Permanent Metering of Sub-Systems - Option 1 / D

Hi Doug, Submeters are not required (actually they never were required despite the language in v2.1 since the IPMVP never required them, that was a mistake and the EA TAG regretted it for quite some time). It is possible to develop a M&V Plan which gathers the necessary data through spot measurements and short-term trending. The real issue is related to the cost of optaining the data. For small facilities without a central control system it makes sense to not install sub-meters, especially on the electric end. For large ones a sub-metering system will likely be far more cost-effective than gathering the data via more manual methods. Projects should do either (or both) in alignment with common sense. Get the data the cheapest way possible. Yes all you need for EAc5 is what you describe. The Plan is the key. Regarding this specific issue - will the Plan gather the data needed to calibrate the model? There are multiple ways to do so and all are legitimate. Yes measuring, not metering, by energy end use is required to sucessfully calibrate a model. Not necessarily every end use but the ones not measured need to be derived from measurements. For example, if the lighiting and HVAC are measured one could derive the plug loads (assuming that covers all the electric loads).

Marcus - thanks for the excellent response. We should put in big bold letters -"Measuring, not Metering".

I agree that some of the highly variable loads need more thorough measurement or metering. Projects most certainly can trend data in an EMS. It is probably by far the most common way to do so in larger facilities which have one. This type of measuring definately does qualify under IPMVP and LEED. Not sure if there is a recognized level of accuracy for meters in general. What is acceptable does depend on the level of accuracy required by the project since typically higher accuracy cost more money. The IPMVP does not specify meter accuracy ranges, as far as I know, to allow projects teams to determine what works for the individual project. ASHRAE 14 addresses calibration procedures since the accuracy range is only valid in a calibrated meter. This can be a key component of overall measurement uncertainty which is something that should be addressed by the M&V Plan. Acceptable uncertainty is influenced by budget and complexity. The goal is to reduce the level of uncertainty as much as possible. The overall acceptable level of uncertainty will influence the acceptable range of individual metering accuracy. The overall effect of the system being metered will also influence the desired level of accuracy for that meter(s). So if your overall acceptable level of uncertainty is +/-5% then your individual meters can't be +/-5% since they would then take up all of the allowable uncertainty. With all that said we would typically like to see electrical meters in the +/-0.25% to +/- 1.0% range and gas meters in the +/-2% range.