Essential Tools for Every Refrigeration Technician: A Comprehensive Review
Are you intrigued by the inner workings of refrigeration systems and the vital role they play in our everyday lives? Whether you’re an aspiring refrigeration technician or a seasoned pro, understanding the tools of the trade is essential.
In this comprehensive review, we delve into the top tools that every refrigeration mechanic should have in their arsenal. These tools are not mere conveniences; they are the very instruments that empower technicians to diagnose, repair, and maintain refrigeration systems efficiently and effectively.
1. Manifold Gauge Set: Refrigeration mechanics rely on manifold gauge sets to simultaneously measure high and low side pressures in refrigeration systems. These sets are like the eyes of the technician, providing critical insights into the system’s condition. By providing real-time data, refrigerant gauges are essential for diagnosing issues and ensuring optimal system performance.
2. Vacuum Pump: A vacuum pump may seem unassuming, but its role is monumental. It evacuates air and moisture from refrigeration systems before the introduction of refrigerant, ensuring that the system operates efficiently without unwanted contaminants.
3. Leak Detection Tools: Finding elusive refrigerant leaks is a challenge without the right tools. Leak detection tools, including electronic detectors and bubble solutions, play a crucial role in environmental protection and system efficiency by pinpointing these leaks.
4. Digital Multimeter: An HVACR technician’s electrical diagnostic prowess relies heavily on a digital multimeter. This tool measures voltage, current, and resistance in electrical components, making it indispensable for troubleshooting electrical issues.
5. Pipe Cutters and Flaring Tools: Copper pipes are the lifeblood of many refrigeration systems, and pipe cutters and flaring tools ensure these essential components are accurately cut and shaped for the job.
6. Pipe Benders: The importance of smooth, kink-free bends in copper pipes cannot be overstated. Pipe benders are the secret to achieving these precise bends without compromising the integrity of the pipe.
7. Thermometers and Thermocouples: When it comes to temperature measurement, accuracy is key. Thermometers and thermocouples help technicians monitor temperatures at various points in the system, assisting in both diagnostics and cooling optimization.
8. Tubing Tools: Properly preparing tubing for installation is a fundamental step in any refrigeration project. Tubing tools, such as deburrers and reamers, ensure that tubing is ready for action.
9. Hex Key Set: Hexagonal screws and bolts are commonplace in refrigeration systems. A set of hex keys is a technician’s trusty companion for swiftly disassembling and reassembling components.
10. Oil Pump and Oil Injector: Lubricating oil is the lifeblood of compressors. Oil pumps and injectors ensure that the compressor functions optimally by delivering the right amount of lubrication.
11. Torque Wrench: Precision matters in refrigeration systems. Torque wrenches guarantee that bolts and nuts are tightened to precise specifications, safeguarding components and maintaining proper seals.
12. Digital Scale: In the intricate world of refrigeration, precision is paramount. This is where a digital scale steps in as a silent but indispensable partner for refrigeration mechanics. Why? Because refrigerants, lubricants, and various chemicals must be added to systems with meticulous accuracy.
A digital scale ensures that the right quantities are added, helping maintain the system’s efficiency, performance, and, perhaps most importantly, the environment. It’s not just about getting the job done; it’s about getting it done right, and that’s where the digital scale shines. So, let’s weigh in on the importance of this often-overlooked tool in the refrigeration technician’s toolkit.
These tools are the cornerstone of any refrigeration technician’s toolkit. Stay tuned as we dive deeper into each of these essential instruments, unveiling the art and science behind their usage, and why they’re indispensable for refrigeration technicians around the globe.
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.
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.
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.
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 in Historical Pricing HVAC Equipment 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)
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.
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.
HVAC Piping Unit Pricing Calculator for Copper and Carbon Steel from 1/2″ to 14″
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).
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.
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.
Minimum Condensate Drain Pipe Sizing Chart
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
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 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 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 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
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.
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.
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.
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.
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 AcademyEstimating Spreadsheet starting at the back of the Excel spreadsheet and working our way toward the front summary page last.
