Why does the AC Sizing gets smaller when I change to VRF from Unitary?

Hi, I have been wondering, when I am using the Template VRF systems with almost identical inputs to the Template Unitary systems, my AC sizes have been reduced by 10-15% in each of my simulations. I was attributing this to the fact that the VRF are more efficient systems, but if they both have the same exact heat load, why would the sizing be different?

Thanks in advance, Cheers. Link to IDF files

My guess would be the cooling capacity as a function of temperature curves. If they are not the same the capacity will change. Coil Capacity = Zone Load / CapFT.

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rraustad

answered 2023-08-21 07:52:01 -0500

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Ahh I see, do you happen to have an example of what a system's temperature curves look like? I don't think the AC suppliers in my area have that kind of data unfortunately.

And also another question, I have noticed that the Unitary unit I am using is locked into a SingleSpeedDX coil, in this the same as a Non-Inverter AC that is still popular in Asia? Thanks for the help Richard

kirakatsui (2023-08-23 21:04:02 -0500) edit

Yes, single speed is non-inverter. The variable speed coil is really the only thing close to inverter based systems where each speed is close to inverter performance and performance is interpolated between speeds.

rraustad (2023-09-20 09:55:23 -0500) edit

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Why does the AC Sizing gets smaller when I change to VRF from Unitary?

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Why does the AC Sizing gets smaller when I change to VRF from Unitary?