Four Airflow Values You’ll Use Daily

September 24, 2018

David Richardson

Airflow is an essential measurement to diagnose HVAC equipment, system, comfort, and efficiency problems. Before you troubleshoot, you’d benefit from understanding the related airflow application, how it affects the system, and how you can measure it.

Airflow is a general term that’s easy to misinterpret. When I first learned about airflow, I had to classify it into four values that made sense to me. The easiest options are the measurement location or source of the airflow reading.

Once you understand the four airflow values, how they tie together, and the variations between them, you can systematically eliminate each as a potential suspect when solving a problem. Let’s look at four airflow values you can use daily and the opportunities they provide.

REQUIRED AIRFLOW

Before you measure airflow, you need to know how much the system needs. This is called required airflow. It establishes a target to aim for. There are many applications for required airflow, the most common being fan airflow. Other applications include individual room airflow and outside air.

“The four airflow values in this article offer a different opportunity for you. If our industry would only take advantage of the first two airflow values, we would see a significant improvement in callbacks, warranty costs, and customer complaints. Add in the third and fourth airflow values, and you begin a comfort revolution.”

Required fan airflow depends on various factors like elevation and equipment application. To keep this simple, most technicians stick to basic industry standards. One resource I’d like to offer is the National Comfort Institutes’s (NCI’s) Required Fan Airflow Quick Reference. If you would like a PDF copy, send me an email request at the address at the top of the page.

Required room airflow is tricky to determine due to the variables that affect room heat loss and gain. A proper room-by-room load calculation is the most accurate way to make this determination. Many contractors also estimate room airflow with their customers. This process involves the customer in the redesign of their system and creates a desire in them to solve their comfort problems.

Required outside airflow is a value we often overlook. HVAC system ventilation is typically left to building leakage and open windows. This approach rarely gets the job done and creates huge opportunities for contractors who look for it. Old outside air design rules are 15 cfm per occupant. Recent code changes take a different approach and allow airflow values for the occupants and the building.

Know required fan and room airflow before you begin to measure. This information is the baseline that you will compare all your measurements against. Comparing design airflow to measured airflow enables you and your customers to quickly understand the meaning of each reading.

FAN AIRFLOW

Once you establish required airflow, you need to compare it against what happens at the air-moving equipment. Fan airflow is the second value you need to understand. It’s the foundation of proper system operation. If it is incorrect, everything else will also be incorrect.

Every system is a little different and must be treated that way. Contrary to popular belief, fan airflow isn’t automatically set at the factory. Don’t assume high speed for cooling and low speed for heating — those days are long gone. You must set fan airflow to manufacturer specifications on each installation to ensure correct and trouble-free operation.

The quickest and easiest way to determine fan airflow is to plot it on the manufacturer fan tables found in most installation instructions. The fan-speed setting and measured total external static pressure (TESP) are two pieces of information you’ll need for it. Find these two points on the fan table and intersect them to determine fan airflow. It’s important to note that the blower must be clean. If it is dirty, clean it first, and then proceed with your tests.

Since fan airflow measurement is rarely perfect, there is usually a tolerance most standards allow. The most common value is ±10 percent of required airflow. It’s best practice to get as close to required airflow as possible, but there are times when this isn’t possible. The percentage allows you some cushion in those situations.

You can see the importance of fan airflow measurement on systems that pair 5-ton blowers and 3-ton condensers. These systems often suffer from excessive noise and poor comfort because they are left in the default airflow position. The fan tries to push 2,000 cfm through a coil designed for 1,200 cfm. The fix is to lower the blower speed so the proper airflow moves across the coil and heat exchanger. How many systems around the country currently operate in this condition?

When you start measuring fan airflow, you’ll uncover the source of many service headaches that disappear once the fan is set correctly.

DELIVERED AIRFLOW

Once fan airflow is set to manufacturer specifications, you need to look at delivered airflow. It is what delivers comfort and efficiency into the living space and determines true system performance.