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.
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 SpreadsheetHVAC & Plumbing Equipment Sheets
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 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.
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
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 SpreadsheetSpecialty 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
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.
Shop Fabrication Summary
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.
Rental Sheet in Estimating Spreadsheet
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.
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 PageMEP Academy Estimating Spreadsheet Summary
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.
Bid Risk Assessment
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.
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.
A Variable Air Volume (VAV) Box DDC Controller is a digital control device that regulates the amount of conditioned air delivered to a specific zone in a building. It’s part of a DDC (Direct Digital Control) system and typically interfaces with the Building Automation System (BAS). The controller modulates the VAV damper actuator, manages heating valves, monitors airflow sensors, and processes input from zone sensors such as temperature or occupancy.
How VAV DDC Controllers Work
Each VAV box serves one thermal zone, and its DDC controller ensures occupant comfort by adjusting air volume and, when applicable, reheating the air during heating demand.
1) Mount the Integrated Controller/Actuator on the VAV Damper Shaft
We start at the VAV terminal. Slide the integrated controller/actuator onto the damper shaft, align the position indicator with the damper blade position, and tighten the set screw. Add the anti-rotation bracket so the actuator body can’t twist. The actuator’s job is simple but critical: it rotates the damper blade to control how much supply air enters the zone. The controller—mounted with it—reads sensors, runs the control logic, and commands the actuator to hit exact airflow targets.
Pro tip: Label the damper’s “0%/100%” orientation while you can still see it.
2) Connect Differential Pressure Tubes to the Inlet Flow Sensor
Next, connect the high and low pressure tubes from the controller to the VAV inlet flow sensor—often a flow ring or cross with two Pitot taps. This sensor measures velocity pressure (ΔP). The controller converts that to airflow using the box’s K-factor: CFM = K × √(ΔP).
If you prefer metric, L/s = 0.4719 × CFM. This is how the controller knows how much air the box is delivering—vital for minimum ventilation and comfort control.
Pro tip: Keep tubing runs short, neat, and kink-free; match HI/LO correctly.
3) Wire the Room Sensor to the Controller
Now we connect the wall-mounted room sensor. Many controllers use a pre-terminated cable to an RJ-11/RJ-12 jack; others land on a terminal strip. Some systems use RJ-45 style connectors, but remember: it’s not Ethernet unless the manufacturer explicitly says so.
VAV DDC Controls
The room sensor sends zone temperature and often provides a local set point slider, occupancy button, or timed override. Optional add-ons include CO₂ and humidity sensing. The controller can use those to reset minimum airflow for demand-controlled ventilation or to respect a humidity limit by avoiding overly low supply temperatures.
Pro tip: If the sensor chain supports it, note which conductors carry power vs. signal. Don’t mix with Ethernet switches.
4) Connect the Hot Water Reheat Valve and Actuator
For zones that need heating, we wire a reheat valve actuator—typically 0–10 VDC, floating (3-wire), or two-position. The controller modulates this valve to warm the discharge air when the room drops below the heating set point. Most VAV sequences drive airflow down to a heating minimum CFM and then add heat by opening the valve. Use a normally-closed, fail-safe actuator when possible, and install unions, a strainer, and isolation valves for service.
In some regions, instead of hot water, a VAV box may use an electric reheat coil. In that case, the controller’s output drives a relay or contactor that energizes the electric heating elements. Because electric coils draw much higher current, a separate power circuit (typically 120 V, 208 V, or 277 V) is required, and the installer must follow the manufacturer’s wiring diagram, breaker sizing, and interlock requirements to ensure safety and code compliance
Pro tip: Confirm signal type (analog vs. floating) in the controller I/O map before powering up.
5) Install a Discharge Air Temperature (DAT) Sensor
Place a DAT sensor downstream of the reheat coil and before any branch takeoffs. The controller uses the DAT to stabilize reheat, limit discharge temperature (e.g., keep it < 95–100°F / 35–38°C), and catch failures like a stuck valve. Some projects run heating by zone temperature only; others regulate to a discharge setpoint with high-limit protection. If you have hot-water reheat, a DAT is cheap insurance.
