Wednesday, July 25, 2012

Flawed Specifications


I was recently asked to review a specification provided by a consulting engineer for a project at a large university. I was appalled at what I found. I started to list the flaws in the specification, but after listing about a dozen, I gave up. The specification was so filled with inconsistencies and incredibly obsolete references that it made no sense to continue.

I wrote an article for the Construction Specifier magazine back in 2004 (which can be found at http://www.krueger-hvac.com/lit/pdf/conspecvav.pdf) where I outlined a number of items found in specifications which were impossible to meet, as they were either referencing obsolete standards, required performance which could never be obtained, or were simply self-contradictory. Nevertheless, our reps and their customers are required to meet these flawed requirements.

The specification I mentioned above was worse than any I cited back in 2004. Issues found included:

- Reference to ADC 1062-R2. This standard was superseded by -R3, -R4 and finally was discontinued when the ADC stopped certifying air distribution devices in 1084. I believe -R2 was released in about 1973. It never dealt with VAV boxes in a comprehensive manner and was replaced by ASHRAE Standard 130 and ARI-880.

- There were requirements for "medium speed", an SCR speed controller, and then required ECM motors on fan boxes. There is no “medium speed” on the required ECM motors and they do not use SCR speed controllers.

- The spec called for a specific brand of pneumatic controller and then, in the same paragraph, specified DDC controllers.

- The spec then required “snap acting” actuators, “normally open”. This is a $200 add over conventional electric actuators, and “normally open” is a pneumatic control sequence.

- The acoustical portion of the spec was completely ineffective. It listed octave band sound requirements with no description of the set up which was required to measure these values, and the values themselves were unlikely to be achieved under any conditions. There was no mention of AHRI 885, the acoustical calculation specification which has been in place since 1989 and is required by manufacturer’s to use when presenting NC values in catalogs.

The challenge now is for the rep to call on the engineer and somehow point out his flawed requirements without insulting either their competence or intelligence. I have attempted to do so in the past with a large consulting engineer who continues to flatly specify a device whose published performance data is based on 1980 instrumentation and cannot be repeated under today’s Standards (ASHRAE Standard 70) and greatly underreport the device’s throws. When challenged, I was told that “fixing the specification now would, in effect, be an admission that our spec was flawed for the past 30 years”. (It was.)

At some point, consulting engineers need to review their “standard” specs for flaws, inconsistencies, and obsolete references. Meanwhile, of course, everyone will continue to bid their work, knowing that the specs  cannot be enforced.

Authored by: Dan Int-Hout, Chief Engineer Krueger

Saturday, July 14, 2012

Slots are adjustable? Who knew!

I made a call on a design engineer firm today to do a “Basics of Air Distribution” Lunch and Learn. It turns out that I learned something (which I usually do). It seems a number of young engineers weren’t aware that linear slots were adjustable. They assumed they were placed at the window and designed to blow down. No wonder so many perimeter environments are uncomfortable and drafty.
Here’s the deal. Almost all linear slot diffusers are adjustable from horizontal to vertical. There are a few with fixed deflection. (Often, of course, these are located where they should have been adjustable.) The deflectors in most slots can be switched from deflecting left to deflecting right (and of course, down). When shipped, the factory has no idea how they should be adjusted, and often there is a wide degree of variance in the factory settings, which are also subject to shipping, installer manipulation, and general handling issues.
In practice, almost all slots should be adjusted to blow air horizontally along the ceiling. For a perimeter, the ideal location, according to research published by several manufacturers back in the late 70’s when we were actually researching this issue, is a couple feet away from the window, set to discharge some air towards the window, and some into the room. This results in a good compromise between heating and cooling performance, and has a chance of complying with the requirement in ASHRAE 62.1 that the 150 fpm throw make it to within 4.5 feet from the floor. (Failure to comply with this requirement requires a 25% increase in ventilation air to compensate for the inevitable short circuiting that will result). There is also a requirement that the discharge air not be more than 15-deg F above room temperature, or the same penalty applies. The data (and the ASHRAE Handbook) also explains that delivering air more than 15-deg F above room temperature will likely exceed the ASHRAE Standard 55’s maximum room vertical stratification limits, and void compliance with the Standard.
Failure to adjust slots in interior spaces results in cold air being directed down on occupants. This is always unacceptable. I can’t begin to tell you the number of times I have suffered in an ASHRAE technical meeting in a fancy hotel where there was a slot overhead blowing cold air directly on me. I have learned to wear a sport jacket in all ASHRAE meetings. I am tempted to take gloves and a scarf.
Adjusting a linear slot requires that the design engineer state clearly in the design documents that the slots must be adjusted, per instructions, prior to balancing. When adjusted from vertical to horizontal, the pressure drop almost always increases significantly, and must be accounted for in the system balance. While some may argue that a balancer won’t do this even if required to, it is assured that if the engineer does not state this requirement, it won’t happen.
The ball is in your court Mr. Design Engineer.
Authored by: Dan Int-Hout, Chief Engineer Krueger