Unfortunately, our industry has become a little too confident in design, and we assume that delivered airflow automatically happens. We think if the airflow value is from a computer program or a decades-old table, it must be correct. A 6-inch duct always delivers 100 cfm, right? Delivered airflow measurement has repeatedly proven these assumptions couldn’t be further from reality.

Delivered airflow is measured with a good-quality balancing hood and rotating vane anemometer. The balancing hood is the main test instrument you will use. The anemometer measures grilles and registers you can’t access with the hood.

If you have required room airflow values, you can compare design airflow to measured airflow — what it truly delivered. If measured airflow isn’t within ±10 percent of design, you have some work to do. After all supply registers are measured, add all their airflow values to determine total delivered supply airflow into the living space. It should be within ±10 precent of required and measured fan airflow. You can follow the same process for return grille measurements.

It’s common to notice a slight difference in plotted fan airflow and total delivered airflow. The variance is due to different measurement methods and test instruments. Don’t assume a discrepancy in airflow readings is completely due to duct leakage — it might be variations in your readings.

Delivered airflow measurement moves you beyond your competition and allows you to see hidden defects only found through testing. If you want to see how your systems work in the real world, measure airflow into the living space.

OUTSIDE AIR

The last airflow to understand is outside air. It provides HVAC system ventilation needs when brought in from an acceptable location. Many contractors avoid this essential airflow because they fear how it will impact the system and are unsure how to offer it as an option.

To counteract these doubts, many assume that building leakage provides enough ventilation for the customer’s needs. Rarely does this work, especially in newer homes that are tightly constructed. The other forgotten aspect is the outside air source.

Outside air can enter a system intentionally, such as through a dedicated outside air duct, economizer, energy recovery ventilator (ERV), heat recovery ventilator (HRV), or ventilating dehumidifier. It can also be brought into a system unintentionally through duct leakage or pressure imbalances. Air from an intentional source comes in through a known location. If air enters from an unintended location, you’ll have no idea where the source of that air is. Your customers could breathe air from a crawlspace or attic just as easily as from windows and doors.

You can measure intentional outside air with a traverse. The source will determine if you need to traverse with a thermal or a rotating vane anemometer — each application is different. You can traverse a dedicated duct with a thermal anemometer or traverse an economizer inlet with a rotating vane anemometer.

Unintentional outside air measurement is tied to both the duct system and building leakage. If you measure these interactions, you’ll need special test equipment that measures leakage with calibrated fans and gauges.

You can provide a new type of service and solve many comfort complaints when you add intentional outside air and offer your customers a healthy air source. Don’t assume where the outside air is coming from.

THE OPPORTUNITY WITH AIRFLOW

The four airflow values in this article offer a different opportunity for you. If our industry would only take advantage of the first two airflow values, we would see a significant improvement in callbacks, warranty costs, and customer complaints. Add in the third and fourth airflow values, and you begin a comfort revolution.

To add these airflow values to your services, start with required airflow. Email me for the Required Airflow Table and see where you need to be. Next, begin to measure fan airflow. The problems you discover and solve with this single addition will surprise you.

Once you have a good grasp on this, take it up another notch and add delivered airflow. See what happens on a room-by-room basis. Finally, offer outside air to your systems and provide the best ventilation you can for your customers. Each airflow measurement is a building block to provide true comfort and efficiency from your systems. With a little imagination, you can apply this knowledge daily to provide the solutions your customers want and need.

Publication date: 9/24/2018

Four Tips to Avoid Losing an HVAC Sale

How to show you’re the right choice for the customer

August 6, 2019

Will Merritt

As contractors, we wonder constantly: From quote to quote, why did we win this job but lose that one?

“They had a lower price.” That’s what we think in the heating and air conditioning business. But getting sales involves far more than a low price. Here are some other aspects to consider.

Provide the solution the buyer is looking for

It’s more than price these days. Would-be buyers have become very tech savvy. They have so much information at their disposal regarding the products we sell. Often, buyers don’t really know what they want, so we have to lead them down the path. The consumer may mention a particular brand, but studies show they still trust the contractor’s recommendation.

