Our project is a major renovation to an existing college faculty office building with very low floor-to-floor heights. The lack of plenum space made air distribution ducts infeasible... however, all rooms have access to operable windows (the building was built in 1914, and was therefore designed for natural ventilation). Heating and cooling is provided by a 4-pipe fan coil in each room. Our application for IEQc7.1 is pending, because the LEED reviewer wants us to demonstrate that the fan coil units that serve the individual offices are designed to handle the ventilation loads with operable windows fully opened. Why would this be necessary? Isn't it safe to assume that an occupant will adjust/close the windows when thermal comfort falls outside the parameters? It seems to me that we should only have to demonstrate that the loads are met with the windows open to meet minimum ventilation requirements. Has anyone else run into a similar situation?

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Lindsay Austrom

Mechanical Engineer

Stantec

LEEDuser Premium Member

18 thumbs up

Thu, 05/02/2013 - 16:57

Eric, it sounds like your design is using the windows for natural ventilation and the fan coils for mechanical conditioning. Section 5.3 in ASHRAE Standard 55 outlines a method for using operable windows to naturally condition spaces, but sounds like it won't apply to your design. In that case, I think your fan coils must do the work to maintain thermal comfort conditions, including the heating/cooling/dehumidification loads from unconditioned ventilation air. The windows are for ventilation only, not conditioning. How much difference is there between the window "minimum opening for ventilation" and fully open? Is it clear to the occupants when or how much they should open the windows?

Anil Bhari

Min engineering inc

LEEDuser Basic Member

2 thumbs up

Tue, 08/06/2013 - 14:34

Eric, i am also in same boat. i am using operable windows for ventilation in apartments. do you know how to demonstrate it? Thanks anil

Eric Shamp

Associate Vice President

CannonDesign

LEEDuser Premium Member

55 thumbs up

Tue, 08/06/2013 - 16:18

Anil, we ended up abandoning the credit, since we were able to achieve Gold certification without it. I would have liked to push for a resolution, but time and fee just wouldn't allow it. Lindsay, here's how the occupants know when to open the window: it's when they feel stuffy and/or when the weather is nice, just like they did it in 1914 when the building was built. We complied with ASHRAE 62.1 using the natural ventilation floor/window ratio method. The rooms are all different: floor area, number & type of operable windows, so there's no consistency. In some rooms, there is a significant difference between minimum opening for ventilation and fully open. So, if the windows are fully open on the hottest day of the year, can the fan coil handle that load? Of course the answer is "no". The design team rightfully assumed that if the room is hot on the hottest day of the year with the window open, the occupant would close down the window and let the A/C do it's thing. The building is full of smart people -- college professors -- and we like to think they know what to do with an operable window. ;) Unfortunately, we can't "engineer" user discretion, so it won't pass muster with the LEED reviewer.

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