Working with Prototype Systems

All pre-defined controllers, configurations, default values, and autosized values are meant to be a starting point. This starting point provides defaults for ASHRAE baseline systems, a means of facilitating the rapid use of systems without excessive setup effort, and an example of how the system are intended to be set up. In other words, the pre-defined configurations, default values, and their relationships are meant to be instructive and illustrative, but not set in stone. Except in the case of autosized ASHRAE baseline systems in the context of the 90.1 PRM, it is recommended that users modify inputs and configurations as needed to accurately represent the systems in each actual project.

The following are strongly recommended when learning something new, starting a complex project, or experimenting with new strategies for a significant project:

5. Start with a small model that represents what you’re exploring is the simplest terms, then save to a new name just before trying something new so that the experiment can be readily tossed out and started again without any significant loss of investment.

6. Use short simulation runs of one to three select days (very hot, very cold, should season, etc.) to explore new configurations of models and systems prior to running full annual simulations. This facilitates rapid and efficient cycles of experimentation and learning.

7. When setting up the model of the full project, combine separate rooms into thermal zones within ModelIt to the extent feasible, given the diversity of space uses, solar exposures, other loads, and the required resolution of results. Any actual internal partitions should be retained. In most cases, there should be no fewer thermal zones than there will be actual thermostats in the building.

8. If already well underway with a large model and there is need to use some aspect of this model to test a new HVAC system configuration or controls, etc., place the portion of the building that will be represent what is being tested—e.g., all zones on one particular HVAC air handler that is to be controlled differently—on a unique layer within ModelIt and turn all other populated model layers OFF. If there are other systems in the HVAC system file, save a copy of the file and remove all but the system required for the experiment. This facilitates thermal modeling of just the selected zones or rooms and just the system associated with them. The simulation run could be performed for just one important or representative space in the building with other zones/multiplex layers temporarily removed from the system. This is bounds the experiment, significantly reducing simulation run times and improving the ease of initial analyses and detection of input/configuration errors as the first stage of an efficient means of attempting adjusted, new, complex, or innovative configurations and control strategies. Once corrections and refinements have been competed in this context, the user can re-introduce other building zones, systems, etc., perform short runs to refine this, and then perform longer runs to generate needed whole-building annual results, etc.

Loading, saving, and retrieving prototype systems

Maintaining autosizing capability for components and controllers with autosized parameters

The following system elements depend upon the relationships to the System Parameters interface:

Room/zone-level airflow sizing process, including oversizing factors, turn-down ratios, etc.
- Zone cooling min & max flows
- Zone heating min & max flows
- Ventilation rates
- Minimum OA setting the OA economizer damper set
Settings from the AHU parameters dialog
- Heat recovery operating power
- Heat recovery latent effectiveness
- Heat recovery sensible effectiveness
- Heat recovery enabling
- OA Economizer DBT high-limit value
- OA Economizer enabling
- AHU heating coil LAT values
- AHU cooling coil LAT values
Supply fan power curves (static pressure and efficiency values) in PRM baseline systems that are used in PRM Baseline models.

Avoid unnecessarily deleting and replacing controllers in autosizable systems; however, if a controller does need to be replaced and the intent is to preserve relationships to the room/zone-level sizing spreadsheet for the system elements listed above, the following rules apply:

Any controller linked for autosizing (having an “A” next to one or more input fields) must retain the appropriate system parameter ‘link’ setting in the controller dialog in order for the autosizing function to be retained for those values.
The controller must be the same type with the same active elements—e.g., with “Proportional control” enabled—if the same input fields are to receive autosized values that would have gone into the pre-defined controller.
Users can also add controllers that re-purpose any given system parameter ‘link’ to have the newly added controller pick up the same autosized values.
- For example, if it is helpful for some reason to have the Heating Airflow values obtained using the ‘Heating coil – AHU min SAT’ link show up in a controller that is be added to a customized version of a pre-defined system, the new control would need to be the same type as the pre-defined controller, use the same controlled variable, and would need to have the ‘Heating coil – AHU min SAT’ link set in the controller dialog.