1.1 Zone-level loads and sizing

The zone-level autosizing process sets zone-level and airside control inputs in the context of basic system-level parameters.  Depending upon the specific system type, these include the following parameters:

·       zone-level heating and cooling load oversizing factors

·       zone-level airflow for VAV boxes, fan-coil units, fan-powered boxes, active chilled beams, etc.

·       outside-air ventilation rates as well as CO₂ sensor control thresholds, where DCV is employed

·       exhaust airflow and inter-zonal transfer airflows (typically as make-up air for exhausted air)

·       reheat coil leaving air temperatures and flow rates

·       radiator and chilled ceiling panel water flow rates (as of version 6.5)

·       outside-air economizer damper minimum flow rates (incl. optional ASHRAE 62.1 calculations)

·       outside-air economizer dry-bulb temperature high limits*

·       energy recovery engagement, sensible and latent effectiveness, and device power*

·       coil leaving air temperatures, temperature resets, and zone humidity control*

For prototype systems, the zone-level autosizing process provides means of engaging or disengaging system features, such as outside air economizers and airside energy recovery, from within the System Parameters dialog, in a addition to manually changing these within the Loads Data spreadsheet for each system or within the ApacheHVAC airside network itself. The controllers in pre-defined systems also use pre-defined control profiles (which you may also use as you see fit). This allows system-operating schemes for unoccupied hours—e.g., temperature setback only, setback with fan cycling, or setback with fan cycling but no outside air—to be selected along with system schedules and setpoints. While these parameters and operating schemes can be manually changed, the dialogs provide basic inputs and automation for pre-defined systems.

The System Schedules dialog (see additional description below) sets room heating and cooling set points, operating schedules, including start-up and after-hours operation, and the control scheme to be used during unoccupied hours. It does so via automated editing of a pre-defined set of profiles that are referenced within the prototype systems and also applied to Space Data in the Apache Thermal view. The application of heating and cooling set points from the System Schedules dialog to Space Data for each conditioned space provides the fundamental basis for autosizing.

The System Parameters dialog (see additional description below) provides initial inputs for many of the zone- and system-level parameters in the list above, such as zone load oversizing factors and both air-handler and zone coil leaving air temperatures, as inputs to the autosizing of zone-level airflows, etc. It should be noted that oversizing factors are separately set with coils, water loops, and other heating and cooling equipment that is autosized only in the system-level stage of the process.

While otherwise accessible to any ApacheHVAC user, the ASHRAE 90.1 Performance Rating Method (PRM) Navigator in the VE provides additional interface dialogs and tools for ASHRAE 62.1 ventilation rates, exhaust airflow settings, and application of PRM Baseline fan curve inputs. The PRM Navigator interface is described in a separate user guide. The more manual approach to these parameters is described below.

IMPORTANT: Through version 6.4 and variants thereof, the automated zone-level sizing procedure requires that the target ApacheHVAC system file is named “proposed.asp”. This file name must be in place prior to using either System Parameters or Room Load Calculations in the System Prototypes & Sizing navigator. If not, the parameter changes and/or sizing process will not populate the Loads Data spreadsheet according to the rooms or zones assigned to the correct target system. The target system name of “proposed.asp” must also remain in place (or be reinstated) for the Assign system parameters and room sizing data action in the sizing navigator. The ApacheHVAC file name can be subsequently changed without consequence. For version 6.5 an onward, this naming convention will not be required, nor is it required for the System-level loads and sizing process described below.