A reader writes:

I was researching natural ventilation for a project and came across your web site. The project will use waste heat from a power plant, in the form of cooling tower water, for use in a radiant floor heating system. We are also trying to incorporate natural ventilation. My primary concerns include air filtration, as the spaces include food processing, and the limitations of the natural ventilation system during the winter months. I was wondering if you have any experience with high intakes ducted to a location low in the space or filtration (to eliminate road dust problems) and with winter control over the system. I'm familiar with the standard design elements of a naturally ventilated building.

-- chris schaffner (chris@greenengineer.com), February 20, 2002

Answers

Unfortunately, I have no naturally ventilated buildings in my portfolio. I'm working on a couple of mixed mode buildings, but they are all designed with full heating & cooling systems to pick up the peak loads.

You may already be familiar with a great resource I've found. It's the CIBSE Applications Manual AM10:1997 - Natural Ventilation in Non- Domestic Buildings (CIBSE is short for Chartered Institution of Building Services Engineers, the UK equivalent of ASHRAE). I highly recommend it.

I don't have any particular experience with the questions you mention, but I'll give you my opinion anyway.

CIBSE recommends the use of trickle ventilators for minimum winter ventilation, 400 mm2/m2 of floor area minimum, located high in the space, to minimize cold drafts. These can be incorporated into the window frame, or similar. This seems to work in office spaces. I suppose one could put some kind of filter media into these, although you'd have to increase the opening size, to get the same airflow at a higher pressure drop.

Another possibility is some kind of intermediate space between the food processing area and the outdoors, which would allow non- mechanical air movement, but might slow air velocities enough to let "big chunks" settle out before entering the processing area.

Having said that, I think your best bet in a food processing environment is a more standard HVAC system, with an appropriate level of filtration. Depending on what's being processed, I'd think you would want to be able to control possible contamination sources more carefully than you might be able to with a strict natural vent system.

-- chris schaffner (chris@greenengineer.com), February 20, 2002.