Guest guest Posted February 24, 2006 Report Share Posted February 24, 2006 Ian, Right you are. However, there is also a default value of 17 cfm/person based on an assumed occupant density of 5 persons/1000 s/f for office spaces. I usually say "should be about 15-20 cfm/person" when I perform ventilation assessments using CO2 measurements (not for engineering design purposes). If levels are elevated, further assessment of the HVAC system design and operation is indicated (unless I can make the levels come down by switching the T-stat to "fan on"). Steve Temes In some recent posts over the last few weeks I've seen some outdated numbers being thrown around for ASHRAE ventilation rates. ASHRAE no longer has a 20 cfm/person ventilation rate for office spaces. The rate is now broken down into cfm/person and cfm/square foot. The current standard is only 5 cfm/person and 0.06 cfm/SF. You add the two together. See ASHRAE 62.1-2004 When dealing with homes, it's best to reference ASHRAE Standard 62.2- 2004. Their recommendations for a standard 2000 SF home with 4 bedrooms is 57.5 cfm of outdoor air if you do the math. These have been around for a while so everyone should update their libraries. Just bein' an engineer! Ian Cull, PE, CIE Quote Link to comment Share on other sites More sharing options...
Guest guest Posted February 24, 2006 Report Share Posted February 24, 2006 In some recent posts over the last few weeks I've seen some outdated numbers being thrown around for ASHRAE ventilation rates. ASHRAE no longer has a 20 cfm/person ventilation rate for office spaces. The rate is now broken down into cfm/person and cfm/square foot. The current standard is only 5 cfm/person and 0.06 cfm/SF. You add the two together. See ASHRAE 62.1-2004 When dealing with homes, it's best to reference ASHRAE Standard 62.2- 2004. Their recommendations for a standard 2000 SF home with 4 bedrooms is 57.5 cfm of outdoor air if you do the math. These have been around for a while so everyone should update their libraries. Just bein' an engineer! Ian Cull, PE, CIE Chelsea Training www.invironment.com www.LabComparisons.com Quote Link to comment Share on other sites More sharing options...
Guest guest Posted February 24, 2006 Report Share Posted February 24, 2006 Dear Ian: If the modification to the ASHRAE minimum recommended ventilation rate to achieve " acceptable " IAQ now includes a term that is based on square footage of the space being ventilated, I ask if the intent of this change is to address the air contaminants off-gassing from the furnishings, and since this off-gassing occurs on a 24/7 basis, should the ventilation minimum recommendation be provided on a 24/7 basis as well? What I'm seeing is aggressive ventilation rates being provided during peak occupancy, on the order of 24 cfm person of outdoor air delivered. But thev limited hours of operation of this ventilation provided in a tight building leaves a residual of bioeffluents, and presumably air contaminants off-gassed during the overnight interval, that persist until occupancy the next morning. In terms of good engineering practice, shouldn't a complete flushout of the previous day's bioeffluents be achieved overnight, so the building's air doesn't seem stale upon reentry by people the next day? Does ASHRAE deal with this issue? Sincerely, W. Bearg, PE, CIH Building Scientist Concord, MA -- Director of IAQ Programs AIRxpert Systems, Inc. www.AIRxpert.com -------------- Original message ---------------------- In some recent posts over the last few weeks I've seen some outdated numbers being thrown around for ASHRAE ventilation rates. ASHRAE no longer has a 20 cfm/person ventilation rate for office spaces. The rate is now broken down into cfm/person and cfm/square foot. The current standard is only 5 cfm/person and 0.06 cfm/SF. You add the two together. See ASHRAE 62.1-2004 When dealing with homes, it's best to reference ASHRAE Standard 62.2- 2004. Their recommendations for a standard 2000 SF home with 4 bedrooms is 57.5 cfm of outdoor air if you do the math. These have been around for a while so everyone should update their libraries. Just bein' an engineer! Ian Cull, PE, CIE Chelsea Training www.invironment.com www.LabComparisons.com Quote Link to comment Share on other sites More sharing options...
