Monday, November 11, 2013

Vertical Stratification Limits

In their infinite wisdom (just ask them), the academics on the ASHRAE Standard 55, Thermal Comfort, are proposing that the 5°F vertical stratification limit be only for seated persons, and that standing persons should be allowed 7°F or more. I posted the following to members of the committee. 

While it is a wonderful thing that we are looking to research and make our standard as accurate as possible, we are missing the forest for the trees. An academic approach is certainly defensible, but sadly, it is of little use to the design engineer. The number one reason for occupants not renewing the lease in commercial spaces continues to be, as it has for the last 25 years, occupant dissatisfaction with the thermal environment.

The majority of commercial spaces in North America are supplied with overhead, well mixed air distribution systems, and a huge percentage of these are VAV. If air outlets are not designed to work at low flows, the space becomes stratified. Since hot air rises (I know this is obvious to all the academics on this committee, just not to many practicing mechanical engineers), it becomes cold at the floor. The only tool available to convince engineers this is an issue is Standard 55 – and you are all conspiring to take that single tool and throw it out the window.

I was asked to chair TC 2.1 back in ’78 because I was the only non-academic on the committee who was willing to express an opinion at that time. I was also involved in Standard 55 at the same time, again as a non-academic, trying to force some real world logic into the standard. As an ASHRAE DL (Possibly the only one on this committee?), I see over a thousand mechanical engineers, contractors and sales reps a year, and have done so for 20 years. The practicing engineer is woefully ignorant of the nuances of Standard 55 and has a lot of other things to worry about. But, they are most often hired by the architect, and often seeking LEED accreditation. Compliance to Standard 55 is only one point out of 100 (that’s 1% for any non-academics who might read this). Requiring analysis of a project at the design stage leaves few tools for the ME. ADPI is one that can at least be performed using software, which is available from a number of manufacturers. We on the manufacturing side have shown for many years that an ADPI of 80% of greater ensures a vertical stratification that meets the 5.4°F limitation in the present standard. The GBCI reviewers have accepted this in a number of cases, as reported to this committee in the past.

More importantly, using ADPI analysis, one can easily show that several types of air outlets do not perform well at turn down, particularly the face mounted deflector perforated outlet. This was at one time the highest selling type of air outlet in North America, due in part because it was the cheapest. Thanks in large part to Standard 55, it has, thankfully, fallen from favor, despite architects’ wishes. Standard 55 and LEED have been tools in this conversion, forcing architects to use a better performing device. The “swirl” diffuser, so highly promoted (touted?) by our European friends, also performs poorly at low airflows (VAV is seldom used in Europe).

Opening the vertical stratification limit to greater than 3°C eliminates ADPI as a limiting design factor. While Gwellen is correct in stating that an ADPI of 80% is assurance of meeting Standard 55 (and that it is not necessarily so in reverse), it is the only tool available to the design engineer. (CFD has not, to date, been shown to be a validated method of predicting air distribution performance, at least not in any peer reviewed papers readily available – I’m sure Peter has several that he can let us peek at, but cannot be circulated).

Overhead air distribution assumes a well mixed space. 3°C in a 6’ high comfort zone is a pretty well mixed space. 4 or 5°C is not. Well mixed spaces are necessary for thermostats to function properly. When air outlets “dump” at low flows (ok, exhibit “excessive drop” for you academics), not only is it cold at the floor where those not wearing socks will be uncomfortable (which applies to most women working in offices, and likely some males, especially in Berkeley), but thermostat response is significantly longer. I know of one courtroom where the thermostat response went from 55 minutes to 5 minutes by fixing the ceiling air distribution to stop it from ‘dumping’. I have repeated this many times in a number of places by simply adjusting the diverters in slot diffusers to produce a horizontal air pattern. Allowing non-well-mixed air distribution, which opening up the vertical stratification limit will permit, will have the effect of allowing the architects to again select air outlets that perform poorly at low flows, which will result in greater occupant dissatisfaction and poor thermostat response. It will also allow installing contractors to ignore the requirement (sadly seldom enforced) that adjustable slot diffusers actually be adjusted. With an allowed 6 or 7°F vertical stratification, we are in effect saying “what does it matter?”

It does matter, though. We are doing a horrible job of designing comfortable spaces. If you would actually get out there and ask folks how they feel, you might get some idea of the extent of the poor comfort conditions we have created. Almost all the complaints are “it’s too cold at the floor”, followed by “it’s too cold”, period. Resetting VAV minimums lower, eliminating code required dead bands (which force the system to control to 68°F once they go into reheat as a result of sub cooling), and using air outlets that perform well at low air flows are all strategies that need to be implemented. Opening up stratification limits, which may be technically accurate, is only going to allow us to continue our apparent practice of creating uncomfortable spaces, which will now comply with the Standard! 

