Window Contacts / FCU Operations

Allison Wilson

Sustainability Director

Ayers Saint Gross

LEEDuser Basic Member

5 thumbs up

August 16, 2022

Hi there Hive Mind! Hope everyone's doing well and staying cool in the heatwave all over.

An engineer on one of my projects reached out about contact switches for operable windows that are empowered to shut down the associated FCU in dormitory bedrooms when the window is open. This functionality allows the FCU to run at something like 50F for freeze protection, but stops the FCU from running concurrent to when the window is open which would waste energy.

My engineer tells me ASHRAE90.1 has may indirect references to avoiding simultaneous heating and cooling, but they have not been able to find a specific reference pertaining to operable windows and/or window contact switches.

Is anyone aware of any specific requirements either in LEED's Minimum/Optimize Energy Performance language, ASHRAE90.1, or other energy codes that relate to this relationship between FCU operations and operable windows?

Thanks in advance,

Aley

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Casey Ross

Director of Sustainability

Lorax Partnerships, LLC

LEEDuser Basic Member

0 thumbs up

Tue, 08/16/2022 - 23:10

Hey Aley, I have some experience designing systems with these types of interlocks. ASHRAE 90.1 (looking at the 2016 version at least) has a section 6.5.2. which prohibits mechanical reheating or recooling, with some notable and common exceptions. ASHRAE 90.1 also has requirements for operable windows, but is generally limited to prescribing what minimum U-value, etc. they must be constructed to. In my experience, there is no specific requirements spelled out in either LEED or ASHRAE here. Psychrometrics, however, will tell us that in many climates, an open window mixed with an air conditioining system will generate a lot of wasted energy and uncontrolled moisture dripping out of the air. I'm also not certain that LEED would accept any modeled energy benefits of the system as you describe if opening the window would be user-controlled and not an automated process. Similar to window shading, if it's up to the users, you have to assume the worst.

Ramya Shivkumar

Director of Energy & Sustainability

Windward Engineers & Consultants

LEEDuser Basic Member

1 thumbs up

Wed, 08/17/2022 - 13:40

Hey Aley, Please confirm the ventilation strategy complies with ASHRAE 62.1 as well. I would look into how you are ventilating the space before deciding to shut down FCU. If ventilation is decoupled from FCU (i.e used for sensible cooling only) then its not a problem.