- Why take the time to verify?
- Start with a good design.
- Provide for adequate air flow.
Each of us wants to deliver quality. Quality is a good thing, especially when it comes to the birth of an air conditioning and heating system. Our industry has finally embraced the idea that a system's birth is not the day the equipment rolls off the production line, but in its final installation. Let's take a look at some elements of a Quality Installation you can verify for your customers. You can prove you have delivered safety, comfort and efficiency in the air conditioning systems you install and service.
Why Take the Time to Verify Quality?
Let's get this one straight first....to earn more money has to be one reason. And there's nothing wrong with that. Before embarking on a quality mission, it’s important for you to understand that good customers are happy to pay for real quality and are enjoy doing so.
Think of your favorite tools, you paid more for them, but you've never regretted it. In the long term, everyone understands when you spend more, you should get more. Give your customers the opportunity to get more. Some customers have not yet learned this principle, but still give your customers the opportunity to choose and receive a higher quality job.
Start With a Good Design
We all have our methods for designing an HVAC system. Good principles include determining the heat loss or heat gain of the building, then selecting equipment that will get the job done.
Next, you’ll need a method of determining room by room ventilation to match the load and finally you design a duct system that delivers the needed airflow to each room. You must also include in your design duct locations and insulation that assures limited duct temperature loss and registers that distributes the air properly throughout each room.
Airflow can be accurately measured at three places in the system. Fan airflow can be plotted on the manufacturer’s fan tables using the operating fan total external static pressure and by verifying the the fan speed. Compare fan airflow to the system required airflow. Quality installs need actual fan airflow to be plus or minus 10% of design.
Airflow can be measured using a commercial grade balancing hood at each supply register and return grille.
Measure and add together the supply register airflows and compare to fan airflow. Do the same on the return side. And then compare the airflow in each room to your room design airflow. Adjust until design airflow and actual airflow are within 10% at each register and grille.
When all these airflows line up, you can be assured you have delivered quality performance in the airflow department.
Low Duct Temperature Loss
This just takes a few minutes, but is the element of quality and performance that is most often missed.
Measure and record the air temperature at the farthest return grille. Then measure the air temperature entering the equipment. Subtract to find the difference. If the difference exceeds more than 5% of the temperature change over the equipment, you either have duct leakage and/or inadequate duct insulation. More work may be needed to assure a high performing system, perhaps even exceeding code insulation requirements.
Next, do the same on the supply side. Measure the air temperature leaving the equipment. Then measure the air temperature at the farthest supply register. Subtract to find the difference. Apply the 5% rule again.
Fix any problem by sealing ducts or adding more insulation until the supply duct temperature loss falls within the 5% of equipment temperature change.
Verify Delivered BTUs
You can do this at the equipment by multiplying fan airflow times the temperature change thought the equipment times the heating or cooling BTU multiplier. Compare the delivered equipment BTUs to the equipment rated BTU under current operating conditions.
To measure system delivered BTUs (which is different from equipment delivered BTUs) Measure and add together the supply register airflows and multiply the total supply CFM by the difference in temperature from the average return grille air temperature to the average supply register air temperature and multiply the appropriate BTU multiplier. (If you're not sure how to calculate BTUs, email me for a free procedure at the end of the article.)
Compare system delivered BTU to the equipment rated BTU. Great quality requires system BTU to be within 90% of equipment rated BTUs. Good quality is within 80%. Fair quality is within 70% and if you want to be like everyone else, just be sure your system delivered BTUs is below 60% of equipment rated capacity.
Assure the Building Envelope Matches Your System
Best practice requires you to check the building envelope and assure your customer the building envelope matches the quality of your system. While many miss this step, if you want to really deliver quality, don’t bypass this opportunity.
Be assured you don't have to tell your customers they have to replace their light bulbs, windows and plumbing fixtures and install solar panels to take this step, just address the envelope as it pertains to the load of the building. A quick blower door test and an infrared scan will do the job.
Diagnose and repair the envelope as you did your duct system. Seal the leaks in the envelope and add insulation as required. Perfection isn't required, just an improvement that fits your customer’s budget. Sub this work out until you are in the habit of making it part of each job, and then consider bringing a crew in-house when the time is right. Be sure you measure the envelope performance after repairs and verify your envelope matches your HVAC systems performance.
Assure Installation Matches Your Design
If you consider the steps we talked about in this article, you’ll see that we measured every step of the way. That's the key here; when you measure you can actually claim quality and performance, without it you're only dreaming you have done a good job. Know this, your customers are happy to pay for your measurement and reporting, because this is only way you and they will be assured quality was delivered.
Checklists insinuating quality was delivered is a nice idea to write a standard about, but when it comes down to real quality, measurement and verification of the actual improvement in performance is the only real measurement of quality.
Rob “Doc” Falke serves the industry as president of National Comfort Institute an HVAC based training company and membership organization. If you're an HVAC contractor or technician interested in a free procedure describing how to calculate system delivered BTUs, contact Doc at firstname.lastname@example.org or call him at 800-633-7058. Go to NCI’s website at nationalcomfortinstitute.com for free information, articles and downloads.