Pro tip: Insulate around strap sensors to avoid reading duct skin temperature.
6) Bring in Electrical Power via a 24 VAC Transformer (with Service Switch)
Power time. Most VAV controllers run on 24 VAC from a step-down transformer. Feed the transformer with local line voltage and add a clearly labeled service switch on the primary side. Land the 24 VAC and common at the controller. This is Class 2 low-voltage wiring—keep it separate from line voltage. A single transformer can feed multiple boxes, but size it by total VA: controller + actuator + accessories per box, then add margin. Avoid daisy-chaining 24 VAC over long runs; voltage drop and nuisance resets will haunt you.
Pro tips: • Bond one leg to ground only if manufacturer specifies; many want a floating secondary. • Fuse the secondary or use a resettable breaker. • Label the transformer with its load list.
7) Daisy-Chain the BACnet MS/TP Network (CAT5/6 as RS-485 Cable)
Next, tie the VAV into the BAS. We use BACnet MS/TP (RS-485) on a true daisy chain—controller to controller to controller—ending at the air handler controller. Use a twisted pair (CAT5/6 is common as a cable, but you’re using it as RS-485, not Ethernet). Maintain consistent polarity—A(–) to A(–), B(+) to B(+). Terminate the segment with 120-ohm resistors at both ends only, and provide bias per the BAS standard. Avoid star connections; RS-485 wants a clean, continuous trunk.
Pro tips: • Typical segment limit ~4,000 ft with ~30–64 devices (check spec). • Keep shield drain on one end only to avoid ground loops.
8) Configure from a Room Sensor Service Port
Many systems include an RJ-12 or micro-USB service port on the room sensor or a small display interface. You can view live values—zone temp, airflow, damper position—and make setup changes like min/max CFM, heating minimum, and PI gains without climbing into the plenum. This speeds startup and reduces ceiling tile disturbance.
Pro tip: Save a ‘commissioning profile’ so the next box is a two-minute clone.
9) Air Balancing and Flow Verification
After rough-in and base configuration, we balance. First, verify the controller’s K-factor matches the VAV box model and size, and perform any zeroing the manufacturer requires. Then confirm actual flow with a hood or traverse at the diffuser and compare to the controller’s reported CFM. Tune the K-factor or sensor offset if allowed so reported CFM ≈ measured CFM at several flow points—typically minimum, mid, and maximum.
Air Balancing of VAV Terminal and Occupied Space
Pro tips: • Check damper blade direction and actuator rotation; a reversed mapping will wreak havoc. • Record final min/max CFM setpoints on the box label.
10) BACnet Addressing & BAS Integration
Each VAV controller needs a unique identity. On BACnet MS/TP that’s a MAC address (0–127 typical) set with DIP switches or software. The device also has a BACnet Device Instance number that’s unique across the BAS—usually set in software.
Once addressed, the VAVs appear at the AHU controller and on the front-end workstation. The BAS can trend zone temp and CFM, reset the AHU’s duct static pressure based on damper positions, alarm on low flow or sensor faults, and let you tweak setpoints remotely.
Pro tip: Keep a segment map: MAC addresses in order along the trunk, with cable lengths and termination points.
11) Modes of Operation (Cooling, Deadband, Heating w/ Reheat)
In cooling, the controller opens the damper from minimum CFM toward maximum CFM to drive the zone back to setpoint using the cool air from the AHU. While in deadband, the damper holds minimum CFM with heating and reheat off—sipping ventilation.
In heating with reheat, the damper drops to heating minimum CFM and the reheat valve modulates to meet load. If a DAT sensor is present, it trims the valve to maintain a discharge target and enforce a high-limit.
Pro tip: Occupancy inputs can bump setpoints and minimums (e.g., standby vs. occupied).
12) Final System Checks & Documentation
Before we call it done, verify: correct sensor values, damper travel end-to-end, valve stroke direction, alarm list clean, correct MAC/device instance, proper network termination, and transformer load within VA rating. Print or upload the point list, min/max CFM, addresses, and final BAL report so the service team has a single source of truth.
