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How do you recommend modeling VRF multi-zone heat pump systems in CBECC?

asked 2015-05-14 16:26:51 -0500

Dustinl gravatar image

updated 2015-07-14 11:33:19 -0500

I am having trouble modeling a Multi-Zone VRF heat pump system in CBECC... None of the system types available match up to the definition of a central heat pump condenser. Does anyone have any recommendations as to how to model a multi-zone VRF system with a central Condensing Unit and 23 fan-coils?

I am using CBECC's-COM and importing my .xml from Energy Pro 6.5.



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answered 2015-05-14 18:02:11 -0500

pflaumingo gravatar image

@Dustinl, there is no easy way to do this in CBECC-Com or for compliance. You could make a few assumptions and model it as a more efficient heat pump using a zone system simulating something more similar to a VRF heat pump (VRF without heat sharing), but you won't get the part load performance you would from a true VRF system and CBECC-Com forces you to use a single speed compressor and fan, which doesn't help. Seeing as it is just compliance, you may want to try this and see if it passes. This will largely depend on what your baseline is; if it's chilled water VAV then odds are it won't pass, but if the building is small enough to have a PVAV baseline then it may work.

If you want to model VRF then my suggestion is to take the .osm model produced by CBECC-Com and open it in OpenStudio to create the VRF system as needed. This will mean that you will have to pursue the exceptional compliance pathway, but there isn't any other mechanism to show true performance of most advanced systems. I spoke with an LG rep recently and it looks like a few VRF manufacturers have teamed together to fund a VRF component for CBECC-Com that should be available in v4, which is still a little ways off as the next version coming out is v3c.

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Thanks for confirming what took me a complete day to unsuccessfully find a workaround. You have saved me possibly another day and a missed deadline... Back to Energy Pro for this one!

Dustinl gravatar imageDustinl ( 2015-05-14 19:40:29 -0500 )edit

@Dustinl, I'm not sure what you mean by "back to Energy Pro", but if it's to use the EnergyPro VRF module then I would be careful because it's not a T24 approved module and won't be acceptable for compliance.

pflaumingo gravatar imagepflaumingo ( 2015-05-15 13:03:03 -0500 )edit

With Energy Pro thee is a workaround where you can model VRF/VRV's using a split DX system using minimum values and imputing the fans (combined) in the central system. Its crude and does not due justice to the efficiency of the system but at least it can be done. By back to Energy Pro, I mean I have been steering away from it due to the fact that it is "behind" in the roll-out of the Energy+ engine. They are using still using v3a.

Dustinl gravatar imageDustinl ( 2015-05-15 13:24:44 -0500 )edit

Yup, that's fair. I just wanted to make sure I didn't steer you in the wrong direction.

pflaumingo gravatar imagepflaumingo ( 2015-05-15 13:43:58 -0500 )edit

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Asked: 2015-05-14 16:26:51 -0500

Seen: 797 times

Last updated: May 14 '15