Month: July 2017


I know I’m gonna get some eye rolling here but it needs to be said.

When we teach electricity to new techs we use a lot of “water” metaphors. We talk about volts like PSI, amps like flow and Watts like GPM. Even the word “flow” gives us a vision of water moving.

Then we talk switches and circuits and we say “open” to mean no path / no flow and “closed” to mean a path or flow.
That’s the opposite of water…

With water, we “open” the tap when we want flow and close it to stop the flow.
With a switch, we “close” when we make a circuit and we “open” when we break a circuit.

Someone pointed out to me that describing an “open” switch or circuit like a drawbridge may be better. Cars (electrons) can move when the bridge is closed and cannot move when the bridge is open.

It struck me that this water metaphor may be one reason newbies struggle to grasp relays.
Or maybe I’m just overthinking it.

— Bryan

I’m a big dummy when it comes to my own air conditioning maintenance. I talk about the importance of changing air filters to customers and techs but I never stay up on replacing my own.

Yesterday I walked into my mechanical room and my 2-ton air handler sounded like a vacuum cleaner about to implode.

My filter was nasty… nasty to the point that I wasn’t willing to leave the filter in. So I pulled it out and think to myself “I’ll just grab a filter from the office tomorrow”. well… I forgot and I live 35 minutes from my office.

So today I grab a filter from my nearby hardware store, a common brand and pull it out of the plastic wrap to install it. Sure it was a MERV 11, but that was the only option other than the cheap, spun fiberglass “bug catcher”.

I know what you’re thinking, I should have known better

I’ve got to give it to this filter manufacturer for actually printing the static pressure drop on the filter (shown above).

My system is setup for 350 CFM(594.65 m3/h) per ton so it’s required running at right around 700 CFM(1189.3 m3/h) which means on my system this filter is going to add 0.26″wc(64.69 pa) of extra static to the return side of the blower.

With most systems being rated at 0.5″wc(124.4 pa) TESP (total external static Pressure) this makes up more than half of that, before any ductwork, grilles, registers, balancing dampers or coils in the case of furnace systems.

On a PSC blower motor this extra static from this filter would result in lower airflow, poor system performance and poor air distribution.

With an ECM motor this extra static can result in higher blower motor power consumption and condensate drainage issues / difficulty maintaining trap.

While some systems may be able to deal with the extra static, many will have issues ESPECIALLY on older systems that have PSC motors and furnaces with coils.

This is why larger filter cabinets with lower pressure drop filters often make sense or oversized filter back return grilles.

When choosing a filter remember that airflow (Pressure Drop) is just as important to consider as filtration (MERV rating)

— Bryan

The photo above is from a video one of my techs took of proper condenser cleaning. I must say, he did a GREAT job of cleaning the coil and he was very careful with the top. However I STILL would have liked to see the top get completely removed during a full maintenance. Pulling the top usually just requires disconnecting the fan wires, cutting a few wire ties, taking out some screws and then removing the fan grille or the entire top and laying it top down in the grass.

This is ACTUALLY how I performed a maintenance, even before I started my own business.

Here is why –

  • If you wash from the outside – in you are not doing the best possible cleaning. Everyone knows that washing from the inside out is a superior method of cleaning.
  • If you lay the fan on top of the unit (like shown above) you risk twisting / damaging the wires, scratching the paint and bending the fan bade.
  • When you pull the top entirely you can more easily clean the dirt and leaves from the inside of the condenser, this should also be part of a proper maintenance because that dirt can reduce coil capacity as well as hold moisture against the base, compressor and accumulator resulting in corrosion.
  • With the top off you can get a better view of any wire rubouts or potential wire rub outs and address them before they cause a problem.
  • You can also visually inspect the compressor terminals for signs of heat and corrosion, potentially preventing a major issue such a terminal failure / “blowing a terminal”.

Obviously it will take about 5 mins longer and you will need to rewire it properly with the terminals snugly installed.

So what do you think?

— Bryan

P.S. – Here is the video in case you want to see what I mean and yes… he knows that cleaner isn’t always required when washing a coil but he used it for demonstration purposes

Courtesy of Emerson

It is important to have refrigerant that is free from debris and contaminants and we control these issues on many different fronts.

  1. Proper tubing handling preventing copper shavings, dirt and water from entering while installing
  2. Flowing nitrogen while brazing to prevent carbon build up
  3. Deep vacuum of 500 microns or less to remove air, nitrogen and moisture
  4. Installation of a liquid line filter drier to keep contaminants from hitting the metering device

But in all of this we can forget the role that suction driers can play in protecting the compressor and the compressor oil.

