Guest guest Posted September 25, 2006 Report Share Posted September 25, 2006 I am in the process of designing a ventilation system for a large metropolitan bus terminal. Most of the buses (I assume) have diesel engines. I am in the process of locating the air inlets and outlets. Does anybody know whether deisel exhaust is heavier or lighter than air at the same temperature? Thanks. Tom in St. Louis Quote Link to comment Share on other sites More sharing options...
Guest guest Posted September 27, 2006 Report Share Posted September 27, 2006 Tom - It depends on the constituent…diesel exhaust has many (SOx, NOx, Soot, VOCs). I was involved in a NIOSH project in which we looked at this a few years ago at the San Francisco bus terminal; Look for the NIOSH HHE report by Leo Blade (~1999). There is a ventilation design recommendation in that report. Call me if you have questions. __________________ Roegner, MPH, CIH Industrial Solutions Group, Inc. 1776 Mentor Avenue, Ste 225 Cincinnati, OH 45212 ph. fx. Diesel Exhaust I am in the process of designing a ventilation system for a large metropolitan bus terminal. Most of the buses (I assume) have diesel engines. I am in the process of locating the air inlets and outlets. Does anybody know whether deisel exhaust is heavier or lighter than air at the same temperature? Thanks. Tom in St. Louis Quote Link to comment Share on other sites More sharing options...
Guest guest Posted September 28, 2006 Report Share Posted September 28, 2006 Why would you assume that the temp of the exhaust would become the same as inside the terminal? The diesel exhaust will be very hot and therefore rise when it first leaves the exhaust pipe. It also has throw velocity due to the pistons pushing the combustion gas out of the engine exhaust ports. Some diesel buses have exhaust stacks above the height of the bus, some exhaust pipes are underneath and behind the bus. Will the terminal have a heating and/or cooling system serving the area where the buses are idling? This is an important consideration for energy efficiency and comfort with respect to the location of the exhaust vents. You would want to avoid short-circuiting of supply air to the building exhaust. I would think that there would not be time for these combustion gases to "stratify out" either way. Convective and mechanically driven air flow patterns would dominate the movement of the exhaust-laden air. How about creating laminar flow with terminal exhaust at or near the roof and clean outdoor (maybe tempered) makeup air entering at ground level where the people will be? The purpose of the exhaust ventilation is ensure that the people breathe cleaner air, isn't it? I don't think you would want to drag the diesel exhaust down to them with exhaust vents located near the breathing zone. Just my immediate thoughts on the options, Steve Temes , Right now, I am just trying to find out if the density of typical deisel exhaust is greater or less than air at the same temperature. If it is lighter than air, I will want to locate the exhaust vents high. If it is heavier than air, I may want to locate the exhaust vents low. Thanks. Tom in St. Louis Quote Link to comment Share on other sites More sharing options...
Guest guest Posted September 28, 2006 Report Share Posted September 28, 2006 , Right now, I am just trying to find out if the density of typical deisel exhaust is greater or less than air at the same temperature. If it is lighter than air, I will want to locate the exhaust vents high. If it is heavier than air, I may want to locate the exhaust vents low. Thanks. Tom in St. Louis > > Tom - It depends on the constituent.diesel exhaust has many (SOx, NOx, Soot, > VOCs). I was involved in a NIOSH project in which we looked at this a few > years ago at the San Francisco bus terminal; Look for the NIOSH HHE report > by Leo Blade (~1999). There is a ventilation design recommendation in that > report. Call me if you have questions. > > > > __________________ > > Roegner, MPH, CIH > > Industrial Solutions Group, Inc. > > 1776 Mentor Avenue, Ste 225 > > Cincinnati, OH 45212 > > > > ph. > > fx. > > > > Diesel Exhaust > > > > I am in the process of designing a ventilation system for a large > metropolitan bus terminal. Most of the buses (I assume) have diesel > engines. I am in the process of locating the air inlets and outlets. > > Does anybody know whether deisel exhaust is heavier or lighter than > air at the same temperature? Thanks. > > Tom in St. Louis > Quote Link to comment Share on other sites More sharing options...
