Free cooling module on Chillers(Open Studio)

asked 2016-09-15 09:37:27 -0600

Nithya
362 ●5

updated 2017-09-09 13:34:02 -0600

Hi all, I am trying to model 2 air-cooled chillers that have a free cooling component to disable the chiller when applicable. I have tried a couple of approaches listed below and haven't been able to figure out the right solution.

Approach #1- Heat Exchanger in parallel with chillers. Then,attaching the HeatExchanger:FluidToFluid to a condenser loop with cooling tower on the supply end. Since the control needs to make sure the chillers are off when the free cooling is available- make this control to component override. 2 problems with this approach 1a-Heat exchanger always get pushed to the end in the sequence making this last priority with sequential distribution on the loop. 1b-component override option needs a demand side component inlet node, which I believe based on this post https://unmethours.com/question/14606... is chiller's condenser inlet node. Since this is air-cooled chiller I don't have a node to refer to!

Approach #2-attaching the HX in series with each chiller. The sequencing problem is addressed from Approach#1 but the Component override node problem still remains

Approach#3- attaching HX right after pump. The nodes required for this to work is still 1 set of chiller nodes, I have 2!

Approach #4- Set the HX in parallel and change the control to Cooling setpointOnOff. This seems to avoid the node references but the HX seems to work only for the first half of January!

Can anyone shed light on a working approach for this?

Thanks, Sri

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answered 2016-09-15 11:51:18 -0600

Annie Marston
4337 ●5 ●32 http://www.resustain.com

When I model free cooling on the plant / condensor loop, I do it in the following way:

Attach one heatExchanger:FluidtoFluid for each chiller, all chillers and heat exchangers are modelled parallel in both the condensor loop and chiller loop. In the heatExchanger:FluidtoFluid object it asks which component you are overriding, put in chiller nodes here. The control for the free cooling is also in the heatExchanger:FluidtoFluid object it is under "Control Type", there are a multitude of different options in here. If you look at the input output reference guide in your E+ folder it will describe what each of these does. I have attached the inputs for a heatExchanger:FluidtoFluid that I modelled recently (this was in energyPlus but it should be the same for OS) image description

Comments

Thank you Annie. Just to confirm- I believe in this approach you don't need the component override nodes since the control is CoolingSetpointOnOff. These inputs are only triggered when CoolingSetpointOnOffWithComponentOverride gets choosen. I do not have a chiller node on the condenser side(Air cooled chiller). So, the control type is restricted to CoolingSetpointOnOff. This strategy works fine in january but does not trigger even when the loop input to oat is ~25 F delta in december. This makes me think that this is not working as expected! In summation, works only10% of the potential hours!