Q: part 1: The first, if I make an optimization in the boiler system to reduce energy consumption in heating and domestic hot water, should I base myself on option C or B?

A: part 1: Either could be acceptable/applicable but depends on considerations such as the following:

Intent and goal for the M&V – is the goal to relate the verified savings ultimately to the utility bill/facility meter or is the goal focused on the boiler retrofit performance itself?
Baseline data availability;
If the boiler and hot water systems are currently supplied by a dedicated meter (natural gas or electric), for which the boiler/heater systems represent a large part of the load, with complete 12 months (or longer) data and a statistically valid regression model can be developed based on available relevant independent variables, then an Option C could be viable. If the savings are less than 10% of the metered data, then refining the data for regression to hourly or weekly intervals could help.

If the boiler and hot water systems have historical data regarding energy consumption such as trend data from a BAS, as well as ideally other operational variables such as temperatures, flow rates, heating load supplied (energy meter) or that data can be collected for an appropriate amount of time to capture full range operational characteristics, then an Option B could be viable. All parameters would then be required to be measured post retrofit for the reporting period Option B savings verification.

Q: - part 2: The other question, if I want to optimize the use of a Water Chiller and I do not have 12 months of electricity bills, how can I measure the savings after the MEE, do I consider option B?

A: part 2: Yes. Similar to the approach above for the boiler system, pertinent baseline data would need to be collected to establish the retrofit isolation baseline and then the corresponding measurement plan in place for the post, reporting period to capture the energy and operational characteristics of the chiller (after the MEE). Considerations should be included regarding where the retrofit isolation measurement boundary is established, ie is it just the chiller itself or is the chilled water plant including the pumping, cooling tower (if applicable) to represent the entire plant and associated capturing of improved performance for total chiller plant savings.