Refrigeration Technicians Best Tools

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September 4, 2023

In this article we’ll answer a question that we get all the time. What filter, if any, can filter out the SARS-CoV-2 virus which leads to COVID-19, the disease? We’ll show you how efficient the different air filters are at filtering out various items for asthma and allergy sufferers, and the virus that leads to COVID-19.

If you prefer to watch the Video of this presentation, then scroll to the bottom or click on the following link. Air Filters vs COVID-19

The ability of an air filter to remove microorganism, dust, pollen, dust mites, mold spores, pet dander, bacteria and viruses is indicated by a numerical value. This number, which is indicated as a MERV rating, states the filter’s efficiency at removing various sizes of these items. We’ll show you which filters, if any, work the best to protect you from these potentially harmful organisms.

Table of Contents

MERV Rating

Minimum Efficiency Reporting Values, or MERVs, indicate the filter’s ability to capture larger particles, those 0.3 microns and larger. The higher the numerical rating, the greater the air filter is at removing particles from the air stream. A MERV-13 is better than a MERV-11 filter at removing particles, but how good are they against bacteria and a very small virus that leads to COVID-19.

Virus and Bacteria Removal

According to ASHRAE, research has shown that the particle size of the SARS-CoV-2 virus that leads to COVID-19 is around 0.1 microns. This is much smaller than what may be picked up by these air filters. As this chart shows, the virus lives in the invisible region, while others like dust, cat dander and human hair are visible to the human eye.

Sizes of various items shown in Microns. Invisible items in black area on chart, including the SARS-CoV-2 Virus.

Luckily, the SARS-CoV-2 virus doesn’t travel through the air own its own. It rides on respiratory droplets and droplet nuclei (dried respiratory droplets) that are predominately 1 micron in size and larger. These filters have various efficiencies at capturing the viruses that are in the 1-to-3-micron range according to ASHRAE.

The SARS-CoV-2 virus riding a respiratory droplet in the 1 to 3 micron range

ASHRAE

As the chart shows, ASHRAE recommends using a minimum of a MERV 13 filter, which is at least 85% efficient at capturing particles in the 1 to 3-micron size range. A MERV 14 filter is at least 90% efficient at capturing those same particles. High-efficiency particulate air (HEPA) filters are even more efficient at filtering human-generated infectious aerosols.

MERV Rating and Air Filter Efficiency for Particle sizes 1 to 3 microns in size

By definition, a HEPA air filter must be at least 99.97% efficient at capturing particles 0.3 micron in size. This 0.3-micron particle approximates the most penetrating particle size (MPPS) through the filter. HEPA filters are even more efficient at capturing particles larger AND smaller than the MPPS. Thus, HEPA air filters are more than 99.97% efficient at capturing airborne viral particles associated with SARS-CoV-2 which leads to COVID-19.

Checkout these HEPA Filters for your Home or Office

HEPA filters can capture and trap microorganisms, including viruses and bacteria, helping to reduce the risk of respiratory infections. So, if possible, use the highest MERV rated air filter with your system, or get a portable HEPA air filter for your room or office. HEPA filters are the most efficient at capturing small microorganisms like the SARS-CoV-2 virus.

Where are HEPA Filters used?

HEPA air filters are used in residential, commercial, and industrial facilities. In homes there are portable types that can be moved from room to room, and others that can be installed in a central air conditioning system serving the whole house.

HEPA air filters are also used along with ULPA filters in cleanrooms, labs, and other spaces requiring a very clean environment.

Asthma and Allergy Management

For individuals with asthma, HEPA filters help reduce asthma triggers like airborne irritants and respiratory allergens. According to the Asthma and Allergy Foundation of America (AAFA), nearly 26 million people have asthma in the United States. There are 4.8 million children under the age of 18, and nearly 21 million adults suffering from asthma. On average, 10 people in the unites States die every day from asthma. A total of 3,517 deaths in 2021.

According to the AAFA over 100 million people each year in the United States experience various types of allergies. Allergies are the sixth leading cause of chronic illness in the U.S. HEPA filters are highly effective at removing allergens such as pollen, dust mites, and pet dander, providing relief to allergy sufferers.

Editorial Process:

Some of the links in this article may be affiliate links, which can provide compensation to the MEPAcademy at no cost to you if you decide to purchase. Our reviews and articles are made by an industry professional experienced in the engineering and construction of commercial buildings.

