Thursday, July 5, 2018

The Journey Continues

It has come to my attention that this is my 100th blog entry and that I should think about something special to say. Like all the previous ones weren’t meaningful. HA! Perhaps a bit of reflection now and then isn’t a bad thing.

I attended the Houston Annual ASHRAE meeting a couple of weeks ago. I believe this was my 83rd ASHRAE meeting, but I don’t have data going back that far, as it was before personal computers… A lot has changed since the mid 70‘s when I got involved in the science of air distribution. I had the pleasure and privilege of knowing Dr. Miller and Dr. Nevins of Kansas State who literally wrote the book “Air Distribution”. They, along with industry figures like Harold Straub of Titus and Bill Waeldner of Anemostat, were gracious enough to let me in on the secrets of converting test results into catalogues, both printed, and later, electronic. The Krueger KEC electronic catalogue was released in 1984 for the MS-DOS operating system. 

I also got to know Dr. Fanger and Dr. Gagge, who laid the foundations for our understanding of thermal comfort. I worked with those two to get a compromise on a computer algorithm combining the “two-node ET* and the PMV equations. Sadly, the ASHRAE Comfort committee (SSPC 55) is thinking about dropping the “graphical method” of compliance, in favor of computer models which either must be purchased or only run online from a university web site. There is of course, a free graphical model (the only one available) on the Krueger website. (

I also got to know the outgoing ASHRAE President, Bjarne Olesen, who was a protégé of Dr. Fanger and was who I replaced as chair of Standard 55 when he started his rise to the top at ASHRAE. The current ASHRAE President, Sheila Hayter, is the daughter of Dick Hayter, president of ASHRAE back in the 70’s. He was also at Kansas State back in the day. The involvement of Kansas State in the science of air distribution was a critical one. The ADPI predictions that are used to verify compliance to Standard 55 were developed at KSU in the late 60’s. Recently validated and updated at UT Austin through an ASHRAE research project, the ADPI predictions are valid down to minimum ventilation rates. A heating ADPI prediction is in development from the UTA data.

I went through the development cycle of DDC controls from earlier pneumatic devices in the 80’s. We had to learn that pressure independent airflow control was mandatory if multiple spaces were to be served from a single air source. It would appear that when (not if) ventilation supply is decoupled from comfort control, a pressure independent ventilation control system is also required.

Now, I am involved in the Residential Building Committee at ASHRAE. It seems we are entering the multifamily dwelling industry with about the same level of understanding of the rules for effective ventilation as we did for commercial buildings 40 years ago. I find myself doing the same training on airflow control as I did in the 80’s to a new generation of mechanical engineers who never had any training on this subject. So, job security.

And the wheels keep going round and round…..

Authored by: Dan Int-Hout, Chief Engineer Krueger

Wednesday, June 20, 2018

Inlet Plenum Claims

I was asked recently by an engineer whether there is any truth to the claims that a 12” inlet plenum attached to a diffuser would reduce inlet generated sound by ~10NC.

The answer is no, not really. Keep reading to understand why…

There was an ASHRAE research project conducted at UNLV on inlet effects. The short of the story is that diffuser NC values are obtained under ideal test conditions (specified by ASHRAE 70) where there are several diameters of straight duct used. In reality, when you account for the effect of a sharp 90° flex duct bend and realize that rooms don’t really absorb 10dB, the reported value may be underestimated by about 5NC.

At Krueger, we used to sell 90° inlet plenum boxes, but we were shipping mostly air and local contractors could always under bid us. We reported (in 1982) that it would reduce sound by 3 NC.

Where we should be looking is at the ducting…

A straight, hard duct connection to a plenum box will transmit system noise to the diffuser. Even though straight, it may result in being louder than a flex connection, as flex duct has a high “insertion loss” with a low “breakout”, meaning that it makes for an excellent system sound attenuator.

As far as what we've seen in the field, there's often a 90° bend at the connection to the diffuser (outlet). Doing this can seriously affect the discharge pattern. As it turns out, more air will come out of one side, which then results in a longer throw in that direction. In some situations, this may cause occupant discomfort. (PS: This is bad.)

In my experience, air piled to one side by a hard 90° connection will remain piled to one side unless the plenum is HUGE. So to go back to the initial question we were asked, 12” won’t do it, and neither will placing a perforated plate in the path. It will still stay piled to one side. In fact, we found in testing that after 10 feet of 14” spiral duct that follows a 90° connection that the air was still not very uniform at the discharge. So anything that promises to work, just expect that it will add both noise and pressure drop.

In my opinion, I think the approach in unnecessary and likely ineffective. I think it’s better to support the flex duct so it doesn’t lay on the adjacent ceiling tile. Doing this will likely cost a lot less.

Authored by: Dan Int-Hout, Chief Engineer Krueger

Thursday, May 3, 2018

Specifying Control Logic

The controls on VAV boxes have changed quite a bit since their conversion from pneumatic in the early 80’s. Back then, we often referred to overly complex control sequences as ‘Klingon Spaceship controls.’ One would think when DDC controls arrived, that things would be much simpler. Of course, this isn’t what happened.

