© Copyright CalCERTS, Inc. 2019
Code Cycle: 2016 Standards
Performance Compliance Approach - New Construction
Ductless systems are not the only option. Any system may have all ductless indoor units, or all ducted indoor units, or a mix of both ducted and ductless. Both ducted and mixed indoor units are rapidly becoming commonplace.
Let’s discuss the modeling of this type of system for the 2016 Energy Code cycle. The 2019 cycle is anticipated to add features that will allow the user to better define the system earlier on by declaring the
number of indoor units per outdoor unit, ducted or non-ducted, but the modeling basics will still apply.
There are suggested guidelines to avoid pitfalls. We will use EnergyPro 7.2.6 and the CalCERTS HERS Registry for the following discussion.
1. Identify the “Systems” – Each HVAC system defined at the CF1R level is treated individually for compliance purposes. Model each “outdoor” condensing unit and one indoor unit as a “Split DX” system. Disregard the number of additional indoor units connected to the one outdoor unit at the modeling level. The additional indoor units will be addressed within the HERS registry after the CF1R-PRF is uploaded and registered.
2. Ductless – If an individual outdoor unit has one or more “ductless” indoor units, and no “ducted” indoor units, then model the air distribution system as ductless. Note that if ducts are added later, this cannot be changed without a CF1R revision, so coordination with the contractor, designer, and installer is imperative.
3. Ductless High SEER/EER HERS Ratings – When the cooling distribution system is modeled as ductless, the modeled system will be simulated to calculate energy usage based on 14 SEER/11.7 EER, regardless of the modeled ratings. There are a few exceptions to the ratings based on capacity, but the simulator is typically blind to the variances. If a higher SEER/EER Rating is modeled, no credit is given regardless of the claimed rating. A CF2Rand CF3R-MCH-26 HERS verification will still be triggered and the HERS Rater is then required to match the system to the appropriate AHRI Certified Rating. Therefore, it serves no purpose to model a ductless system higher than 14 SEER/11.7 EER/8.2 HSPF. Both the 2016 and 2019 ACM discuss ductless systems:
- 2019 ACM 2.4.5: Until there is an approved compliance option for ductless heat pumps (ductless mini-split, multi-split, and variable refrigerant flow [VRF] systems), these systems are simulated as a minimum efficiency split-system equivalent to the standard design with default duct conditions.
4. Ducted – If an outdoor unit has one or more “ducted” indoor unit/s, then model the system as a ducted Split DX system. Surprisingly, you may discover that the ducted system may bring in a higher compliance margin due to high efficiency ratings or if the ducts are located in conditioned space.
5. Duct Location – If there is more than one duct location, model the worst case, such as “Attic.” A ducted system that is modeled as “in conditioned space” will trigger HERS verification. The HERS Rater must be able to visually verify the duct installation prior to covering with drywall, as in a soffit, and prior to covering with insulation, such as in an attic. The verification must be coordinated and scheduled to avoid failed verification's. A failure will typically result in a CF1R revision to remove the duct location credit. This can be problematic when modeled with a low compliance margin.
6. Ducted High SEER/EER/HSPF HERS Ratings – When the distribution system is modeled as ducted, the system will be simulated to calculate energy usage based on the modeled SEER/EER/HSPF efficiency ratings. If a higher than minimum SEER/EER rating is modeled, a credit is taken. A CF2R- and CF3R MCH-26 HERS verification will be triggered and a HERS Rater is then required to match the system to the appropriate AHRI Certified Rating. It is important to model the efficiency ratings based on a known AHRI certification. If the ratings cannot be HERS verified, two options remain: 1) install a system that meets the
requirements of the CF1R, or 2) revise the CF1R to reflect the efficiencies of the installed system. If the compliance margin is small, then a revision could be problematic. In addition, all CF2R and CF3R documents must be untested and then resubmitted after the revised CF1R is uploaded. This is especially cumbersome on large projects, such as subdivisions and group sampling projects.
7. Duct Leakage HERS Verification – Each entirely new ducted indoor unit requires duct sealing and leakage verification. This creates a challenge for both the HERS Rater and the installer. The duct leakage target is calculated based on “measured airflow,” rather than nominal tonnage, meaning that each duct system requires an airflow measurement at the return grille. The duct leakage target is then calculated by multiplying the measured airflow by the maximum allowed duct leakage rate – such as 5% for new systems. Airflow on multi-split systems is typically lower than a traditional system, thus resulting in lower leakage rates. The installer must be aware of his/her capabilities. Very lengthy duct systems can create high static pressures that are beyond the capacity of this type of air handler. It is best to design these duct systems shorter than traditional split system designs.
8. Refrigerant Charge HERS Verification – If this verification is modeled on the CF1R, the installing contractor must coordinate with a HERS Rater for an observed weigh-in charging procedure. It is common for an installer to be unaware of this process and charge all systems prior to the arrival of the HERS Rater and without recording lineset lengths and refrigerant data. This is an automatic fail, which is typically resolved by revising the CF1R for cost effectiveness, but still costly. Also note that this verification
is not supported by group sampling.
9. Airflow and Fan Efficacy – These HERS verification's typically appear on the CF1R-PRF as required. However, systems with multiple indoor units can claim an exemption on the CF2R-MCH-01 to change this verification to “not required.”
Now that the system has been modeled properly, how do you create the additional indoor units in the CalCERTS HERS registry? For performance runs, this task is easily implemented from the CF1R screen using the “System Names” tab.
Let’s say that there are two Ductless Split HP systems, and each system has two ducted indoor units. Since each “system” is considered to have one outdoor unit and one ducted indoor unit, you will need to add a
second ducted indoor unit for each system. This is done on the CF1R screen as shown below:
For modeling mini/multi-splits for an E+A+A project, please see article tilted "2016 Performance Approach - Mini/Multi splits for E+A+A".