cooling load calculation question...

[sfcontrols]

Hi Guys

First to all, I'm a toddler in HVAC design..but I have a question..I'm sure you can help me...
I'm reviewing a Hotel project where there is main lobby at ground floor, and then, there are four levels of corridors
above (2nd to 5th) where in both side of the corridors are "open to below"..in other words, you can see the main lobby from above....one wall of the lobby is glass up to 5th level..and the "corridors" are 20'apart of glass wall...
The engineer has specified 5 AHU'S (one per floor) with the same capacity...(all equals)...and supplying air with side wall diffuser to both side of the corridors to "open to below" area.. ...(from 2nd floor to 5th floor) my questions is:
When you make the cooling load calculation...Have you make it for each floors separate.. including the "open to below" area..and it's associated wall glass...(lights,o/a, etc)...for each floors?...
Is't a good practice to supply air to the "open to below" area..where nobody it's going to be there?
What Ahu's shall take the wall glass load?..
How you would make it?

 

[Vellum]

That is a tricky question that I don't think anyone could answer without looking at a drawing set. Things to keep in mind is that heat rises so the corridor at the top will probably be hotter then the other floors and that designing around a space with a lot of glass and air distribution is not an easy art form. I've seen some bad outcomes.

 

[GMcD]

Vellum: "Heat" doesn't rise - warm air does though. What SFControls is looking at is a typical blind "all mixing" approach to HVAC design for a large atrium space where the load calculation just takes into account a full mixing situation and neglects the stratification issues - that would take a few more steps of CFD modeling to do properly.

If the HVAC design was to be approached from the point of view of heating and cooling the people in the space, rather than heating and cooling the whole space, I'm sure that equipment sizes would be rationalized down as well as the energy requirements. Some localized cooling along the upper exposed corridors will be needed and the only large cooling load would be what is required for the people on the ground floor where most of the comfort load will be.

The glass load needs to be dealt with as a separate zone - I don't know what climate zone this project is in, but a lot of the heat gains in a large open atrium space can be de-rated, so to speak, by using warm air stratification to your advantage, so only the lowest level gets enough cooling to deal with people loads and whatever solar load hits the floor and warms up the floor.