We have a debate going in our office about whether Sub-Meters are required (or Not) for the Option D - Whole Systems Simulation method. In LEED NC V2.1, sub-meters were explicitly required, but over the years things have changed....2.2 and 2009 have softened their requirements for sub-metering and they refer to the IPMVP Volume III for Guidance.
We've been doing sub-meters / sub-measurement on new projects because we think it is worth the cost; therefore we haven't even tried M&V without sub-subsytem feedback. We now have a commissioning agent that is seriously questioning our decision to sub-meter / sub-measure the project systems, but we think the project complexity warrants some feedback at the systems level and depending on the interpretation - that the credit would require it.
What is the general opinion? Are Sub-Meters totally up to the discretion of the team, on any project (excluding C&S applications)?
Is a high quality, calibrated energy model compared against the whole building meters one year after the completion of commssioning (along with a M&V plan and recommendations for improvements) all that is needed to earn Option 1 / D - no matter what?
And last but not least - Is the issue here really a language barrier around the definition of "Metering" and "Measuring" sub-system performance? I.E. Is 'Measuring' sub-systems potentially required?
Looking forward to the Opinions on this one...
Doug
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5912 thumbs up
September 28, 2010 - 9:02 am
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).
Christopher Schaffner
CEO & FounderThe Green Engineer
LEEDuser Expert
963 thumbs up
September 29, 2010 - 3:12 pm
Marcus - thanks for the excellent response.
We should put in big bold letters -"Measuring, not Metering".
Doug Pierce, AIA
Architect / Sustainability StrategistPerkins+Will
235 thumbs up
September 30, 2010 - 10:45 am
Marcus and Christopher - Thanks for the response! This is very helpful.
We reached a similar conclusion - that permanent sub-metering is not required per IPMVP. However, in my experience, some 'Real-Time' feedback is needed for non-constant loads like daylight dimming, VFD's, and other loads to accurately calibrate the model (as your comments point to Marcus).
From your experience, would it be appropriate to say the trending data through an energy managment system would (likely) meet the sub-system feedback needs for most M&V applications / model calibration?
One last question(s) - Is their an industry recognized definition that provides clarity around the term 'Metering' (I.E. is there a level of accuracy or an accepted method for the design of instruments that make them qualify as 'Meters'?). AND would digital measurement from a Energy Management System, that may not be as accurate as other kinds of 'Metering' qualify as 'Metering' for the LEED Credit (I'm sure the answer could easily be 'it depends').
Thanks in Advance for you reponse!
Best Regards,
Doug
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5912 thumbs up
September 30, 2010 - 11:37 am
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.
Doug Pierce, AIA
Architect / Sustainability StrategistPerkins+Will
235 thumbs up
September 30, 2010 - 11:40 am
Thanks Marcus! This is great information.
Doug