In air conditioning, we rarely install suction driers unless there is known acid contamination such as in the case of a compressor burnout. Interestingly Copeland actually recommends suction driers in ALL applications in bulletin AE24-1105 R5 .  While I certainly don’t think that we need to change our practices and begin installing suction line filter driers on every single installation, it does get you thinking about the role a suction drier can play in protecting a compressor.

In a typical burnout application where acid is present, it is a good practice to –

  • Remove / Flush as much contaminated oil from the system as possible considering the application including any oil traps, separators or accumulators
  • Install a high capacity acid removal suction and liquid drier or removable core(s)
  • Some contractors will add acid neutralizers such as Acid Away in certain applications
  • Return after running the system for a while and test for acid and replace high capacity filter/driers with new ones if required
  • Once acid is no longer present, return and remove the suction filter/drier and install a standard liquid line drier or core

These practices above are good, general practices to follow, but you may consider replacing the suction drier with a standard, high capacity, low-pressure drop suction drier with two pressure ports instead of just straight piping it. This will provide you an extra layer of protection for the compressor should any acid or contaminants from the burnout make their way to the compressor.

Table Courtesy of Emerson

If you do choose to LEAVE a suction drier in a system there are a few things to consider.

  • Just like with a liquid line filter drier, make sure to install a suction filter/drier that is large enough for the system capacity. Read the info on the drier or the manufacturer’s data to make sure it is large enough so you don’t start off with a restriction
  • Make sure you don’t burn the paint on the drier when installing. Because suction driers on air conditioning will often be exposed to the elements you want to make sure the paint is intact so they don’t rust.
  • Use a suction filter/drier with ports on both sides and measure the pressure drop whenever you service the unit. make sure the pressure drop does not exceed the levels shown in the chart above.

All in all, having a suction drier in the system is a good thing, so long as it isn’t contaminated, rusty or restricted.

— Bryan

P.S. – Sporlan has a great catalog of filter/driers HERE

This article is written by Neil Comparetto. Neil is one of the smartest and most thoughtful techs I know online. Thanks Neil.


Why measure static pressure? Because it’s fun

I enjoy drilling holes in things. I rarely leave a house without drilling a hole in something. I also believe it’s an essential step to commissioning and diagnosing a forced air piece of equipment. Let me explain why.

Commissioning 

I think we all can agree that proper airflow is necessary across the indoor coil. You should set the airflow before adjusting the refrigerant charge, right? Yes. Well, how do you know what fan speed to set the blower at?

Whether it’s a PSC, X-13, or an ECM motor you have fan speed options. The easiest way to set the blower speed is to measure TESP (total external static pressure), cross reference the TESP to the manufacturers blower chart in the installation manual, and adjust the blower speed. Sure, there are other ways of estimating or measuring airflow, but for commissioning a system in cooling, static pressure and a blower chart is easy and accurate enough.

350-400 CFM(594.65 m3/h – 679.6 m3/h) per ton works in my neck of the woods. If you are in a very dry climate, or at high altitude the CFM per ton requirements may be higher, often 450 – 500 CFM( 764.55 m3/h – 849.51 m3/h) per ton.

Even when commissioning a furnace in heating I like set up my airflow first, or at least know how many CFM the blower is moving. Typically it’s between 130 and 150 CFM(220.87 m3/h – 254.85 m3/h) per 10,000 input BTUH.

How many times have you serviced a system installed by others, there is no evidence of airflow being measured, and the blower speed is set too high? My guess, everyday.

There’s a better than good chance the airflow is wrong, and has been since day one.

Benchmarking

The airflow is set, now what? Take it to the next level, benchmark your pressure drops.

The pressure drops across the return duct, air filter, indoor coil, and supply duct can be valuable pieces of information when servicing the equipment in the future.

Imagine knowing exactly what the pressure drop across the coil was when commissioned 7 years ago. In a typical arrangement of the evaporator coil on top of a furnace a visual inspection of the coil for cleanliness can be difficult.

Knowing the original pressure drop can save time diagnosing, and justify taking further action. TESP by itself will not give you this information, only that there is an issue somewhere in the supply air side of the system. (It is recommended to record the dry and wet pressure drops across the coil, they will be different).


Same applies for the air filter. I typically install 5” media filters on our installations. On a furnace I aim for a .10” pressure drop across the filter when new.

Air handlers can typically handle a higher pressure drop across the filter (because the coil is included in the TESP rating), but at the cost of filter efficiency. Generally these filters are good for 6-12 months. Knowing the before and after pressure drop of the filter in this system will help you determine how frequently it needs to be changed.