13) Important Caveat on Manufacturer Requirements
Last note: always follow the controller and VAV manufacturer’s specific wiring diagrams, addressing rules, termination/biasing instructions, and power limitations. Models vary on I/O types, sensor pinouts, grounding, network polarity, and configuration workflows. The steps we showed are the industry pattern—your submittals and manuals are the final word.
Ever wondered how fan powered terminal units keep your building comfortable and efficient? In this video, we’ll break down exactly how FPTUs work — from their internal components to how they control airflow and temperature in both overhead and underfloor systems. We’ll cover series versus parallel configurations, how primary and return air mix, how they perform during winter conditions, and what drives the CFM needed to meet heating loads. Let’s get started.
A Fan Powered Terminal Unit, or FPTU, is part of a variable air volume system that uses a small fan and mixing chamber to blend primary air from the air handler with return air from the plenum. This allows precise temperature and airflow control in individual zones. FPTUs are popular because they improve comfort, maintain proper ventilation, and efficiently provide heating and cooling right at the zone.
Key Components
Inside each unit, you’ll find several major components: a primary air damper with a flow sensor, a fan section—usually with an ECM motor—an induction opening for return air, and often a reheat coil, which can be either electric or hot-water. Some units also include sound insulation, filters, and a controller with temperature and flow sensors. All these elements work together to maintain the right air mix and temperature for your zone.
How Airflows Mix
Here’s how airflow mixing works. The terminal receives cool, dry air from the air handler. It blends that with return air from the ceiling plenum to temper the discharge air. When the space needs heating, the reheat coil adds warmth. The local fan ensures steady mixing and maintains airflow, especially at low primary air volumes.
Series vs Parallel FPTUs
There are two main types of FPTUs — series and parallel.
In a Series FPTU, the fan operates in series with the primary airstream. That means all supply air passes through the fan. The fan runs continuously during occupied hours, delivering a constant discharge volume even when primary airflow modulates. This provides stable ventilation and consistent diffuser throw, which is ideal for interior zones or spaces that need steady air movement.
Series Style Fan Powered Terminal Unit
In a Parallel FPTU, the fan is in a parallel path to the primary air. During cooling, the fan stays off—air flows directly from the duct to the space. When heating is needed, the fan turns on, drawing warmer plenum air across the reheat coil. The result is quieter cooling, lower energy use, and excellent perimeter heating control.”
Parallel Style Fan Powered Terminal Unit
Dedicated Outside Air Connection for Enhanced Ventilation
Some fan powered terminal units, such as the Titus TFS model with IAQ connection, can be equipped with a dedicated outside air opening to introduce conditioned ventilation air directly into the terminal unit. This design allows a controlled amount of outdoor air to mix with return and primary air at the zone level, helping meet stringent indoor air quality (IAQ) and ventilation code requirements such as ASHRAE Standard 62.1. The dedicated intake enables precise balancing of outdoor airflow and ensures each zone receives the required minimum ventilation CFM, even when the primary air volume is reduced during part-load conditions.
When and Why to Use FPTUs
So when should you use a fan powered terminal instead of a standard VAV box? Typically, it’s when the zone requires heating with limited primary airflow or stable ventilation. Standard VAV boxes can’t effectively provide heat at very low primary airflows. FPTUs can, because they induce warm plenum air and mix it with a small amount of primary air. They’re ideal for perimeter zones, spaces that need constant diffuser throw, or areas with stringent ventilation requirements.
Climate Considerations
Fan Powered Terminal Units are most common in colder climates, like the Northeast, Midwest, and Pacific Northwest, where buildings experience significant heating loads at their perimeters for much of the year. In these climates, perimeter zones lose heat through windows and walls, even while the core might still need cooling. FPTUs are the perfect solution — they pull warmer plenum air and add reheat to maintain comfort without overcooling.