Instead, we got a proverbial ‘black box’ with “Trust me” written on its side in disappearing ink. Simply broken down, there are two types of controls for VAV boxes, line and block. A line controller is essentially a programmable device with its code written in a ‘line-by-line’ manner. A block controller’s code is written in pre-programmed blocks that work together, hopefully. Technically a ‘line-by-line’ program is broken into functional blocks too. So the question is: What functions are the blocks performing?

It’s difficult to get control suppliers to program controls to do what we expect them to do. We (Krueger) have discussed it a lot with Specifying Engineers and some of our reps. There is a lot of ‘push-back’ from control contractors who want to reuse what they can, and charge the maximum amount for inventing what they feel are new, ‘custom’ sequences. Specifying engineers have told us that they feel the control contractors really don’t understand what the specified products can or should do.

ASHRAE Guideline 36: High Performance Sequences of Operation for HVAC Systems is going to be available this June, and it should provide a basis for writing specifications for VAV systems. I’ll be cutting and pasting from this document to try to put together a guide controls specification for a VAV Series fan box with a sensible cooling coil. Stay tuned for updates!

Authored by: Dan Int-Hout, Chief Engineer Krueger

Friday, April 13, 2018

What A Long Strange Trip It Has Been

As we train new employees and I look ahead to eventually winding down my career, I tend to look back over my 40+ years in the Air Distribution field. I can say the journey has been, to say the least, interesting. 

I started my adventure in HVAC after a tour in the Air Force. I ended up back in the town in Central Ohio, where I went to school (Denison U in Granville, Ohio), with a degree in Biology. I was hired as a “Scientist” in a product testing lab by Owens Corning Fiberglass at their research center there. I got involved in an air distribution problem and joined ASHRAE to learn more about the technology of air distribution. That began my journey in air distribution research, standards and building codes, which continues to this day. I chaired the ASHRAE thermal comfort standard committee (Standard 55), the comfort and air distribution technical committees (one of them twice), as well as several other related technical committees. I even got involved in Acoustics, managing the development of an Acoustical Application committee in AHRI. I was involved in different capacities with the ventilation standard 62.1, and I’m still the air distribution consultant to that committee. I have since become both an ASHRAE Fellow and a Life Member. I even spent three years as a Director at Large of the society, likely the first degreed Biologist to do so.

One of the advantages (some would say disadvantage) of having been around as long as I have is the ability to sometimes see where all this is headed. I was asked by a customer several years ago what I thought would be the “next big thing”. I predicted that someday there would be a requirement to deliver (measured) ventilation air directly into every occupied space. The new Washington State commercial building code requires just that. 

Having been involved in the development of VAV from its crude beginnings in the early 70’s, I watched the progression from pressure-dependent to pressure-independent flow control. I also experienced the transition from pneumatic to digital controls. Does anyone still remember how to set pneumatic velocity controllers? What is apparent to me is that we are going through a similar progression with ventilated air. We are still working to get the control sequences we need to be implemented in DDC controllers.

VAV boxes went from system powered and constant volume induction types to parallel fan powered units, then series fan powered units. The ECM motor, introduced 20 years ago (really, 20 years ago?) is now required by code in many jurisdictions, and analog outputs on DDC controls allow fans to vary airflow. This results in variable volume series flow terminal units. We are challenged today with getting controls to properly manage this exciting technology.

Back in 1973, it was difficult to measure low air speeds. The required anemometer was found to have an accuracy of +/- 50 fpm at 50 fpm! I attempted to verify a GSA specification of 20 fpm minimum air speed with this crude device. Working with an anemometer manufacturer, we developed the omni directional anemometer as well as ASHRAE Standard 113, which defined a repeatable method of test for its use. Eventually, we developed methods of predicting air distribution performance using techniques established by a research project conducted by ASHRAE (Then ASHVE) at Kansas State University in the 60’s. The KSU research was validated at today’s lower air flows in a subsequent research project at the University of Texas at Austin in 2013. The premise that “there is no minimum air speed for comfort” (included in the first release of ASHRAE Standard 55 in 1979), was finally validated in a research project that took place in a million square foot building in 2012. Sometimes these things take a while.

While visiting California and Arizona last year, I was promoting the concept of using a variable volume series fan box, (and a sensible cooling coil), to deliver a measured quantity of ventilation air, as well as efficient and flexible operation of economizer (both air side and water side) to commercial spaces. This concept has been in use in Washington DC (starting with the Pentagon) for 16 years. Imagine a concept starting on the east coast and spreading west (instead of the other way around). Operating a series fan box at the lowest possible airflow, while meeting demands, can provide a comfortable environment as well as an energy efficient solution. The energy consumption of ECM boxes has been documented through joint ASHRAE / AHRI research at Texas A&M University. That data is being added to HAP TRACE Energy Plus and other energy use computer programs. Three published ASHRAE journal articles describe the research and its implications.

I am proud to have been involved in all aspects of this technological development. Starting with an impossible specification in a GSA building in 1973, we in the air distribution industry have finally figured out how to effectively and efficiently manage indoor environments in a measurable and controllable fashion. Using ADPI prediction techniques developed in the late 60’s, and validated in the last few years, we can provide design guidance for engineers to lay out air distribution in a way that will ensure occupant comfort at today’s low interior loads, taking advantage of the latest DDC controls and variable fan speed technology. I look forward to assisting the newcomers to this industry as we take the technology into the future.

Authored by: Dan Int-Hout, Chief Engineer Krueger