[Bldg-sim] M&V metering of VRF systems

Chris Balbach cbalbach at psdconsulting.com
Fri May 23 06:11:26 PDT 2014


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


-----Original Message-----
From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Aaron Smith
Sent: Friday, May 23, 2014 8:08 AM
To: Jones, Christopher; bldg
Subject: Re: [Bldg-sim] M&V metering of VRF systems

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.

Sent from my BlackBerry 10 smartphone on the TELUS network.
  Original Message
From: Jones, Christopher
Sent: Thursday, May 22, 2014 14:02
To: bldg
Subject: [Bldg-sim] M&V metering of VRF systems

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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