In warmer climates, such as Southern California, Texas, or Florida, you’ll see far fewer FPTUs. Those regions use standard VAV boxes with reheat because perimeter heating is rarely needed beyond what the VAV box with the reheat coil can already provide. Climate drives design: cold regions lean heavily on parallel units for perimeter heating, while mixed climates may use series units for consistent ventilation.”
Winter Design and the Heating Formula
Let’s talk about what happens during peak winter conditions and how airflow relates to heating capacity. The heat delivered to a space is defined by the formula:
Q = 1.08 × CFM × ΔT or Q = (1.2 × L/s × ΔT)
where Q is in BTUs per hour, CFM is airflow, and ΔT is the temperature difference between discharge air and the space. During winter, your minimum ventilation airflow might not be enough to meet the heating load. For example, if you only have 200 CFM (94 L/s) at a 28°F (15.6°C) rise, you can deliver about 6,000 BTU/hr (1.76 kW) — not nearly enough for a perimeter zone needing 12,000 BTU/hr. (3.5 kW)
That’s where FPTUs come in. The fan draws additional warm plenum air, increasing the total discharge airflow to, say, 600 CFM (283 L/s). Using the same formula:
Now the terminal easily covers the heating load — without requiring extra primary air from the main air handler. This ability to decouple ventilation CFM from heating CFM is the key advantage of fan powered terminals in cold climates.”
Control Sequence of Operation
Control sequences for FPTUs follow a predictable pattern. In cooling mode, the primary damper modulates to maintain zone temperature. The fan stays on continuously for series units, or off for parallel units. In heating mode, series fans keep running while reheat engages. Parallel units start their fan only when the space temperature drops below setpoint. Building automation systems monitor minimum ventilation airflow, fan status, and reheat control to maintain comfort and indoor air quality.
Applications
In overhead VAV systems, parallel units work best for perimeter zones that require frequent heating. Series units are preferred in core zones where maintaining constant airflow and diffuser performance is critical. For UFAD—Underfloor Air Distribution—systems, fan powered terminals can be placed beneath the raised floor to locally mix and heat air near the perimeter.
Selection & Design Tips
When selecting an FPTU, review manufacturer data carefully. Check airflow ranges, fan power, pressure drop, and coil performance. For quiet operation, use ECM motors and optional attenuators. Always specify a pressure-independent control damper with calibrated flow sensors and confirm your minimum ventilation CFM meets code requirements. Don’t forget about accessibility and orientation — parallel units must be installed level, and underfloor terminals need removable panels for service.
Commissioning & Common Pitfalls
During commissioning, verify primary airflow calibration, fan rotation, and coil operation. Trend zone temperature, primary airflow, and reheat valve position. Common mistakes include not maintaining minimum ventilation flow, short-cycling parallel fans, or overlooking acoustic treatments. Proper setup ensures efficiency and occupant comfort.
Fan powered terminal units play a vital role in modern HVAC systems—blending air, maintaining ventilation, and improving zone control. Whether you choose series or parallel, overhead or underfloor, or design for a cold or warm climate, understanding their operation helps you design smarter and troubleshoot faster.
What if you could combine the zoning flexibility of VRF with the safety and simplicity of water-based systems — all in one design? That’s exactly what the new generation of Hybrid VRF systems promises. It looks familiar from the outside, but what’s happening inside is completely different. In this article, we’ll break down how this technology works, why it’s changing the way we think about HVAC design, and where it makes the most sense to use it. Let’s get started.
The outdoor unit in a Hybrid VRF system works just like a traditional VRF heat pump. It’s the heart of the system — where heating or cooling is generated. The unit uses refrigerant to absorb or release heat to the outside air, depending on the season.
Hybrid Branch Controller
The Hybrid Branch Controller is the key component that makes a Hybrid VRF system different. It acts as the bridge between the refrigerant and the water loops. Inside the controller, the refrigerant transfers its heating or cooling energy into water, which is then circulated to the indoor units. This setup keeps refrigerant contained to the mechanical area and uses only water inside the occupied spaces — making the system safer, easier to install, and more flexible for zoning. The Hybrid controller contains two small pumps to serve the hot and cold-water loops.