Guest guest Posted February 24, 2006 Report Share Posted February 24, 2006 Building codes (IBC) still use 20 CFM as does the ACCA/ANSI Manual J design criteria. Tony ........................................................................... " Tony " Havics, CHMM, CIH, PE pH2, LLC PO Box 34140 Indianapolis, IN 46234 cell 90% of Risk Management is knowing where to place the decimal point...any consultant can give you the other 10%â„ This message is from pH2. This message and any attachments may contain legally privileged or confidential information, and are intended only for the individual or entity identified above as the addressee. If you are not the addressee, or if this message has been addressed to you in error, you are not authorized to read, copy, or distribute this message and any attachments, and we ask that you please delete this message and attachments (including all copies) and notify the sender by return e-mail or by phone at . Delivery of this message and any attachments to any person other than the intended recipient(s) is not intended in any way to waive confidentiality or a privilege. All personal messages express views only of the sender, which are not to be attributed to pH2 and may not be copied or distributed without this statement. ASHRAE Ventilation Rates In some recent posts over the last few weeks I've seen some outdated numbers being thrown around for ASHRAE ventilation rates. ASHRAE no longer has a 20 cfm/person ventilation rate for office spaces. The rate is now broken down into cfm/person and cfm/square foot. The current standard is only 5 cfm/person and 0.06 cfm/SF. You add the two together. See ASHRAE 62.1-2004 When dealing with homes, it's best to reference ASHRAE Standard 62.2- 2004. Their recommendations for a standard 2000 SF home with 4 bedrooms is 57.5 cfm of outdoor air if you do the math. These have been around for a while so everyone should update their libraries. Just bein' an engineer! Ian Cull, PE, CIE Chelsea Training www.invironment.com www.LabComparisons.com FAIR USE NOTICE: This site contains copyrighted material the use of which has not always been specifically authorized by the copyright owner. We are making such material available in our efforts to advance understanding of environmental, political, human rights, economic, democracy, scientific, and social justice issues, etc. We believe this constitutes a 'fair use' of any such copyrighted material as provided for in section 107 of the US Copyright Law. In accordance with Title 17 U.S.C. Section 107, the material on this site is distributed without profit to those who have expressed a prior interest in receiving the included information for research and educational purposes. For more information go to: http://www.law.cornell.edu/uscode/17/107.shtml. If you wish to use copyrighted material from this site for purposes of your own that go beyond 'fair use', you must obtain permission from the copyright owner. Quote Link to comment Share on other sites More sharing options...
Guest guest Posted February 25, 2006 Report Share Posted February 25, 2006 , My understanding is that the cfm/square foot in the new ASHRAE Std. 62.1-2004 is indeed to address the building's contribution to unacceptable IAQ. This is a huge improvement on the previous standard that only considers the human contribution. You make a great point that I didn't consider. The human contribution only happens when the space is occupied, and when it's occupied, the outdoor air is being brought in. There may be little/no ventilation to deal with the building's contribution at night. To my knowledge, ASHRAE doesn't address the night set back issue. Just to be safe, I did a word search on " night " and " set back " on my electronic copy of 62.1. Not a single word came up. To add to the problems of not running the HVAC during off hours, building pressurization gets thrown out of whack and humidity may build up. These are not the words that energy engineers would like to hear! Ian Cull, PE, CIE Chelsea Training www.invironment.com www.LabComparisons.com > > Dear Ian: > > If the modification to the ASHRAE minimum recommended ventilation rate to achieve " acceptable " IAQ now includes a term that is based on square footage of the space being ventilated, I ask if the intent of this change is to address the air contaminants off-gassing from the furnishings, and since this off-gassing occurs on a 24/7 basis, should the ventilation minimum recommendation be provided on a 24/7 basis as well? > > What I'm seeing is aggressive ventilation rates being provided during peak occupancy, on the order of 24 cfm person of outdoor air delivered. But thev limited hours of operation of this ventilation provided in a tight building leaves a residual of bioeffluents, and presumably air contaminants off-gassed during the overnight interval, that persist until occupancy the next morning. > > In terms of good engineering practice, shouldn't a complete flushout of the previous day's bioeffluents be achieved overnight, so the building's air doesn't seem stale upon reentry by people the next day? > > Does ASHRAE deal with this issue? > > Sincerely, > > W. Bearg, PE, CIH > Building Scientist > Concord, MA > > -- > Director of IAQ Programs > AIRxpert Systems, Inc. > www.AIRxpert.com > > > -------------- Original message ---------------------- > > Quote Link to comment Share on other sites More sharing options...