The law of Unintended Consequences is about to rear it’s ugly head. Sadly, I fear I will once again be able to say “I told you so”.              

Wednesday, October 9, 2013

My ASHRAE Journal Articles

I now have 5 of the 6 promised articles published in ASHRAE Journal. The first 4 are posted in the newly redesigned Krueger website under the menu “Learn” > "White Papers" (

#1 - The first article was about adjusting adjustable diffusers, primarily linear slots (which are seldom adjusted, it seems). In discussions since the publication of this article, I have learned that this is likely a major cause of occupant discomfort in office spaces, as it seems no one ever adjusts them. When slots blow down, they create significant stratification in the space; cold air settles to the floor without very much mixing; hot air rises and the thermostat thinks the room is satisfied, which is true only in a thin layer the same distance above the floor as the sensor. The resultant cold layer causes great discomfort for those occupants not wearing socks; leading to the ubiquitous 1500 watt heater. Perhaps, more importantly, the thermostat response is greatly slowed in this scenario, often 10 times slower than when properly mixed at the ceiling. Adjusting the diffuser then requires that it be rebalanced, which is best done at installation. A combination of instructions from the specifying engineer to the installing contractor is likely the best path to getting this done. 

#2 - The second article was on the tradeoff between energy and comfort. As I reported in my last blog, this one drew comments from a couple energy zealots who, apparently, are still not convinced that making people uncomfortable in order to save energy is counterproductive in terms of both energy and cost. I suspect that anyone who makes a living as an “energy consultant” has misplaced priorities. Worse, there doesn’t seem to be a market for “comfort consultants” to counter them – and there should be, as salaries are on the order of 100x energy costs in most buildings. If we are not careful, we will have buildings that qualify as “Net Zero Satisfaction Buildings (another article I wrote for ASHRAE last year (

#3 - The third article was on the validation of high turndown VAV systems, based on recent ASHRAE research conducted on several California buildings. Two significant results (in addition to others) were that loads are so low in a modern office interior zone that spaces are often sub cooled, and that operation at very low air flow rates, with good diffusers (plaque-type, in this case) provide excellent occupant responses. This opens the door for a number of energy saving strategies, including variable volume series fan powered terminal units and fan coils using ECM motors. In both cases, however, maintaining proper code required ventilation rates requires measured and controlled ventilation dampers. There will be an article on this subject in the ASHRAE Journal in the near future from another contributor (who beat me to the punch!).      

#4 - The fourth article was on the issue of area factors for balancing diffusers and discussing why we really can’t publish them anymore, as the choice of the instrument used to measure discharge velocity from a diffuser has become a significant variable in the calculation of the constant to convert velocity to air flow rate. The old stand-by, Alnor Velometer, is seldom used anymore, as the new digital anemometers can store and average data. Sadly, they all respond quite differently to the thin high velocity air jet that is created by today’s air outlets, so there is no single Ak for any device, rather, each device has a different factor. Our advice is to carefully measure the airflow rate for one diffuser/zone on a project and then determine the Ak for that diffuser and velometer.

#5 - The fifth article, which we haven’t yet posted because we haven’t yet received a web-friendly copy back from ASHRAE, is about the lack of validation data on calculations/predictions of a number of building variables, including air motion, energy, and acoustics. The result is that energy predictions often fall far from the mark; spaces are noisy and occupants feel drafts. None of the available building energy programs properly account for the energy consumption of either series or parallel fan powered terminal units, which typically overstates (grossly) the energy use of those with ECM motors. While the savings from variable flow ECM series fan boxes is obvious, one has to “make up” the calculations. Similar issues are found for displacement, underfloor, and chilled beam systems. A literature search will turn up almost no actual energy use data for any of these “energy savings” strategies. Calculation of acoustics for ducted devices is in much better shape, as AHRI 885 has been in place, with a spreadsheet, for a number of years. All that is required is octave band sound power for the devices in question, which has been certified for VAV boxes for many years via the AHRI 880 program. Other ducted devices can be tested to AHRI 260. LEED V4, out this month, will recommend AHRI 885 for proof of compliance with the 40dBA HVAC sound levels prerequisite in classrooms.   

I’ll be working on the 6th article, scheduled for December ASHRAE Journal over the next week. It will either be on water coil calculations for VAV boxes, or on the many “magnification factors” being used to define the performance of inlet probes on VAVC terminals. Stay tuned….

