IPVMU Certified | 05/19/15 07:21pm
#1: I believe maintenance cost and manageability is the biggest benefit of centralized UPSes.
One big battery bank is easier to maintain, service, and secure than many smaller units spread out over a wide area.
Ease of scalability may also play a role. Every time you add a camera or switch, a distributed system could prove expensive to grow.
On the flip side, a distributed system may make it easier to manage loads. If one subsystem needs more power, you just locally add bigger/more batteries.
For your #2: Do you mean use both distributed and centralized UPSes at the same time?
IPVMU Certified | 05/19/15 11:29pm
In addition to Brian's excellent points I would add a couple others.
Central UPS Benefits:
- Initial Purchase Price, dollars per kVA is likely to be lower due to larger cells, as well as shared components like cases, power conditioners, electronics etc.
- Less Excess Capacity need be purchased. Buying smaller individual units means rounding up to the next highest capacity model on every unit. For instance requiring 600 kVa but having to buy a 800 kVA model.
- Power can not be dynamically distributed. In a central UPS during an outage, decisions can be made depending on the circumstances and the prognosis for power resumption, to limit power reserves to certain areas over others. All reserves could be directed just to a keeping critical servers running after 10 minutes, say. In a distributed system, it's every UPS for themselves.
- Single Management Interface
- More Predictable Uptime, with distributed UPSes determining how long each zone will last can be complicated with various vendors equipment and capacities. For example it may not help if the video wall stays on 30 minutes if the VMS servers only last 20.
Distributed UPS Benefits:
- No new wiring necessary since units are presumably close to their targets. On the other hand Centralized UPSes still need to deliver the power to where it is consumed. Depending on the topology this can be a large expense in adding dedicated, discrete circuits.
- Add-Hoc Growth Distributed UPSes can be organically added as a company grows. Centralized UPS requirements need to be carefully forecast at time of first purchase. The penalties for overshooting or underestimating can be large.
By cascading do you mean for redundancy when two similar units are put in series with a 'make then break' bypass switch, i.e, as opposed to a parallel load sharing configuration?