Guest guest Posted September 28, 2006 Report Share Posted September 28, 2006 Tom: I don't think some of the responses to your questions have been well thought-out. Let me try to provide you with some guidance relative to ventilation systems I have designed. This said, the bottom-line is to provide a sufficient number of air exchanges, and locate make-up air supply-vents, to keep air within the bus terminal from becoming a problem. The trick is....define: problem. Question #1 - Is the terminal enclosed or relatively open? Question #2 - What are the climate control requirements? Is the terminal located in an extremely cold environment, therefore, is heating the make-up air relevant? Question #3 - Is the terminal used by the public, or just Metro staff? To ask if diesel exhaust is heavier/lighter than air " at the same temperature " is sort of odd. Combustion exhaust is, by nature, warmer than the surrounding air and buoyant. Diesel exhaust is a combination of particulate matter (i.e., the black stuff) and gaseous chemicals. The particulates are, more often than not, heavier than air, and will eventually settle with time. But they can remain airborne and buoyant due to thermal gradients of the exhaust plume. They are also " sticky " and will adhere to all surfaces. The gaseous chemicals are also, more often than not, heavier than air; but not all of them To specifically answer your question....Assuming that the exhaust has cooled to ambient temperatures, diesel exhaust is, as a whole, much heavier than air - particulates and gaseous components combined. Air is approx 1.3 mg/cc at O-degrees C and 1 atm. Based on this, go figure. Some gaseous components of exhaust (e.g., carbon monoxide) are lighter than air, others (e.g., carbon dioxide) are heavier. This said, don't get all excited and assume that all the CO will go the the ceiling. Given the air currents that buses induce, not to mention the building's ventilation system, most everything with stay well-mixed. I design ventilation systems in such facilities to achieve four to six air exchanges per hour - less if the facility is " open " architecture. This said, I have not had an opportunity to design a similar ventilation system in an extremely cold environment where heating would be required; this would significantly complicate things, and be more expensive, if the make-up air required heating prior to discharge. I also pay very close attention to WHERE I duct/discharge the make-up air. If the terminal is used by the public, I duct make-up air to where the public will be standing-waiting for buses. Essentially creating a " fresh air bubble " in that area and push the other stuff, e.g., smelly exhaust, elsewhere. I also design/locate exhaust fans in opposite areas to suck the smelly stuff away from the public. Be VERY careful where you located make-up air intakes and exhaust air discharges - give ample separation to these features!! This cannot be emphasized enuff! And don't discharge the exhaust where is can be re-entrained into a neighboring building - it may induce a claim based on professional negligence and 3rd-party harm. Also of merit....Be aware of stagnant air spaces, i.e., spaces that are not affected by the make-up air and/or exhaust air systems. These tend to be unhealthy spaces to work in due to accumulating contaminants. It is best to design a ventilation system to " sweep " the terminal with cross ventilation, and eliminate any stagnant air. Bottom line...Don't bother with densities or trying to figure out the lighter/heavier components to diesel exhaust. In my opinion, it is not all that relevant. Spend you time designing air exchanges, locating ducting for make-up/exhaust air, and provide air " sweeping " to eliminate stagnant air. It is much more effective. For what it is worth..... -- Geyer, PE, CIH, CSP President KERNTEC Industries, Inc. Bakersfield, California www.kerntecindustries.com > I am in the process of designing a ventilation system for a large > metropolitan bus terminal. Most of the buses (I assume) have diesel > engines. I am in the process of locating the air inlets and outlets. > > Does anybody know whether deisel exhaust is heavier or lighter than > air at the same temperature? Thanks. > > Tom in St. Louis > Quote Link to comment Share on other sites More sharing options...
Guest guest Posted September 29, 2006 Report Share Posted September 29, 2006 Tom If your system does not catch the exhaust before the temperature difference is small (the temperature is the same) you will get nothing but complaints. While it is still hotter it is lighter. Any scheme that does not catch it high, but locally, will fail. A former company that I worked for did a lot of work in this area and the above was their general conclusions. Jim H.. White SSC 4b. Re: Diesel Exhaust Posted by: "tom_engr123" mullt@... tom_engr123 Thu Sep 28, 2006 2:16 pm (PST) ,Right now, I am just trying to find out if the density of typicaldeisel exhaust is greater or less than air at the same temperature. Ifit is lighter than air, I will want to locate the exhaust vents high.If it is heavier than air, I may want to locate the exhaust vents low.Thanks.Tom in St. Louis Quote Link to comment Share on other sites More sharing options...
Guest guest Posted October 3, 2006 Report Share Posted October 3, 2006 Tom: The answer, relevant or not, is that the exhaust MW is very similar to that of air. Most of the diesel fuel is converted to CO2 and H2O. The molar concentration of H2O will slightly exceed that of CO2. There will be a very low concentration of CO and a low concentration of unused O2, to go along with the mostly unconverted N2. Don Schaezler tom_engr123 wrote: > > I am in the process of designing a ventilation system for a large > metropolitan bus terminal. Most of the buses (I assume) have diesel > engines. I am in the process of locating the air inlets and outlets. > > Does anybody know whether deisel exhaust is heavier or lighter than > air at the same temperature? Thanks. > > Tom in St. Louis > Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You are posting as a guest. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.