Authored by: Dan Int-Hout, Chief Engineer Krueger

Thursday, August 29, 2013

ASHRAE Journal Articles

I have had 4 of the 6 promised “Engineer’s Notebook” articles published in the ASHRAE Journal. I received permission to post these on the Krueger website, which I will do as soon as they send me back the “approved” versions. We’ll update this blog entry with links as soon as they become available.

I have had a lot of very positive feedback from these articles, but today I got my first negative critique. The responder, a consultant (I assume an energy consultant) from Seattle, complained that “this kind of thinking will prevent ASHRAE from progressing the art of design”. I responded with this:

While I fully agree that oversized equipment may lead to occupant dissatisfaction, as the system attempts to operate efficiently at part load (see my most recent article in the Journal ), there are a large number of "energy efficient" buildings where occupant comfort has taken a back seat to energy savings. Following the publication of the article in question, I received a comment regarding a government building in your city, which is going for an energy award with both Underfloor Air Distribution (UFAD) and Chilled Beams. An occupant posted a picture on the internet of a temperature sensor on his desk indicating it was 90°F there. I'm sure they will have low energy use, but at what cost? Supposedly, there are umbrellas duct taped to office dividers to keep the sun off the occupants.  

I fully agree that "Energy efficiency does not make buildings uncomfortable; but the lack of good mechanical engineering design does." Sadly, so does poor understanding of how a building is supposed to operate. Innovative systems need much more building operations training than more traditional ones. Construction of innovative designs is also often compromised by poor construction. As indicated in the recently released ASHRAE UFAD Design Guide, the key to a successful UFAD system starts at the first day of construction in order to avoid issues with leakage in the end, which may be impossible to locate or remedy. 

But, the biggest issue I have with energy efficient designs is the apparent lack of validation of the energy calculations created to get owner and code acceptance (and LEED points). There are plenty of examples of buildings using far more energy than was predicted. Some schools are reporting that their expensive schools (at more than twice the cost/unit area of any prior schools in that area) are the highest energy users (again in terms of energy/unit area). I suggest that validation is lacking in many of these claims. An internet search for peer reviewed cases of proven energy savings of innovative designs will show you there isn't much out there. If these designs are so good, I'd expect the internet to be flooded with glowing reports. Sadly, that doesn't seem to be the case. Maybe all the successful building owners and designers are just bashful?

Authored by: Dan Int-Hout, Chief Engineer Krueger

Wednesday, August 21, 2013

Is it September yet?

It must be nearing quickly, as I already went to South Dakota in early August for the annual motorcycle rally. And I’m now seeing school busses on my drive to work. ASHRAE was in Denver this summer, a few issues were resolved, most notably the 40 fpm issue reported in my last blog. I have finally rolled off the USGBC’s Indoor Environmental Task Group, but can report that LEED V4 has been fully certified and will be out in the next few weeks.

We had hoped to get ASHRAE 55 2013 out in time to be referenced by the new LEED, but it will probably be in an addenda. ADPI is still the best way to prove compliance to 55 with overhead air distribution; both 55-2103 and the next ASHRAE Handbook (Applications) should be aligned to reference each other to make this proof easier to validate. I have actually been working on this, clarifying this relationship since about 1981, so I’m glad it is finally all coming together. I suspect the secret was to outlive all those who couldn’t grasp the reality of this relationship.

AHRI Standard 885 is one of two compliance paths in LEED V4 for schools. The prerequisite of 40 dBA (typically about 31 NC) for the classroom HVAC system can be substantiated by either AHRI 885 or the ASHRAE Handbooks. As there is still no reference in the ASHRAE Handbooks to the joint ASHRAE AHRI research study (RP755) conducted in the late 90’s at NRC Canada on the transmission of sound from plenum located sound sources into a room, which has been in 885 all along, I suspect AHRI 885 will be the primary documentation path. The spreadsheet associated with 885 makes both calculation and documentation quite easy. The incoming chair of TC 2.6, Sound and Vibration, has made the inclusion of the RP755 results in the Handbooks a priority, but until that happens, 885 is the best validation method.

I now have 3 of the 6 promised articles published in ASHRAE Journal. The first was on adjusting adjustable diffusers, primarily linears (which are seldom adjusted, it seems), the second was on the tradeoff between energy and comfort, and the third was on the validation of high turndown VAV systems, based on recent ASHRAE research. The next one will be on area factors for balancing diffusers and discussing why we really can’t publish them anymore, as the instrument used has become a significant variable. We will be posting them on the Krueger website when all six are out there.   