Air Filters vs COVID-19

HVAC Equipment Cost Database

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May 10, 2021

Are you paying too much for your HVAC equipment? How do you know if the quote you received for your equipment is a fair price? Do you have a method of comparing what you have paid for various HVAC equipment with what is being quoted currently?

Keeping track of the cost of HVAC Equipment allows you to quickly provide budgets and check the cost of equipment before you purchase. This database allows you to easily keep track of the most common HVAC equipment.

HVAC Equipment Cost Database

Using an HVAC Equipment cost database will save you a lot of money by avoiding the costly mistake of paying too much for equipment.

Air Conditioners price per ton and price per square feet historical equipment pricing database — Air Conditioners in Historical Pricing HVAC Equipment Database

Get your copy here. HVAC Equipment Cos t Database

The HVAC Equipment Cost database keeps track of all your equipment quotes or purchases for easy reference and parametric checks, such as cost per ton ($/Ton), cost per CFM ($/CFM)

HVAC Piping Unit Pricing

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August 31, 2020

For an HVAC Piping Estimators the need for quick budgets for the installation of piping is best handled with a spreadsheet of different material types and sizes. Having an estimating software program can make this process a lot easier, as the material pricing is always up to date and can be entered into the spreadsheet quickly. You can get a copy of this spreadsheet to help you price piping fast and efficiently.

Table of Contents

HVAC PIPING UNIT PRICING

Often the requirements of the RFP or bidding instructions will call for the price per foot to install piping beyond that which is required by the contract drawings. Such pricing maybe used for change-orders. Having these numbers available and updated often also gives you a quick reference for budgeting projects. It’s good to know when doing job site comparisons of different piping options or during discussions with engineering, what the cost is for the various piping sizes and types of materials.

COST PER FOOT

The cost per foot for the installation of piping needs to include fittings and hangers prorated into the value. It’s best to look at a standard length of pipe and then figure that you will have a Tee and 90 degree elbow in that length.

So for example, using twenty feet of copper water pipe with a Tee and 90 degree elbow plus the hangers to build a unit price would represent a field condition of a fitting every ten feet.

For higher density projects like Hospitals you could put more fittings in your unit pricing. Total those cost up and then divide by 20 to derive at a cost per foot for that particular size and material type.

20 feet of pipe + 2 Fittings + 3 Hangers / 20 = Cost per Foot

If the piping is insulated, you can also put the values in for insulation.

The Estimating Wizard provides two spreadsheets for tracking unit pricing, one for HVAC Piping and the other for Plumbing piping. Get a copy and start tracking your cost per foot, or be prepared to give a quick budget based on your knowledge from your spreadsheet of unit prices. Watch the video below to see how quick and easy it is to track the cost per foot for various sizes and material types.

MEP Academy HVAC Piping Unit Pricing Spreadsheet

The MEP Academy provides a spreadsheet that makes calculating unit pricing simple. The spreadsheet is available by following this link, HVAC Piping Unit Pricing Spreadsheet

HVAC Piping Unit Pricing Calculator Example

In the screenshot above there is a place for you to build your hanger requirements (#1), and a place to put your tax rate and hourly labor rate (#2).

For each size of pipe and material type you would insert the unit cost for Material (#3) and Labor (#4).

Under item (#5) you would build your typical run of pipe and enter the quantity of fittings you might expect for the type of building and system. You would add whatever you think will be required for every so many feet of pipe. In the example above we are showing that for every 20 feet of pipe you will have 1 Elbow and 1 Reducing Tee.

Under item (#6) you would add the cost per lineal foot for insulation if required. You could also look at insulation as a separate value and leave the pipe bare.

Line item (#7) is where you indicate the hanger spacing, and for each hanger you defined under item (#1) you will get the quantity as defined by the linear feet in item (#5) divided by your hanger spacing, which will affect your cost.

Line item (#8) is the calculated cost per linear foot of piping for that size and material type of pipe.

Summary Sheet

After you have all your unit pricing information inputted into the spreadsheet, all you have to do to get a budget for installing piping is to enter the quantity of piping (#9) for each size and material type (#10). The system will automatically calculate the cost (#11) to install that run of piping based on your unit pricing data. The total cost will be shown at the top of the spreadsheet (#12).

