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:

1. 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.

2. 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.

3. 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.

4. 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

Pre-defined and user-defined prototype systems

Maintaining connection to referenced schedules and profiles

Selecting, moving, copying, and naming systems

Maintaining autosizing capability

Modifying pre-define prototype systems

Maintaining autosizing capability for components and controllers with autosized parameters

The following system elements depend upon the relationships to the Loads Data spreadsheet:

o 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

o Settings from the AHU parameters dialog

AHU cooling coil LAT values
AHU heating coil LAT values
OA Economizer enabling
OA Economizer DBT high-limit value
Heat recovery enabling
Heat recovery sensible effectiveness
Heat recovery latent effectiveness
Heat recovery operating power

o Supply fan power curves (static pressure and efficiency values) in PRM baseline systems that are used in PRM Baseline models.

Currently, updating system parameters and autosizable values in components controllers in a design or proposed system—i.e., not the system for a PRM Baseline model—using the “Assign system parameters and room sizing data” action requires that the target ApacheHVAC system file is named “Proposed.asp”. As of version 6.4.1, there will be a list for selecting the target ApacheHVAC file when performing a Room Loads Calculation, using the System Parameters dialog, or using the “Assign system parameters and room sizing data” action, much as there is presently in the ASHRAE Loads dialog for System-level sizing.

The “Baseline0.asp,” “Baseline90.asp,” “Baseline180.asp,” “Baseline270.asp,” file names are and will continue to be required for autosizing of baseline systems for the PRM Baseline model.

Note, however, that for non-Baseline models only the four elements listed above under Room/zone-level airflow sizing are significantly challenging to manually determine, edit, and/or modify directly in the ApacheHVAC system file without the link to the spreadsheet. The others are about as easy to change in either place, provided the next point is understood.

If any autosized or autosizable values (with an “A” next to the input field) are manually edited in the ApacheHVAC system file, care should be taken to prevent these being overwritten if the user wants to avoid losing the changes if/when a subsequent “Assign system parameters and room sizing data” action is used to update other numbers in the same ApacheHVAC system file. If this is a concern and the user may again want to apply the “Assign system parameters and room sizing data” action for a particular ApacheHVAC system file, then preserving manual edits to a component or controller requires removing the alpha-numeric designation and colon at the beginning of its reference name—e.g., deleting the “S2:” or “MC3:” bit of the component or controller name.

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 mapped for autosizing (having an “A” next to one or more input fields) must retain the alpha-numeric designation and colon at the beginning of its reference name, as in “MC3:” , 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-use the alpha-numeric designation and colon at the beginning of the reference name, as in “MC3:” , if they would like to have the newly added controller pick up the same autosized values as the identically designated controller of the same type within the same HVAC system category.

o For example, if it is helpful for some reason to have the Heating Airflow values in MC4 for system type 07 show up in a controller that is be added to a customized version of a pre-defined system that has a 07 at the beginning of the name, the new control would need to be the same type as the pre-defined controller and would need to have “MC4: “ at the beginning of its reference name.

o Once the new controller is added and properly named, clicking Save for the ApacheHVAC file will complete the link and a black “A” should show up next to the corresponding input fields (the same fields that receive the autosized values in the pre-defined controller that normally uses the chosen alpha-numeric designation).

Users can substitute non-autosized controllers, if desired. This is a workable approach in the case of any controller for which inputs will be the same for all or most multiplex layer instances—e.g., a supply temperature reset controller that will be set to have a range of 58 to 68°F for all layers in the multiplex—or when the system has a very small number of layers, which makes manual editing much more straightforward.

Maintaining connection to referenced schedules and profiles