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nklr
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Norm Keller
- Posts: 712
- Joined: Thu Apr 01, 2004 7:48 am
some piping numbers
#ygrps-yiv-1028887321 blockquote.ygrps-yiv-1028887321cite {margin-left:5px;margin-right:0px;padding-left:10px;padding-right:0px;border-left:1px solid #cccccc;} #ygrps-yiv-1028887321 blockquote.ygrps-yiv-1028887321cite2 {margin-left:5px;margin-right:0px;padding-left:10px;padding-right:0px;border-left:1px solid #cccccc;margin-top:3px;padding-top:0px;} #ygrps-yiv-1028887321 .ygrps-yiv-1028887321plain pre, #ygrps-yiv-1028887321 .ygrps-yiv-1028887321plain tt {font-family:monospace;font-size:100%;font-weight:normal;font-style:normal;} #ygrps-yiv-1028887321 a img {border:0px;}#ygrps-yiv-1028887321 {font-family:Tahoma;font-size:12pt;} #ygrps-yiv-1028887321 .ygrps-yiv-1028887321plain pre, #ygrps-yiv-1028887321 .ygrps-yiv-1028887321plain tt {font-family:Tahoma;font-size:12pt;} I'm always trying to improve my understanding and "feel" for what happens with regards flows. A flow bench can absorb endless hours if one has the patience, but that's less the case these days. 
Some "numbers" I heard when talking with a journeyman who was installing a new condensing furnace in my parents' house was with regards venting of the combustion air. These are the furnaces which use plastic pipe to bring in combustion air from outside and to vent the combustion gasses. The exhaust temperature is not much more than room temperature because the gasses pass through a heat exchanger which passes heat from the combustion gasses (exhaust) into the air for heating the house. He mentioned that this furnace uses 2 inch plastic pipe and can run 60 feet to the outlet without excessive restriction/back pressure. More than about 60 feet and the furnace will not operate which I suppose is a safety practice based on monitoring pressure differential but didn't ask. A 45 degree elbow produces about the same restriction as does 5 feet of straight pipe. Using 3 inch pipe allows the venting length to reach 100 feet. I found these made some interesting factors on which to speculate. I do know from flow bench work that a 45 degree or other bend is much more restrictive than is a curve and that abrupt changes in size can introduce a vortex which can act as a large solid object in the exhaust. In other cases, an abrupt increase in diameter can be beneficial in both reducing restriction and in blocking reflected waves. Just thought it might be fun to throw that out there as others may have more refined observations. I've often found that someone in an unrelated area may provide more insight than those working there. Often the person who knows nothing about the system in question, simply doesn't recognize that they work with a similar system and have much more understanding of the principles. So, I'm fishing for that also. 
Some "numbers" I heard when talking with a journeyman who was installing a new condensing furnace in my parents' house was with regards venting of the combustion air. These are the furnaces which use plastic pipe to bring in combustion air from outside and to vent the combustion gasses. The exhaust temperature is not much more than room temperature because the gasses pass through a heat exchanger which passes heat from the combustion gasses (exhaust) into the air for heating the house. He mentioned that this furnace uses 2 inch plastic pipe and can run 60 feet to the outlet without excessive restriction/back pressure. More than about 60 feet and the furnace will not operate which I suppose is a safety practice based on monitoring pressure differential but didn't ask. A 45 degree elbow produces about the same restriction as does 5 feet of straight pipe. Using 3 inch pipe allows the venting length to reach 100 feet. I found these made some interesting factors on which to speculate. I do know from flow bench work that a 45 degree or other bend is much more restrictive than is a curve and that abrupt changes in size can introduce a vortex which can act as a large solid object in the exhaust. In other cases, an abrupt increase in diameter can be beneficial in both reducing restriction and in blocking reflected waves. Just thought it might be fun to throw that out there as others may have more refined observations. I've often found that someone in an unrelated area may provide more insight than those working there. Often the person who knows nothing about the system in question, simply doesn't recognize that they work with a similar system and have much more understanding of the principles. So, I'm fishing for that also. Who is online
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