Guest guest Posted August 16, 2010 Report Share Posted August 16, 2010 Hi Tug, I've been reading on and off some of these posts... so forgive me if any of this has already been said. If your crawlspace is musty (active microbial digestion = wet w/ mold growth) and you're sensitive to mold, and you seem worse off when the home is warm in the afternoon.... put the clues together for a possible hypothesis.... I recently had a client who swore she could smell mold, but only at night. I looked where she said the mold smell was and found no evidence of moisture intrusion. I crawled under the home and found excessive moisture on the soil and a visible white fluff I assume was microbial growth. I was fully suited up under the home, but before going in I did smell the " musty " odor associated with mold growth. So I had found a potential source.... but what was the pathway? Inside the home I opened a hallway closet that contained a furnace. Bam! Musty smell. There was no visible evidence of moisture damage in this closet, but there was an opening directly down to the crawlspace. I didn't have to use a manometer to tell that air was flowing up from the crawlspace directly into this closet - I could feel the draft and smell the crawlspace! While under the home I noticed that not all plumbing/electrical penetrations had been sealed, and it appeared the fiberglass insulation around some of the ducts was acting as a filter (dark spots around flex duct seams). Putting it all together. This lady had mold growing under the home (source), tremendously leaky ducts and some direct openings to the crawl (pathway), and when the temperature differentials were right (cold below/outside, warm in home, and warmer in attic) the stack effect of hot air rising provided the force to pull the pollutant into the home. Some moisture mitigation under the home, duct sealing, running a duct to supply air to the furnace (instead of a gaping hole in the floor to the crawl), and finally some extensive air sealing.... and she's feeling better and no longer complaining of smelling the musty odor. Remember that mold doesn't have to smell (be wet or growing) to be harmful. Perhaps the stack effect is pulling air into your home from the crawlspace? -- Stadtner Healthy Building Inspections www.HBILLC.com Quote Link to comment Share on other sites More sharing options...
Guest guest Posted August 16, 2010 Report Share Posted August 16, 2010 Stack effect in winter is hot air moves up but in summer moves down. Hot air moves toward cold air regardless of whether it is up or down in the stack. Thinking hot air rose caused alot of confusion in my home. See 'home sealers association' for diagram. Stack effect is so frequently believed to be 'hot air rising' that some people refer to it as 'reverse stack effect' but it is really not. Its a law of thermdynamics. High energy moves toward low energy. > > Hi Tug, > > I've been reading on and off some of these posts... so forgive me if any of > this has already been said. > > If your crawlspace is musty (active microbial digestion = wet w/ mold > growth) and you're sensitive to mold, and you seem worse off when the home > is warm in the afternoon.... put the clues together for a possible > hypothesis.... > > I recently had a client who swore she could smell mold, but only at night. I > looked where she said the mold smell was and found no evidence of moisture > intrusion. I crawled under the home and found excessive moisture on the soil > and a visible white fluff I assume was microbial growth. I was fully suited > up under the home, but before going in I did smell the " musty " odor > associated with mold growth. So I had found a potential source.... but what > was the pathway? > > Inside the home I opened a hallway closet that contained a furnace. Bam! > Musty smell. There was no visible evidence of moisture damage in this > closet, but there was an opening directly down to the crawlspace. I didn't > have to use a manometer to tell that air was flowing up from the crawlspace > directly into this closet - I could feel the draft and smell the crawlspace! > > While under the home I noticed that not all plumbing/electrical penetrations > had been sealed, and it appeared the fiberglass insulation around some of > the ducts was acting as a filter (dark spots around flex duct seams). > > Putting it all together. This lady had mold growing under the home (source), > tremendously leaky ducts and some direct openings to the crawl (pathway), > and when the temperature differentials were right (cold below/outside, warm > in home, and warmer in attic) the stack effect of hot air rising provided > the force to pull the pollutant into the home. > > Some moisture mitigation under the home, duct sealing, running a duct to > supply air to the furnace (instead of a gaping hole in the floor to the > crawl), and finally some extensive air sealing.... and she's feeling better > and no longer complaining of smelling the musty odor. Remember that mold > doesn't have to smell (be wet or growing) to be harmful. > > Perhaps the stack effect is pulling air into your home from the crawlspace? > > -- > Stadtner > Healthy Building Inspections > www.HBILLC.com > > > Quote Link to comment Share on other sites More sharing options...
