I wanted to see peoples thoughts on aged equipment efficiency, such as a HW boiler or DX cooling coil.
I think that without a doubt it can be agreed that the the efficiency of a piece of equipment at the 10 year mark is going to be less than the efficiency of the equipment when it was first installed. This may be attributed to dirt build up on condenser fins, decreased lubrication of bearings, changes in the thermal properties of materials, or general mechanical wear for example. The only way I'm aware of to determine the actual efficiency would be to perform a laboratory test on the piece of equipment which isn't realistic the majority of the time. This is however, a very important concept to capture in the modeling of an existing building. Without this the replacement of an old unit with a new unit may produce artificially low savings.
I've done a few strolls through the interwebs, but wasn't able to find much, especially with respect to energy modeling. I found this report with respect to residential equipment that I think was fairly concise and relevant (even though it's not applied to commercial buildings). It references an NREL report, but I wasn't able to find it as the links that were given were broken. I like the concept of simply factoring the original EER by the square of what's effectively an 'aging' factor directly related to how well the unit was maintained.
Anyway, just wanted to see if anyone was willing to share how they capture aged equipment in their models.
