Wednesday, May 25, 2016

Daikin VRV Pro Tour

VRVProTour_Banner_Contractors.small

I took part in the Daikin VRV Pro Tour in Houston this past week. This was the first VRV Pro tour aimed specifically for HVAC Educators. The idea is pretty straight forward. There are way too few techs who understand variable refrigerant flow systems, and Daikin is trying to recruit some help from those of us whose job is teaching HVAC. The tour included a mix of class time and tours of the Daikin facilities in Houston. Daikin is making a very large investment in manufacturing and training facilities here in the US. They are serious about expanding the VRV/VRF footprint in the US. 

What is VRV/VRF? VRV stands for Variable Refrigerant Volume – and is a Daikin trademark name. VRF is variable refrigerant flow – the same idea without the trademark. The idea is to modulate refrigerant flow based on system load, and to achieve system zoning using refrigerant instead of air. Instead of ducting air throughout a building, you are piping refrigerant throughout the building. Indoor units are placed in the zones they are conditioning. Refrigerant is sent to the indoor units based on the needs of that unit. So in effect, you are zoning using refrigerant instead of air or water. 

The compressors are controlled by inverter drives, the metering devices are electronically controlled expansion valves, and the controls are communicating digital controls. Now imagine how difficult it is to find people who are properly trained to work on these, and you understand Daikin's quandary. They HAVE to ramp up their educational effort if they are to have any hope of expanding their market here. 

So did I enjoy the tour? Absolutely!
Should you go if you have an opportunity? Absolutely!
Did a two day class and tour teach me all I need to know to install and service VRV systems? Well...

If you want to learn more about Daikin products, go to daikincity.com and click on "Library" in the middle towards the bottom. That takes you to a page that allows you to download installation and application manuals for all their products.

Sunday, May 15, 2016

Condensate Drain Cleaning

It is time for annual spring AC maintenance calls. One thing you should be doing is cleaning out the condensate line and checking to see that the condensate drain is working properly. The customer is paying you for a seasonal maintenance to avoid having problems – such as a mess caused by something as simple as a clogged drain line. If you can get to the condensate drain easily, you can blow it out with nitrogen using a rubber stopper with a 1/4” copper pipe and flare connection.

Gallo Gun









Another option is the Gallo Gun that uses CO2 charges. Both of these options require access to the drain opening inside the evaporator drain pan. The drain opening is usually accessible on cased coils by removing a panel on the front of the coil casing. Likewise, the drain opening for the coil in most heat pump air handlers can be accessed by removing the front panels.


However, for coils in hard to reach places, or coils installed inside a plenum with no access panel, it may be easier to suck out the muck using a Sludge Sucker. The Sludge Sucker is installed on the drain outlet. Nitrogen pressure creates a vortex which makes a strong suction on the drain line, sucking out the water and muck in the entire drain system.
Uniweld Sludge Sucker


Foe some systems you may need to clean out the condensate line trap. If  the drain is already plugged, then chances are the trap is plugged. Most manufacturers require condensate line traps. The trap is designed to stop air from sucking in through the condensate line during operation. Unfortunately, because traps tend to trap stuff, they get blocked with crud. Most codes now require that condensate lines have clean-outs which allow the trap to be cleaned without cutting out the existing trap and replacing it. For many site built traps, this has been common for many years. The only practical way to clean them was actually to just replace them.

If you do have to cut out and replace a condensate trap, make sure that what you replace it with can be opened and cleaned. This can be done by installing tees in a couple of places where you would normally use ells and plugging or capping the unused branch. Alternatively, you can use a manufactured product such as the Rectorseal EZ Trap of the All-Access AA1 cleanout.
Rectorseal EZ Trap
All Access AA1
































Another solution would be to remove the traditional trap and replace it with a product designed to provide a drain seal without trapping water. Three types are available – the Cost Guard condensate drain seal by Trent Technologies, the Air Trap by Des Champs Technologies, and the Rectorseal Waterless Kit for their EZ Trap. I will talk more about how these work in a future post.
Trent Technologies Cost Guard

Des Champs Air Traps
Rectorseal Waterless Kit


If the system you are working on does not have a safety overflow switch installed, consider adding one. The safety switch is typically wired in series with “Y” to prevent the outdoor unit from operating and creating more water.  Some are installed in the primary drain clean-out, and some are installed in the secondary drain port. They are inexpensive, easy to add, and help prevent property damage. In the case of coils installed on top of furnaces, they can prevent the destruction of expensive electronic components inside the furnace from an overflowing condensate drain.
Rectorseal Safety Switch in primary drain

Diversitech safety switch in secondary drain


Monday, May 9, 2016

Politics Poisons Working Relationships

This 2016 presidential election promises to be an especially exciting and event-filled campaign. Many people are bound to get caught up in the excitement and fury to come. However, please do not make the mistake of discussing politics at work. People can get emotionally wrought up in their politics, causing unkind remarks that are impossible to un-say. Discussing politics at work can poison a healthy working relationship.