Guest guest Posted August 17, 2010 Report Share Posted August 17, 2010 Hi Barb (and Tug), I will respectfully disagree about warm air moving downward in the summer... All other things being equal, that is to say if there are no other forces working in the system, hot air (less dense) will rise compared to cold air (more dense). Yes, there will be some mixing and transferring of heat energy where the two air masses meet. But warm air does rise - there's really no scientific question about that. It's why hot air balloons work. The same principles of thermodynamics are found in lake water stratification. If there is nowhere for the heat to escape there will become stratification - such as what you may feel toward the ceiling when you're reaching to change a lightbulb. If there is a place for warm air to escape out the top it will create a draft - just like a chimney (or smoke 'stack'), and this will draw cooler air into the system (from somewhere) and up into the chimney. In my world this is a well understood and thoroughly researched topic. While its effects are less dramatic in the summer, the stack effect still occurs... and due to the temperature differential requirements the force is more noticeable during the evening hours. In the eight years I've been working with sustainable design/build teams - this has always been referred to as the " stack effect. " Here are some non-profit and governmental resources referring to the phenomenon for those interested in learning more: http://en.wikipedia.org/wiki/Stack_effect http://www.epa.gov/iaq/homes/hip-glossary.html http://www.epa.gov/iaq/schools/tfs/guide2.html http://www.wbdg.org/resources/naturalventilation.php - > > Stack effect in winter is hot air moves up but in summer moves down. Hot air moves toward cold air regardless of whether it is up or down in the stack. Thinking hot air rose caused alot of confusion in my home. See 'home sealers association' for diagram. Stack effect is so frequently believed to be 'hot air rising' that some people refer to it as 'reverse stack effect' but it is really not. Its a law of thermdynamics. High energy moves toward low energy. > Quote Link to comment Share on other sites More sharing options...
Guest guest Posted August 17, 2010 Report Share Posted August 17, 2010 (and Tug), Stack effect got its reputation of hot air rising before there was air conditioning, keeping heat inside was the goal and challenge and so hot air rising out of roof was main concern. Air conditioning has changed all that but little notice has been given to it. 2.) The effect is less in summer of heat sinking due to less temperature differential than in the winter but it still takes place. 3.) In summer hot air is heavier due to all the humidity it is carrying. 4.) If you belong to indoor air q group ,talk to Jim White about it. I will also provide links in a separate posting. > > Hi Barb (and Tug), > > I will respectfully disagree about warm air moving downward in the summer... All other things being equal, that is to say if there are no other forces working in the system, hot air (less dense) will rise compared to cold air (more dense). > > Yes, there will be some mixing and transferring of heat energy where the two air masses meet. But warm air does rise - there's really no scientific question about that. It's why hot air balloons work. The same principles of thermodynamics are found in lake water stratification. If there is nowhere for the heat to escape there will become stratification - such as what you may feel toward the ceiling when you're reaching to change a lightbulb. > > If there is a place for warm air to escape out the top it will create a draft - just like a chimney (or smoke 'stack'), and this will draw cooler air into the system (from somewhere) and up into the chimney. In my world this is a well understood and thoroughly researched topic. While its effects are less dramatic in the summer, the stack effect still occurs... and due to the temperature differential requirements the force is more noticeable during the evening hours. > > In the eight years I've been working with sustainable design/build teams - this has always been referred to as the " stack effect. " Here are some non-profit and governmental resources referring to the phenomenon for those interested in learning more: > > http://en.wikipedia.org/wiki/Stack_effect > > http://www.epa.gov/iaq/homes/hip-glossary.html > > http://www.epa.gov/iaq/schools/tfs/guide2.html > > http://www.wbdg.org/resources/naturalventilation.php > > - > Quote Link to comment Share on other sites More sharing options...
Guest guest Posted August 17, 2010 Report Share Posted August 17, 2010 Links to hot air sinking, nicknamed 'reverse stack effect' but actually is 'stack effect' because reasons for it are the same, air is doing the same thing: hot air is moving toward cold air, humid air toward dry air, high pressure toward low pressure, etc. http://www.trane.com/commercial/library/vol31_2/index.asp , http://www.grc.nasa.gov/WWW/K-12/airplane/thermo0.html , PAGE 185, Figure 2: http://customer.honeywell.com/techlit/pdf/77-0000s/77-E1100.pdf Next one, PG 36, Figure 5, paragraph " The Stack Effect " , see last sentence: http://epb.lbl.gov/publications/energy_eff_ventilation.pdf Also this one that I have posted before: http://www.airsealers.com/ME2/Default.asp > > Hi Barb (and Tug), > > I will respectfully disagree about warm air moving downward in the summer... All other things being equal, that is to say if there are no other forces working in the system, hot air (less dense) will rise compared to cold air (more dense). > > Yes, there will be some mixing and transferring of heat energy where the two air masses meet. But warm air does rise - there's really no scientific question about that. It's why hot air balloons work. The same principles of thermodynamics are found in lake water stratification. If there is nowhere for the heat to escape there will become stratification - such as what you may feel toward the ceiling when you're reaching to change a lightbulb. > > If there is a place for warm air to escape out the top it will create a draft - just like a chimney (or smoke 'stack'), and this will draw cooler air into the system (from somewhere) and up into the chimney. In my world this is a well understood and thoroughly researched topic. While its effects are less dramatic in the summer, the stack effect still occurs... and due to the temperature differential requirements the force is more noticeable during the evening hours. > > In the eight years I've been working with sustainable design/build teams - this has always been referred to as the " stack effect. " Here are some non-profit and governmental resources referring to the phenomenon for those interested in learning more: > > http://en.wikipedia.org/wiki/Stack_effect > > http://www.epa.gov/iaq/homes/hip-glossary.html > > http://www.epa.gov/iaq/schools/tfs/guide2.html > > http://www.wbdg.org/resources/naturalventilation.php > > - > Quote Link to comment Share on other sites More sharing options...
Guest guest Posted August 17, 2010 Report Share Posted August 17, 2010 Moist air will move to dry air with a greater force than hot to cold. > > > > > > Quote Link to comment Share on other sites More sharing options...
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