Piping Unit Pricing Calculator Summary Page

You can get your copy here. HVAC Piping Unit Pricing Spreadsheet

AC Condensate Drain Sizing and Layout

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August 17, 2020

The proper sizing and layout of condensate drain lines is important for the protection of property and for the proper functioning of the air conditioning equipment.

If you prefer to watch our YouTube version of this presentation, scroll to the bottom.

Table of Contents

Condensate Drain Pipe Sizing

The size required for the condensate pipe is dictated by the local code. Enclosed you will find the requirements for many local codes, but be sure to check your code for your local requirements. If the outlet size of the equipment’s condensate drain is larger than what’s shown in this chart then your required to use the larger outlet size.

Slope to be at least 1/8” per foot or 1 percent, that is for every 12” horizontally there must be at least an 1/8” drop vertically.

Condensate drain piping to slope a minimum of 1/8" per every 12" horizontal — Condensate drain piping to slope a minimum of 1/8″ per every 12″ horizontal

Attics or Furred Spaces

If the Air Conditioner is suspended above an inaccessible ceiling, such as a gypsum board ceiling or attic space then you will need to provide a means for protecting the building elements from the overflow of the primary drain and for indicating that there is a leak.

Also, drain pans that are poorly drained can cause water to stay in the pan risking the possibility of algae and bacteria growth. Below are some possible solutions, but as always check your local code for the approved method.

Option 1 – Secondary drain pan with drain piping. This would hang below the Air Conditioning unit in case the A/C units primary pan overflowed. Also, there is a requirement to provide secondary drain piping to a point of termination that would provide notification to the occupants that there is a leak, such as terminating above a window or doorway.

Option 1 - Secondary drain pan with piping terminating in observable location — Option 1 – Secondary drain pan with piping terminating in observable location

Option 2 – An additional drain pipe connection that sits above the primary drain connection and whereby the secondary drain piping terminates in a location to alert the occupants of the clogged primary drain.

Option 2 - Secondary drain piping connection to primary drain pan — Option 2 – Secondary drain piping connection to primary drain pan

Option 3 – Leak detection device that automatically shuts down the Air Conditioner if the primary drain becomes clogged.

Option 3 - Primary drain with leak detection device — Option 3 – Primary drain with leak detection device

Option 4 – Secondary drain pan with leak detection, located beneath the coil that shuts down the unit upon a leak.

Option 4 - Secondary drain pan with leak detection — Option 4 – Secondary drain pan with leak detection

The additional drain pan or drain pan connection shall be provided with a drain pipe that will determinate in an observable area, such as in front a window or above a doorway, and be of a size not less than 3/4”. Secondary drain pan shall not be less than 1-1/2” in height and extend 3” wider on each side of the coil or AC unit.

Secondary drain piping terminating above window. Pipe doesn't have to be visible as shown. — Secondary drain piping terminating above window. Pipe doesn’t have to be visible as shown.

Drain Termination

Where can and can’t you terminate the air conditioners condensate drain piping? There are several options where you can terminate the condensate drain line;

Indirect Drain
Condensate Pump to Indirect Drain
Drywell
Leach pits
Landscaped areas that are properly designed to handle the volume of condensate
To Properly designed stormwater treatment systems.

Indirect Drain

Lavatory tailpiece in the same tenant space as the air conditioner
Laundry standpipe
Janitors Sink
Inlet of Bathtub Overflow – Must be accessible
Collect and send to cooling tower (See description below)

Cooling Coil condensate to sink tailpiece.

The connection to a plumbing fixtures tailpiece has to be made within the same tenant space as the air conditioner cooling coil that is generating the condensate.

Drywell

A drywell can be used for the termination of your air conditioners condensate drain. Check your local code for the specifics, but generally it includes some or all of the following depending on whether it’s for residential or a commercial project:

A minimum size hole, such as 2 foot by 2 foot by 3 feet deep, or a round hole such as 12” diameter by 3 feet deep.
A minimum of 6” of soil or concrete shall provide cover above the rocks
Some form of barrier between the soil and the top of the drywell where the rock begins, such as building paper or plastic
Drywell to be filled with gravel or crushed rock, often with a stated minimum size rock such as 1 inch diameter
The termination of the condensate drain pipe shall connect indirectly to the drywell drain pipe.
The drywell drain pipe to be a minimum of 1-1/2” PVC or other approved material.
Drywell to be at least three feet away from the building structure or any footings.