Authored by: Dan Int-Hout, Chief Engineer Krueger

Wednesday, July 3, 2013

40 FPM Issue Resolved

The members of ASHRAE 55 have finalized the draft of an upcoming revision to the standard. We have moved the entire “guidance” wording to informative appendices, and what remain are now all “normative”, or mandatory requirements. This will greatly improve the use of the standard when referenced in codes, standards, and of course, LEED. In addition, they have changed the name of the section which was called “Adaptive” to “Naturally Ventilated Spaces”. (I have always had issue with the term “adaptive”.)

If you have been following my blogs, you know I had a concern regarding implementation of ASHRAE Standard 55 (Comfort). There are several compliance paths available in the standard. The most used is the “graphical method”. This is the method used in Krueger’s thermal comfort program ( Apparently, I, along with most users, ignored a statement that says if the airspeed at the point of interest exceeded 40fpm, one could not use the graphical method. A similar clause shows up in the second method, direct calculation of PMV using the supplied BASIC program, or the ASHRAE Comfort cool program. It all came to light when some folks submitting to LEED for the comfort point were either denied on the lack of a stated airspeed or stating an airspeed greater than 40 fpm. Since manufacturers only show throw to 50 fpm, this is a significant road block.

However, in the upcoming revision to Standard 55, which is expected to be printed in late summer, it has been taken care of in a couple of ways (subject to some final tweaking, but not likely). The Standard points to a section called “Elevated Air Speed” when air speeds are higher than 40 fpm (30 fpm if the setpoint is 72°F or below.) This section uses a methodology called ‘SET’, which calculates what the temperature would be at 30-40 fpm, providing the same thermal environment as at the elevated air speed.

UC Berkeley’s CBE has posted an on-line thermal comfort program that includes a graphical display. When one uses the step-by-step methodology for air speeds less than 70 fpm, it has the effect of moving the comfort box an almost immeasurable distance to the left! We also added a comment in the informative part of the Standard that points to the ASHRAE Application Handbook, where we will include a statement that references Standard 55. Included in the Standard is the following: “Spaces with air distribution systems which are engineered such that HVAC system supplied air streams do not enter the occupied zone will seldom have averaged air speeds that exceed 40fpm. See the ASHRAE Applications Handbook Chapter 57 on Air Distribution for guidance on selecting air distribution systems.” 

It is very likely that with any air distribution system designed with an ADPI >80%, there will be points in the occupied zone where the air speed will be greater than 40 fpm at air flow rates of 2.0 cfm/sf or less. The average in the comfort zone, however, will likely never exceed 40 fpm. It is also safe to say that at an ADPI >80%, the vertical stratification in the occupied zone will not exceed Standard 55’s limit of 5.4°F. Between the Standard (prepared by the Standard 55 committee) and the Handbook (prepared by ASHRAE TC 5.3), both the GBCI reviewers and the engineers submitting designs can point to these references to prove compliance to the Standard at the design stage.

As final note, I have finally served 4 years on the USGBC’s Indoor Environmental Task Group and will roll off. LEED V4 just passed all hurdles, including internal and external reviews, and will be released in October, as promised last year. I was pleased to get AHRI Standard 885 included by reference in both the 40 dBA HVAC sound requirement prerequisite in LEED for schools, and as a path for a point when meeting the acoustical requirements in all other sections. The AHRI 885 spreadsheet is available on the Krueger website and includes a room sound calculator for calculation NC, RC, and dBA combining discharge, radiated, and air outlet octave band room sound pressure levels.    

Authored by: Dan Int-Hout, Chief Engineer Krueger

Wednesday, June 5, 2013

Another Trip to Canada!

It’s been a while (a month!) since my last blog. I had the opportunity to take yet another trip to Canada, this time to speak to the NEBB (Air Balancers) National meeting in Montreal. I spoke on the latest Standards and some of the basics of Air Distribution. Again, it seems that one cannot get too basic in a discussion of air distribution basics, as it seems this is a subject neglected in both universities and the real world. I had several invitations to speak to local NEBB chapters as a result. 

We discussed one of my favorite subjects, the adjustment of adjustable diffusers. It seems to be a consensus that the balancers are neither responsible for, nor prepared to adjust linear diffusers. I guess the engineer and the installing contractor are left to take care of this. Failure to do so will likely result in rooms that are stratified, slow to respond to load changes, and will result in uncomfortable occupants. Other than that, I guess there will be no problems.

