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Too high energy savings of VRV system over RHFS, modeled in eQUEST for same 3 floor building

asked 2015-03-31 06:01:42 -0500

Ashok Dhayal's avatar

updated 2015-08-20 12:11:45 -0500

building model with VRV is having shading with fins. where would i get simulated comparative energy performance analysis of both systems and reasoning for savings obtained other than COP and part load efficiency?

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Changed the VRV tag to VRF since I believe VRV is trademarked by Daikin. Also this was the only VRV tag (lots more VRF tags).

MatthewSteen's avatar MatthewSteen  ( 2015-08-20 12:15:45 -0500 )edit

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answered 2015-03-31 12:39:06 -0500

updated 2015-04-08 13:02:08 -0500

I'm a little unclear about what you are asking here. It looks like you have included a table showing the cooling energy for a RHFS and a VRV system. How have you modelled the VRV system in eQUEST? Are you concerned that the energy savings for space cooling are too high? Is there something in particular that makes you think that they are too high? Given that the VRV building is said to have shading and given that the RHFS may have zone reheat (i.e. simultaneous heating and cooling) the results my be accurate. You might want to look at the output reports from eQUEST to try to get a better understanding of where the additional cooling energy in the RHFS system is coming from. For example, the LS-C report shows the peak cooling and heating load. You might want to check here to see if the shading drops the peak cooling load substantially. Also, the SS-E report shows the number of hours of coincident cooling-heating load for the building and the SS-C report shows the number of hours of coincident cooling-heating loads for an individual system. You can open the .SIM file in a text editor (it's in the same directory that the project files are saved in) or by selecting "Tools" -> "View Simulation Output" from the menubar.

From looking at the input files you sent me the following stand out:

  • EL1 West Perim Spc (G.W1) is modelled as CONDITIONED in Proposed and UNCONDITIONED in Standard; same for "EL2 West Perim Spc (G.W1)”;
  • LIGHTING-W/AREA = 1 in Standard and 0.5 in Proposed. A lower lighting power density will greatly reduce the cooling load in the Proposed model.
  • In the Standard Model under the spaces you are using TEMPERATURE = ( 77 ). There is no equivalent setting in the Proposed model. According to the DOE-2 Dictionary, this is the space air temperature used for the LOADS calculation. I’m not sure what affect this setting has, is it just for sizing or does it affect the actual energy calculation?
  • As you noted, the Proposed model has fins, and the Standard model does not
  • The fan power is higher in the Standard model with defaults set to 0.000396 kW/cfm in the Proposed and 0.000652 kW/cfm in the Standard; it also appears that different supply air flow rates are used in each model.
  • the windows in the Proposed have GLASS-CONDUCT = 0.33 and in the Standard have GLASS-CONDUCT = 0.59

If you are trying to figure out the cause of the difference in cooling savings I recommend that you start by looking at each change in the model in isolation.

  1. Try setting the fan power and supply air flow rate to be the same in each model. How does this affect the cooling savings?
  2. Try removing the fins from the Proposed model to match the Standard model. How does this affect the cooling savings?
  3. Remove the TEMPERATURE setting from the Standard model. Does this ...
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@Daniel: Thanks for response, I have modeled VRV as per this pdf My proposed case is modeled with VRV and standard with RHFS so I am interested for real saving of VRV over RHFS. As per discussion with other experts around me this saving is too high. Only cooling is done with RHFS.

Ashok Dhayal's avatar Ashok Dhayal  ( 2015-03-31 23:48:40 -0500 )edit

Without more information about your model it's hard to say what's happening. Have you tried comparing the part load curves for the RHFS and the VRV system? What is the seasonal performance of each system? What is the climate zone? How does the fan power compare in each system? Is it higher in the RHFS? Could this be increasing the heating load? I'm guessing the RHFS is constant volume and the VRV fans are variable speed? Can you attach your .INP and .SIM files to your question?

Daniel's avatar Daniel  ( 2015-04-01 08:24:44 -0500 )edit

@Daniel: I am unable to attach INP and SIM file here in question. Could you please write me your email?

Ashok Dhayal's avatar Ashok Dhayal  ( 2015-04-03 10:15:34 -0500 )edit

@Daniel: Many thanks for your time, I have tried to keep same air flow rate for both HVAC systems, this results in high number of unmet hours in proposed case if i keep same cooling design CFM as in standard case.

I cannot remove fins of proposed case and keep same lighting in both cases, because i need to compare energy consumption of real proposed building with standard code compliance building.

I have attached new cooling energy consumption results in question, My worry is about savings obtained in March, April and October.

Ashok Dhayal's avatar Ashok Dhayal  ( 2015-04-09 04:46:43 -0500 )edit

You're most welcome. Best of luck in figuring this one out. As I noted above, I recommend experimenting with the model to see what you can learn about it.

Daniel's avatar Daniel  ( 2015-04-09 11:18:38 -0500 )edit

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Asked: 2015-03-31 06:01:42 -0500

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Last updated: Apr 09 '15