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Heat Recovery mode of Variable Refrigerant Flow (VRF) in OS1.6

asked 2015-03-19 11:52:37 -0500

updated 2015-04-13 13:54:04 -0500

Dear modelers,

Has anyone simulated the VRF with heat recovery mode successfully?

I simulated two cases and the only difference between them is "Heat Pump Waste Heat Recovery": in Case 1, it was set as "Yes" and Case 2 used "No". I expected a lot of energy saving in heating since my model is simply 5-zone building with large core zone, I think it could provide much cooling for parameter zones during winter. However, the results show that the space heatings of the two cases are almost the same (<0.1% difference). Is there anyone who has similar experience?

I checked EnergyPlus model and the Field Description of "Heat Pump Waste Heat Recovery" says "This field is reserved for future use. The only valid choice is No". Does it mean that the heat recovery mode of VRF is currently not available yet?



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@Kyle Benne might know the answer to this

macumber's avatar macumber  ( 2015-03-25 13:49:43 -0500 )edit

Would the answer to the posted question have changed between OS1.6 and OS1.7? @Kyle Benne

keb's avatar keb  ( 2015-06-01 14:20:57 -0500 )edit

3 Answers

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answered 2015-06-18 19:36:13 -0500

hongtz's avatar

It is far beyond changing a single input in an IDF of VRF-HP systems to model heat recovery type VRF systems. There needs to have different curves, controls, and other inputs.

We/LBNL are developing and implementing a new VRF-HP model in EnergyPlus, as Edwin mentioned. We have (unfortunately the PDF file cannot be attached at this site) an ASHRAE conference paper describing the new VRF-HP model. A corresponding VRF-HR model will be implemented too in future.

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Thanks for the info! I have found the paper online. BTW, in current model, I also use Daikin curves for VRF, but they are transferred from curves used for eQuest model (IP units). Will the openstudio have the function of using VRF-HR model? Or I have to go to EnergyPlus?

Yan's avatar Yan  ( 2015-06-19 07:42:59 -0500 )edit

@hongtz, is this the paper you mention: "A New Model to Simulate Energy Performance of VRF Systems"? It seems it is for the mode "either cooling or heating is provided but not simultaneously"(in Abstract)?

Yan's avatar Yan  ( 2015-06-19 08:03:03 -0500 )edit

@Yan, we are working with a number of manufacturers to get their performance data into the Technology Performance Exchange, which makes it available in any OpenStudio application. This thread discusses the topic further.

ljbrackney's avatar ljbrackney  ( 2015-06-19 09:10:09 -0500 )edit

answered 2015-06-02 08:58:14 -0500

The VRF simulation code does consider that field, so yes, it should be working, and yes, the IDD is out of date. I have made an issue out of the IDD part, and pushed a commit to fix that, and opened a pull request to get it merged into the main branch.

As far as how well the heat recovery is working, one output variable you might want to check is: VRF Heat Pump Heat Recovery Status Change Multiplier That will give a clue as to whether the unit is trying to accomodate heat recovery operation throughout the simulation.

In addition to this, I'll note that another VRF model is under development that may ultimately provide a higher level of possibilities for simulation VRF systems than the current model. In the meantime I'd suggest opening up a ticket on the EnergyPlus Helpdesk so that assistance can be provided by the appropriate developer on the EnergyPlus team.

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answered 2015-06-01 16:37:57 -0500

I have used the Heat Pump Waste Heat Recovery field and have gotten mixed results. I have found that the heating energy decreases (gotten as much as 10-15% for a small hotel, but usually under 5%) but the cooling and fan energy increases, almost negating my energy savings. I also noticed the heat recovery would sometimes have a significant impact on the number of unmet hours, reducing them quite a bit.

I do see that the +.idd file says "This field is reserved for future use. The only valid choice is No." but I believe that is out-of-date. The Input Output Reference document says differently and the Engineering Reference even goes into a fair amount of detail about the Heat Recovery Mode and it's effects, which would be a good resource to look at.

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I only second what @Matt Larson answered above. Just want to add one small point, for example for a large building at a given location with many thermal zones and at a given timestep, if the building needs 60% cooling and 40% heating (arbitrarily chosen) and if this type of load conditions exist for much of the year then savings from heat recovery might be significant. But if building is small and loads are cooling dominant for majority of the year then not much advantage from heat recovery may be expected. Also, the comment "This field is reserved for.." should be removed from idd.

Chandan Sharma's avatar Chandan Sharma  ( 2015-06-02 06:41:46 -0500 )edit

IDD is fixed here

Kyle Benne's avatar Kyle Benne  ( 2015-06-02 09:09:38 -0500 )edit

Thanks @Kyle Benne, @Edwin HVACTemplate:System:VRF object also has it in addition to AirConditioner:VariableRefrigerantFlow object. I was searching for the Note and it showed up in two places otherwise would have missed.

Chandan Sharma's avatar Chandan Sharma  ( 2015-06-02 10:05:54 -0500 )edit

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Asked: 2015-03-19 11:52:37 -0500

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Last updated: Jun 18 '15