Why get a professional load calculation and duct design for your new air conditioning system?

At Building Energy Compliance Testing I’ve been testing HVAC systems in the Bay Area since July 2014. In that time, I’ve tested hundreds of heating and air conditioning systems that don’t comply with code. The problem? They were guessed together using outdated rules of thumb. I commonly see furnaces and air conditioners that are 200 or 300% of the size they need to be. The ducts usually have return ducts and filter grills that are puny compared to what engineered systems call out and wildly undersized according to what the California Energy Commission states in title 24, part 6. None of these systems are designed to get the exact amount of air to each room according to what the room needs to stay comfortable. They don’t provide comfort, economy and clean interior air.

The problem. When you have a big furnace or air conditioner with a small return duct system you get low airflow with a lot of heat or cooling. This causes short cycling, the systems comes on and then turns off shortly thereafter because all that conditioned air satisfied the thermostat. Meanwhile, there is no air circulation or air filtration. Often the farthest rooms stay uncomfortable. This tends to make people in the house uncomfortable and unhappy about the expensive system they just installed. It also does not make for the lowest energy bills or long system lifespan. The home owner who just spent $7,000 or more on what they assume is a state of the art system has a bunch of equipment that is not optimized for they home and they are stuck with it.

What the code requires
California’s energy code and Calgreen, the green part of the code, require manual J, Manual D and Manual T system design. LEED and Build It Green’s Green Point Rating also require that Calgreen be adhered to. These above code, green building documentation systems also give points for such HVAC design. Cities such as Palo Alto and Santa Monica also call out, again, on the plans, that approved HVAC system design shall happen. On a typical set of plans for an addition or remodel, system design might be called out three times. These plans are signed by the architect, builder and homeowner. Still, California energy experts state that 99% of HVAC systems in homes in California do not get designed according to accepted engineering protocols.

Problems with guessed-together systems
Inadequate  air flow from small return duct.
Short cycling
small, quickly clogged air filters that strangle air flow
furnace/air handlers with old style, low efficiency motors
Lack of dampers on ducts to control airflow room by room.
Register grills that don’t direct air where it belongs
Outdated register placement the contractor’s Grand Dad brought from the east coast in 1947.
Wrong filters, hampering airflow or allowing contaminants in the home’s air.
Lack of air duct mastic on joints, leaking conditioned air, wasting energy and allowing in contaminants.
Long duct runs causing excessive static pressure in the system.
Rooms that don’t heat/cool because the door gets closed for privacy.
Register/duct placement where it does not need to go or lacking where it should.

I seem some combination of the above problems every day. We know how to avoid them all. When you eliminate these problems and incorporate proven energy design, you end up with systems that keep homes comfortable, quiet, energy efficient and provide superior air quality.

Further, when a system is designed using state-of-the-art design and built with advanced equipment and assembled professionally with ducts sealed tight with mastic at every connection and then commissioned so that every performance test is passed, you get systems that really perform.

What Design protocol is acceptable? There are a variety of ways to achieve Manual J Load calculations, Manual D duct design and Manual T air grill design. Energy experts tend to agree that Wrightsoft Universal software is the gold standard design software. This company in Cambridge, Massachusetts is the leader in HVAC design software. We at BECT use Wrightsoft and love it. The software is a joy to use, the company has outstanding support help and it is committed to educating its users how to use the product. They have scores of videos on how to use every facet of the software from homes to multistory commercial buildings.

At BECT we can take your home plans and design a custom home comfort system that incorporates our knowledge of ducted air systems and home energy efficiency to bring comfort and value.

Hiring BECT to do load calcs and duct design can save you money. Often times, a contractor will “rule of thumb” a system at 4 tons of air conditioning. When we calculate the plan of the house, room by room, including how much insulation is in the walls, ceiling and floor, window type and how the house is oriented, we have, a number of times, come up with around 2 ton as the proper size. Two tons of AC cost less than four. Money saved.

We’ve seen some houses where a contractor wants to install two systems. While this is usually best for 2 story houses, we’ve seen cases where, upon calculation of sizing, a single system can suffice,  saving capital costs.

Need a closet? Sometimes a family needs more space for coats, hats and the vacuum cleaner. We sometimes get clients a new closet by moving the furnace into the attic or garage as part of the new design. The added space makes it easier to get access to the new system so the contractor can assure that the plenums and duct start collars are accessible so they can be sealed properly. This adds value to your home.

Allergies or respiratory health issues?
Sometimes a respiratory ailment is not from disease but from the environment. The environment we live in today is inside houses and office buildings. All the air in buildings moves through HVAC systems. Is your interior environment designed to keep contaminants out and make the air clean?

Planned, well-thought-out, engineered systems always work better than those hastily thrown-together. If you want comfort and economy with long term performance, load calcs and duct design are something a homeowner wants to incorporate into their strategy.

At BECT, we have decades of experience in energy efficiency in buildings.

www.bect.us