Drywall for Air Conditioner Cooling Coil Condensate

There are various methods of providing drywells depending on the local code. There are prefabricated drywells that can be used and ones that are made by using a large diameter piece of PVC pipe or similar material.

Some codes will require you to collect the condensate from cooling coil drain pans and return it to the cooling tower if the equipment is served by a cooling tower and the total combined capacity of the HVAC cooling coils exceeds a certain amount like 65,000 btu/hr.

This is a water conservation measure, and there are some exceptions to this requirement, such as if the total capacity of the AC Equipment cooling coils are less than 10% of the total capacity of the cooling tower, or if the location of those AC Cooling coils are in a remote location, far from the tower.

Some locations where you can’t terminate condensate;

Public ways
Sidewalks
Driveways
Alleys

No termination of condensate on public area ways

Excluded from Code Requirements

Excluded from these codes are non-condensing type of equipment like radiant cooling panels that are designed to prevent condensate from occurring by keeping the temperature of the chilled water above the dew point temperature/vapor pressure of the surrounding air. These are system designed to operate in sensible cooling only modes.

Piping Material

The material types that can be used for condensate drain piping varies by jurisdiction but the most commonly cited materials are:

Copper
PVC – DWV
CPVC
ABS – DWV
Polyethylene
Galvanized steel
Cast iron.

Also the use of short radius 90-degree elbows are often prohibited. You can normally use standard fittings until you reach a certain size at which point you might be required to use drainage pattern fittings (DWV)

Traps

Traps are to be installed as required per the manufactures recommendation. No traps are required on the secondary drain pan, this is to allow immediate notification that the primary drain has failed.

Cleanouts

Cleanouts are required in case of plugged drain pipes. Provide as required to prevent the need to cut drain pipes for unplugging. Some of the following maybe used for cleanouts if approved by your local code authority;

Plugged tees
Union connections
Short clamped hoses at the unit (see image above)

When you have more than one air conditioning unit condensate tied to a main condensate pipe, then every change of direction shall have some method of cleanout. Check your local code as this maybe a requirement for even a single air conditioners condensate piping.

Condensate Pumps

Condensate pumps can be used to elevate the condensate vertically to a point where it will then discharge into a code approved gravity sloping condensate drain line. The condensate pump should be interlocked with the Air Conditioning Unit to prevent its operations if the condensate pump is inoperable.

Checkout these Condensate Pumps

Please remember that code requirements are always changing, so check for the most current code in your area at the time of design and installation. Or ask an inspector for the current installation practice.

Refrigerant Line Sets

Video of this Article

MEP Academy Estimating Spreadsheet

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July 14, 2020

Sheet Metal, Piping & Plumbing Estimating Spreadsheet

Having an MEP Academy Estimating Spreadsheet that automates portions of your estimates, will save you valuable time that could be used to make more sales. All aspects of the cost of furnishing and installing an HVAC and/or a Plumbing system is contained in one spreadsheet made specifically for the MEP industry. For plumbing only see below.

For a Plumbing only Spreadsheet, use this Commercial & Residential Version. Plumbing Only. For a simple Residential HVAC & Plumbing Spreadsheet. Residential version.

Table of Contents

Dashboard

The Main Dashboard provides you with all the information you need to make a quick decision on whether to make further adjustments, or if one of the metrics looks out of place based on historical data. The Dashboard gives you a quick overview of all that is going on within the Estimating Spreadsheet.

Estimating Dashboard within the MEP Academy Estimating Spreadsheet

Your MEP Academy Estimating Spreadsheet needs to be able to handle rental equipment, general conditions, subcontractors, piping and plumbing takeoffs, sheet metal, labor rate tables with crew mix capabilities, , and a bid summary. Each sheet in the estimating spreadsheet automatically calculates the values you enter, showing you a new total bid amount.

Will cover portions of the MEP Academy Estimating Spreadsheet starting at the back of the Excel spreadsheet and working our way toward the front summary page last.

Labor Rate & Crew Mix Table

Choose your crew mix based on the level of experience and the different pay scales based on each project. Pick any combination and quantity of tradesman based on the requirements of the project.

Labor Rates and Crew Size within the MEP Academy Estimating Spreadsheet

There is a separate crew labor rate for HVAC Piping Shop & Field, Sheet Metal Shop & Field, and Plumbing.

HVAC & Plumbing Equipment

Enter the project equipment price and labor to rig the HVAC and Plumbing equipment into place. Compare supplier pricing easily side by side. The MEP Academy Estimating Spreadsheet automatically selects the lowest bidder but lets you override that decision.

