If we don’t change how we design HVAC systems, we might find our trade splat up against a wall someday. Rules of thumb don't sound so appealing, do they?I understand there are a number of software design packages. Poor airflow from undersized SEALED ducts meant that fan motors and compressors became collateral damage.Typical fans failed when subjected to higher-than-tolerable static pressure. The proposed size of the duct is 22.5" x 7.5" (or 10.5" or 14" depending on numerous "rules of thumbs"). ft. per ton sizing rule, but things didn’t work the same any more. Plumbing and electrical penetration leaks were blasted out of existence with carloads of canned foam.

It would be crazy to change the way we do things just because somebody came up with a new insulation.Now people say the 500 sq. So, what gives?Nothing else in 30 years ever came close to a 1000 sq. Bids were easy to figure.

We also test the performance of those systems.

Well, not everybody.In the trades, we are responsible for properly ventilating homes. We just guess. We’ll start with a look back over 40 years of our industry and where our design assumptions have gotten us.As an industry, we’ve been taught from the outset that sizing HVAC systems is a matter of using the “500” rule of thumb.For starters, those of us who have been servicing and installing residential air conditioning systems for the last two or three decades pretty much had it figured out that if we sized systems at the ratio of one ton for every five hundred square feet, it generally worked.

Remember, when HVAC contractors use rules of thumb to size air conditioners, they usually pick a number between 400 and 600 square feet per ton ... Ductwork sizing… Best Practice for Right- Sizing HVAC.

The duct main being limited to 2,000 fpm is a typical value on the medium pressure side, to keep noise to a minimum assuming the duct is above a ceiling. So, are we supposed to believe that?Worse yet, the rated R-value per inch for the typical ½ pound SPF product is the same as fiberglass batts. They swept in like mercenaries, caulking and sealing the daylight (no joke) out of our homes. © 2001-2017 Abraxas Energy Consulting, LLC. Equipment selection and sizing 3. No difficult load calculations were necessary. ft. per ton rule no longer works. We do a lot of them. The resulting lower air flow across the evaporator meant compressors suffered frequent refrigerant flood-back.

Installed ducts rarely perform like they do on paper; they must be adjusted individually after installation, using proper testing and balancing methods and accurate instruments. 5.28 Domestic Hot Water Recirculation Pump/Supply Sizing 50 5.29 Relief Valve Vent Line Maximum Length 50 5.30 Relief Valve Sizing 50 5.31 Steel Pipe Equations 53 5.32 English/Metric Cooling and Heating Equations Comparison 53 5.33 Cooling Tower Equations 55 5.34 Motor Drive Formulas 55 PART 6. No.

Have you ever met a masonry contractor who didn’t believe in installing concrete? Duct and register sizing. The answer is the same as when an irresistible force meets an immovable object.

As an industry, we’ve been taught from the outset that sizing HVAC systems is a matter of using the “500” rule of thumb. Even powerful ECM motors bit the dust when the amp draw went sky high as “silver bullet solution” fans tried to overcome the new restricted air flow in tight undersized ducts.

Hello HVAC experts, In trying to learn some of the concepts, I came across this Youtube video that made a lot of sense to me while watching it, but wanted to make sure the implied "rules of thumbs" mentioned in the video is accurate in the professional industry.

Obviously, since we haven’t done anything different for 30 years, how could we be blamed for causing the clammy feeling people were now experiencing.

per ton or 100 sq.in. This total 93sq" which exits above the furnace into a metal mixing box.

There wasn’t much need for us to But the story didn’t end there. They don’t believe in it.

V Max should be approximately 2/3’s to 3/4’s of VAV box V Nom V Min should be approximately 1/3 to 1/4 of VAV box V Max; IMHO, rules of thumb are only useful to trigger further analysis.All rules of thumb should be considered inaccurate and dangerous. It doesn’t, according to the EPA and many other sources)!The average home in the U.S. is maybe 2500 sq. Now fans were acting like they were blowing air through a drinking straw. Basically, insulators sold their product and put a big sign on ours, “Air Conditioning Systems 50% Off.” Most HVAC contractors are not ready for this. That means no more rules of thumb. ft. per ton. Short Answer (using “rules of thumb”) . ft. per ton. It's a science. An advantage the HVAC people also have is the fancy tools to measure the actual air flow, pressure, temperature, etc. Put your presentation title or confidentiality info here.

ft. × 500 =  3  tons.We did it this way for years and everybody was happy. Miles of weather-stripping went up like a Maginot Line.

Infiltration was just as much a problem as before. John, yes, there are indeed other methods. It was as easy as one, two, three. Why is right- sizing so important? That’s like telling people Clorox doesn’t kill mold on wood (Another myth.

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