Redundant system

[alanchow]

The client want us to design a 50% redundant HVAC system for them. In my opinion, 50% redundancy means we need 3 rooftop units with 50% capacity for each, anytime we just run 2 units to get 100% capacity and another one will be the backup, is that correct? Thanks.

 

[imok2]

In engineering: serving as a duplicate for preventing failure of an entire system. That said I would Have one unit for 100% load and another as a stand by.

 

[MintJulep]

See faq403-1308

 

[alanchow]

thanks all. two unit each with 100% load means 100% redundancy. now the question is about 50% redundancy.

 

[mechanicaldude]

You need one AHU sized for 100% of the load and another backup size for 50% of the load. That is the 50% redundancy. Sometimes owners want this because they don't want to pay for two 100% units, so they feel that if something should go wrong with the main unit that they can get by on 50% temporarily until the broken one is fixed.

 

[marcoh]

I just had a similar discussion with a client the other day andhe statement can be somewhat ambiguous and needs to be confirmed with the client. Their reasoning was:

- 100% redundancy means if anything fails 100% capacity is available, ie two units at 100% capacity, 3 units at 50% capacity, 4 units at 33% capacity etc

- 50% redundancy means if anything fails min 50% capacity is available, ie two units at 50% capacity are required (or 3 at 33% etc)

For this particular project the requirement was 75% redundancy so four units at 25% full load are being installed, if any one fail 75% capacity is available which is still sufficient for most of the time.