HVAC Equipment page within the Estimating Spreadsheet

General Conditions

Do you need a jobsite trailer or onsite management? Enter the quantity and level of the staff required to run the project, whether one person or dozens. Set the quantity and duration of each general condition, along with the rate. General Conditions is broken down into three sections as follows: #1 – Management, #2 – Construction Office (Non-Reoccurring Expenses), and #3 – Construction Office (Reoccurring Expenses).

HVAC & Plumbing Subcontractors

HVAC & Plumbing contractors often subcontract out for Air & Water Balance, Sheet Metal & Piping Insulation, Water Treatment, Building Automation, Excavation and other specialty trades that they don’t self-perform. This spreadsheet was made especially for the HVAC & Plumbing contractor and their most often used subcontractors.

Subcontractors – Rentals – GC’s – Engineering Pages

Plumbing Fixtures

For those contractors that do plumbing the following Plumbing Fixture sheet will give you a place to record your vendors quotes and the labor it takes to install each type of fixture. What is also revealed is the overall cost per fixture.

Plumbing Fixtures page within the Estimating Spreadsheet

MEP Specialty Sheets

Each trade has a specialty sheet for those items that aren’t considered equipment or a fixture, but for which there is a cost impact. The MEP Academy Estimating Spreadsheet includes Sheet Metal, HVAC Piping & Plumbing Specialty sheets.

HVAC and Plumbing Specialty Pages within the Estimating Spreadsheet

Specialty Sheet In Estimating Spreadsheet — Specialty Sheets in Estimate Spreadsheet

Material & Labor Summary Sheets

You will find a Sheet Metal, HVAC Piping & Plumbing material & labor summary sheets where all of the other specialty sheets are summarized for your review and last minute edits. Each sheet will be divided between field & shop fabrication work. The first section covers the field installation items.

Sheet Metal Material and Labor Summary – Estimating Spreadsheet

Field Summary Section

This is where you will put your material takeoff information for the following:

Rectangular & Round Ductwork
HVAC Piping
Plumbing Piping

This is also where the other sheets that you filled out will be summarized, such as the following;

HVAC & Plumbing Specialties
HVAC & Plumbing Equipment Labor
Plumbing Fixtures

Material & Labor Summary Sheet in Estimating Spreadsheet — Material and Labor Summaries

Each of the field labor summary sheets contain a row to add for the following

Material Handling
Consumables
Punch List
Cleanup
Detailing
Supervision

Shop Fabrication Summary Section

For those of you that have a fabrication shop, there is a section to add material and labor.

Rentals

For those HVAC air conditioning and Plumbing projects that require a crane, fork lift, scissor lift or any other equipment that you don’t own but will be required on the project. Having a spreadsheet that maintains a list of the most common equipment you normally rent along with their rental rate will save you time and money while avoiding having to call for pricing on every job.

Engineering

If you do your own design then you should have a sheet of each of the personnel responsible for spending time on the engineering task. If you’re doing design/build work, but don’t do the engineering yourself, but hire a third party, then you should add some engineering review time. It’s your responsibility to manage your third-party engineer to make sure they design within your cost parameters.

Estimate Summary

All of your estimates are summarized on the last tab of the MEP Academy Estimating Spreadsheet for easy review. You can quickly scan each of the categories to see where all the project cost has shown up. There is the labor and material summary for HVAC Sheet Metal, HVAC Piping, and Plumbing and another section for Subcontractors, General Conditions, Rentals, etc.

Estimating Spreadsheet Summary Page

Estimating Summary — MEP Academy Estimating Spreadsheet Summary

Bid Risk Assessment Form

The MEP Academy Estimating Spreadsheet contains a bid risk assessment form that rates the success of winning any particular project that you are contemplating pursuing. The risk assessment form will help you determine if the project is worth bidding based on a set of questions that rate your answers.

The answers to these questions will give you a score from which you can use to see how the project rates on a scale of risk and reward. The total risk assessment score will also inform you which level of approval is required within your company depending on how you rate your risk values as the example shown below. The total score is 25, which according to this contractor would require the Vice President to sign-off on the project or approve the decision to pursue bidding on the project.

MEP Academy Estimating Spreadsheet Summary

The MEP Academy Estimating Spreadsheet is used to gather all the information for estimating a project, putting it into a format where you can make quick adjustments and decisions while the spreadsheet gives you an immediate update on the price.