Hybrid VRF System
Refrigerant Piping
Refrigerant piping connects the Outdoor unit with the Hybrid branch controller using only two pipes, such as in a typical split system heat pump. This is the only refrigerant piping required for this system, so the amount of refrigerant is limited to the distance between the outdoor unit and the indoor Hybrid branch controller. There are various rules for the allowable distances but should be find for most applications as we’re talking hundreds of feet.
Indoor Fan Coil Units
There are several options for indoor units, such as the ceiling cassettes, wall mounted fan coils and concealed ducted fan coil units.
Water Piping
In each zone, water (hot or chilled) is delivered, enabling heating or cooling in each indoor unit without refrigerant piping in that zone. Water piping is run between the Hybrid branch controller and the indoor fan coil units. The piping can be run in copper or polyethylene as indicated by the manufacturer.
This effectively replaces the refrigerant piping portion to indoor units with water piping, thus making indoor spaces “refrigerant-free.” Many of the safety, regulatory, and leak detection challenges associated with refrigerants in occupied areas are reduced. Another advantage is that only two pipes need to be run between the branch controller and the fan coil instead of the four pipes run in a chilled water and heating hot water 4-pipe system.
Because the HBC supports simultaneous heating and cooling, heat recovered from cooling zones can offset heating in other zones, just as in advanced VRF systems. In effect, hybrid VRF combines the zoned flexibility of VRF with the safety, piping ease, and hydronic advantages of conventional chiller boiler systems.
Next, you’ll need the main water supply to the branch controller with a strainer, shutoff valve and PRV. Since this is a hybrid system where water is heated, an expansion tank will be required to be attached to a port on the controller. The size of the expansion tank will need to match the amount of water contained in the system. The expansion tank needs to be at the same height or above the Hybrid branch controller.
Electrical
The hybrid branch controller will need 208 230 voltage for power. Of course, power is also required at the outdoor unit and each of the fan coils.
Multiple Zones
The hybrid branch controller allows you to connect to three fan coils on a single port with some exceptions. This would require that all the zones have a similar thermal profile as only one mode of operation is allowed for the connected group. All connected zones must either be in heating or cooling mode together as there is only one set of pipes that can carry either hot or cold water.
Condensate Drain lines
The Hybrid branch controller requires a drain as do all of the fan coils. Often wall mounted fan coils require an internal condensate pump to lift the condensate into the attic space where it can pitch by gravity to the main drain line.
Controls
The control wiring is like the standard VRF system. Each remote controller or thermostat is connected to their respective fan coil, and then each fan coil is daisy chained together all the way back to the hybrid branch controller.
Hybrid VRF System Control Wiring
The branch controller is than wired to the outdoor unit. This allows the outdoor unit to discover all the connected components. If the occupant wants a remote controller that oversees the system from a convenient location, then a main controller can be mounted in the building facilities office and wired back to the outdoor unit.
Key Benefits
1. Reduced Refrigerant Charge & Lower Risk
By localizing refrigerant to only the outdoor-to-HBC loop, the total refrigerant required is substantially lower compared to fully refrigerant-based configurations. This can simplify compliance with refrigerant concentration limits (ASHRAE 15 and 34) in tight or low-volume spaces. The occupied zones are free of refrigerant piping, reducing the risk of leaks in critical areas.
2. Simplified Interior Piping & Installation
Water piping (especially modern composite or multilayer pipes) is often less expensive, easier to route, and easier to join (no brazing, welding) compared to complex refrigerant piping. The system typically does not require external pumps, valves, sensors, or actuators (beyond what’s built into the HBC), reducing installation complexity. Furthermore, the hybrid system uses only two refrigerant pipes (not four or three), saving piping runs relative to more complex systems.
3. Simultaneous Heating & Cooling with Heat Recovery
Like advanced VRF systems, hybrid VRF supports simultaneous heating and cooling by shifting heat from zones requiring cooling to those requiring heating (via the water loop). This internal heat reuse improves overall efficiency and avoids wasting excess heat. In many cases, hybrid VRF can reduce total energy consumption and maximize seasonal efficiency.
