Compact HVAC Setback temperatures

sezzeldin · Posts: 14

Hi,
I want to simulate a compact HVAC (CAV) System but I need to know:
1) How to set a setback temperature to this compact HVAC system as in the simple HVAC system that allow a setpoint temperatures of 24C and 27C during the Occupied and Unoccupied hours respectively
2) How to simulate the CAV system in DB but with purchased heating and purchased cooling as in E+ (Which means that only the air loop that is calculated in details without focusing on the water loop)?
Could you please help? I'll appreciate very much your support...
Kind regards,
Sherif

Laurent_Support · Posts: 275 Location: Vincennes

Hi again Sherif,

To answer your first question, I think my last post on the other thread could help. I will add you should enter a 0.5 value in you Heating/Cooling schedule when building is unoccupied to make heat Heat/Cool at setback schedule.

Presently there is not this option in DesignBuilder you can use Purchased Air (ie Simple HVAC) or Compact systems. If you don't want that Compact systems use default boiler or chiller, you will need to adapt the EnergyPlus idf manually.

Regards,
Laurent

sezzeldin · Posts: 14

Hello Laurent,

Thanks for your help
I can easily control the system thermostat to changeover from the setpoint to the setback for the simple HVAC by using 0.5 and 1, but when I changed the system to Compact HVAC, I remarked:
1)There is no difference in the results by setting the schedule using always 1 (to activate the system all the time) and 0.5 (to use the setback during weekends and at night)
2) I'm setting the cooling setpoint and setback at 24C & 27C, but i'm getting the same result with schedule using 0.5 and 1; air temperature at 24C during the day and around 21C during the weekends and at nights, don't know where the 21C came from?
3) I've read in the help documentation that the compact system use only 0 and 1, so how can i set the setback?
could you please help?

regards,
Sherif

Laurent_Support · Posts: 275 Location: Vincennes

OK, could you tell me what version you're using and post your dsb file so I could look forward?

Thank you.
Laurent

sezzeldin · Posts: 14

Hello Laurent,

I'm using Design Builder version 1.4.0.056
I'm attaching my dsb-file
You'll figure my problem when you changeover from simple to Compact HVAC
same schedule but different Air Temperatures
Thanks for your support
Sherif

Laurent_Support · Posts: 275 Location: Vincennes

Hi,

I made some test on your file. I found two reasons:
1) the cooling schedule is set to your Occupancy schedule and not you cooling one, that alters setpoint commands. Changing this will let internal air temperature grows up (20,5 to 24°C)
2)the other reason is because the system supply the zone with air all day long (not at the same rate all the day but it always run). Because the air distribution is done at 14°C, you've got cooled air always supplied to he zone. So temperature could not rises.

If you select for instance a fan-coil system instead of a CAV one, you will see the same behavior as the Simple HVAC mode. This is because Simple HVAC simulation answers accurately to the demand as fan-coil try to.

Note:
I try the fan-coil system on your building, it works as intended but you should set your Plant Sizing option to Autosizing or Adequat to let EnergyPlus adapt your power for the new system.

Laurent

sezzeldin · Posts: 14

Hello Laurent,

Thank you Laurent for your help

Kind regards,
Sherif

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