Purchase this spreadsheet at its currently reduced price of ONLY $245.00, which usually sells for ~~$599.00~~

Watch the YouTube video below to see the MEP Academy Estimating Spreadsheet in action.

How to Read a Psychrometric Chart

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July 10, 2025

Ever looked at a psychrometric chart and thought, ‘What is this crazy spider web of lines? You’re not alone. But today, we’re going to break it down simply—no fancy math, just real-world HVAC understanding. You’ll learn how to read a psychrometric chart and use it to solve a basic problem you might face on a job site or in a mechanical plan review.

https://youtu.be/-SbfdTXGjhM

Table of Contents

What is a Psychrometric Chart?

A psychrometric chart is a graphical representation of the properties of air. It helps HVAC pros analyze air conditioning and ventilation processes. Think of it like a map of air behavior.

Here are the key components of the chart:

Dry Bulb Temperature Lines

The horizontal axis shows Dry Bulb Temperature — the air temperature is in degrees Fahrenheit. Moving to the right the air temperature gets warmer, while moving left the air temperature gets cooler.

Relative Humidity Lines

The vertical curved lines are Relative Humidity lines, from 0 to 100 percent. These curved lines show the amount of moisture in the air compared to how much it can hold at a given temperature. It’s expressed as a percentage. When the relative humidity is 100 percent, the air is fully saturated, meaning it can’t hold any more water vapor and condensation may occur. This 100 percent relative humidity condition also happens when the dry bulb and wet bulb temperatures are the same, which is why that point lies right on the saturation curve of the chart.

For example, if we follow the 70-degree dry bulb line toward the 70-degree wet bulb the relative humidity keeps increasing until we reach this curved line which indicates the air has reached 100 percent relative humidity and is fully saturated.

Humidity Ratio

The vertical axis on the right shows Humidity Ratio, or grains of moisture per pound of dry air. The vertical axis on the psychrometric chart represents the humidity ratio—the actual amount of water vapor in the air. It’s measured in pounds of moisture per pound of dry air. As you move up this axis, the air holds more moisture.

Dry Bulb. Wet Bulb and Relative Humidity Lines on a Psychrometric Chart

For example, let’s look at the 70 degrees Fahrenheit dry bulb temperature line. As you move along that line and pass each increasing relative humidity curve—from 20 percent, to 40 percent, to 60 percent, and so on—the humidity ratio increases. That means there’s more water vapor in each pound of air.

When you reach the point where the dry bulb and wet bulb temperatures are both 70 degrees Fahrenheit, the air is fully saturated at 100 percent relative humidity. At that point, the humidity ratio is at its maximum for 70 degrees Fahrenheit air—about 110 grains of moisture per pound of dry air. That point lies right on the saturation curve.

Saturation Line

The curved upper boundary is the Saturation Curve — that’s 100 percent relative humidity. This outer curved boundary is called the saturation curve. It represents 100 percent relative humidity—air that is fully saturated with moisture. Along this curve, the dry bulb temperature and wet bulb temperature are equal. At any point on the saturation curve, the air cannot hold any more water vapor without condensation occurring

Wet Bulb and Dew Point Lines

Diagonal lines show Wet Bulb Temperature, Enthalpy (total heat energy), and Dew Point. The diagonal lines that slope upward to the left are wet bulb temperature lines. Wet bulb temperature reflects the lowest temperature air can reach through evaporation. On the 70 degrees Fahrenheit dry bulb line, as the wet bulb temperature increases—from, say, 55 to 65 degrees Fahrenheit —the humidity ratio also increases, meaning there’s more moisture in the air. At the same time, the relative humidity rises. When the wet bulb temperature reaches 70 degrees Fahrenheit —equal to the dry bulb—the air is fully saturated at 100 percent relative humidity and lies right on the saturation curve.

Why It Matters in HVAC – Real Use Cases

In HVAC, we use the chart to: Size dehumidification or humidification equipment. Analyze cooling coil performance. Control air mixing and ventilation and troubleshoot comfort complaints.

For example, let’s say your client is complaining about it feeling ‘muggy’ in their office—even though the thermostat reads 72 degrees Fahrenheit. The psychrometric chart can help you figure out if the humidity is the real culprit.

Let’s walk through a simple HVAC scenario.