I ran into the editor of the ASHRAE Journal while I was at the conference. He invited me to write a series of articles for the “Engineer’s Notebook” of the Journal. Naturally I accepted, and in fact the first two are already on the way and will appear in the June and July issues of the Journal. If they seem a bit familiar, they are based on blogs I posted here in the past few months. Hopefully more folks will get my rants, or rather - thoughtful messages.

Authored by: Dan Int-Hout, Chief Engineer Krueger 

Monday, April 15, 2013

Webinars and Blogs

In case you all haven’t noticed, we are doing more webinars these days, and now they are being recorded and posted on the website. We assumed that the recordings would only be used for back up, but have found that in fact, folks are doing a lunch event watching the recorded webinars!

We have had great attendance at several of the webinars, including a "sold out" session on the “Basics of Air Distribution” last month. I recently presented my talk on “Building Loads” last week. Next month, I’ll do a two part talk on “Methods of Effective Room Air Distribution,” which was a two part article in the ASHRAE Journal last year.

Stay tuned and we’ll announce upcoming webinars, which will be recorded and available at whatever time is most convenient for you. My blog has also been well viewed, which is good, as I’d hate to be sending the blog into the wind!

If you have a subject that you would like me to comment on, please send me an email (

Authored by: Dan Int-Hout, Chief Engineer Krueger

Thursday, April 4, 2013

Energy Targets!

As a member of the ASHRAE Technical Activities Committee (TAC), my assignment is to manage the new Multidisciplinary Task Group (MTG) committees. One of them is focused on energy target, and they are working on tweaking their scope. It appears that the term “Energy Target” has a specific meaning in the energy industry that has nothing to do with energy conscious design in buildings. The term seems to have been assigned to the practice of forcing electric utilities to use more renewable energy in their generation of electricity. This is an example of how the whole issue of energy use and the prediction of energy consumption have corrupted the goal of providing efficient and comfortable buildings.

Recently, the LEED Environmental Quality (EQ) committee had a strong disagreement with a couple members of the Energy and Atmosphere (EA) committee when establishing credits for LEED V4 (due out in October). It seems the USGBC had applied weighting factors to all possible credits, and only 100 were allowed. They had several times greater weighting to energy than to occupant wellbeing. As a result, a number of EQ credits were going to be dropped in favor of energy credits. When we asked for disclosure of weighting factors, the USGBC was reluctant to disclose them, but in the end caved in under embarrassing data on the economic values of productivity vs. energy consumption (building salaries are 100x energy costs). At one point, one of the EA members said “but think of the children!” We wound up with equal weighting between energy and occupant issues.

The zealots who force renewable energy or energy conservation on building designers and architects without regard for the end goal (to provide a safe and acceptable environment for the occupants of the buildings) are doing us no favors. It leads to complex energy calculations based on no facts, only on wild assumptions, which in the long run are proving to be unattainable. The result is that many LEED projects are not even coming close to the predicted energy savings. The same can be said of a number of Energy Star projects. Meanwhile, BOMA reports that the #1 reason for not renewing the lease in high rise buildings is occupant dissatisfaction with the thermal environment (for the last 20 years).

I would suggest that in addition to ‘targets’, the goals should include some means of validation of the calculated energy use. Maybe the word “realistic” needs to appear somewhere. Sadly, there is little or no basis for many of the assumptions being input into current computer models. These modifications are necessary for them to be able to calculate energy use for “innovative’ systems not listed in the software. It would be great if we could get some data on the existing main-stream computer models ability to accurately predict the energy use of these non-traditional systems. The data would likely show ‘issues’ with the assumptions often employed, and help explain why they are so often grossly underestimating energy use. Case in point is the GSA’s claim that they have 10 million square feet of non-performing underfloor systems, resulting in the pulling and rewriting of ASHRAE’s UFAD design guide (which sadly is still lacking any real energy savings information).

In the meantime, practicing engineers are forced to “make stuff up” in order to calculate energy consumption for systems not included in the available computer models. In the end, buildings use more energy than predicted and tenants fail to renew the lease as they continue to look for the fabled “comfortable space” in which to work.

Authored by: Dan Int-Hout, Chief Engineer Krueger

Wednesday, March 27, 2013

March Madness

Wow! It’s almost the end of March, can you believe it?! I have been to Philadelphia and Springfield Missouri ASHRAE Chapters, as well as a week in Florida with the motorcycle for bike week. We just had an all-day training session for Texas engineers yesterday at our facility (subject being “Basics of Air Distribution”). I also did a 30 minute webinar on the “Basics of Air Distribution” a couple of weeks ago, which is recorded and available on the Krueger website. I will be doing a webinar on the “Application of Dedicated Outdoor Air Systems” on April 10, and a two part webinar on the “Methods of Effective Air Distribution” in May, which was a two part ASHRAE Journal article in November and December, last year. We are certainly getting a lot of stuff in front of engineers, which is hopefully of some use.

