VRF COP Calculation

[Tayters]

I've been asked to work out the COP of a VRF system.

I've gone through the design manual (Fujitsu) and following the example you need to work out capacity of indoor at design conditions to get the diversity, then follow the outdoor unit tables at the diversity just worked out (maybe interpolate to get the correct value) and design conditions to get outdoor capacity.

Lovely, then I can work out COP quite easily but do I have to take into accout the multiplying factors for pipe length and defrosting. This is the bit I'm not sure on.

To work out COP I just divide outdoor capacity by input power. Would I have to get my outdoor capacityat design conditions, multiply by the correction value then use this as the capacity but keep input power the same?

I've attached the pages from the manual (sorry seperate due to the size) if that helps this all make a bit of sense.

Many thanks,
Andyexample1.pdf

[nevinjohn]

COP determination of VRF cannot be guarenteed, it can be determined for the full load conditions only. As the compressor varies its speed, the COP fluctuates as per the load!

[Rob White]

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Hi Tayters COP in the true sense is the Refrigeration Effect divided by the Work Done.
Refrigeration Effect is RE and that is the evaporator and Work Done is WD which is the
compression cycle.

The old

RE
WD

Formula

You are talking about Energy Efficiency Ratio (EER) which is slightly different.

Energy measured in KW can be calculated to work out the EER and is as simple
as dividing the output power by the input power.

So in heating mode if you were delivering 8KW of heat output you divide that by
the 2 ish KW of power input and end up with an EER of 8 divided by 2 = 4

If you were working out cooling then it is the same calculation just different numbers.

Regards

Rob

Ps just read the date of the first post I'm quick aren't I

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[Tayters]

Hi Rob,

I remember that query...

Yes, of course EER is power out/power in but weirdly the Fujitsu bumpf lists this as COP in cooling and EER in heating. Just down to terminology I guess and looking at it Fujitsu info for over a year I kinda got used to it.

Question arose because the EER (COP!) figures are given for nominal values which I guess are at 100% diversity. If I add more/less indoors then how does this alter the value.
Well, what has crossed my mind is that if diversity is over 100% then you can only get so much from the outdoor so this is just divvied up between the indoors so EER will remain the same.

But...

Looking at tables for an S-Series a while ago they seemed to suggest that if for instance you had a 28kW outdoor unit with 110% diversity then the outdoor duty available was 30.8kW for the same nominal conditions thus contradicting the last paragraph. Didn't get any further with that as really had to get some productive work done but it made me question what I thought I knew. That wasn't much in the first place anyhow!

Putting any design in the Fujitsu VRF simulator just gives EER for the outdoor unit as published in the specs and any combo of indoor units makes no difference. I wasn't sure if this was an oversight or correct. In fact the more I looked into it, the less I remembered what the orignal question was anyway!

Will stick to water leaks for the time being.

Cheers,
Andy.