PROBLEM: You’re conditioning air in a commercial office building. Outdoor air is coming in at 95 degrees Fahrenheit dry bulb and 60 percent relative humidity. You need to condition it to a comfortable indoor design condition of 75°F dry bulb and 50 percent relative humidity.

Air Conditions Plotted on a Psychrometric Chart

Step 1: Plot the Outdoor Air

This is your starting point. Use the dry bulb and move up to the 60 percent relative humidity curve to find the outdoor air condition.

Step 2: Plot the Desired Indoor Air

This is your target condition—comfortable for most people.

Step 3: Draw a Straight Line Between These Points

This represents the path air must take through cooling and dehumidification.

Step 4: Analyze What Happens Along the Line

As air moves across this line, it cools down and loses moisture. The cooling coil removes sensible heat and latent heat (humidity).

Step 5: Estimate How Much Water Is Removed

At 95 degrees Fahrenheit and 60 percent relative humidity, the humidity ratio is about 120 grains per pound.
At 75 degrees Fahrenheit and 50 percent relative humidity, it’s about 65 grains per pound.
So the cooling coil removes 55 grains of moisture per pound of dry air.

This is a simple explanation of how the psychrometric chart is used to solve problems and determine what happens to the air at various conditions.

Step 6: Total System Load (Optional Advanced)

“If you know the airflow rate—say 2,000 CFM—you can estimate total moisture removed per hour using formulas. But for now, just know this: The chart tells you how much cooling and dehumidification your system needs to achieve comfort.”

Why Low Suction Pressure Happens

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June 24, 2025

Are you seeing low suction pressure on your gauges and wondering what’s going on inside the refrigeration or air conditioning system? Low suction pressure is one of the most common indicators that something’s not right — and if misunderstood, it can lead to compressor failure and costly downtime. In this article, we’ll break down the causes of low suction pressure, how to diagnose it properly, and what steps to take to correct it.

Why Low Suction Pressure happens in HVAC Refrigeration Systems.

Today we’re diving deep into the causes and consequences of low suction pressure in HVAC and refrigeration systems.

Table of Contents

What is Suction Pressure?

Suction pressure refers to the pressure of the refrigerant vapor entering the compressor from the evaporator. This pressure tells us a lot about what’s happening on the low side of the system — particularly in the evaporator coil and the refrigerant lines leading back to the compressor.

In most air conditioning and refrigeration systems, normal suction pressure typically ranges between 60 to 85 psig (4.1 to 5.9 bar) for R22, or 120 to 145 psig (8.3 to 10 bar) for R410A, or 115 to 145 psig (7.9 to 10 bar) for R32 depending on the system and ambient conditions.

When this pressure drops too low, it usually means the system isn’t absorbing enough heat — but the reason why can vary.

Symptoms of Low Suction Pressure

Here are some telltale signs of low suction pressure:

Suction gauge reading abnormally low. Frost or ice on the evaporator coil or suction line. Poor cooling performance. Compressor running longer than usual. Hissing or bubbling sounds from the evaporator

These symptoms mean it’s time for a diagnosis.

Common Causes of Low Suction Pressure

1. Low Refrigerant Charge (Undercharge)

This is the most common cause. If the system is undercharged — due to a leak or improper service — there won’t be enough refrigerant in the evaporator to absorb heat, leading to reduced pressure at the compressor inlet.

Check for leaks at joints, coils, and service valves. Use an electronic leak detector, soap bubbles, or UV dye.

2. Restricted or Blocked Filter Drier or Capillary Tube

A clogged filter drier or metering device reduces refrigerant flow into the evaporator, starving it of refrigerant. Less evaporation means less vapor returning to the compressor — hence low suction pressure.

Look for a significant temperature drop across the filter drier — it shouldn’t exceed 3°F (1.7°C).

3. Faulty Expansion Valve (TXV/TEV)

If a thermostatic expansion valve (TXV) is malfunctioning — sticking closed or sensing incorrectly — it won’t deliver enough refrigerant to the evaporator.

Check the sensing bulb placement and charge. Also, feel for a frost line just after the TXV outlet — that’s a red flag.

4. Evaporator Coil Issues (Frozen, Dirty, or Undersized)

If the coil is dirty or iced over, airflow is restricted. This means less heat is absorbed by the refrigerant, resulting in reduced vaporization and lower suction pressure.

Inspect coil cleanliness and ensure proper defrost cycle operation if it’s a freezer system.

