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Ice Storage Controls

asked 2015-08-12 13:35:28 -0500

bbrannon4 gravatar image

updated 2018-01-18 03:23:08 -0500

Is there a way to control the ice storage objects in E+ with a little bit more control then just availability and setpoint schedules? I could make something work with EMS, but I just wondered if i'm missing something in the native control objects. I'm having the issue where ice is being made way too much - it seems to be charged continuously by the chillers. I'd want the ice to be made to capacity at night, and then stop, and then discharged during the day, and then remain discharged until a certain time when the chillers can start making ice again. It's the "stop charging when full" that I can't figure out.

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answered 2016-07-12 08:35:09 -0500

Archmage gravatar image

I also find it takes EMS to do ice storage controls well. Use an EMS sensor on the tank charge fraction for the problem you describe.

It also helps for controls to set up the plant topology differently. I put the detailed ice tank on its own loop and connect it to the main chilled water loop using a heat exchanger on the chilled water supply outlet branch. This way the chillers can run on cooling load based operation scheme while the ice tank can run on component setpoint based operation scheme (which it requires). The EMS can control flow to the ice tank by manipulating temperature setpoints on the heat exchanger using its dual setpoint cooling control. These setpoints are separate from the main chilled water loop setpoint controlling the chiller. This allows for more complex modes where the chiller is both charging the tank and cooling the building at the same time or where the building loads are being met with both the (smaller) chiller and ice tank discharge. For ice charging mode it helps to add a plant load profile object in parallel with the cooling coils and use it to call for flow (flow only, no load) on the demand side when you need to get the chillers running to charge the tank.

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Hello Archmage! I'm also having a lot of trouble to make an ice tank to behave the way bbrannon4 has described. I liked the solution you described but didn't understand it completely. Do you have any image, sketch, SVG file, or anything that could help me to understand the topology you have described? I'm relatively new with all these HVAC stuff and it would really help me a lot. Thanks!

A.K gravatar imageA.K ( 2018-02-22 12:11:01 -0500 )edit
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answered 2016-07-11 12:57:51 -0500

rkbest gravatar image

You can use EMS:sensor to get schedule value at any time as ChargingTime or something, and have your pragram check the time before turning the charging on. Something like:- If ChargingTime==1, If IceFrac<1.0, Run ......

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answered 2015-08-17 09:57:07 -0500

NickC gravatar image

updated 2015-08-17 09:59:57 -0500

In E+ v8.3, both ThermalStorage:Ice:Simple and ThermalStorage:Ice:Detailed have a "Capacity" input field. Have you set these? The capacity is in gigajoules. I've been looking into ice storage modeling a bit but don't have any practical experience yet. You've probably already read the following links, but here they are just in case.

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Nick, Yes, I have set the capacities, but that doesn't really have anything to do with control, other than define a peak storage amount. Thanks.

bbrannon4 gravatar imagebbrannon4 ( 2015-08-17 11:44:09 -0500 )edit

Does the ice storage object cycle off (charging rate = 0) once the capacity (ice-fraction) reaches = 1? If not, then I'm thinking perhaps this is a bug. The E+ Engineering Ref document states the following:

"Charging

When charging is requested, the following limits are calculated to determine the actual charging rate: ... 3. If the current fraction of ice stored is 1.0, the tank is fully charge, and the charging rate is zero"

In the OP you stated that "stop charging when full" was an issue; it seems like this shouldn't be a problem if I'm reading the ref. guide correctly.

Best, -N

NickC gravatar imageNickC ( 2015-08-17 13:46:04 -0500 )edit

I should have been clearer. Yes, it does stop and won't charge over 100%. However, it potentially starts charging again after some capacity has been used. I want to be able to make it do something like: "start charging at 11:00pm until full, and then don't start charging again until the next night at 11:00pm. When full, don't start discharging until 10:00am, and then I would want some logic (maybe just has to be done with EMS) to control how the discharge happens to optimize the demand reduction" The former being my main issue at the moment. Ben

bbrannon4 gravatar imagebbrannon4 ( 2015-08-18 12:49:29 -0500 )edit

bbrannon4, were you able to solve this problem? I'm trying to simulate the same situation on EnergyPlus.

A.K gravatar imageA.K ( 2018-02-08 18:15:29 -0500 )edit

Not really, unfortunately. That project reduced it's scope and we just did some hand calcs. I marked the answer correct that I did because it seems like you have to play with some control in EMS to make it work, because the built in controls don't have the ability to do everything.

bbrannon4 gravatar imagebbrannon4 ( 2018-02-08 23:35:48 -0500 )edit

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Asked: 2015-08-12 13:35:28 -0500

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Last updated: Jan 18 '18