Indeed SAK, very good point.
I agree, this is a very good application for Displaced Ventilation. Interesting approach.
This is what these forums should be about - people should volunteer ways to solve the problem differently, better yet, eliminate the problem instead of improving the proposed solution by the OP.
I'd add to your suggestion if I may - One could supply air at much higher temperature (say 63 to 64) and even higher (as much as 70F) during low-occupancy (which is most of the time, i.e no competition), thus taking advantage of longer hours of air-side economizer and ignore lighting and roof from the load along the way. Adding cool roof technology reduces load even more.
You'd still combine with Total enthalpy recovery to your minimum fresh air intake
Now throw in some pre-cooling control method for pre-determined high occupancy periods, and you have removed the fear of equipment down-sizing.
If still afraid of down-sizing - One could up-size somewhat ductwork and have space for additional equipment to supplement the system (IF if happens to be undersized or fearful or record days).
If this is a single story facility, one could easily add natural ventilation or a combination of (PRV's on roof and open windows and doors between 70 and 75 outdoor temperature) and still get adequate comfort.
I'd look into hydronic in-floor radiant heat for heating if this is a new facility and it is in a cold climate. Solar thermal using low-grade heat (90 - 110) for in-floor radiant heat will go a long a way towards reducing heating costs.
Let me throw-in a different approach - if this is hot and dry climate, this space would be a very good application for evaporative cooling and you have removed 90% of air-conditioning - you don't even need to down-size since your energy (water) consumption is in direct relation with outdoor wet-bulb.
There is a huge opportunity for energy savings - you could look at possibly achieving LEED Platinum for such an application.
FEAR is what makes people do stupid things, such as over-sizing in high occupancy spaces. Fear that it may not work, what if we have record days, I don't want to get sued, etc.. One could get numbers on paper and a common sens presentation to owner and have him sign-off and be ready to add equipment IF it does not work. Have easy solutions to remove the fear as indicated above. Any owner would jump at a solution reducing his first cost, operating costs and improve air quality and comfort.
