controlled ventilation (DCV)--defined as "a ventilation system capability that provides for the automatic reduction of outdoor air intake below design rates when the actual occupancy of spaces served by the system is less than design occupancy
" --offers a means to ensure adequate outdoor airflow (OA) for acceptable IAQ while reducing energy consumption at part-load conditions.
This replaces the usual high flow based on maximum design occupancy
According to ASHRAE 62.1 User's manual, the breathing zone outdoor air flow rate at design occupancy
and minimum outdoor air rate under steady-state conditions are shown in the following equations:
* The required C[O.sub.2] concentration at the design occupancy
[C.sub.z-design] is determined by Equation 3 and using [P.sub.z] at design occupants ([P.sub.z-design]).
Relative to design occupancy
levels versus actual real-time occupancy, we have two observations.
* The required fresh air based on the design zone population [V.sub.oz-design] is determined by Equation 1 and using [P.sub.z] at the design occupancy
The airflow rate per square foot of building floor area is based on the design occupancy
density and the required flow rate per person, adjusted to reflect the air-distribution system used.
In addition, as it is costly and difficult (but not impossible) to estimate accurately the actual occupants in each space, the standard procedure is mostly based on the design occupancy
profile, leading to over-ventilate the spaces yielding less than design occupants and consequently waste of energy.
The article does not attempt to specify "a single number that does not change with occupancy" or "that one should use a fixed C[O.sub.2] level and that the cfm/person never changes for a given room," as his letter states, but rather simply the upper limits of C[O.sub.2] to reasonably expect for a given space if designed according to the ventilation rate procedures of Standard 62.1 and at default design occupancy