When you start a new career you start at the bottom of both the payroll and knowledge end of the spectrum for a reason. Experience in a career better enables you to make good decisions that save time and help to keep failures low. It’s no different in a craft or trade. The hope is that you learn as you work and hopefully from those that have been in the industry longer than you. Unfortunately in the HVAC industry there’s no universal vetting process to ensure technicians or business owners are qualified or competent. I speak from experience and in this article we are going to discuss one of the biggest lies in my industry that really bothers me.
One of the most common complaints that I hear from clients about their homes is different rooms being drastically different temperatures. I’m going to tell you right now without a doubt in my mind that this is typically (99% of the time) a duct work issue and often time accompanied by oversized equipment. I say that because we are going to discuss the excuses and lies that I keep hearing to try and either sell people false solutions or deceive people just to make a sale.
Lie number one that hear is that a variable speed/multi capacity system will fix this issue. The reason this lie gets told is because the thought process is that if you can circulate the air in a home for a longer period of time without drastically changing the core temp of the home, then you will achieve an equilibrium throughout the home. This sounds so great that even I believed it at one time. The flaw with this idea is that oversized equipment and improperly designed/installed duct systems can’t be magically fixed by a motor. As a matter fact in our humid environment, this will typically have no effect or worse, make those spaces less comfortable. When poorly installed duct systems in humid environments have air running through them when the hvac equipment is not running or running at a lower capacity, they tend to pick up excess moisture/convection gains (from attic duct systems) and distribute that into the home. To make matters worse, most of the time these same systems are oversized so they don’t run long enough to dehumidify in the first place leading to increased indoor moisture levels. You can’t expect a band aid to seal a gaping wound. Putting in a very expensive multi capacity/variable speed unit can’t fix duct work issues. The ducts are responsible for distributing the air throughout the home and keeping the spaces relatively close to the thermostat set point.
Lie number two is that variable speed systems will lower energy bills. Variable speed systems can reduce energy consumption, so long as they are installed correctly on properly designed duct systems. I have a story that I’ve referenced in a past blog about a home owner who was sold a 23 seer inverter driven heat pump and regrated it every day since. This client has a home about 1000 sq ft in eastern North Carolina where they were sold arguably one of the highest performing split heat pump systems on the market. They were lead to believe that their energy bills should go down drastically. The opposite actually happened, their electric bill went up; why? They called me out there to check out the equipment as it had been down three times in the first year of service and the installing contractor always had a great excuse for these interruptions and blamed their lack of energy saving on windows. What I found was a duct system that barely met installation practices for a 1.5 ton unit that had a permanently split capacitor (PSC) blower motor. We haven’t used that style blower motor in a long time, but a PSC could handle poorly designed duct systems and keep on ticking. The blower motors we use now are only able to achieve higher energy savings when duct systems are designed for them. Our newer high efficiency systems require larger ducts for the motors and equipment to perform the way we expect. In this client’s situation, the new 2 ton split high efficiency heat pump was actually using the same if not more energy to do the work that their old 1.5 ton dinosaur was. An added nuisance in this situation was that the extremely low air flow was causing the equipment to fault on error during peak loads (when it’s extremely hot or cold outside), making this install a complete disaster. This is an extreme example of what can happen, however I see similar situations time and time again where clients are told that this really expensive system is going to save them a ton of money.
I’m not saying that high efficiency systems are bad or not worth the money, they are amazing works of art that serve some clients very well. What I am saying is that it all depends on the duct systems. This is true even for our lower efficiency units on the market now. Go back even 20 years ago (the average age of a heat pump in operation right now), and 99% of all units installed had a PSC blower motor. When we look at the fan data performance charts for these motors we will find that they could easily handle up to 1 inch of water column of static pressure from a duct system. Imagine static pressure like ballon pressure in a duct system, as the blower motor turns on, the ducts restrict the airflow naturally to a point and guide that airflow to the desired location. Since the PSC could handle such high pressure, we could use smaller ducts (in comparison to now) and achieve normal performance and life of the equipment. As the industry and government standards changed and efficiency requirements became more stringent, manufacturers were forced to start using different blower motors. The status quo of a minimal efficiency unit now is called the electronically commutated motor or ECM for short. We love acronyms in our industry. The average fan data performance chart for an ECM will show that highest allowable (notice I didn’t say recommended) static pressure is down to .6 inches of water column, that’s nearly half of what the PSC could handle. The “recommended” performance range for these motors to operate optimally is actually about .3 inches of water column. What this means is that the ECM was not designed to push against the higher pressure duct system that your old PSC was, and truth be told, the duct system probably should be replaced or at least tested to ensure it will perform somewhere near normal. Anyone who falls in this category that had a PSC replaced with an ECM system and no duct modifications has likely dealt with a “premature” ECM failure and likely didn’t understand why. I can tell you why but I think you already know by now.
Variable speed motors are very similar to the ECM and require the same due diligence in terms of having a properly designed duct system for you to truly reap the benefits of the equipment’s capabilities. Anyone who reads my blogs know that I push the ACCA manuals like a desperate drug dealer. That’s because they are the holy grail of guides to ensuring we are designing and installing equipment in a way that will serve the public positively. The ACCA manual D lays it out in black and white exactly how to design a duct system for a specific unit and to ensure that airflow is properly distributed throughout the home so that all spaces heat and cool evenly. The contractors that sell the lies are doing so for one of two reasons. Reason one is they don’t know better, they don’t understand ductwork, static pressure, and are ignorant to best practices. Reason number two (and the most disgraceful to me), they just don’t care about anything other than numbers and sales. This one bothers me, if you know the difference between right and wrong yet you still do it wrong, it’s deceitful. The worse part of number two is that if you want bigger numbers and high efficiency equipment brings that, a new properly designed duct system makes those numbers even bigger. So it really makes me question what the motive is behind this approach. If you are considering high efficiency equipment or even a new system and yours is more than 10 years old, it’s in your best interest to have the ducts evaluated to ensure they are properly designed for your new unit. This will ensure not only that you truly get the energy savings, but also the equipment should operate properly with minimal failures.
Comments