Several years ago a student went to work for a local company. At first all was bliss. The student talked about how nice the owner was and how much he was learning. The company owner remarked on how smart the student was and how quickly he learned. Then all of a sudden the reports changed. The student now called the owner a racist bigot and the owner said the student was lazy and stupid. Digging a little deeper I discovered the core issue: one day at work the student had offered his negative opinion of then president Ronald Reagan. He had made the assumption that because both he and his employer were on friendly terms and were polite to each other, that they felt the same way regarding politics. However, the employer thought Reagan had saved the country. The ensuing discussion left both of them so angry that the student could no longer work there. The student really needed the job, and truth be told, the company really needed his help. Both parties lost a valuable working relationship because of a casual remark about politics.

If you are an employee, offering your opinion on politics to fellow workers or your boss can jeopardize your relationship. If you are the boss, think about the effect offering your opinion has on your employees. They can’t safely disagree – so you won’t likely get honest discussion. They may quietly agree, even if they don't agree. Or, they may decide you're a racist bigot and quit. And of course you should NEVER start a political discussion with customers. If the customer starts the discussion, agree with whatever they say and get out of the discussion as quickly as possible. Who loses if the customer gets upset because of political differences? You and your company.

I know you probably feel that the country’s existence depends upon your candidate winning. But the truth is whoever is elected president will be there four years, maybe eight years. Hopefully your career will extend far beyond eight years. The president will come and go and you will still be making the world a better place by keeping folks comfortable. So what happened to the two techs in the story? They are both doing fine – separately. I am sure that they support different candidates. They each are fine men, good techs, and do our trade proud – I just won’t discuss politics with them.

Wednesday, April 27, 2016

Pressure Transducers

On my last post I discussed common refrigeration pressure switches. As the name implies, these are switches which are opened and closed by pressure changes. They can make or break circuits, but they cannot indicate pressure. Pressure transducers are often used for electronic controls because they can actually indicate system pressures.

The word “transduce” means to change from one form to another. A pressure transducer turns pressure changes into analog electrical signal changes. This is most often a change in a DC voltage, typically 0 – 5 volts DC. This changing voltage can then be interpreted as a pressure by the electronic control to which it is connected.

The most common pressure transducers used in HVAC use a small stainless-steel diaphragm with strain gauges bonded to it. A change in pressure causes the diaphragm to bend, which causes the strain gauges to change resistance. These transducers have three leads: two are wired to DC+ and DC- and the third carries the signal. Pressure transducers ohm out like a potentiometer. On diagrams this looks like a potentiometer with a pressure bellows connected to the wiper arm. The resistance between the two leads that connect to DC voltage should stay the same regardless of the pressure. The third lead changes resistance relative to the two other leads as the pressure changes.




When the two other leads are connected to 5 volts DC, the signal connection will vary between 0 and 5 volts DC depending on the pressure. The control then interprets this voltage and controls the system based on the board’s program. If you want to check the transducer signal, read the voltage between the signal lead and DC- and then compare this voltage to a chart published by the manufacturer. Here are a couple of links to more information on presure transducers

Omega Transducers

Emerson Climate Technologies

 

Tuesday, April 19, 2016

Pressure Switch Lingo

Pressure Range
The range of a pressure switch is the  minimum to maximum pressure at which the switch can be set. Because refrigeration systems have two basic pressure areas, high side and low side, pressure switches are often described as either high or low pressure switches, based on which side of the refrigeration system the switch is designed to operate. However, this is a bit of an oversimplification. It is possible for two pressure switches with identical ranges to behave very differently if they have different switching actions.

Switching Action
The switching action  describes what occurs when pressure rises above the switch set-point. Basically, only two things can happen: the switch either closes or it opens. So, pressure switches are classified as either close on rise, or open on rise. For refrigeration system safety applications, close on rise switches are used to protect against low system pressure, and open on rise switches are used to protect against high system pressure. But there are many other applications for pressure switches. For example, a close on rise pressure switch can be used for condenser fan cycling to maintain head pressure. The condenser fan is energized when the condenser pressure rises to the switch cut-in point. Similarly, an open on rise pressure switch can be used to control the harvest cycles on an ice machine. When the evaporator pressure drops to the switch cut-in point, the harvest cycle is initiated. The safest way to describe pressure switches is by both their switching action and their pressure range.

Cut-in, Cut-out, and Differential
It is important to understand that the switch contacts cannot both open and close at exactly the same pressure – there has to be a difference between the pressure when the switch closes and the pressure when the switch opens. This difference is called differential. Three terms are used when describing pressure switch settings: cut-in, cut-out, and differential.  Cut-in is the pressure when the switch closes, cut-out is the pressure when the switch opens, and differential is the difference between the two.





















High Event and Low Event
Sometimes the terms high event, low event, and differential are used. In the case of a close on rise pressure switch, the high event would be the cut-in and the low event would be the cut-out. In the case of an open on rise switch, the high event would be the cut-out and the low event would be the cut-in.

