Saturday, June 24, 2017

Measuring System Airflow Using a Ductblaster

If you install systems in a state which requires duct leakage tests on all new installations, chances are you have a ductblaster which you use for that purpose. Your ductblaster is more accurate at measuring airflow than just about any tool you have. Afterall, the way it works is to pressurize the ductwork and measure the airflow required to maintain that pressure. You can use the ductblaster to measure system airflow using a procedure called pressure matching.

Operate the air conditioning system normally and use the ductblster manometer to measure the static pressure in the supply plenum or trunk. You should measure after the coil but before any takeoffs. Record this pressure. Now, turn the system off and connect the ductblaster to the blower on the return side. You will need to block the return air trunk off so air only goes through the unit and into the supply ducts.

Now turn on the ductblaster. Once again, measure the supply air static at the same location where you measured it with the unit operating.  Dial the ductblaster up until the measured supply air static equals the reading you took when operating the system. The amount of airflow the ductblaster is moving is the same as the airflow through the system when it was operating.

How does this work? You are matching the airflow required to create a supply static equal to the supply static created by the system blower. Note that this does not require any particular manufacturer’s data. This procedure allows you to make an accurate airflow measurement using a tool you may already have. It also allows you to get more from your investment in the ductblaster.

Friday, June 16, 2017

Refrigerant Don'ts

With summer now upon us and the price of R22 skyrocketing there are many questions regarding replacement refrigerants. This discussion could fill a book, so I am going to restrict this post to a list of don'ts. The intent is to help people avoid issues that can be caused by improper application of 400 series R22 replacements.

Do NOT use a flammable replacement refrigerant in ANY system originally designed for R22. There are some hydrocarbon (propane) based replacement refrigerants sold online. They are NOT EPA approved and represent an explosive hazard when charged into a system that was not designed for flammable refrigerant.

Do NOT add ANY replacement refrigerant on top of an existing R22 charge. This is an EPA violation. You are essentially creating a “new” refrigerant which has not been tested or approved. There are NO replacement refrigerants which are legal to add in on top of an existing R22 charge. You must first remove ALL of the R22 when doing a conversion.

Do NOT use ANY 400 series refrigerant in a flooded system. Even refrigerants which are advertised to work in systems with mineral oil will still separate in the flooded portions of the system because they are not truly miscible. There is a difference between miscibility and solubility, but that is the subject for another whole article.

Do NOT use ANY replacement refrigerants in ANY system using an electronic expansion valve. This would primarily be older R22 minisplits, multisplits, and VRF systems. Trane hyperion heat pumps can sometimes have an R22 charge. In that specific case, the indoor air handler is designed for both R22 or R410A, so switching to R410A and changing the refrigerant dip switch solves that problem for the indoor air handler. Unfortunately, you will still have to replace the outdoor unit with one designed for R410A.

Do NOT use ANY 400 series replacement refrigerant in systems which were originally designed for R22 and have Trane 3D Scroll compressors. The lubrication system that specific compressor design uses does not work well with HFC refrigerants, including ones advertised as being compatible with mineral oil.

This all come down to one main strategy for replacing R22 in most older systems: it is generally best to replace the whole system. Not only does this avoid application problems, it usually provides a significant efficiency upgrade as well.

Wednesday, June 7, 2017

Latent Cooling and Variable Capacity Systems

If you live anywhere other than the southwestern part of the US, you probably need latent cooling in the summer. The word latent means hidden. Cooling capacity is required to condenses water on the evaporator coil. This is referred to as latent cooling because there is no temperature change involved, you can’t sense, or measure the heat change using temperature, but cooling capacity is required. Two things help increase latent cooling: long run times and reduced airflow across the evaporator. These increase the percentage of system capacity used for latent cooling.

I have a brand new communicating, 20 SEER system with a variable speed scroll and an ECM indoor blower motor. One fun thing about the thermostat is that it reports the compressor speed and the furnace reports the blower CFM. I have been watching both.

The compressor is most often operating less than 50% capacity, but stays running most of the day once it starts. This ability to match system capacity to the load makes for long run times, which helps control humidity. It does not use more power, even though it is running a lot because it is using much less electricity while it is operating.

I have noticed that the fan almost never runs at the traditional 400 CFM per ton. For example, on one occasion I found the compressor running at 96% while the fan was moving 1230 CFM. It is a 4 ton system, so traditional CFM math would place the “normal” airflow at 1536  (4 x 0.96 x 400 = 1536). However, the system was operating at only 320 CFM per ton ( 1230 / (4 x 0.96)).

The thermostat also lets you set the indoor relative humidity and reports the indoor relative humidity. I set it at a fairly low 45% and the system has kept it between 45% and 50%. During the day when the system is running, it keeps it right at 45%. It accomplishes this by using long run times at reduced capacity with lower than normal airflow. Summer comfort in the southeast involves more than controlling temperature, it also involves controlling humidity. One bonus of the variable capacity systems is that they do a better job of controlling humidity than fixed capacity systems.

Sunday, May 21, 2017

Motor Rotation

Many single phase motors can only turn in one direction. For example, pump motors and fan motors. Since the pumps and fans they operate only work in one direction, the motors that drive them re usually built for one direction.  This can pose a problem for service techs when replacing these motors. Often, service motors solve this problem by being reversible. However, OEM replacement motors are generally not reversible, so you must specify the correct motor rotation. To do this you need to understand the terminology that is used to describe motor direction.

