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I want to control the temperature of two zones in a residential building with Energy plus

asked 2021-07-14 19:41:15 -0500

Melina gravatar image

updated 2021-07-18 14:14:35 -0500

Hello, I want to control 2 different zones in a residential building in Ottawa with energy plus. the whole building area is 120 m^2 and the Zone 1 Area is 104 m^2. My HVAC system has a cooling coil:DX: single speed and a Heating coil:fuel. The air loop HVAC that I have defined is Unitary:Furnace: HeatCool. I have defined different set points and setbacks for each zone at different times of the day in the schedule: compact. The thermostat control is Dualsetpoint and I have defined 2 thermostats (one for each zone). I have one supply fan and no return fan. I have defined a zone splitter, air terminal single duct, and a zone mixing air system. The problem is that when I run the system there are no errors and it says all nodes and branches and connections are correct but when I see the variables (Mean air temperature of each zone) it seems that there is no control on the zones and the HVAC system is not working. for example, the Indoor air temperature reaches below 10 C!

could you please guide me about the problem that would exist? How can I define a controller for a zone and set the setback and set points?

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answered 2021-07-15 17:29:40 -0500

sashadf1 gravatar image

You should verify how much load the HVAC system is delivering to each zone. Some good variables for this are:

Output:Variable,,Zone Air System Sensible Heating Energy,hourly; !- HVAC Sum [J] Output:Variable,,Zone Air System Sensible Cooling Energy,hourly; !- HVAC Sum [J] Output:Variable,,Zone Air System Sensible Heating Rate,hourly; !- HVAC Average [W] Output:Variable,,Zone Air System Sensible Cooling Rate,hourly; !- HVAC Average [W]

Verify what your control zone is by looking at the control zone name field. It is possible that the control zone is being well conditioned while the other "slave" zones are not being conditioned. You mentioned you want to control 2 different zones. It is possible that the control zone is being conditioned while the other zone is not. Are the mean air temperatures for both zones not behaving?

https://bigladdersoftware.com/epx/doc...

You should also examine the Unitary:HeatCool objects Availability Schedule; make sure the schedule values are not 0 when they should not be, as this would indicate that the system is forced off for that timestep, and cannot come on to condition your zone.

https://bigladdersoftware.com/epx/doc...

"correct specification of the heat/cool furnace requires specification of the following objects in addition to the furnace object:"

-list of objects

I would look at the inputs for the below two component objects especially, particularly looking at the Rated Air Flow Rate, the rated capacities (Gross Rated Total Cooling Capacity for dx cooling coil and Nominal Capacity for furnace/burner), and the Capacity Function of Temperature curve object for the dx cooling coil.

cooling coil (Coil:Cooling:DX:SingleSpeed) https://bigladdersoftware.com/epx/doc...

heating coil (Coil:Heating:Fuel) https://bigladdersoftware.com/epx/doc...

Similarly to the Unitary:HeatCool object's Availability Schedule, I would check to ensure the Availability Schedules of the individual Coil:Heating:Fuel and Coil:Cooling:DX:SingleSpeed are not 0 when they should not be.

https://bigladdersoftware.com/epx/doc...

https://bigladdersoftware.com/epx/doc...

https://bigladdersoftware.com/epx/doc...

https://bigladdersoftware.com/epx/doc...

"The output of this curve is multiplied by the gross rated total cooling capacity and the total cooling capacity modifier curve (function of temperature) to give the gross total cooling capacity at the specific temperature and air flow conditions at which the coil is operating."

If the rated capacities and rated airflow rates are too small, that may be causing under conditioning of your zone. If the capacity function of temperature curve object coefficient inputs (for the DX Cooling Coil) are "bad," that can result in very low actual cooling capacity during the course of the simulation.

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Comments

Thank you so much for your answer. Actually, After defining the HVAC system, the software showed me an error that was saying that I have to define Sizing: system, so I did so to eliminate the error but as I am a beginner, I was not sure about the parameters that this sizing part wants. For example, I have to define the Preheat design temperature, preheat design humidity ratio, central heating design supply air temperature and etc. I think maybe the problem is here and the numbers that I have set are not enough according to the setpoint that I've defined (22C).

Melina gravatar image Melina  ( 2021-07-16 13:16:46 -0500 )edit

I tried different numbers just to see the result and the mean air temperature for each zone and now I've defined the preheat design temp. on 28 C, preheat design humidity ratio on 0.6, Central heating design temp. on 44 C and for cooling design I've defined the precool design temp. on 20 C, precool design humidity ratio on 0.3 and Central cooling design temp. on 10 C. with these numbers, The zones have almost reached the setpoints and setbacks (Although, I believe I have to work on it!) but I have no idea about the rationality of the numbers that I have defined!!

Melina gravatar image Melina  ( 2021-07-16 13:24:29 -0500 )edit

About defining the coils and curves as I needed the constants to define the curves so I got help from BEopt and I used the constant that BEopt had used for a residential building with the same HVAC system and almost the same area. I have no idea how and from where I can define the numbers for the equations of the curves. About the Rated Air Flow Rate and other gross capacities, I've used autosize!!

Melina gravatar image Melina  ( 2021-07-16 13:35:23 -0500 )edit

I don't know how Sizing:System interacts with the other components of an airloop HVAC unitary system, but having higher preheat design temps and lower precool design temps makes sense to me. Glad to know your setpoints and setbacks are being attained now.

Autosizing Rated Air Flow Rate and Capacities should help you achieve your setpoints and setbacks, though even with autosizing there can be a few hours out of the year where you get unmet hours.

In my models, EnergyPlus autocalculates the coefficients for the coil curve objects through its own algorithm, but you may be able to input them.

sashadf1 gravatar image sashadf1  ( 2021-07-16 19:48:08 -0500 )edit

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Asked: 2021-07-14 19:41:15 -0500

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Last updated: Jul 15