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# Difference between two types of HVAC?

I am working on modifying DOE reference buildings with new types of HVAC, but first am attempting to replicate the results of the METER output data from the DOE IDF within Open Studio. I am not seeing the item AirLoopHVAC:UnitaryHeatCool in Open Studio 8.3, but am currently using AirLoopHVAC:UnitarySystem instead. I am not getting matching results for the cooling electricity usage even when setting the electric reheat for this system to zero. Still using Fan:OnOff, DX CoolingCoil Single Speed, and gas heat. Can anyone explain the differences between AirLoopHVAC:UnitarySystem and AirLoopHVAC:UnitaryHeatCool so that I can better find a solution for my problem?

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As far as I can tell, AirLoopHVAC:UnitarySystem was introduced later and is supposed to be able to represent all the older AirLoopHVAC:Unitary... systems. I'm not sure why exactly the older objects remained in EnergyPlus as they are supposedly antiquated.

If you set them similarly you shouldn't see a difference in energy usage. Your problem might come from a whole lot variety of problems.

Anyways, what follows is not the answer to your question, but hopefully it should be very helpful nonetheless for your underlying goal. There is a project undergoing to create all the DOE reference buildings in OpenStudio using measures. This is available on Github, and is called OpenStudio Prototype Buildings.

It is not a 100% complete project as some building types are missing - such as MidRiseApartment - but the ones that are in there do work. For now you can just put the entire repository in your C:\Users\...\OpenStudio\measures (or wherever your os measure folder is located) folder and use it on a blank model in the OS App using the 'Apply Now' function.

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Yes Julien is right. AirLoopHVAC:UnitarySystem is the one unitary to rule them all, and it came out after the other ones. In the interest of minimizing the number of types that OpenStudio has to support, we just consolidated on AirLoopHVAC:UnitarySystem. We did have AirLoopHVAC:UnitaryHeatPump sneak in before the super unitary was introduced and have left it in place to maintain backwards compatibility.

( 2015-10-03 23:31:02 -0500 )edit

In my previous experience (early August) that measure was not complete and did not lead to replication of the DOE Reference Buildings to OSM format. Using this measure was our first idea, but it did not pan out and seemed to be a work in progress.

( 2015-10-05 10:49:44 -0500 )edit