Adding a HVAC template in OpenStudio

asked 2016-06-08 12:11:20 -0500

Wilson

533 ●1 ●11

updated 2017-05-06 08:35:05 -0500

__AmirRoth__

4436 ●5 ●17 http://bleedinggreenna...

Hi! I'm trying to model a single zone building with OpenStudio. I'm trying to insert a HVAC system that works only with electricity. The type of system is not important to my study and I apreciate if you could advise the most appropriate one.I need to add the HVAC system because my study will be focused in the set of setpoints that gives the lowest HVAC energy cost.I added a Packadge Rooftop Heat Pump and attached to it my single thermal zone. The AVAC system is not working correctly. The "Coil heating DX single speed" and the "Coil Cooling DX single speed" presents electricity consumption when the interior temperature is between the cooling and heating setpoints. There are also situations where we can verify heating and cooling energy consumptions at the same time. My knowledge in HVAC system is far to be good and some help is needed. For this simple AVAC system do I have to add other(s) component(s) to the selected HVAC system or the HVAC template provided by OpenStudio is enough to my system works correctly? I appreciate if you could check my project to give me a clue for what I have to do to add the HVAC system correctly. Thank you

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Comments

In the current state of your question I doubt you'll get many answers. You need to elaborate.

What system do you want to model? What's wrong with the current system?

Julien Marrec ( 2016-06-08 12:13:32 -0500 )edit

Thank you for your suggestion Julien Marrec. I eddited my question.

Wilson ( 2016-06-08 12:52:23 -0500 )edit

Depending on the setpoint manager your using the behavior when the zone temperature is between setpoints will change. Most managers will predict zone cooling or heating load and adjust the SAT accordingly, so even though you're within setpoint you may still have cooling energy in an effort to prevent it from hitting setpoint, if that makes sense. That's my understanding at least. The small spikes you're seeing at night is just noise in the calculation, in my opinion.

Adam Hilton ( 2016-06-08 13:14:48 -0500 )edit

Thank you for your comment adhilton! For this study I can't use those managers that predicts the cooling or heating load that you refer. I have to know what is happening "in real time". I think the small spikes are significant, specially when we try to optimize the building electricity consumption. But it is my opinion and I'm not an expert in this subject.

Wilson ( 2016-06-08 13:38:43 -0500 )edit

Can you add the supply air temperature to your plot?

Adam Hilton ( 2016-06-08 14:20:19 -0500 )edit

see more comments

answered 2016-06-08 16:38:48 -0500

ericringold

10527 ●31 ●8 https://www.nrel.gov/b...

updated 2016-06-08 20:00:30 -0500

If you set the reporting frequency of your output variables to 'Detailed' you will see that there is actually not simultaneous heating and cooling; that heating occurs at the end of the night temperature setback to raise the temperature to the daytime heating set point, and cooling occurs when the zone temperature is right at the daytime cooling set point to maintain that temperature. This is how I would expect this system to operate.

Reporting the variables hourly will obscure how the system is actually performing, since HVAC systems are simulated at sub-hourly time steps.

Here is a plot from your model with variables reported hourly:

Here's the same plot with variables reported at Detailed frequency:

And here it is at detailed frequency with 6 time steps per hour:

If you require the system to be off at night no matter what, you should apply an availability schedule. In OpenStudio this can be done in the Air Loop control view (see here).

For how air system control is simulated in EnergyPlus, see here.

Comments

Thank you for your answer Eric Ringold! I set the reporting frequency to "detailed" and I can see that there's no simulataneous heating and cooling.There's one thing I don't understand.In the begining of the day(1am) the system "knows" that at 9am the heating setpoint is higher(from 19C to 22C) and starts to heat despite de interior temperature is between the chosen setpoints?But we also can see cooling working during the night... This cooling during the night I don´t understand. Is there a way we can put the cooling and heating working at the trully setpoints limites that we choose?Thank you

Wilson ( 2016-06-08 17:43:44 -0500 )edit

In this plot you can see applied my weather data. The temperatures are higher so I think there is no need to heat the building during the night. If the AVAC system heats "automatically" the building during the night to me that's a problem because I want to study strategies to refrigerate the building during the night to save in the energy costs.

Wilson ( 2016-06-08 17:54:44 -0500 )edit

Edited my answer to show how differences in reporting frequency and simulation time step can show results you might not expect. To prevent the system from heating at night at all, you'll need to apply an availability schedule.