With ACV coverage, after a partial claim you will receive exactly what you had at the time of loss. For example, 30 year old kitchen cupboards would be replaced with the value of 30 year old kitchen cupboards. Any claim would be depreciated.
After a total loss, you will receive the insurance amount or the market value of the building, whichever is less. Customers are usually not very happy after a claim with this type of coverage, but it can be a way to provide catastrophic coverage for an investment property that might not be worth having a great deal of coverage on.