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How to stop chiller from running while thermal energy storage still has capacity?

asked 2019-02-26 11:15:08 -0500

mldichter gravatar image

I'm looking into the IceStorage-Series-ChillerDownstream.idf energyplus example file which uses a ThermalStorage:Ice:Detailed object and other controlling objects to use thermal energy storage for cooling.

In particular, I'm trying to decrease the Time Dependent Valuation (TDV) total for a building. Thermal energy storage is perfect for this since the tank can be charged with a chiller during off peak hours at night and discharged during on peak hours for cooling instead of the chiller.

However, I ran the IceStorage-Series-ChillerDownstream.idf energyplus example file during the months of June, July, and August and measured the TDV with and without use of the Ice Tank, and the difference in TDV was small, and sometimes increased if I autosized certain values.

Looking deeper into the simulation results, looks like the Ice Tank isn't being fully utilized with the chiller still running most of the time.

image description

As you can see, the chiller is running when it's hot outside during on peak hours and the Ice Tank still has a lot of cooling capacity left.

I tried making the Ice Tank capacity 100 times larger, so WAY more than the building needs, but the chiller still turns on when the Ice Tank could easily handle all the cooling load.


So my question is: How do I get the chiller to run only when charging the Ice Tank at night, or during the day AFTER the Ice Tank has been completely used up?

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answered 2019-03-05 17:21:16 -0500

mldichter gravatar image

updated 2019-03-05 17:21:53 -0500

I was dismayed when I found that even the IceStorage-Parallel.idf did not work as I had hoped. Charging and discharging did not always occur at night and work hours respectively.

I won't be accepting this answer as I was never able to get the ice tank and chiller to behave exactly as I wanted using built in control objects in energyplus, and even using EnergyManagementSystem objects did not fully work, but mostly worked.

However, at least the person reading this will know to skip the built in objects and try EMS for controlling the ice tank.

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Hi, @mldichter, did you find the way to solve this problem? I am now trying to model a series chiller and ice storage loop which can chilled the fluid in two different way, one is only with ice storage and the other one is go through chiller first then entered in ice tank. Could you please give some tip to model this scheme?

szsz gravatar image szsz  ( 2020-06-10 10:37:57 -0500 )edit

@szsz Sort of. I got it working better. I had one plant loop with a frictionless pump that was always on, chiller, ice tank, and perfect heat exchanger. The other side of the heat exchanger was in the loop with the actual demand object supplying cooling. It's not perfect, but I was able to control the ice tank plantloop exactly how I wanted and I could transfer any cooling provided by the chiller or ice tank to the plant loop with the demand equipment. There is an energyplus github issue, but there hasn't been activity in a while. https://github.com/NREL/EnergyPlus/is...

mldichter gravatar image mldichter  ( 2020-06-10 11:01:53 -0500 )edit

@mldichter Actually, the chiller and ice storage in my model is connect with heat exchanger, but as long as the chiller is on the upstream of ice storage, it will be operated when ice storage discharging. Full charged ice storage never chilled the fluid by itself. I don’t know what’s wrong with my model...

szsz gravatar image szsz  ( 2020-06-10 13:10:40 -0500 )edit

@szsz I had to put the chiller setpoint node between the chiller and ice tank. The chiller setpoint would be something like -5C when charging the ice tank and 7C when discharging the ice tank. The ice tank charge and discharge schedules have to match up with the chiller charging and discharging/providing cooling.

mldichter gravatar image mldichter  ( 2020-06-10 13:14:31 -0500 )edit

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Asked: 2019-02-26 11:15:08 -0500

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Last updated: Mar 05 '19