5. Poor Airflow Across the Evaporator

No matter how perfect the refrigerant charge is, if there’s not enough warm air crossing the evaporator coil, you’ll get poor heat absorption.

Check air filters, fan motors, belts, and blower speed settings.

6. Oversized Metering Device or Undersized Evaporator

An oversized TXV can allow too much refrigerant into the coil, leading to potential floodback — but paradoxically, if it’s underfeeding due to poor sensing, suction pressure drops. Likewise, an evaporator too small for the load won’t provide enough heat absorption.

7. Compressor Valve or Mechanical Problems

While rare, leaky compressor valves or worn internals can cause low suction pressure and poor compression ratio.

Listen for unusual compressor noise and check amp draw.

Diagnostic Checklist

Use this quick checklist when diagnosing low suction pressure:

Symptom	Test	Corrective Action
Low pressure, poor cooling	Leak test, weigh refrigerant	Recharge and repair leak
Frost on suction line	Inspect airflow, TXV, coil	Defrost coil, clean filters
Pressure drop across drier	Temp readings, IR scan	Replace clogged filter drier
Low superheat	Measure SH/SC	Adjust or replace TXV

Superheat and Suction Pressure

Don’t forget — suction pressure alone isn’t enough. Always compare it with the superheat reading. Low suction pressure with low superheat might mean flooding or a bad TXV. Low suction with high superheat typically points to a starved coil.

Summary and Takeaways

Low suction pressure is a symptom — not the problem. Whether it’s a refrigerant issue, airflow problem, or restriction in the system, your job as a tech is to dig deeper and find the root cause.

Check refrigerant charge. Inspect airflow and evaporator conditions. Test metering device function. Use superheat readings to confirm diagnosis

Heat Pump – Single Stage vs Variable Speed

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June 24, 2025

Heat Pump Single Stage vs Variable Speed

If you’re trying to decide between a heat pump variable-speed vs single-stage, this article will break it down clearly — performance, comfort, energy savings, and what’s best for your climate. Whether you’re an HVAC tech, contractor, or homeowner — this one’s for you.

Single Stage versus Variable Speed Heat Pumps

Table of Contents

What are Single Stage and Variable Speed Heat Pumps?

Let’s start with the basics.

Single Stage Heat Pumps
These units are either ON or OFF. When they run, they run at full capacity — 100% — every time. Simple, less expensive, but not always the most efficient.

Variable Speed Heat Pumps
These units operate anywhere from 30% to 100% capacity, depending on the heating or cooling demand. They use advanced compressors — usually inverter-driven — that ramp up or down in speed to match load requirements more precisely.

Comfort Comparison

Comfort is where variable speed shines.

Single Stage: Tends to overcool, shut off, then repeat the cycle — which can cause noticeable temperature swings and humidity issues.

Variable Speed: Maintains more consistent indoor temperatures and better dehumidification by running longer at lower speeds.

Single Stage vs Variable Speed Heat Pumps

Energy Efficiency and Cost Savings

Now let’s talk about your energy bill.

Single Stage: Lower upfront cost, but higher operating cost over time. Running at 100% uses more power even when it’s not needed.

Variable Speed: Higher SEER2 ratings. It adjusts to the load, running longer but using less power overall. Think of it like cruise control for your HVAC system.

Noise Levels and Wear-and-Tear

Another factor is noise and long-term durability.

Single Stage: Louder when starting and stopping. More mechanical stress from frequent cycling.

Variable Speed: Quiet and smooth. The compressor doesn’t slam on — it ramps up gently, reducing wear and tear.

When to choose Which

So, which one’s right for your project or home?

Go with Single Stage if:

You’re in a mild climate with short cooling seasons.
If Budget is the top concern.
If you’re replacing a unit in a rental or low-use property

Go with Variable Speed if:

You live in hot/humid regions or have long summers.
If comfort, humidity control, and energy savings matter.
If you want the latest in HVAC tech and system longevity

Maintenance and Installation Tips

Regardless of which heat pump you choose, installation and proper setup are key.

Make sure ductwork is properly sized and sealed.
Match the unit with a compatible thermostat.
Educate the homeowner on how variable-speed systems work — especially the fact they run longer by design

Still not sure which one’s right for your situation? Drop a comment below — we make an effort to respond to every HVAC-related question.

What is Flash Gas in a Refrigeration System

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June 10, 2025