Knowing the supply and return duct pressure drop can be useful as well. It’s not unheard of for vents to be closed, return grilles blocked, internal liners to collapse, flex duct to get smashed, or even disconnected. A static pressure reading of the ducts referenced to the pressure drops when commissioned can quickly tell you if there are any discrepancies, and better yet what actions to take.

Does benchmarking lengthen the time it takes to commission the system? Yes. Does it give you the information necessary to quickly and accurately diagnose airside issues during future servicing? Yes it does. In reality, once you do it a few times and develop a system it doesn’t take much longer at all.

If you have not listened to Bryan Orr and Jim Bergmann’s podcast on checking the refrigerant charge without gauges please do. They make a case for an even more comprehensive benchmarking procedure. Listening to it was one of those ah-ha moments for me.


Servicing 

Take TESP to verify airflow against benchmarks and / or blower charts. In my experience most of the time airflow is incorrect. If this system is new to you and will be part of a service agreement I recommend that you check all four pressure drops (return, filter, coil, supply) for reasons mentioned earlier.

I find a lot of air filters that are too restrictive (small) on service calls. Air filters can be low hanging fruit if the equipment is not getting to proper CFM. It’s not uncommon to get .30” pressure drops on new filters.

If you find issues with the existing duct system, and it’s exposed, static pressure readings can help pinpoint where the restriction is.

Many times the restriction is obvious. A nasty reverse elbow then it turns twice, transitioning from 20” to 10” into some kind of cap-and-tap contraption. Sometimes the restriction is internal, or not obvious. Collapsed duct liner or a closed damper can be found with static pressure strategically measured across portions of the duct system.

If there are issues with the duct system let the homeowner know. This conversation might expose some comfort problems that they are experiencing. At the least it will make them (and you) aware that there are issues that may need to be addressed when it’s time to replace the system.

I’m not advocating to check static pressure every time you run a service call. I know that’s not always practical. I am advocating for installing the pressure ports, and benchmarking on commissioning as well as measuring airflow against the benchmarks during service when the call type calls for it. Future service techs will thank you and you will come to a faster and more accurate diagnosis.

— Neil

This is a video tech tip from our friend Brad at HVAC in SC.

In this video Brad demonstrates that using a cap off of a refrigerant tank on a system can depress the Schrader core on the system in some cases. Make sure to use proper caps that have seals or brass flare cones.

Transcript

If you’re ever on a service call and you need to use a replacement valve cap, do not use the ones that are on the refrigerant tanks. Here’s a perfect example the one on the right is just a standard plastic cap you can see the circle o-ring in there the one on the left you can sort of see the dimple in the center it’s just got a flat piece of rubber across the bottom of the valve cap. What actually happens is where you see that depression is what’s pushing against the valve core. As you can see this is all oil and what’s happening is when they screw this on it depresses the valve cap and slowly leaks as you can probably hear. So that’s how this system lost its refrigerant charge, just make sure you’re using the proper caps make sure they have rings inside of them.
— Brad Hicks

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I don’t do much in the way of “rack” refrigeration, but I recently had a conversation with experienced rack refrigeration tech Jeremy Smith and he got me thinking about EPR valves.

I’ve heard EPR (Evaporator pressure regulator) valves called suction regulators or hold back valves. In essence they hold back against the suction line to maintain a set evaporator evaporation or boiling temperature.

In refrigeration rack systems EPR valves play a vital role in ensuring that the product is cooled consistently and nearly constantly.

In an A/C system we have a TXV that maintains a constant superheat at the evaporator outlet. The evaporator temperature itself will fluctuate up and down depending on load.

In a refrigeration case you must first ensure you have full line of liquid using a sight glass or by checking subcooling. Then you make sure the case has proper airflow etc… then you set the EPR to maintain the proper coil evaporation temperature (by holding back pressure as needed) and then you check and / or set the TXV to the proper superheat. This ensures BOTH proper coil feeding as well as proper coil temperature.

Pretty cool right? (Pun intended)

— Bryan

Photo by Stephen Rardon

Whenever someone brings up undesired condensation on an air handler cabinet, or on a supply air duct or in a ventilation duct or on a vent like the one above, someone will inevitably say “condensation occurs where hot meets cold”.

Early on in my career, I believed this, so when I saw a vent like the one above I would either increase the air flow to warm up the supply air or I would seal around the vent or even pile insulation on top to make the ceiling “less warm”.

The trouble was, the problem almost never went away  just by trying to keep hot from cold

Then in 2003 – 2005 we had some of the most active hurricane seasons in Florida on record with numerous land strikes and tons of power outages as well as weeks with high latent (humidity load) and low sensible load (low outdoor temperatures).

condensation and mold growth EXPLODED

In the Summer of 2004 I had a few things happen that opened my eyes to the reality of condensation.

