Which side of the plant loop for Solar Collector in E+/OpenStudio?

asked 2017-11-09 04:30:45 -0600

updated 2020-02-03 05:50:27 -0600

I have to admit I'm slightly confused here, as I am seeing contradicting information on how to model solar collectors in EnergyPlus and OpenStudio.

On one hand, everything on EnergyPlus side seems to imply the solar collector must be on the demand side of the plant loop.

In the I/O reference guide, there is a section Solar Collector Heating System Plant Connections, which says the following:

The solar collector must be connected on the demand side of the plant loop. Multiple collector modules can be combined in series and parallel using the normal plant connection rules. The supply side of the plant loop should contain a water heater with the solar collector loop connecting to the Source Side Inlet and Source Side Outlet nodes

The example files such as SolarCollectorFlatPlateWater.idf do implement it this way.

On the other hand, there are numerous questions about OpenStudio here that show the solar collector on the supply side, for example Active indirect solar hot water collector modeling and solar collector panel to DHW.

So I could see two explanations, which one is right?

The I/O reference guide and example files are outdated, and it is possible to put it on the supply side of the plant loop
OpenStudio is doing some "magic" in Forward translation, to create a plant loop where it's on the demand side (a cursory look at source files didn't reveal anything obvious... Edit: It isn't)

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Here's further evidence to support demand-side placement.

ericringold ( 2017-11-09 10:24:48 -0600 )edit

As of OpenStudio 2.3.0, solar collectors are not allowed on the demand side of plant loops.

MatthewSteen ( 2017-11-30 14:20:28 -0600 )edit

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answered 2017-11-09 06:37:07 -0600

Avi
4320 ●2 ●11

updated 2017-12-03 11:04:39 -0600

In the model I am working on in OS the Collector is on the Plant's supply side and also in the in.idf after the forward translation the collector remains in the plant's supply side. if you need I can post pictures and code fragments.

Ok, After some testing and reading this is my take on that: The E+ measure I wrote to add AM to the collector loop didn't change much. Even when you run the E+ example file you will get freezing, and if you change weather file to hot weather you will get overheating.

Your observation about OS is correct, it won't let you add Collectors on the demand side as the E+ example is set. After doing some tweaking I found out that the collector performance curve is the most important. One have to make sure that coefficients are correct. After that said it is still reasonable to get some overheating since that is what happens in the real world. In order to prevent that, measure like pressure relief valve, drain - back or covering should be taken.

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And does it work? I mean, do you get reasonable results?

Julien Marrec ( 2017-12-01 02:49:57 -0600 )edit

The simulation produce 5.8 GJ a year which is about 1.6 MWatt Hour. That is quiet reasonable. The only problem is that the collector outlet getting too hot. I am in the middle of writing E+ measure to add Availability Managers into the loop. Will let you know how it works.For implementing Availability Managers I am using OS and following the E+ example : SolarCollectorFlatPlateWater.idf.

Avi ( 2017-12-01 07:34:52 -0600 )edit

You might be interested in this Pull Request I have made #2844, where I added every availability managers to openstudio, as well as the ability to add several (currently one only is allowed) AVMs for a given plant loop. This will allow to properly control Solar collector loops (and many more). It got merged in develop so should be available in the upcoming new release of OpenStudio. Xmas is early :)

Julien Marrec ( 2017-12-01 08:41:35 -0600 )edit

Yes I red about it and waiting for that release.

Avi ( 2017-12-01 12:03:53 -0600 )edit

I understand that availability managers including differential temperature (which would be useful for a solar collector) are available in OS 2.3.0. However, when I try to find them under controls for my plant loop, I see a message that says "Control options are currently only available for air systems". Should I look somewhere other than controls for the availability managers? When will control options be available for water systems?

michael ( 2017-12-05 14:31:12 -0600 )edit

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answered 2017-11-30 19:30:33 -0600

michael
41 ●2

I am in the process of modeling an indirect solar water heating system...not finished yet but here is what I have learned. I added a new Empty Plant Loop and called it ServiceHWLoop, and then put a Water Use Connection on the Demand Side and a Water Heater Mixed on the Supply Side.

Then, I added a new Empty Plant Loop and called it SolarLoop. Next, I went to My Model (not Library) and dragged the Water Heater Mixed into the SolarLoop on the Demand Side. The Water Heater Mixed now shows four connection points - I interpret two of these to be the Source Side and the other two the Use Side consistent with the EnergyPlus nomenclature. I plan to put a pump and Solar Collector Flat Plate Water on the Supply Side of SolarLoop and then add controls, schedules, etc.

I will update in a day or so to indicate whether this works.

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@michael , did it work ?

Raghda Derbel ( 2018-09-19 15:09:23 -0600 )edit

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