We as contractors must ask the right questions on the sales call:

• Do you have hot and cold spots in the home?
• Have you considered zoning?
• How does your ductwork look?
• How long do you plan to live in the home?
• Do you have allergies?
• Would you like to be able to access the system remotely?
• Did or does your current system keep your home comfortable?
• How are your utility bills?

Sometimes the competition is asking the right questions and getting the homeowner involved in the purchase process. Homeowners can and will get excited about the buying process. We just have to uncover what their true needs are, and we must satisfy those needs for them. Often, if we ask the right questions, we may uncover needs they didn’t know they had.

Today’s consumer thinks buying a new heating and a/c system is like purchasing a standard home appliance. They look at different brands or manufacturers, look for similar specifications or features, and then they compare price.

The consumer doesn’t understand that it is more about the contractor than the brand of equipment. Customers are ready to buy on features and price. But contractors have to come out to measure, check ductwork, see if the electrical matches up, check installation limitations, and more.

Work around the customer’s schedule

For many years, contractors had “contractor” schedules. This didn’t really align with the consumer’s schedule. We went to work early in the morning, so we could leave in the afternoon. This worked well for us, but not so much for our potential customer. The average consumer is very busy during those hours. It is often difficult for them to take time off of work to be home to meet us. And heaven forbid we cancel an appointment or delay it! Many of today’s heating and air companies are beginning to work around the consumer’s schedule. For example:

• Weekend appointments
• After hours
• Whenever it’s convenient for the customer

Try it sometime. You may be surprised how well it works, and I bet you’ll increase your closure rate. Your employees may prefer the non-traditional work hours too.

Make it easy for customers to do business with you

Difficulty of doing business may be one of the biggest reasons we lose sales in the residential HVAC business. We can lose sales to other companies because they made it easier to do business with them. Try these things to make your company easier to work with:

• Great customer service
• Installing around the buyer’s schedule (nights and weekends)
• Offering financing
• Accepting credit cards
• Online scheduling

Have a professional appearance

The general public sometimes has a stereotype when it comes to contractors. They have become accustomed to bad service, poor quality, poorly dressed, and generally unprofessional business practices. What if we change all of the consumer’s misconceptions? What if we provide great service, show up on time, uniformed, and deliver beyond their expectations? Here are some things that will help create a professional appearance for your company:

• Uniformed employees
• Spotless vehicles
• Great online reviews
• Community involvement
• Background checks and drug testing
• Employee photo ID’s

Conclusion

Often we find out the other contractor awarded the job had a higher price. Studies show that only a small portion of the population buys on price. The vast majority make purchase decisions based on the highest perceived value. Let’s spend our time and energy working on how we can deliver higher value, versus seeing how we can cut costs so we can do the job cheaper. If we all work on what matters to today’s consumer, we will all win more jobs.

Danfoss’s annual Refrigerant Week event will return for the third time from September 16 to 20. This year, the focus will be on equipping contractors and installers for refrigerant change and presenting the solutions that are ready today.

The global event will prepare contractors and installers — along with retailers, wholesalers, operators, and OEM engineers — to handle the refrigerant transition’s accelerating pace through a packed program of webinars, podcasts, and local training events.

“Refrigerant transition is an issue that affects contractors and installers all around the world, and the global nature of our Refrigerant Week reflects that,” said Torben Funder-Kristensen, head of public and industry affairs, Danfoss Cooling. “We want to help professionals everywhere to stay abreast of the latest issues and trends, but more importantly, to contribute to the conversation and give their view.”

