Modeling Variable Speed Air Cooled Screw Chillers

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Hi all,

How we can model a Variable Speed "Air Cooled" Screw Chillers in eQUEST? The
available variable speed chillers curves in eQUEST are only for the
centrifugal .

Thanks,

Mohammad Al-Masri

Mohammad Almasri's picture
Joined: 2011-09-30
Reputation: 400

Mohammad,

You will need to ask the manufacturer for information on how the chiller
unloads at part load so you can create an EIR-FPLR curve of your own. That
shouldn't be too hard. It looks like there's no problem with having the
water from the chillers flow using variable speed pumps so that part's there
if you want it. Let me know if you need help creating a curve.

Carol

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If you ask a manufacturer's rep how a chiller unloads at part load, the answer might be "good". So I suggest you specifically request part load points at 10% intervals with and without AHRI condenser relief. That should enable you to make or confirm both the EIR-fPLR&DBT and the EIR-fCHWT&DBT curves.

If you want to go even deeper, you could ask for those part load points at different chilled water supply temperatures and then make or confirm a Cap-fCHWT&DBT curve. That seems like overachieving to me, but my chilled water supply temperatures rarely deviate very far from AHRI standard conditions.

Good luck,

Paul Riemer, PE, LEED AP

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Dear Paul,
how I can get those data points to build the EIR-fPLR&DT curve? is it
available in the manuals and chillers data sheets? or I should ask it from
the suppliers directly?

Please advice,

Mohammad Al-Masri

Mohammad Almasri's picture
Joined: 2011-09-30
Reputation: 400

Mohammad,

I will answer you if you don't mind. Tell the manufacturer that you need to
know how the chiller unloads based on the outside air temperature (DBT) and
the leaving chilled water temperature (CHWT), in other words, the chilled
water temperature you are delivering to your systems. You will find when you
go into your online help manuals that you need to normalize all your data
around the ARI design conditions. That means that your EIRs will look like
1.0, 1.09, .98, etc., depending on whether your part load EIR is higher or
lower than the EIR at the ARI design condition. If that is confusing to you
still, after doing your diligence and reading the DOE2/eQUEST online help
manuals, let us know.

Carol

cmg750's picture
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On the energy design resources website (www.energydesignresources.com)
there is a design guideline called "HVAC Simulation Guidelines" which
includes a section on "energy efficient chillers" and has a procedure
for developing custom chiller curves for DOE-2 -- including a table to
send to the manufacturer to get the required information.

There is also the CoolTools spreadsheet tool which also generates the
DOE-2 curve coefficients -- but I haven't played with it much so will
let others comment on its use/applicability to screw compressors.

bfountain's picture
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Many thanks for your help.

I just sent my request to York . But I hope if anyone have those curves fit
to send it to me for time saving. The chiller that I have is air cooled
screw "variable speed", and the full load capacity is 340 Ton .

Mohammad Al-Masri

Mohammad Almasri's picture
Joined: 2011-09-30
Reputation: 400