M&V metering of VRF systems

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I am developing an M&V plan for a building with a VRF system. I am wondering if it is possible to meter the heating, cooling and fan energy of the VRF units given that the unit power is provided by a single feed.

It seems like a complex task to accurately measure the heating and cooling energy given that the system includes the VRF cassettes, water cooled condenser, the fluid cooler, the branch controllers, and the boiler.

Thanks for any insights!

Christopher Jones, P.Eng.
Tel: 416.644.4226 ? Toll Free: 1.888.425.7255 x 527

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Chris Jones
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Dear Christopher,

It is a bit daunting, but seems do-able with trend data and a data base of equipment information. We make extensive use of BMS trend data to assess performance of existing buildings. Trends can show all sorts of interesting problems! While they do not reflect energy directly, the data can be used to inform an energy calculation. We put together some examples (attached) for some of our clients and your casual reading ?.

There are a number of SaaS platforms that are aimed at efforts similar to M&V and may be worth investigating. Our favorite is www.retroficiency.com. They are fast, use actual weather data, provide convenient calibration tools and their support is exceptional. They?re located about 5 time zones to the West of you, but seem to answer email and phone calls at all hours.

Other platforms include Noesis, EnergyCAP, First Fuel and a few others ? we?re not too familiar with them, however.

Depending on how detailed you need to be, there are a few tools now available for parametric analysis (Open Studio, DesignBuilder, jEPlus and maybe gEnergy) Another option is to use GenOpt in conjunction with EnergyPlus to get the best R-squared correlation between predicted and actual energy use. We wrote a small program to semi-automate that task.

That?s all for now.

p.s., I don?t think Retroficiency can simulate VRF yet, but you may be able to create a water-source heat pump workaround.

James V Dirkes II, PE, BEMP, LEED AP

www.buildingperformanceteam.com

Energy Analysis, Commissioning & Training Services

1631 Acacia Drive, Grand Rapids, MI 49504 USA

616 450 8653

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Fan power for the FCU/cassettes may be supplied separately in your building, so that maybe monitored if the distribution is separated from other electrical distribution in your building. If the project is residential however, these may be in common with the rest of the circuits for each apartment. In that case the M&V may have to focus on monitoring by apartment rather than end-use.

For heating/cooling you?ll need to trend status of the equipment, along with power consumption in order to determine end-use. At times the unit may be capable of producing heating and cooling at the same time if your system has that added functionality, which may not be allocated to end-use in the same manner as the simulation program.

In terms of M&V, the power use seems to be more important for your plan than actually applying towards heating or cooling end-use.

David

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Grumman/Butkus Associates

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Chris,

I've talked to my local Mitsubishi rep in the past about installing VRF ?systems in a condo building. Apparently they offer a package that monitors the expansion valve positions of the indoor units along with the branch box modes and energy use of the outdoor unit so that it can assign an energy use to each condo for billing purposes. ? It probably isn't up to measurement canada specifications but may be fine for M&V.

I'd be interested in how your system performance plays out. You may be aware of the reports of the GSHP out-performing VRF (VRF uses much more than expected) ?at ASHRAE headquarters. I haven't done M&V on a VRF system but the building energy use for a couple of our (air and water cooled) projects is much higher than expected. ?

Something that we've noticed ?on a recent air-cooled project that we're modeling with HAP is that it shows a significant penalty for systems that have a vertical height difference - it says the 1st floor would use 33% more heating energy than the 10th floor with roof mounted outdoor units. I realize there is a capacity reduction (which varies by manufacturer) but there must also be a corresponding increase in compressor electricity use. Or at least that's what I gather from the results. ?I'll need to request their algorithms.?

Hope that helps,
Aaron

Aaron Smith, P.Eng
M&R Engineering Ltd.

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Aaron, et al.:

Along the lines of a specific GSHP system outperforming a specific VRF system @ ASHRAE HQ - my understanding is that this is not such an easy claim to make. The two different technologies serve different space-types within the HQ building - making a comparison of actual energy use/EER between the two technologies not that useful, IMHO. Never mind that a GSHP system with a grossly oversized ground exchanger and good pump controls can outperform nearly any system that I am aware of.

A more interesting comparison of the ASHRAE HQ experience, from my point of view, would be to compare the predicted vs actual energy use of each technology - to learn how well current modeling tools/methods/procedures can be applied to better predict the performance of either of these complex HVAC technologies.

This leads us to the issue of what can sometimes be described as the 'black art' of the current state of VRF modeling used by practitioners modeling VRF in most simulation tools - But things are changing on that front as well. EnergyPlus has included a fully documented and tested method of VRF modeling for several releases. Some of you may have caught the importnant DOE /LG press release 10 days ago - http://www.energymanagertoday.com/lg-puts-air-conditioning-attributes-technology-exchange-0101043/ . In this release, DOE announced the uploading of the first set of expanded performance tables from a major VRF manufacturer into the TPEx (Technology Performance Exchange) portal. TPEx is a simulation agnostic web portal for supporting technology evaluation, which has been designed to seamlessly exchange data with the BCL (Building Component Library). BCL is another (simulation agnostic) warehouse of downloadable modeling components, currently populated with mostly OpenStudio modeling components.

Which brings us full circle. Expect, within several weeks, to see a method made available for direct extraction of manufacturer's VRF equipment expanded performance charts/tables from the TPEx to create BCL objects (VRF Performance Curves) for direct import into a user's OpenStudio model. True end-to-end data exchange direct from manufacturers most up-to-date published performance data, and sub-hourly. No more manual curve fits. This can radically change the way we currently predict the performance of VRF systems. Once data exchange systems like these are in place, we can start to use our tools to tune models for comparing actual vs predicted energy of specific VRF systems (indoor/outdoor combinations).

PSD will briefly demonstrate this method during our next free OpenStudio webinar, which will covering features available in OpenStudio v1.4.0 - watch for an announcement sometime in June.

All the Best,

_Chris

Chris Balbach, PE, CEM, CMVP, BESA
Vice President of Research and Development
Performance Systems Development of NY, LLC
124 Brindley Street, Suite 4, Ithaca, NY 14850
http://www.psdconsulting.com
ph: (607)-327-1647

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Thanks for all the information Chris. I agree. I seem to remember reading
in an article that the VRF system used more energy than "expected" which is
a much better comparison but even at that, the loads on the system may have
been higher or occupancy may have been different than expected, etc. so a
post occupancy evaluation is required.

And validated modeling software would be great to provide us with more
confidence when we perform modeling to compare systems. Now, I just need to
take the time to learn a new software program!

Aaron

Aaron Smith, P.Eng
M&R Engineering

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