One of the most rewarding experiences in the Passivhaus community has been the very open and collegial nature of the relationships between practitioners. I find folks willing to share ideas, best practices, mistakes and encouragement with an open heart and mind. To that end I regularly receive inquiries from colleagues and regularly inquire of colleagues.
I recently had a colleague inquire about installing a commercial grease hood in a Passivhaus (aka Passive House). After I wrote the response, I realized that other folks may also be interested in my experience doing this. So here is the body of the text of my reply. I hope it may be of help:
OK. Passivhaus commercial kitchen, yes I have done it, first in the world, that I know of, that is in the PH envelope. (See the Hillel Center Passivhaus case study.) In the past folks have kept the kitchen out of the PH envelope, but of course I am too stubborn to do that.
SO, the basic two things are air tightness when not in use and heat recovery when in use. Simple solutions are dampers for the first and heat exchanger for the second, but here are the issues:
- CODE! – I am not sure which building code you are under, but we are under the International Mechanical Code. The IMC does not like dampers in grease hood duct. To get around this you must use a UL listed damper that is integral to the hood and not separate in the duct. You will need to coordinate this with you hood manufacturer and have the damper drawn as part of the hood assembly. Both Halton and CaptiveAir make UL listed dampers for this.
- CODE! – IMC also does not allow for dampers in hoods over gas appliances. Well, the first thing is to attempt to convince the client to use electric appliances (induction ranges, etc). One nice thing about this is that it cuts the interior heat gain in the kitchen considerably because the gas appliances give off a lot of waste heat. If, however, you are not successful doing this, then you need to use appliances that do not have standing pilot lights and then interlock the electronic ignition of the appliances with the hood controls. THEN, you will need to convince your Mechanical Inspector that this is an acceptable solution and meets the intent of the code, because, while it does meets the intent, it is not in the code. So the Inspector must agree.
- PHYSICS – Dampers in grease hoods require more maintenance because there are more surfaces to hold grease.
- PHYSICS – Although in-duct heat exchangers are available, they are a losing proposition because they will cause a huge amount of maintenance down the road. Two simple, not as efficient, but acceptable methods of heat exchange are water or air jacket, duct in duct arrangement so the grease-laden air is unobstructed by the heat exchanger.
- DESIGN – Keeping primary energy in mind, there are now variable speed controls and air monitored hoods that will lower the primary energy of the hood.
- MANUFACTURE – As far as I can tell, the folks that make these dampers make them custom by the order and are not held to very close tolerances. We specify the tolerances we want and have actually had to send them back for re-manufacture. As a side note, on our first damper we added welded stops to make up for the imprecise manufacture, but had to remove the hood because (according to our inspector) we modified the UL listed equipment and so we no longer could consider it UL listed. (That was an expensive lesson.)
- INSTALLATION – You will need to maintain access to the damper actuator, which can be tough. I recommend installing the dampers on the top of the hood and holding the hood below the Passivhaus envelope so it is easily accessible.
I hope this answers some questions for all of you considering grease hoods in Passivhaus projects.