Guest guest Posted February 25, 2006 Report Share Posted February 25, 2006 Dear Ian: Does ASHRAE maintain its definition of " acceptable " IAQ as the case where a substantial majority (80% or more) of the people exposed do not express dissatifaction. " This is what appears in the 1999 version. I also wonder if a statement appears that indicates that increases above the minimum recommended ventilation rate might be needed to reduce the nuimber of dissatisfied people to below 20%. Sincerely, W. Bearg, PE, CIH -------------- Original message ---------------------- , My understanding is that the cfm/square foot in the new ASHRAE Std. 62.1-2004 is indeed to address the building's contribution to unacceptable IAQ. This is a huge improvement on the previous standard that only considers the human contribution. You make a great point that I didn't consider. The human contribution only happens when the space is occupied, and when it's occupied, the outdoor air is being brought in. There may be little/no ventilation to deal with the building's contribution at night. To my knowledge, ASHRAE doesn't address the night set back issue. Just to be safe, I did a word search on " night " and " set back " on my electronic copy of 62.1. Not a single word came up. To add to the problems of not running the HVAC during off hours, building pressurization gets thrown out of whack and humidity may build up. These are not the words that energy engineers would like to hear! Ian Cull, PE, CIE Chelsea Training www.invironment.com www.LabComparisons.com > > Dear Ian: > > If the modification to the ASHRAE minimum recommended ventilation rate to achieve " acceptable " IAQ now includes a term that is based on square footage of the space being ventilated, I ask if the intent of this change is to address the air contaminants off-gassing from the furnishings, and since this off-gassing occurs on a 24/7 basis, should the ventilation minimum recommendation be provided on a 24/7 basis as well? > > What I'm seeing is aggressive ventilation rates being provided during peak occupancy, on the order of 24 cfm person of outdoor air delivered. But thev limited hours of operation of this ventilation provided in a tight building leaves a residual of bioeffluents, and presumably air contaminants off-gassed during the overnight interval, that persist until occupancy the next morning. > > In terms of good engineering practice, shouldn't a complete flushout of the previous day's bioeffluents be achieved overnight, so the building's air doesn't seem stale upon reentry by people the next day? > > Does ASHRAE deal with this issue? > > Sincerely, > > W. Bearg, PE, CIH > Building Scientist > Concord, MA > > -- > Director of IAQ Programs > AIRxpert Systems, Inc. > www.AIRxpert.com > > > -------------- Original message ---------------------- > > Quote Link to comment Share on other sites More sharing options...
Guest guest Posted February 25, 2006 Report Share Posted February 25, 2006 , ASHRAE did keep their definition of acceptable indoor air quality. Although a lot of attention gets focused on the 80% rule, the most important word in the definition typically gets overlooked. I think the most important word is the " and " in the middle of the definition. The definition requires that the air be both healthy and comfortable. The 80% rule deals with the comfort end of things (odors, general subjective " satisfaction " ). Their other half talks about health... " air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities " The 80% rule should be viewed in light of the rest of the definition. Sure the definition has its problems, but it carries the important concept of achieving both health and comfort. For others out there, here is ASHRAE's definition of acceptable IAQ: " acceptable indoor air quality: air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities AND with which a substantial majority (80% or more) of the people exposed do not express dissatisfaction. " -from ASHRAE 62.1-2004 (emphasis on the " and " added by me) , I don't see any mention of increasing ventilation beyond minimums to increase satisfaction beyond 80%. Ian Cull, PE, CIE Chelsea Training www.invironment.com www.LabComparisons.com ---------------------------- Dear Ian: Does ASHRAE maintain its definition of " acceptable " IAQ as the case where a substantial majority (80% or more) of the people exposed do not express dissatifaction. " This is what appears in the 1999 version. I also wonder if a statement appears that indicates that increases above the minimum recommended ventilation rate might be needed to reduce the nuimber of dissatisfied people to below 20%. Sincerely, W. Bearg, PE, CIH Quote Link to comment Share on other sites More sharing options...