I’ll be traveling to Montreal in Late April to chat with the NEBB (air balancers) at their national meeting. You may be assured I’ll speak to the issue of adjusting slot diffusers. I had one contractor at the training session yesterday say that they added 10 minutes to the install time for slots to allow for adjustment in coordination with the air balancers. This is excellent input, but sadly the first time I had heard of it. I asked why they did it, and was told it was in response to complaints from older projects of drafts. I’m glad someone is listening to occupant complaints. I think this is a key issue for both designers and installers: Listen to the occupants!

I was told by an engineer in North Carolina that he had been installing overhead heating at over 100°F for years and no one had complained. I have to conclude that what he meant was that no one had complained to him. In the 1000+ air distribution tests we conducted back in the late 1970’s, there was not a single test with discharge temperatures that high which met , or even came close to meeting ASHRAE Standard 55’s vertical temperature stratification limit of 5.4°F. BOMA continues to report that the number one reason for not renewing the lease in a high rise building is occupant dissatisfaction with the environment. I said it once (actually many times!) and I’ll say it again: Listen to the occupants!

Authored by: Dan Int-Hout, Chief Engineer Krueger

Tuesday, March 12, 2013

Canada in Winter

I went to Ottawa in February. I’d forgotten what winter in the cold North was all about, but it all came back in a rush.

I spoke to the Ottawa ASHRAE chapter with my latest presentation, titled “What A (Building) Load”. I’ve been working on this for a while, as my “Methods of Effective Room Air Distribution” talk is a couple of years old and was published in November and December in the ASHRAE Journal.

Having been on the project review committee of the ASHRAE research project 1515, which was a thorough study of a couple buildings in California, where occupant response, equipment operation and energy use were all mapped, I have a pretty good idea of what was in the final report, presented in Dallas last month. The building loads were all far below what most engineers design for, and required setting the minimums on the VAV boxes at 10% of maximum to keep from going into reheat every afternoon. What was most interesting is that there were minimal complaints at the low air flows, and occupants were generally satisfied at 0.2 cfm/sf. This confirms the idea that there is no minimum air speed for comfort, which has been in the ASHRAE Comfort Standard for some time.

This leads to a conclusion that using a series fan terminal with an ECM motor and varying the air flow rate to as low as possible offers a very energy efficient way to provide HVAC to a commercial office space. It can be even better if a sensible cooling coil is placed at the inlet of the unit. This concept was utilized at the Pentagon in its most recent upgrade and is being used in a number of buildings around the country.

I described this concept to a design build contractor in Ottawa, and when he realized that one could actually eliminate the air handler (using only a DOAS unit) he is going to try this on a couple of designs.

I also did some webinars a couple weeks ago on “the basics of air distribution” and maxed out our number of available connections. I guess going back to the basics is something we have to do once in a while.

Authored by: Dan Int-Hout, Chief Engineer Krueger

Wednesday, February 13, 2013

History of Air Motion and GSA “Peach Book” Specification

In the early 70’s, The GSA (Government Services Administration) developed a set of performance based specifications for buildings, referred to as the “Peach Book”. One of these specifications was that the measured air speed throughout the space shall lie between 20 and 50 fpm at all points. Originally, they specified an air velocity meter that was incredibly inaccurate below 100 fpm. We located an anemometer that was accurate down to 5 fpm but was directionally sensitive. Nonetheless, carefully oriented (using smoke to assure the predominant direction), we developed a repeatable test procedure that eventually became the basis for ASHRAE Standard 113. Using this procedure, we discovered that the specification was not able to be met with any air distribution system. Eventually, a modified specification was agreed upon that allowed 20% of the measured points to exceed 50fpm, and 40% to be below 20, as long as the average was between 20 and 50fpm. 

The measurement devices have greatly improved, and if anything, they are more sensitive than what we used in the GSA tests in '78. The ASHRAE Fundamentals Handbook ADPI data was taken with heated sphere anemometers at Kansas State in the 60's. All those had been calibrated so that they were accurate at low airspeeds, using careful measurements. In the GSA tests, we had a number of distributed 100 watt loads and the designs called for either 0.6 or 0.9 cfm/sf, and resulted in meeting the new GSA specification. The testing was conducted by Dr. Paul Miller (the ADC Engineering Consultant at the time) and myself, with GSA personnel witnessing all the tests.

