Failed HERS Test and Final Inspection - How to Avoid the Pain and Expense and a Solution to the Problem

It happened again, yesterday, doing a HERS test on a new house, HERS testing the air conditioning system.
This was the third time I was at this house testing. The technician, not an HVAC contractor but a tech hired by the owner, had added another duct to coax the 5 ton air conditioner into blowing 1750 cubic feet of air per minute, the minimum required by code.

The system did not perform to code. It moved 1600 CFM but not the 1750 required by the State of California. We looked at his work. He'd added a shiny silver drooping limp flex duct connected to a small return filter box. He told me there was nothing more he could do. I suggested pulling it taught in a straight line to the return. He didn't think that would work. He really did not like my alt suggestion of a straight metal duct to reduce air friction.

I exited the front door with him. He threw is boots hard at the driveway and cursed in anger. I could sense deep frustration and a man who probably won't get paid until the job passes. I felt sorry for him. He did not know that these systems are supposed to be sized according to manual J, Manual D and Manual S in software such as Wrightsoft. The owner or builder had signed off on building to the Calgreen checklist which states that the HVAC system will be sized according to Manual J, D and S. Apparently, no one took that seriously. The City of Orinda building department never asked for this basic engineering. Hence, it never got done.

The technician had guessed the system together. The 2600 square foot house in mild, often foggy Orinda, California somehow received a 5 ton air conditioner, the largest available. When it failed he asked me what to do. I had to tell him that I am not the designer but the State's Energy Commission does have something called the Building HVAC Requirements.  http://www.energy.ca.gov/2013publications/CEC-400-2013-001/chapters/04_Building_HVAC_Requirements.pdf

In these Building HVAC Requirements, under table 4-11 (Standards Table 150-D): Return Duct Sizing for Multiple Return Duct Systems, there is a line that shows a 5 ton air conditioning duct system having two 20 inch return ducts with a minimum gross filter grill face area of 1500 square inches.

The system I was testing did not have anywhere near 1500 square inches of filter grill face. It had two filters equaling 768 square inches, about half what code is requiring.

If this system had actually been designed rather than guessed together by a person using some "rules of thumb", it most probably would have passed the first time. The problem is that this is the 3rd time I've seen this in a ten days. It happens all the time in the affluent, well educated San Francisco bay area, home to so much energy efficiency research and development.

I usually ask air conditioner contractors how they sized the system I'm about to test. Almost invariably they tell me they use the "square footage rule". "What is that?" I ask. They then explain that for every 500 square feet of house they put in a ton of AC. Easy! 2500 square feet of house equals 5 tons of AC. System sizing complete! Sometimes they admit that the guy at the supply house told them what size was needed.

We know the problem. HVAC contractors and unlicensed technicians who install HVAC systems don't size those systems according to protocol of the Air Conditioning Contractors of America. The results are brand new, shiny yet poorly operating systems that will waste energy and perform poorly for decades to come.

Here's the solution. City Building Departments must get manual J, D and S designs before contractors can build that system. Just as seismic engineering is required for buildings before they are built, so to can we require that mechanical systems be engineered before they are built. Then we just have to work with the problem that the residential HVAC industry evades building departments permits and code HERS testing some 90% of the time.