The CLF study on MEP systems might help. There is also a calculator that goes with it. Alternately, looking at the materials and their quantities that go into making a particular system is another good approach, as Boris mentioned.
Calculating pipe or duct impacts are fairly straightforward, equipment is more complex. These systems can have a significant amount of iron, copper, plastics and other materials besides sheet metal and it can be tedious coming up with those material quantities. You should also consider the replacement period and what recycling programs there are for each system since typical lifetimes of MEP equipment is much shorter than a building lifetime.
I believe LETI in the UK worked or is working on another MEP LCA guidance. I believe @louise.hamot may have more info?