The diffuser was a continuous ½”, 2 slot linear diffuser that resulted in a two dimensional air pattern throughout the space. The highest air speeds were recorded under the diffuser, in an upward direction, as expected. In attempting to meet the original specification, we also tested an array of ceiling diffusers and found that at some location, air speeds were always less than 20, and at others (under the diffusers) exceeded 50 fpm.

In the course of running over 1000 air distribution tests (reported in two ASHRAE Technical papers), we found that average room airspeed in the comfort zone is essentially proportional to the room load with any ceiling diffuser type, as long as the primary jet doesn't enter the occupied zone. Therein lays the problem. Some air outlets at low flows are unable to maintain sufficient "Coanda" to prevent the negative buoyancy of the air jet from falling into the space. This is often referred to as "dumping" and we find that perforated face diffusers are the most likely to exhibit this behavior. A number of other types of air outlets are seldom prone to this behavior.

At design flow on the other hand, if the diffusers are too close together, throws collide and drop into the occupied zone. By using ADPI analysis, it is possible for the designer to identify in advance, using published throw data, how different diffusers respond to changes in airflow rate, inlet size, and diffuser separation. If the predicted ADPI is greater than 80% at a given set of conditions, the primary jet(s) are not entering the occupied zone. We have also seen that when the ADPI is greater than 80%, average room air speeds are never greater than 40 fpm at flow rates less than 1.2 cfm/sf. This analysis, of course, is for interior zones in cooling mode.

Perimeter zones are another matter, and while average air speeds in heating are typically 20 fpm or lower, there are always high air speeds at the floor near cold windows. These will always exceed 30 fpm somewhere. (Unadjusted linear slots at the window, which is almost always the case, are likely to deliver jets exceeding 100 fpm into the occupied space, in either heating or cooling mode).

I would expect that anyone taking data today, using modern omnidirectional anemometers and meeting the requirements of either ASHRAE 113 (or the ISO 7726) specification, would get similar results.

Authored by: Dan Int-Hout, Chief Engineer Krueger

Wednesday, February 6, 2013


Well, another ASHRAE meeting is now behind us. This last meeting was here in Dallas. As usual, I was fully committed to a number of technical meetings. I won’t bore you all with the machinery of managing Technical Committees (I am a new member of the Technical Activities Committee, TAC). There were a couple of interesting things that happened at the meeting that I can report on, however.

The committee to rewrite the Underfloor Design Manual finally finished its work and voted a document out for publication. While not pleasing everyone (naturally), it contains a great deal of what we have learned in the several years since the first Design Guide was published. This document is the first time a committee has ever attempted to write a design guide. In the past, design guides are commissioned by a TC and ASHRAE pays a contractor to prepare it. This one was different, as the GSA had complained they had a number of buildings with UFAD systems which are “underperforming”. We have learned this means high energy use and difficult maintenance. Many of the problems stem from a number of buildings being built by first-time contractors without experience in some of the unique construction details required to maintain pressurization in the plenum. Other problems involve the need to manage infiltration when the system is shut down at night and condensation occurs. The guide also describes the issue of heat gain, or “thermal decay” and recommends several ways to minimize this effect. Sadly, there is still little data on actual energy consumption, and claims of energy savings with this technology are still mostly anecdotal and unproven.

The Thermal Comfort Standard (ASHRAE Standard 55) is proceeding towards a revision with most of the informative stuff moved into an informative appendix, leaving only mandatory requirements in the main body. The issue of compliance to a 40 fpm allowed maximum “average air speed” (30fpm when the setpoint is below 72.5) is still an open issue.  

A committee representing the VRF (Variable Refrigerant Flow) suppliers requested to be exempted from meeting the Standard 62.1’s requirement for a MERV 6 filter (ASHRAE 189 is requiring a MERV8) upstream from “:any wetted surface”, which means their condensing coils. This is actually a code requirement wherever ASHRAE 62.1 is included in code (like the 2009 International Mechanical Code). If granted, I see a lot of other devices wanting to be included as well. Frankly, I don’t see the justification. 

The final report from the research project at the Yahoo campus was presented. Interior loads were reported to be less than 6 btuh/sf (vs. the typical design of 22 at 1cfm/sf). This is essentially the ventilation load. At the same time, 62.1 is discussing variable ventilation rates for occupied, temporarily unoccupied, and truly unoccupied spaces. I predict that this will require pressure independent ventilation supply systems for any type of equipment, be it fan coil, VRV, WSHP or even Chilled Beam. It makes one wonder why someone doesn’t just install a VAV system, doesn’t it?

