Currently there is one static default life time for each improvement category. This life time can be exposed and edited on the Improvement/Costs tab. Click on the “Columns: O and M” check box to expose the “Life Time” column. The default for the Upgrade DHW row is 13 years.
I would like to assign a different lifetime to a solar hot water system based on the manufacturer’s information. They last longer than a tank water heater, and this longer lifetime needs to be reflected in the SIR. But I can’t add and item or change anything in the SHW tab – there’s nothing to edit in the Improvement/Costs tab.
We do not currently have a way to store lifetimes for individual units, but we hope to add that sometime in the future. When we do, it will be edited through the screen pictured in your attachment.
Currently you can only edit the general lifetime for the Upgrade DHW improvement, as described in my initial reply. I have attached a screen shot to illustrate. The Life Time column appears as the third from the left, when you have checked the “O and M” box.