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Air-cooled, frictionless centrifugal chiller with free cooling option - eQUEST

asked 2015-03-17 09:07:30 -0600

jng gravatar image

updated 2015-07-10 13:44:11 -0600

I am modelling a new construction in eQUEST that uses a fairly new product that I have not seen before. I was wondering if anyone has any experience modelling this Equipment:

It is a remote air cooled chiller (the chiller is in the basment but the condenser is on the roof 4 floors up). It uses frictionless magnetic bearings, it has 2 compressors and it has an option for water side free cooling which I can't seem to find any documentation on how it works exactly.

In eQUEST, I know that I cannot combine an air cooled chiller with the water side economizer option since I need a condenser loop for the water side economizer and I don't think eQUEST has any built-in performance curves for an air-cooled magnetic centrifugal chiller with 2 compressors.

Does anyone have any ideas of the best way to model this?

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answered 2015-03-29 14:01:54 -0600

301_Hours gravatar image

updated 2015-04-02 09:39:31 -0600

you'll need to request a performance curve from the manufacturer, and then make a curve in eQUEST. It takes 33 selections to make the necessary curves for an air cooled plant so give your rep a heads up on that.

I don't think you need to worry about the condenser being separate as the heat rejection won't change substantially. Perhaps adding pump power as a process cooling load, and as a metered electric load would be the best way to approximate this. Maybe create an 8760 pump power schedule based on the hourly cooling load from the model.

You can create a water side economizer as a separate chiller on the same chilled water loop, and have a dry cooler selected as your cooling tower option in the condenser loop. Set the condenser pump power to zero.

To elaborate on this you'll need the following components in the chiller plant. Best to build it in the following order too:

CHW loop Condenser water loop CHW pump Condenser water pump Air cooled chiller Water side economizer chiller component heat exchanger as attachment to dry cooler heat exchanger pump as attachment to dry cooler Dry cooler Equipment controller Load managment

Then you'll want to create hourly reports for the pertinent chiller plant values to ensure that it's operating correctly.

Please reply to this post your experience here as this is not very straightforward, and 90.1-2010 is requiring more water side economizing. A reliable method of creating these plants should be recorded.

Good luck

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Unfortunately, for this project the chiller described above was not selected since there are not enough competitors that offer this product. I no longer have the hours to properly simulate this chiller since they have changed the design with a more standard chilled water plant design and require new results anyway. I ended up simulating the chiller with an electric hermetic centrifugal air cooled chiller with 2 compressors and I used standard curves supplied by equest for frictionless compressors. I copied the chiller and made my new chiller water cooled with an EIR of 0.0001.

jng gravatar image jng  ( 2015-04-02 12:24:34 -0600 )edit

I then used Equipment controls as described in the answer above to limit the "free cooling" chiller use based on OAT. I used a condenser pump that does not consume energy. I also included the fan power of the real air cooled consenser to the EIR of the real chiller in order to at least approximate the heat rejection energy use.

I think this solution is adequate given the context but I think eQUEST's frictionless compressor curve is underestimating my cooling energy consumption a bit. I will perform more tests when I have a bit mor time.

Thanks for the input!

jng gravatar image jng  ( 2015-04-02 12:29:19 -0600 )edit

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Asked: 2015-03-17 09:07:30 -0600

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Last updated: Apr 02 '15