First, I kept going back to the home of pro golfer and former Masters champion Mark O’Meara and wiping down his vents and ceiling all while frantically attempting to solve the root issue.

Eventually, the vent DIRECTLY over his large, heavy, king sized bed started growing mildew. I tried moving it and it wouldn’t budge, so I ended up STANDING  on his bed, reaching with my tiptoes to wipe down the vent and the ceiling, PRAYING he didn’t walk in and see me that way. That event got me to the point where I understood that simply sealing the boot and vent and insulating above and around it wasn’t doing the trick.

Luckily a month or so later I was able to help participate in installing an Aprilaire whole-home dehumidifier on a test house where they tracked the results vs. a typical home with a variable speed air conditioning system.

The results were incredible, and the house with the dehumidifier had no issues with condensation and was able to maintain target relative humidity no matter the latent or sensible load on the space.

This is what I learned –

Condensation occurs whenever air hits dewpoint. Period.

Dew point is simply the temperature at and below which air containing a particular amount of moisture can no longer contain that moisture and will begin to give up water in the form of condensation. Saying dew point is the same as saying the 100% humidity point.

Air can achieve dew point without coming into contact with a surface at all (see clouds), but often we observe that air hits dewpoint when it contacts a surface of a lower temperature than the air itself. So condensation on surfaces is a function of.

  • The moisture contact of the air
  • The temperature of the surface
  • Contact time on the surface

So what causes air to hit dew point and condensate in undesigned places? It is either colder or more humid than it is designed to be in those places.

Sweating Air Handlers

In Florida we have many air handlers (fan coils) located in unconditioned garages. This is not a great design right off the bat, and add in the fact that we ALSO have high latent (humidity) load so we run the blowers at low CFM output for and we have a recipe for sweating (condensating) air handlers.

The only way to resolve the issue is to warm up the air handler cabinet by running the system at higher CFM (warmer), Decrease the humidity in the garage through supplementary dehumidification (add a dehumidifier) or ventilate the area better which keeps the air in contact with the cold air handler surface for a shorter period of time.

Supply Register Condensation

Common knowledge about sweating vents tells us that when a vent sweats it should be sealed. This is true, because it is just a good practice, but also because it prevents unconditioned, moist air from entering in around the boot or can and condensing moisture around the vent and on the ceiling. In my experience sweating registers are more often caused by high humidity in the space, poor air velocity, low air temperature caused by low system CFM output or a combination of all three.

The problem is that many techs will try to solve this by increasing system airflow. While increasing air flow will increase the register temperature it will also reduce the ability of the system to dehumidify resulting in high relative humidity in the space.
The best way to reduce sweating registers is to reduce or eliminate the effects of moisture “drivers” that introduce new moisture into the space in the first place. This can be done by properly ventilating bathrooms and kitchens, keeping doors and windows shut, improving the airtightness of the conditioned space and using an ERV to keep the space under neutral or slight positive pressure.

Obviously proper Cooling system sizing and duct design will help extend system run times and decrease indoor humidity.

It is also helpful when designing fresh air systems in humid climates to only provide the amount of fresh air required and no more unless an enthalpy control system is in place.

It can also help to redesign registers and branch ducts to output the designed face velocity of the vent for better air mixing in the room. In extreme cases, supplementary dehumidification can be added to stop the issue once and for all.

Duct Condensation 

Ventilation ducts will often condense moisture on the inside when they are routed through spaces that will often be cooler than the air contained inside. This is why it is a good practice to insulate ventilation ducts in most climates unless the duct is run completely in the conditioned space.

Supply air ducts will also condensate at times on the outside when one of the following situations occur –

  • The air in the duct is colder than designed
  • The insulation of the duct is insufficient
  • The insulation of the duct is compressed
  • The ventilation around the duct is poor (some ducts are designed to be buried in insulation and others are not)
  • The moisture content around the duct is high

Usually, when you find condensation on ductwork it is a combination of two or more of these issues.

All of the issues discussed above can usually be prevented by –

  • Proper ventilation of moisture laden air (bathrooms, kitchens)
  • Better sealing of conditioned spaces
  • Better insulation of conditioned spaces and “cold” objects
  • Proper duct design and system airflow output
  • Keeping ducts and air handlers inside the conditioned envelope when possible
  • Placing vapor barriers on the “warm” side of structures to prevent moisture intrusion
  • Use of ERVs to positively pressurize the space (In very warm climates) and neutral in multi-season and cold climates
  • Installation of supplementary dehumidification when required
  • Keep the space no cooler than it must be for comfort
  • Size cooling equipment properly to extend run times and reduce space humidity
  • Do not bring in excessive fresh air during humid outdoor conditions

— Bryan

 

 

 

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