To that end, a series of live, free webinars will be conducted during Refrigerant Week, which include:

• Global trends on refrigerants and regulations: Get an overview of HFC legislation and the main applications for new refrigerants, and some advice from Danfoss experts (September 16).
• Global trends and drivers for cold chain technology: Learn about the current trends and drivers for cold chain technology and see examples of real-world implementation (September 17).
• Handling A2L and A3 refrigerants, charging procedures and how to service: Learn how to safely lower GWP in commercial refrigeration applications using A2L and A3 flammable refrigerants (September 17).
• New system designs and architectures in supermarkets for lower-GWP refrigerants: Get an overview of refrigerant trends and regulations, as well as the available systems and solutions (September 17 and 19).
• Cool tools for transitioning to new refrigerants: Learn about information and tools that can help you implement new refrigerants in retrofits and new installations (September 18).
• Moving on from R-404A in standalone and centralized systems, which refrigerants? What to adapt in the system?: Learn about the main R-404A replacements per application type, as well as system design and product considerations (September 19).
• An efficiency comparison of industrial refrigeration systems using low-GWP refrigerants: Danfoss experts share their conclusions of an efficiency performance test – making it easy for you to apply the findings (September 20).
• Large industrial CO2 transcritical systems- the journey: Learn how you can reduce the NH3 charge in large industrial systems using different layouts (September 20).
• Refrigerant outlook in commercial air conditioning: timing, performance, product adjustments (September 26).
• Leading-edge CO2 applications - advanced system optimization: Gain an understanding of the benefits and operational challenges you’ll encounter when working with CO2 systems (September 27).

All webinars will be scheduled to allow contractors and installers to tune in live, and content will be available in many different languages. Every live webinar and podcast will be available on-demand following the event.

To register for the webinars, visit this link.

Tips for Troubleshooting Air Conditioning Systems

Liquid/suction line restrictions, over- and undercharges, and liquid subcooling

As noted in last month’s article, troubleshooting an air conditioning system often concerns refrigerant, airflow and mechanical problems, either individually or in combination. This installment in this series of articles will deal with an air conditioner’s liquid and suction line restrictions, overcharges and undercharges, and liquid subcooling in the condenser.

 LIQUID LINE RESTRICTIONS

Liquid line restrictions can be caused by multiple problems, including:

• Restricted filter drier;
• Restricted thermostatic expansion valve (TXV) inlet screen/filter;
• Kinked or damaged liquid line;
• Kinked or bent U-bends on lower condenser coil;
• Restrictive solder joint in the liquid line; and/or
• Oil-logged capillary tube.

A restricted liquid line will starve the evaporator of refrigerant, thus causing low pressures in the evaporator. If the evaporator is starved of refrigerant, the compressor and condenser will also be starved of refrigerant, so the evaporator will not absorb much heat for the condenser to reject.

However, most of the refrigerant will be in the condenser and not necessarily cause high head pressures because of the reduced heat load on the evaporator. Because most of the refrigerant charge is in the condenser, liquid subcooling in the condenser will increase. This is a big difference from an undercharge of refrigerant, which will cause low condenser subcooling. If the system has a receiver, much of the refrigerant will be in the receiver, causing lower-than-normal head pressures.

Some other symptoms of a liquid line restriction are:

• High superheats from a starved evaporator;
• Low ampere draw at the compressor from the reduced refrigerant flow through it;
• Bubbles in the sight glass if the restriction is before the sight glass (sight glasses are optional on some systems);
• Low to normal head pressures from a low mass flow rate of refrigerant; and/or
• Local cool spot after a severe restriction from expansion of the refrigerant at the local pressure drop.

RESTRICTED SUCTION LINE

A restricted suction line will cause low suction pressures and also a starved compressor and condenser. The suction line is a much more sensitive refrigerant line than the liquid line, because much less dense refrigerant (vapor instead of liquid) flows through it.

A starved compressor will lead to low compressor amp draw because of its lightened load. The condensing pressure will also be low from the condenser’s light load. Since suction line restrictions starve compressors of refrigerant, the entire mass flow rate of refrigerant will decrease through the system, causing high superheats from inactive evaporators.