Tuesday, July 3, 2012

ASHRAE San Antonio Summer Meeting

Another ASHRAE meeting is now behind us. It was in San Antonio, TX which would have been brutal in June, except that the hotel / convention center are located on the river walk, so it was actually pleasant, even in the heat of the day.

I attended a number of Technical meetings; here is a summary of issues covered and developing:

-- Standard 62.1 has been considering the issue of a minimum humidity limit. Standard 55 (Comfort) eliminated the lower limit in 2004, as there simply wasn’t enough compelling evidence to support a lower limit for comfort. Standard 62.1 is finally coming to the same conclusion on air quality data. Manufacturers of humidifiers, of course, are disappointed. There may well be data to support the need for humidification for health reasons, but the data is not very ‘robust’, and is mostly anecdotal.

-- Standard 55’s issue with a limit of 40 fpm for proper use of both the graphical and PMV methods was discussed. I accepted the assignment to provide alternate wording to the section to indicate the correct use of a 40 fpm value. It is acknowledged that any space, no matter the method of comfort control, or even passive conditions, is sure to exceed 40 fpm at some location, due to convection from local heat sources.

-- The ASHRAE Standard 130 (VAV Box Method of Test) acoustical requirement for pure tone qualification of the reverb room doesn’t make sense if the measurement requires only broadband measurements. A member will look for wording in line with current, existing standards to see if they can come up with a more logical requirement. Much of the existing VAV box data was collected in broadband qualified facilities. The wording then may be applied to Standards 70 and possibly others which have a similar issue.

-- End Reflection data was discussed again. There is an ASHRAE Journal statement from AHRI on the subject in the latest issue. We will post it our site soon. I also covered the issue in previous Blogs.

-- The ASHRAE research project 1515 has been reported to be nearly complete. The significant finding from this research conducted at Yahoo’s facility in California is how low loads are in today’s modern buildings, below 6 BTUH/SF for long portions of the day. Most interior zones are designed with about 22 BTUH/SF as a default interior load. The measured load is close to the minimum ventilation and latent control requirement, indicating that systems that manage outside air most efficiently are likely to be the most efficient and that complicated/expensive systems controlling sensible loads are likely not being used in most interior spaces.

-- I have rejoined the Technical Activities Committee (TAC), this time responsible for managing the new Multi-disciplinary Task Groups (MTG’s). These are composed of representatives from different TC’s who are coordinating cross-committee issues, meeting only by conference calls, much like the USGBC committee I have been involved with for the past 18 months. There is some very interesting work taking place here. I reported earlier that when the Handbook Committee of TC 5.3 (Air Distribution) met with the Standard 55 Committee (Comfort) in Chicago, members had to be introduced, as they hadn’t met before. I suspect there are a lot of other opportunities for interplay between committees.

The next meeting is here in Dallas, next January.

Authored by: Dan Int-Hout, Chief Engineer Krueger