There are only two possible rotations: clockwise and counter-clockwise. However, there are also two perspectives: looking at the shaft end of the motor or looking at the lead end (opposite the shaft end). A motor which turns clockwise looking at the shaft end is turning counter-clockwise when viewed from the lead end! The point is that just stating a direction is not good enough. You must also identify a perspective.

There are several names for the two possible perspectives. The most common are shaft end and lead end. The shaft end can also be called the output end, drives end, or pulley end. The lead end is sometimes referred to by placing “opposite” in front of whatever phrase is used to describe the shaft end; such as, “opposite drive end.”

Normally these descriptions are abbreviated, which tends to add to the confusion. Below is  list of some of the abbreviation used. The graphic above each group uses an arrow to show the rotation looking at the motor shaft.

CCWSE Counterclockwise shaft end
CCWOE Counterclockwise output end
CCWDE Counterclockwise drive end
CCWPE Counterclockwise pulley end
CWLE   Clockwise lead end

CWSE  Clockwise  shaft end
CWOE Clockwise output end
CWDE Clockwise drive end
CWPE Clockwise pulley end
CCWLE Counterclockwise lead end

Friday, May 12, 2017

Clockwise and Counter-Clockwise

Many folks have heard the phrase “righty tighty, lefty loosey.” This little limerick is a clever way of remembering which way traditional right-handed threads turn. However, it can be misleading. The right or left direction refers to the direction the top of the circle will turn. But the bottom of the circle turns in the opposite direction. So while the top is being turned to the right, the bottom is being turned to the left.

I really prefer the terms clockwise and counter-clockwise to describe rotational movement because you don’t have to be concerned if you’ re looking at the top of the circle or the bottom. You only have to remember which way a clock hand moves. Therein lies the problem. In today’s digital age, some people can’t tell you which way a clock hand moves because they rarely see one.

Every program should have an operating analog clock in the class room so students can learn the difference between clockwise and counterclockwise. Notice how the numbers on the clock face progress from the top to the right, creating clockwise motion. Logically, counter-clockwise motion is the opposite.

This little saying also ignores the left handed threads, which are exactly backwards from right-hand threads. Although far less common, left hand threads are often found on connections for flammable gas, such as the regulators and hoses used for Acetylene on an oxy-acetylene torch. In that case it is “righty loose, lefty tighty.” Doesn’t have quite the same ring to it. Left hand threads on torches have a hash mark on them to indicate that they are left-hand threads. The acetylene and oxygen have opposite threads for a reason – to prevent mixing up the regulators and hoses. Mixing the gasses under pressure can create a combustible mixture.

Sunday, May 7, 2017

Intelligent Controls Improve System Charging

"Charge View" by Johnson Controls
Units with intelligent boards that assist in system charging are available. Many VRF systems can assist technicians in charging the unit. They are so complex that some type of automated assistance is really necessary. With multiple heads and variable capacity compressors there is really no way to use system pressures to determine the correct charge. Computer assistance is available through installation and charging applications that run on laptop computers, to evacuation and charging modes built into the system controls.

Trane introduced split system units with “Charge-Assist” back in 2008 in their Xli line. These systems have pressure transducers and temperature thermistors which are used to operate the electronic expansion valves in the unit. The board can also use the input from these sensors to determine if the system charge is correct. An external  “Charge Assist” solenoid can be controlled by the board to allow the unit to charge itself. On these units, the technician only sees a blinking LED on the unit control board.

Johnson Controls (York, Coleman, Luxaire) are now offering units with built in pressure and temperature monitors and a screen to display system pressures, liquid line temperature, suction line temperature, superheat, and subcooling. The system will also tell you if it is correctly charged. It is like having a digital gauge set built into the unit. The main point is that you can check the unit charge without attaching any gauges or temperature probes. That means you will not lose any refrigerant while checking the charge.

These examples represent only the very high end systems from a few different manufacturers, but I believe it shows the direction the industry is headed. Systems will have sensors and intelligent controls monitoring system operation. I am sure that as the technology matures, its cost will come down, making this technology attractive to other manufacturers and in more main line units. Another driving force will be the desire to insure actual equipment performance and efficiency match the design. The most efficient system available installed incorrectly may perform worse than the lowest builder grade equipment available. Designing intelligent controls into a system is a way to improve system installation and service by taking guesswork out of charging. With systems employing these intelligent controls you really have no excuse for leaving the unit improperly charged.

Friday, April 28, 2017

Measure System Capacity and Efficiency

System tune-up time is here. Imagine if you could give your customers a report that shows the system capacity and efficiency before and after your system tune-up! There is a tool that can do that, the iManifold. It not only can measure system characteristics such as pressure, temperature, superheat, and subcooling; it can use the measurements to determine BTUs/hr capacity and system EER. To be sure, you need a few other measurements; namely, dry bulb and wet bulb in and out of the evaporator as well as system operating voltage and current. The iManifold with the correct accessories can measure the characteristics necessary to do system capacity and efficiency calculations and perform the calculations. It can also produce reports showing the details, including system capacity and efficiency. The report can be printed or e-mailed to the customer. The only “report” most customers get now after a traditional system tune-up is a bill. The iManifold and iConnect are the only tools I know of that can do this.

What accessories do you need? You also need two wireless temperature/humidity probes made to work with the iManifold and an electric meter that can communicate with the iManifold. The iManifold and the necessary accessories required to measure system capacity and efficiency are definitely more expensive than many other digital gauges. However, the iManifold does things other digital gauges cannot do.

To learn more about the iManifold chaeck out their web site