What Difference Does it Make?
There are both physical and practical reasons for having a differential. Physically, pressure switches are mechanical devices which use levers that are controlled by springs and pressure bellows. There must be some mechanical motion to open or close the electrical switch contained within the pressure switch. Since this motion is created by a change in pressure, the opening and closing point cannot be the same point. Practically, you really would not want the control system to respond so quickly. For example, once the compressor stops running, the high side pressure almost immediately drops a little, even on systems with hard shut-off expansion valves. If a small drop caused the high pressure switch to close again, the compressor would quickly cycle on and off repeatedly, which would cause more damage than the high pressure alone. I hope this helps explain why there are multiple settings on a pressure switch and what they all mean.



Monday, April 11, 2016

Using Manual D Speed Sheet

The free ACCA Manual D speed-sheet makes properly sizing residential duct work really easy. However, you need to complete three important steps BEFORE you are ready to use the Manual D speed-sheet. You must first do a Manual J room by room load study, select the specific equipment you will be installing, and draw out your duct system in stick form. The speed-sheet will help you size your ducts according to the required heat load in each, the unit output, the unit airflow, and the external static pressure requirements of the unit. There are three basic steps: determining the total effective length of the duct system, determining the design friction rate, and finally sizing the duct.

Effective Length
Manual D looks for the worst case duct run and bases the design friction rate on that longest run. The idea is that if the blower can move the air through the longest run, it can easily push the air through the other ducts. The assumption is made that each run will have a balancing damper, and that the balancing dampers will be used to balance the system airflow once the system is installed. The speed sheet gives you four columns to use for determining the longest effective length. You don’t have to use all of them if the worst case run is obvious. Note that you are NOT entering data for every run, just looking for the longest run.

There are three rows labeled Trunk. They are there for systems which have multiple branching trunks. Most systems will only use one.  Enter the length of the trunk duct from the plenum to the branch takeoff in one of the Trunk rows. Then enter the length of the branch run beside Runout Length. The second set of rows on this tab are for entering the equivalent length of all the fittings. They are arranged in groups of fittings with similar functions. Click on a group to go to the tab showing the different fittings. Choose a fitting that best matches the fittings you will use. You will need to remember it, or jot it down. Click return to return to the Effective Length tab. You will probably NOT have a fitting for every group. Just leave spaces blank which do not apply to your system. Repeat the process for the return. Note that the group numbers change bit because the equivalent length of return air fittings varies from supply air fittings.

Friction Rate
The second tab is for determining the design friction rate. You need to know the specific unit for this part because you will be entering the unit airflow and external static pressure. The idea is pretty simple. All things that the air moves across cause a pressure drop. You list the pressure drop in wc for all the air components. This is totaled and subtracted from the system external static pressure, and what remains is available static to be used for moving air through the ducts.

Since friction charts are based on 100 feet, the friction rate, or wc friction drop per 100 feet, needs to be determined. For example, if your available static was 0.12 and your total effective length is 200 feet, the design friction rate would be 0.06. A duct which would cause a pressure drop of 0.06 per 100 feet would create a total pressure drop of 0.12 by the time the air traveled 200 feet. The speedsheet does this for you based on the total effective length calculated on the Effective Length tab.

Duct Sizing
You need to have a Manual J calculation of the heating and cooling loads for each room before using the final tab, Duct Sizing, Simply list the room name, heating BTUs and cooling BTUs and the speed sheet calculates the duct size based on the friction rate and CFM from the Friction Rate tab. Note that it re-sizes the ducts every time you enter more data – so don’t be alarmed if it tells you the first room you enter requires a 16 inch run. The sizes are not accurate until you have all the room information in.

Trunk sizing is as easy as clicking a box for each branch duct that t trunk feeds. Note there are probably more rows for trunk ducts than you will need.  Returns are also sized the same way. You click the box of each supply run which you believe will be served by that return. This is obviously not an exact science. However,  it is important that each supply run is selected in a return. If you have return trunks, you size them by selecting the return branches which feed into the return trunk.

Creative Application of Manual D Speed Sheet
You can use the Manual D Speed Sheet as a teaching/learning tool by varying some of the entries. For example, play with different equivalent length fittings to see the effect between best case and worst case fittings. Try different external static pressures and airflows to see the effect on duct sizing. Thi is a great way to see the effect different design decisions can have on the end result.

Monday, March 28, 2016

Planning for Success

If you are waiting for success to just drop in your lap, you may be waiting for a long time. Successful people have to work at being successful. Even after achieving a degree of success, you have to keep working to maintain your current level. However, hard work is not the only pre-requisite to success. Planning makes your efforts more productive by focusing your attention on the details and directing your energy to items which you might otherwise overlook. When teaching HVACR, lab work can be chaotic. Planning helps bring the chaos under control. I will be giving a Webinar on " Tips for Running an Effective Air Conditioning Lab" Wednesday, March 30 at 3:00 PM. The webinar is free. To register, got to the following link

https://attendee.gotowebinar.com/register/8836657677340179713