Guest guest Posted February 25, 2006 Report Share Posted February 25, 2006 Dear Ian: Focusing on the words, " no known contaminants at harmful concentrations " , Several questions come to mind. Firstly, is this just long-term harm, are does it include short-term harm, such as caused by irritating air contaminants? How does ASHRAE define " harm " ? Secondly, since people spew air contaminants (i.e., bioeffluents) that can be contagious in nature (colds and flu), do you suggest sampling to document that there are none of these germs present? If increased ventilation rates, above the ASHRAE minimum recommended minimum rates, have been shown to reduce short-term absenteeism (1), presumably by reducing exposures to contagious airborne contaminants, shouldn't the goal of providing a healthy indoor environment make note of this? Just some thoughts. Sincerely, W. Bearg, PE, CIH Concord, MA Footnote (1): Milton, et.al. Risk of Sick Leave Associated with Outdoor Air Supply Rate, Humidification, and Occupant Complaints. Indoor Air 2000; 10: 212-221 -------------- Original message ---------------------- , ASHRAE did keep their definition of acceptable indoor air quality. Although a lot of attention gets focused on the 80% rule, the most important word in the definition typically gets overlooked. I think the most important word is the " and " in the middle of the definition. The definition requires that the air be both healthy and comfortable. The 80% rule deals with the comfort end of things (odors, general subjective " satisfaction " ). Their other half talks about health... " air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities " The 80% rule should be viewed in light of the rest of the definition. Sure the definition has its problems, but it carries the important concept of achieving both health and comfort. For others out there, here is ASHRAE's definition of acceptable IAQ: " acceptable indoor air quality: air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities AND with which a substantial majority (80% or more) of the people exposed do not express dissatisfaction. " -from ASHRAE 62.1-2004 (emphasis on the " and " added by me) , I don't see any mention of increasing ventilation beyond minimums to increase satisfaction beyond 80%. Ian Cull, PE, CIE Chelsea Training www.invironment.com www.LabComparisons.com ---------------------------- Dear Ian: Does ASHRAE maintain its definition of " acceptable " IAQ as the case where a substantial majority (80% or more) of the people exposed do not express dissatifaction. " This is what appears in the 1999 version. I also wonder if a statement appears that indicates that increases above the minimum recommended ventilation rate might be needed to reduce the nuimber of dissatisfied people to below 20%. Sincerely, W. Bearg, PE, CIH Quote Link to comment Share on other sites More sharing options...
Guest guest Posted February 27, 2006 Report Share Posted February 27, 2006 , You ask some great questions. How does ASHRAE define " harm " ? Well they pass the buck to " cognizant authorities " like ACGIH, OSHA, NIOSH and others with exposure limits. That opens up a whole can of worms because these are for occupational settings with healthy adult- aged workers. What about the immunocompromised, allergic and chemically sensitive out there? I like the definition of health from the World Health Organization (who? WHO) that hasn't changed since it came out in 1948: " Health is a state of complete physical, mental and social well being and not merely the absence of disease or infirmity. " I find that it's a huge task to label a space as having acceptable IAQ. Unless you test the air as you suggested, there is no way of knowing. Ian Cull, PE, CIE Chelsea Training www.invironment.com www.LabComparisons.com > > Dear Ian: > > Focusing on the words, " no known contaminants at harmful concentrations " , > > Several questions come to mind. > > Firstly, is this just long-term harm, are does it include short- term harm, such as caused by irritating air contaminants? How does ASHRAE define " harm " ? > > Secondly, since people spew air contaminants (i.e., bioeffluents) that can be contagious in nature (colds and flu), do you suggest sampling to document that there are none of these germs present? > > If increased ventilation rates, above the ASHRAE minimum recommended minimum rates, have been shown to reduce short-term absenteeism (1), presumably by reducing exposures to contagious airborne contaminants, shouldn't the goal of providing a healthy indoor environment make note of this? > > Just some thoughts. > > > Sincerely, > > W. Bearg, PE, CIH > Concord, MA > > Footnote (1): Milton, et.al. Risk of Sick Leave Associated with Outdoor Air Supply Rate, Humidification, and Occupant Complaints. Indoor Air 2000; 10: 212-221 > > > -------------- Original message ---------------------- > > Quote Link to comment Share on other sites More sharing options...
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