In 2015 Energy Star for Homes introduced Revision 8 V2 to be required for all homes seeking Energy Star for Homes certification permitted after January 1st, 2016. With the introduction of REV8 V2 Energy Star took a major and much needed steps to sure up the verification of properly designed and installed HVAC Systems.
The program moved away from a single HVAC System Quality Installation Checklist breaking it into two documents. The first of these is Design Review Checklist which coincided with the HVAC Design Report required to be filled out by the designer of the system. The HVAC Design Report was formatted to assure the designer was using either the ACCA Manual JSD Design process or ASHRAE Fundamentals for the load calculation and ACCA Manual S for equipment selection and ACCA Manual D for duct design. There was also an allowance local JHA requirements if any. The Rater Design Review Checklist contained minimum verifiable items such as conditioned square footage, window area, infiltration levels, average window SHGC, number of occupants in load, as built orientation (WC not allowed), and cooling size limits met. There were some glaring and puzzling omissions as well such as requiring insulation levels used in the load calculation to be verified. The Rater Field Checklist then required other items related to the installation to be verified, such as duct leakage, recording external static pressure, reasonably straight ductwork with no kinks ect. It also gave the Rater the option to collect a "Commissioning Checklist" which required the installing Contractor to document their refrigerant charge test and blower airflow settings.
One of the biggest changes that caused a lot of Raters to jump for joy was in their own words "To improve the clarity and enforcement of cooling and heating equipment over-sizing limits, the limits have been aligned with the new version of ACCA Manual S. In addition, the phrase "next nominal size" has been replaced with a quantitative allowance and an alternative tolerance for low-load spaces has been added." For years Energy Star has used the verbiage "Next Nominal Size "when talking about sizing heating and cooling equipment. This led to an era of Energy Star Certified homes with some of the most egregiously oversized HVAC systems you can imagine! A lot of Raters did a tiny happy dance to Energy Star now requiring something that closely mirrored the ACCA Manual S equipment Selection process. In the most Energy Star way possible of course. Energy Star took the ACCA Manual S sizing limits and doubled them saying they still recommended using Manual S limits but allowed sizing beyond those limits because of the distance between available equipment sizes, they didn't want to put a financial burden on contractors and builders to have to buy a more expensive piece of equipment to meet sizing limits. They even came up with a "low load exception" for spaces under a with very small loads that offered even more sizing leeway. The Energy Star Design Report Sizing portion read as follows: Single Stage Compressor-Recommended: 90-115% (ACCA Manual S Limits) Allowed: 90-130%, Two-Speed Compressor-Recommended: 90-120% (ACCA Manual S Limits) Allowed: 90-140% and Variable Speed Compressor- Recommended: 90-130% (ACCA Manual S Limits) Allowed 90-160%. With this footnote- As an alternative for low-load spaces, a system match-up including a single-speed compressor with a total capacity ≤ 20 kBtuh is permitted to be used in spaces with a total cooling load ≤ 15 kBtuh. A system match-up including a two-speed or variable-speed compressor with a total capacity ≤ 25 kBtuh is permitted to be used in spaces with a total cooling load ≤ 18 kBtuh.
Although not great and when getting into lower load buildings some bad oversizing was still possible, it was still much better than the next nominal size language. And the concern that you would have to buy an expensive piece of equipment to match some of the lower loads or fall with the ACCA requirements was justified because variable speed equipment like inverter heat pumps was still new to the market and a LOT more expensive than other builder grade equipment. Fast Forward to 2022.
Energy code adopted into building code has caught up with insulation levels and air infiltration levels formally only required in green building programs. Many code-built buildings are just as low load as buildings we see in green building programs. There is a nationwide push for electrification and the installation of heat pumps. Every manufacturer of HVAC equipment is racing to get inverter style variable speed "cold climate" heat pumps into there production line. Not just major brands. There are more "independent" and "off brand" inverter heat pumps than almost any other equipment. Most offer sizes well below 12000 btu and not just ductless. There are now more vertical style traditionally ducted air handlers available for inverter heat pumps than every before. Energy Star released in the past couple of years a pathway for Raters to use one of the most forward-thinking Standards in recent years, Standard 310 for Grading the Installation of an HVAC system. This includes a much more robust design review process. But they have done nothing to address what is now with codes where they are, gross oversizing allowances in their program. The heat pump industry is rocketing so fast towards parody with other equipment, in terms cost that the main reasoning for allowing over sizing beyond ACCA Manual S limits is hardly a justification at all. To make matters worse, a few revisions ago Energy Star moved away from strictly requiring designing to the ASHRAE 99% and 1% design temperatures because for years contractors claimed they were too restrictive. They say they still recommend the using the AHSRAE design temperatures but have a looser range of design temperatures up to the ASHRAE Design Temps that can be used.
With weather patterns showing longer periods of extreme humidity than ever before and new construction building loads lower than any time in history, along with cheaper and wider range of size and styles of heat pumps we have had, it's time for Energy Star to take a had look at the over sizing limits in its program. With the world moving towards electrification and a heat pump heavy world, Energy Star needs to lead the charge and continue to update its program as the leader it strives to be.