Software Limitations and Issues

Note: items on this page are current as of the last edited date mentioned above

General Issues

• No resizing of standard design systems if unmet load hour (UMLH) requirement is not met.

Spaces

• Increasing the number of occupants in the space only currently impacts the ventilation calculation when using DCV. It does not increase the prescribed occupant density assumed in the compliance simulation.
• Space without a ceiling can cause unexpected heating/cooling load.

HVAC Secondary Systems

• Simulation of supply air temperature and flow controls may not match ACM requirements
• Specifying DCV for all zones of a multi-zone system results in unexpectedly high energy use.
• The simulated supply air temperature for FPFC systems may be less than expected; which can result in more hours of fan operation and therefore high fan energy use.
• AirSystem SZVAV systems with economizers act as constant volume systems when the economizer is not active. A higher economizer control limit is recommended to alleviate this.
• AirSystem SZVAV systems with water-source cooling coils have higher cooling loads and energy use than comparable air-source cooling coils.
• In some cases with central IAQ systems in multifamily buildings the Standard Design rules are not applied properly and incorrect compliance results may be produced
• Imbalanced air flow with insufficient zone connection of a residential zone can cause CSE air pressure out of range error that leads to simulation termination. But this error is not obvious to users.
• Due to limitations imposed by EnergyPlus, the maximum number of zone exhausts that can be connected to a heat recovery system is capped at eight.
• In a project file with multiple VRF systems, if any VRF system is connected to only one zone system, and heat recovery is specified for one or more VRF systems, heat recovery for one of the units will be disabled causing UMLHs. The current workaround is to avoid having a VRF system connected to only one zone system. If the zone system represents multiple indoor units, divide the thermal zone into smaller zones, and create a zone system for each zone. Otherwise, use mini-split heat pumps to model the single zone VRF systems.
• WSHP stopped providing any heating/cooling after the EnergyPlus upgrade. This will be fixed in the next EnergyPlus upgrade.
• The simulated outdoor air in kitchens is not realistic and causes overestimating heating load and sometimes large numbers of UMLHs.

HVAC Primary Systems

• When a user model includes a condenser water loop for a Water Source Heat Pump (WSHP) system and uses individual variable speed pumps for the boiler and cooling tower, selecting the “Add cooling system to meet load” option (which triggers a sizing run for the proposed design) will cause EnergyPlus to terminate with an error. This issue stems from an EnergyPlus bug that prevents sizing runs from completing successfully with this specific configuration. Potential workarounds for this issue includes:
  • Disable the sizing run for the proposed design by unselecting the add cooling system option, or
  • Use a single variable speed pump placed in the return segment to represent multiple pumps in the design.
• Simulation failures have been observed for WSHP models, where the condenser water loop temperature runs (high) out of the accepted E+ temperature range. Potential workarounds for this issue include:
  • Modeling the WSHP system as an AirSystem (Type = ‘SZHP’ or ‘SZVAVHP’ with ‘WaterSource’ as the condenser type).
  • Modeling CW system with a single variable-speed pump on the return FluidSegment.
  • Modeling CW loop pump in ‘StandBy’ mode.
• VRF and WSHP systems, when modeled for multifamily dwelling units, can yield unreasonable results which could result in incorrect compliance results.
• The capacities of the auto-sized condensing water loop equipment which serve WSHP in multifamily dwelling units are doubled in simulation.
• Some models with constant speed pumps on hot water loops may see errors where the water temperature exceeds upper limits due to an EnergyPlus issue where pumps run and add heat to the loop during periods when there is no heating demand.
• All pumps on primary loop of primary/secondary pumping systems will run if there is any demand on the secondary loop
• Evaporative-only cooling systems that cycle to meet cooling loads are not simulated correctly.
• Multifamily WSHP loop cooling tower pump turns on when boiler pump is on. This happens to the systems with separate ‘constant speed’ pumps serving the cooling tower and the boiler respectively.
• WSHP loop temperature is not properly controlled if the heat rejection device is “ClosedTowerEvaporative” and the pump(s) is variable speed.
• Cooling tower total fan horsepower has not been updated per the 2025 ACM
• Fluid system wet up with primary/secondary pumping control with multiple chiller/boiler pumps is not supported.
• Variable speed fan is not supported for FPFC systems.

Material Data

• The values in Table 4.3.8 of JA4 are being reviewed for potential revision. Spandrel panel and curtain wall material data are based on the current values in the table.