How to create noise and vibration problems
Hvacr subcontractors who have worked on engineered projects have probably come across a practice called “value engineering,” in which a third party or general contractor (GC) makes changes to help the owner cut down the cost of construction/installation. Too often, however, the practice results in bad decisions that cause problems such as noise and vibration, or worse.
Value engineering as it is typically practiced “involves neither value nor engineering,” stated an attendee (ASHRAE policy dictates that forum participants are not identified when the forum is reported on in the trade press).
Although the forum was geared toward engineers, it’s important for subcontractors, as well as design engineers and building owners, to distinguish between formal value engineering and the other, informal cost-cutting practices. Infor-mal value engineering is:
- Marketed as a cost-cutting tool;
- Done by general contractors and construction managers; and
- Limits the involvement of other project team members.
Overall, it tends to reduce the quality of the project by straying from the design intent, and increases liability for just about anyone involved in the project, including subcontractors, unless they take steps to protect themselves from litigation.
Big noise from WinetkaAlthough devalue engineering can adversely affect many areas of an hvac project, acoustic factors, which tend to be subjective, are assigned low value and are likely victims of mistaken value engineering.
According to engineers attending the forum, this leads to a “fix it later” approach, and “builds on a momentum of ignorance.” (You know, the “It’s the way we’ve always done it” attitude.)
And, it typically involves a low-bid situation with a guaranteed maximum price.
Here are some typical devalue engineering substitutions:
- Acoustic cork sandwiches are substituted for spring isolators.
- Inertia bases are “deleted” and pumps are bolted onto slab on base.
- Large, slow fans are substituted with smaller, faster fans.
- Downblast rooftop units are installed instead of horizontal distributing units.
- Fewer, larger vav boxes are used.
- Variable-speed drives are replaced with inlet guide vanes, leading to rumble.
- Vibration isolation is value-engineered out.
The attendees had many horror stories to relate of chillers and other types of large, noisy equipment installed without proper isolation over, say, courtrooms and penthouses. In the courtroom cases, the judges demanded that the work be fixed, which cost more than it would have to stick to the original design. And that penthouse became unsuitable for habitation, losing its high-income potential for the building owner — “a warehouse space with a great view.”
In general, “The cost savings of inept ‘value engineering’ have been eclipsed by resulting retrofits,” a speaker pointed out.
There is an association dedicated to formal value engineering. SAVE International, Northbrook, IL, offers training, certification, networking, and more to its members in 35 countries. (For more information, visit the group’s Web site at www.value-eng.com.)
Out of the loop, counting beansAn attendee wondered how many so-called value engineering plans are shown to the acoustical firm for evaluation before they are put into practice. There was general agreement that acoustical consultants are out of the loop by the time it comes to the value engineering stage.
“The GC and bean counters too often are making the decisions,” complained an engineer. The question then becomes, how to educate the owner?
For starters, “Let’s only call it value engineering when it really is,” one engineer suggested. “Let’s help the owners know when it’s cost cutting versus value engineering.”
Too often, the job was under-estimated in the first place in order to land the contract. Then the value engineering fee is driven by the amount saved for the owner. “They should bring the cost estimator in early on,” was one comment.
“If the ‘value engineer’ offers $100,000 savings, we need to inform the owner about the cost associated with the risks…and don’t give that work away.”
If cuts need to be made, and acoustics will probably suffer as a result, “It needs to be a conscious decision: How much will we let the noise levels rise?”
Moreover, it’s incumbent on the design engineer to warn owners of the ramifications and consequences of cost cutting. Subcon-tractors should consider this as well. Then, document that you told the owner to spare yourself the potential litigation.
“We need to educate owners that when the job goes over budget, don’t take the money out of hvac.”