HVAC behaviour in Designbuilder

asked 2019-10-22 06:27:23 -0500

Tanay's avatar

updated 2020-01-20 10:22:39 -0500


I am currently using the "Heated Floor, Boiler HW, Nat Vent" HVAC Template for designing the heating system. I have used the "Detailed Model Design" in order to write my own HVAC control system using the EMS.

The idea is that the HW supply loop supplies constant temperature (50degC) at constant pressure. Then I can use the EMS to control the actuators in the Heated Floor to control the HW flow with ON/OFF valves.

The logic in the EMS for 2-Position ON"OFF control is that the Actuator for Hot Water Mass Flow will be turned ON if the difference in temperature is greater than 2 degC and will be turned OFF if less than -2 degC. In both Kitchen and Bedroom, the Setpoint is given as 21 degC.


  • Bedroom shows the variation to the given controller. I can see oscillation of 2 degC change in temperature. But it's not the same in Kitchen. It is always flat. But if I change this error range to 1degC for Kitchen, then it works and no longer flat. Can you let me know what can be the reason? I suspect this has to do with the "Loop design temperature difference" in the Edit HW loop in the supply side. If I keep a value bigger than 2 degC, then no room follows the controller and temperature are always set to 21degC.

    • How can I see total Heating hours for each zone in Designbuilder or EnergyPlus?

    • For Boiler, I have kept the Nominal Capacity at 3000W, but in the simulation for Heating shows a peak of 4.1kW. Why? Also, in the Simulation Report for "Component Sizing Summary", I have "Design Size Nominal Capacity [W]" as 1153.11 W. Is this the boiler capacity I can keep? Do I have an over-designed boiler?

    • For the given size of the Room and Bedroom, what do you think is a good sizing parameter for the HVAC for the components, Pipe length and circuit size, Heated Floor Capacity, Maximum Mass Flow Rate in the pipes and Boiler size

I have attached the Designbuilder project for reference.

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