Redundancy with common duct system?
Redundancy with common duct system?
(OP)
What is the typical approach method we use when attempting to provide redundant floor-mounted indoor air handlers if only one duct system will fit in a space? Are they stacked and ducted together at the supply and return flanges? Do we provide duct-mounted motorized dampers to minimize the pressure drop at the common connection points?
Thanks in advance.
Thanks in advance.





RE: Redundancy with common duct system?
Motorized dampers to isolate the non-functioning AHU would be a start.
RE: Redundancy with common duct system?
RE: Redundancy with common duct system?
RE: Redundancy with common duct system?
RE: Redundancy with common duct system?
The clients logic was that the facility runs 24/7, is booked out a year in advance and the additional AHU cost was insignificant to loosing a days revenue and having to reschedule their customers.
RE: Redundancy with common duct system?
was all DX, from pairs of 2000 CFM up to around pairs of 20000 CFM for the main switch
most challenging was a pair of 40 ton lieberts, each liebert had two separte blowers in it.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Redundancy with common duct system?
If the recovery test is done periodically, along with other environmental performance tests, revalidation doesn't take much time.
I would prefer actuated dampers.
RE: Redundancy with common duct system?
The lieberts I was mentioning were in essence, 2 20 ton units in one casing, thwo separate blowers with motors, two separate evaporators, 2 separate semi hermetics and yet being a smidge low on oil takes them out.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Redundancy with common duct system?
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Redundancy with common duct system?
I would suggest it is more like having an automatic back up that switches over when a system goes down, as opposed to having the repair parts on hand and having to wait for the repair to be made. It would take some time to pull a coil and replace it.
Temperature can rise pretty quick in some applications when a system goes down.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Redundancy with common duct system?
Redundant unit is mandatory for BSL-3 (BMBL) and typcial for vivarium. As on renovations, floor space is limited, I have frequently used split case units, such as by Flanders.
Before going too far, I would recommend having "redundant" defined very clearly, as even when it appears to be explicit by criteria, the interpretation will vary widely. An example which I have encountered frequently is on the power side: does redundancy include splitting feeds between MCC's? I've had a BSL-3 drop on failure of normal distribution, meaning the gennie doesn't turn on. Did not happen twice, and the point was no longer argued. Yesterday I spent 3 hours in a meeting going over this exact issue, defing "redundancy" as opposed to only having the word inserted in a contract (a computer center). End result was customer agreeing to more money than orginally expected to provide "redundant" feeders to a dedicated double end for full A-B supply, with separate UPS. As part of the compromise, the customer agreed that "redundant" fuel supply for the gennie was not required, and should improve lead time. For USP 797 compiance, "redundant" meant two sources of cooling medium, chilled water primary dedicated (a 3-TR dedicated unit) backed by house system and no DX allowed. Heating medium was "redundant" with electric (on e-power) as primary and building system as redundant. No redundant AHU or exhuast was needed, and this met the USP 797 criteria for the contract.
Redundancy is very costly, and no assumptions should be made. State exactly what you are proposing before the dollars come due.
RE: Redundancy with common duct system?
RE: Redundancy with common duct system?
Can I know which regulation you are referring to?
RE: Redundancy with common duct system?
This one is tricky, as the criteria is to "minimize" potential release based on risk assessment. On two different jobs on the same floor of a building, redundancy requirements between BSL-3 vs. ABSL-3 have been over $1.3M. The fun stories from those jobs (and a couple more) make me always verify what is intended by "redundant". Adding in biosurety was the final difference between "difficult" and ulcerous.
Very happy to no longer be in that business. Too many unpleasant memories for a life time.