Can VRV-VRF systems be modeled?

fmno · Posts: 7

Hi Andy. I found a discussion topic on the site greenbuildinggenie stating that Energy Plus can't address VRV systems. It's an old discussion. Is it so?

I'll paste the discussion below:

“Engineers rarely have the time and inclination to undertake complex building energy simulations, and current non-proprietary tools such as Energy Plus cannot address VRF systems. Furthermore, ARI has not yet established a certification program for VRF system performance, although it is expected by 2008. ”Source: ASHRAE Journal, April 2007

Software which can simulate a VRV systems:
Energy Pro
Trace 700

Software which cannot simulate a VRV systems:
Visual DOE
eQUEST
Energy Plus

Approximate methods for modeling VRV in various software:

VRV modeling in eQuest
Source: Gary Schrader on Mon Mar 23 2009 on eQUEST mailing list.
“Our office has been modeling Daikin VRV systems in eQuest for a few months now. Don't get too excited... we haven't actually installed one yet so we have no real data with which to prove that we are modeling the systems correctly. That said, we also have only modeled their "Heat-Pump" line and not their "Energy Recovery" line, which allows simultaneous heating and cooling between zones.
We created custom curves with which to model the compressor by taking Daikin Engineering data out of Daikin tables and plugging it into eQuest. Then we model the system using the "Packaged Single Zone" system type. We set the Indoor fan to two-speed and gave it a very light static pressure, due to the fact that the system has multiple indoor fans with low static vs. one fan with lots of static. We hard-keyed the CFMs, the rated capacities, the compressor RPMs, low and high, the minimum cycling part load ratio, the cooling (and heating) EIR, and set the compressor to variable speed type and gave it a minimum unload ratio, again, all from Daikin literature. We used eQuest's default low-speed EIR curve.
The capacity curve and the EIR curves we custom-created using eQuest and Daikin data. The results seem logical. Again, it's hard to prove that things are dead-on because we have no real building to compare our results to. Hopefully, though, that will give you a place to start.
I am not confident that I am modeling defrost correctly, and winter results in general seem more sketchy. I am using eQuest's default defrost running time fraction, which I assume is more pertinent to standard unitary equipment. Daikin's defrost seems more efficient. It also doesn't help that Daikin doesn't use either resistive or reverse cycle for their defrost strategy... it's actually hot-gas bypass.
One last thing, all of the engineering data that we obtained from Daikin was published on their website “

VRV modeling in EnergyPlus

“I think the closest you could get on the cooling side would be to use an AirloopHVAC: UnitaryCoolOnly with AirTerminal: SingleDuct: VAV:NoReheat air distribution units. The power side of the VRF would have to be modeled using a squared curve on PLR where Power is proportional to the square of speed (or PLR). However, with this configuration the fan power will be low since VRF systems typically use constant volume fans. You can modify the fan power in a spreadsheet after the simulation is complete. Sorry if the jpg doesn't come through but it just shows the squared power law of power vs speed. For heating it is much harder. Using the AirloopHVAC: UnitaryHeatPump: AirToAir with AirTerminal: SingleDuct: Uncontrolled will model both cooling and heating, however, the compressor control is limited to a single zone. If the zone loads are balanced (flow through air distribution units are balanced based on load) this will be a fair approximation, at least with what is available in EnergyPlus. You could still use the squared curve for power in this object. So there is no simple answer, you would have to pick a system and review the results to see how close you are to manufacturer’s performance data. Then modify the input to more closely model the system using different configurations. There are many EnergyPlus users that would be interested in your findings. “
Greenbuildinggenie is providing this information to comprehensively collect information on this tip. We neither recommend nor endorse these methods. Some of the software may start supporting VRV modeling in near future. Please check the software before concluding.

fmno · Posts: 7

Any news on this?

Source: Energy Plus Help Serve

Update 1/22/2010: The VRV/VRF model is scheduled to be added to E+ near the end of 2010/beginning of 2011.

The VRV (or VRF) model is not yet included as an equipment type in EnergyPlus and may be added in the future. Heat recovery for VRV systems will not be added until a later date when manufacturers provide sufficient data to develop a model for this performance aspect of VRV systems. Simulating a VRV system with the existing VAV model will only provide valid information when cooling is required. The results will only be as good as the DX cooling coil performance curves allow. The heating side of a VAV system does not use a DX compression system (i.e., uses gas or electric heat) so this part of the VRV system can not be modeled with a VAV system. The air-to-air heat pump model is the closest available model and will provide information for cooling-only or heating-only operation (VRV heat pump mode). Again, VRV heat recovery mode can not be simulated at this time.

lklawrie · Posts: 181

From the EnergyPlus developer:

The VRF/VRV model is going in now and will be available for the next release.

As far as what information is required from the manufacturers to model the VRV system, full load performance data over a wide range of conditions. This is mostly available in manufacturers engineering literature. Part-load curves can be assumed from the combination ratio (or outdoor vs indoor unit capacity) data.

I agree that lab/field data is necessary to validate the model. This is also happening now and will be available in the comming months, or a year or so, depending on when testing is completed.

danigarcia · Posts: 1

Hi all,

any news in VRF simulations in Energy Plus?

lklawrie · Posts: 181

A version of EnergyPlus with VRF simulations has been out since early May. Will be in the upcoming V7 release.

sukreetsingh · Posts: 9

Thats a good news.

When can we see that option integrated in DB?? Will the new beta release have that option??

altensis · Posts: 1

Andy Tindale · Posts: 2432 Location: Stroud

The latest news on VRF is that E+ v8, due for release in Oct 12 is expected to include VRF with heat recovery. DBS are planning to implement this as soon as possible. I can't give a date as to when this will be available within DB but it should be ready in beta form at least by the end of the year.

Richard Raustad at Florida Solar Energy Center is working on developing a set of performance curves to be used in the VRF system. A report on progress can be seen at:

https://securedb.fsec.ucf.edu/pub/pub_show_detail?v_pub_id=4588

We don't plan to implement an interface to the current E+ v7 VRF system which does not include heat recovery.

Andy

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