Authored by: Dan Int-Hout, Chief Engineer Krueger

Monday, January 21, 2013

Top Ten HVAC Predictions for 2013

The long awaited Top Ten HVAC Predictions for 2013.

Let’s hope I can do better than I did in 2012.

1. LEED 2013 will be released in the fall and it will include a reference to AHRI 885 to prove compliance to acoustical requirements.

2. Balancers will continue to ignore the need to adjust linear diffusers before balancing. If adjusted after balancing, rebalancing is required. This is the design engineer’s responsibility, of course, so they need to require adjustment if they specify adjustable slots. I predict this will be ignored. (It’ll be an easy 10 points).

3. ASHRAE Thermal Comfort Standard (55-2010) will be modified to include Normative (mandatory) and Informative sections so that it can be referenced directly in codes. This is already partly accomplished. ADPI will be included in ASHRAE standard 55 as a means of predicting compliance.

4. The updated ASHRAE UFAD Design Guide will be published in 2013.

5. We will see no published, peer reviewed, energy savings data for any of the “new” systems (displacement, underfloor, or chilled beams), but engineers will continue to claim energy savings compared to overhead systems to get LEED or Energy Star ratings.

6. BOMA will continue to state that the #1 reason for not renewing the lease in high rise buildings is “occupant dissatisfaction with the building environment” (ie: comfort). (It has been for the past 20 years; this is likely a ‘gimmee’.)

7. The market for HVAC components will again be relatively flat with local ups and downs.

8. VAV overhead air distribution will continue to be (by far) the most used system in new buildings. As loads decrease, it will become more apparent that the ventilation load in the interior is the predominant building load. ASHRAE RP 1515 will open a lot of eyes.

9. The majority of VAV box schedules will continue to show design discharge temperatures in excess of 90ºF, in spite of the ASHRAE handbook stating this will guarantee non-compliance to Standard 55’s vertical temperature stratification limitation - and without compensating increases in ventilation, as required by Standard 62.1 (and code in most states).

10. Sadly, the Cowboys will continue to disappoint their fans. (Again)

Authored by: Dan Int-Hout, Chief Engineer Krueger

Dan Int-Hout's Prediction Assessment for 2012

As I did last year, here is my self-assessment on the 2012 predictions.

1. LEED 2012 will be released in the fall and it will result in a number of changes in the way building HVAC systems are designed, both for energy savings and acoustics. – Oops, it was delayed a year: 0 points.

2. The ASA Classroom acoustics recommendation (essentially NC = 26, ANSI 12.60) will become a default requirement for new classroom design. The LEED prerequisite will require that either the ASHRAE handbook or AHRI 885 will be designated as a primary method of estimating sound levels in schools and other places as well; Engineers will discover that the 885 spreadsheet is a much easier approach.- Real slow acceptance. 5 points

3. ASHRAE Thermal Comfort Standard (55-2010) will include mandatory language only for the calculations employed. A set of default compliance paths will be developed and put out for public review. - It’s happening, and is in progress: 6 points

4. The updated ASHRAE UFAD Design Guide will come out of committee at the summer meeting. – We vote on it in Dallas: 10 points

5. Displacement Ventilation will continue to see significant use in classrooms due to its low sound generation. – Yup: 10 points

6. Chilled Beams will continue to be used by innovative engineers. While I hope to see some validation of the energy consumption savings, I predict we won’t.- No published energy data yet: 10 points

7. BOMA will continue to state that the #1 reason for not renewing the lease in high rise buildings is “occupant dissatisfaction with the building environment” (ie: comfort). I still see new designs with designed discharge temperatures for overhead systems in excess of 100ºF, which leads to significant stratification.- Sadly, this continues: 10 points

8. The market for HVAC components will again be relatively flat with local ups and downs. – Also sadly, but it is beginning to improve: 7 points

9. VAV overhead air distribution will continue to be (by far) the most used system in new buildings. ADPI will be endorsed by the ASHRAE Fundamentals as a method of predicting both thermal uniformity (complying with the vertical stratification requirement of standard 55), and that the average room air speed is less than 40 fpm, allowing the graphical and PMV calculations of Standard 55. – The 55 committee agrees and is looking for final wording:10 points

10. Sadly, the Cowboys will continue to disappoint their fans. - No brainer. 10 points.

I only got 78 points (out of a possible 100). I’ll try to do better this year.

Authored by: Dan Int-Hout, Chief Engineer Krueger