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Setpoint Manager for HW Heating Coil (openstudio 1.7)

asked 2015-07-29 10:47:11 -0500

Jacob Cherry's avatar

updated 2015-07-29 11:19:37 -0500

I am a graduate student working with openstudio 1.7 to model a small fire station for a research project at the University of Minnesota. The goal of this project is to calibrate an energy model to some real world utility data and examine measures for energy conservation / reduction and propose some feasible retrofits. As this is my first energy model, and there is no expertise in my department with this platform, I'm seeking some advice and a bit of a gut check.

The building is essentially two zones: living quarters, and an apparatus bay with heating only. There is a central boiler which operates unit heaters in the apparatus bay, and a heat exchanger in an AHU for the living quarters. Each zone is controlled by a thermostat. The boiler loop has an OA reset to shut down the loop at times when air temp is sufficient to not require heating.

I am unsure what type of setpoint manager to use on the associated air loop for the living quarters. In general, I have been able to get the model pretty close to observed utility data, but when I try to make changes, the results are often unexpected, which leads me to believe that I have modeled something incorrectly, or... (insert mistake).

I have attached a link to the .osm file for your examination. If you have any suggestions, observations, ideas, etc. (and if I've done something stupid or horribly wrong), please let me know. I appreciate your input.

-Jacob

https://drive.google.com/file/d/0B9CS...

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Looks like the google drive doc isn't public. If you have a single zone on the air loop, then you would typically use a single zone setpoint manager that has a field for the control zone. If you have multiple zones on the air loop then you would typically use a schedule setpoint manager.

David Goldwasser's avatar David Goldwasser  ( 2015-07-29 10:58:23 -0500 )edit

I updated the link. Would you mind taking a look? Thank you.

I have an alternate version on my computer where I've used a Single Zone Reheat setpoint manager but I am unsure what to set the min. and max. supply air temperatures to.

Jacob Cherry's avatar Jacob Cherry  ( 2015-07-29 11:21:12 -0500 )edit

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answered 2015-07-30 21:27:23 -0500

Yep I think SetpointManagerSingleZoneReheat is what you want here. The single zone reheat looks at the zone load, and the supply air flow rate, and computes a setpoint temperature to meet the load. Those min and max settings in the setpoint manager input fields are just bounds. Your real supply temps are going to be somewhere between those points. Design supply flow rate and approximate design supply temperature is influenced by the design days, the SizingSystem object (accessible in OS by clicking in the center of the loop), and the SizingZone object (accessible from the zones tab). I have attached a screenshot of what your system should probably look like with the setpoint manager.

You don't need or want the oa reset setpoint manager on the coil outlet. Although energyplus is going to need a setpoint on that node, OpenStudio will put the appropriate thing there for you. In this case it will be a mixed air setpoint manager which will reference the single zone reheat setpoint manager on the supply outlet node, but adjust for the fan heat.

Your plant will cycle off on its own when there is no demands from the coil. It is possible to use a "plant operation scheme" to completely make the boiler unavailable based on oa conditions, but that operation scheme is not yet available in OS. It will be in the coming 1.9 release of OS. I think you will have a fine approximation without it.

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Asked: 2015-07-29 10:47:11 -0500

Seen: 571 times

Last updated: Jul 30 '15