Designbuilder - HVAC

designbuilder

asked 2026-01-07 16:28:48 -0600

Hello everyone!

I am working on my first DesignBuilder model for ASHRAE 90.1/LEED certification. I am running into some issues with the HVAC module not allowing me to exactly replicate the systems currently designed for the project. Specifically:

1) The project HW loop is heated by a fluid HX fed by a district steam system. I can't connect district heating to a HX in the HW loop supply side, and I can't control anything about the district heating itself. I believe I need to include district heating efficiency in my LEED calculation. How do I model this?

2) The project CHW loop is set up to be "geothermal ready" meaning that the water is chilled by a water-source heat pump. Currently, the WSHP is connected to a large rooftop adiabatic cooler rather than the future ground loop. Designbuilder will let me connect the WSHP to a condenser loop but I can't add a dry/adiabatic cooler to the loop - just a cooling tower or fluid cooler. I'm concerned that this will affect accuracy. Is there a way to make this correct?

3) The project has two large rooftop DOAS units with heat recovery. These are essentially ERVs with enthalpy wheels. When I try to configure these DOAS units in DesignBuilder it shows them as though they need additional components connected to the intake and exhaust instead of functioning as they would with intake and exhaust grilles on the unit itself. I can't figure out how to fix this and it's making my whole model fail to simulate! Help would be appreciated.

Finally, I would be so appreciative if someone would be able to look over the whole model and flag egregious errors and omissions. I know that's a big ask but would be happy to discuss terms for that kind of support offline.

Thank you all.

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answered 2026-01-09 11:52:21 -0600

Greg Estep
1244 ●43 ●8

Energyro, regarding, question 1: The district heating object is a HW object not a steam object. The energy consumption reported in the ABUPS report for district heating is simply the thermal energy transferred to the building (implicit efficiency of 1.0). If you want to capture the efficiency of district heating, then you should model it as the heating source (i.e. boiler). Regarding connections, you can add two HW loops. one for the district (boiler, or district object) and connect it to the other HW loop via the fluid to fluid HX. you can control the loops accordingly.

question2: I think equipment called "dry adiabatic cooler" is the same thing as the designbuilder object fluid cooler. Thus, you can add a condenser loop and use the fluid cooler object and connect the demand side of the condenser loop to the WSHPs.

question 3: I model ERVs by inserting a generic air loop setting up the loop to size on ventilation load and make the necessary setting in the AHU to behave like an ERV. Don't check the box that says DOAS on the outdoor air system tab. That checkbox allow for connection to another air loop that would be the DOAS, not the active unit.