Restricted and/or dirty suction filters are the major cause of suction line restrictions. Liquid subcooling in the condenser will be normal to a bit high, since a lot of refrigerant will be in the condenser coil but not being circulated very fast. The condenser subcooling may be normal to a bit high if there is a receiver in the system. This subcooling in the condenser indicates that there is refrigerant in the system and that an undercharge of refrigerant can be ruled out.

OVERCHARGE

A system with an overcharge of refrigerant will have higher-than-normal condensing temperatures because of liquid backing up in the condenser and robbing it of useful condensing area. In reciprocating compressors, the elevated head pressure causes the volumetric efficiency of the compressor to decrease because of higher pressures of the re-expanding clearance volume vapors in the clearance pocket of the compressor. The amp draw of the compressor will increase from the higher head pressure, creating higher compression ratios, and the entire system will have reduced capacities.

If the system has a TXV metering device, the TXV will still try to maintain its superheat, and the evaporator pressure will be normal to slightly high, depending on the amount of overcharge. The higher evaporator pressure will be caused from the decreased mass flow rate from the higher compression ratio, and the evaporator will have a hard time keeping up with the higher heat load of the warmer entering air temperature. The TXV will have a tendency to overfeed on its opening strokes due to the high head pressures.

If the system has a capillary tube metering device, the same symptoms occur except for evaporator superheat. Remember, one reason a capillary tube system is critically charged is to prevent flooding of the compressor on low evaporator loads. The higher head pressures of an overcharged capillary tube system will have a tendency to overfeed the evaporator, thus decreasing the superheat. If the system is more than 10 percent overcharged, liquid can enter the suction line and get into the compressor’s valving and/or crankcase. This will result in compressor damage, and soon, failure.

UNDERCHARGE

Low suction and discharge pressures, low condenser subcooling, and high superheat in the evaporator are all indications of an undercharge of refrigerant. Undercharged systems have less mass flow rate or refrigerant throughout the entire system. Severely undercharged systems will run very low condenser subcooling because of no refrigerant to subcool.

If the subcooling drops to zero, the hot gas in the condenser will start to leave the condenser with some liquid; thus, bubbles will form in the sight glass (if the system has one). Compressor amp draw will be low because of the decreased refrigerant flow. Service technicians can be confused as to whether the problem is an undercharge of refrigerant or a liquid line restriction, because symptoms are very similar. Remember, a liquid line restriction will give the system a lot of subcooling in the condenser, whereas an undercharge will not.

REFRIGERANT SUBCOOLING

Condenser subcooling can be measured at the condenser outlet with a thermometer or thermocouple and a pressure gauge. Subcooling is defined as the difference between the measured liquid temperature and the saturation temperature at a given pressure. Simply subtract the condenser out temperature from the saturation temperature at the condenser outlet to get the amount of liquid subcooling in the condenser.

The saturation pressure has to be measured at the condenser outlet and converted to a temperature. Always take the pressure at the same point the temperature is taken, as this will alleviate any pressure drop error through the condenser. A forced air condenser should have from 6° to 10°F of liquid subcooling if charged properly. However, the amount of condenser subcooling depends on the static and friction line pressure losses in the liquid line, and will vary from system to system. The 6° to 10° of liquid subcooling is assuming no liquid amplification pump is pressurizing the liquid out of the condenser. Condenser subcooling can be an indicator of the refrigerant charge in the system. For receiverless systems, the less the refrigerant charge, the less the subcooling.

Another factor that will affect condenser subcooling is the air entering the condenser. As the condenser air entering temperature increases, the liquid subcooling will decrease. This is because higher condensing (head) pressures will force more of the subcooled liquid through the metering device to the evaporator. This will also affect evaporator superheat. The evaporator superheat will be less from the increased flow rate through its coil, assuming the system has a capillary tube or restrictive orifice as a metering device. TXV metering devices should hold a somewhat constant evaporator superheat under all system conditions, as long as the TXV valve’s rated conditions are not exceeded.

Original Source: https://www.achrnews.com/articles/141744-tips-for-troubleshooting-air-conditioning-systems-part-2