4. Regulatory & Safety Advantages
Because occupied zones are refrigerant-free, many regulatory burdens (such as leak detection, ventilation requirements, refrigerant containment) are alleviated. This is especially significant in small rooms, multi-family units, medical or educational facilities, or spaces with occupancy constraints. Designers are not limited by refrigerant concentration regulations in each zone.
Additionally, the use of water as a distribution medium is benign and safe from toxicity or flammability issues associated with refrigerants.
5. Scalability and Flexibility
The hybrid VRF architecture is modular and scalable. Sub-HBC modules can be added to expand the number of zones or increase capacity. Because the indoor units are water-fed, there is more flexibility in routing piping and integrating with other hydronic systems (e.g. integration with radiant panels, floor heating/cooling, or domestic hot water systems). Additionally, hybrid VRF can intermix with conventional VRF systems in projects where some zones are better served by direct refrigerant, and others benefit from hydronic delivery.
Because the outdoor condenser loops and control systems are similar or identical to conventional VRF outdoor systems, many design and control elements can carry over.
Challenges & Considerations
No technology is without trade-offs. Below are key challenges for hybrid VRF systems.
1. Higher First Cost / Complexity
Because hybrid VRF is relatively new and specialized, component costs (especially the HBC) may be higher, and supply chain or market familiarity may be limited. The integration between HVAC, controls, and hydronic design requires careful coordination.
2. Hydronic Balancing & Pumping Losses
While water piping is simpler, hydronic systems require careful balancing, pump sizing, and flow control. Pressure drop, head loss, and delta-T control must be well managed to avoid losses that offset the efficiency gains. Systems operating with low ΔT (temperature differential) require more flow and thus higher pump energy. Also, the design of water piping (routing, insulation, pipe sizing) becomes important.
3. Control Complexity
Because hybrid VRF bridges two domains (refrigerant and water), the control logic must handle coordination, zone water temperature resets, valve control, fault handling between the HBC and indoor units, and integration with building automation systems (BAS). Mistuning or poor control design can degrade comfort or efficiency.
4. Thermal Buffering & Thermal Storage
In systems with rapidly changing loads, the hydronic loop may require buffering (e.g., small buffer tanks) to smooth flow transients and avoid frequent cycling. Designers must consider thermal inertia, water temperature reset schedules, and response times.
5. Limited Product Competition (for now)
As of now, one of the most widely cited hybrid VRF systems is this specific two-pipe hybrid VRF implementation as being the first of its kind. It is sometimes claimed that this is the only commercially available two-pipe hybrid VRF solution with simultaneous heating/cooling. That said, other manufacturers are exploring or offering hybrid or hydronic-VRF variants (for example, VRF systems with hydronic heat recovery, or VRF systems connected to chilled water loops), though not necessarily with the same architecture.
Because competition is limited, specification, maintenance know-how, parts availability, and installer training are critical considerations.
6. Efficiency Trade-offs at Extreme Conditions
In extreme ambient conditions, the efficiency of the hydronic heat exchange or temperature lift in the HBC may degrade performance compared to conventional VRF. The HBC becomes a central device whose thermal performance is crucial; losses there can erode gains from reduced refrigerant usage.
Future Trends & Outlook
Given rising focus on refrigerant regulation, electrification, and energy efficiency, hybrid VRF is likely to gain more attention. Industry commentary already positions hybrid VRF as one of the key trends in HVAC for 2025. As more manufacturers enter the market and product maturity improves, the first-cost barrier may come down. Hybrid VRF may evolve to support lower-GWP refrigerants, modular HBC designs, and tighter integration with other hydronic systems (e.g. radiant heating, domestic heating).
Additionally, some VRF manufacturers are already exploring or offering variants of hydronic integration, such as VRF systems that can drive or recover heat to/cold from chilled water loops or “hydro kits” that convert refrigerant energy to water heating.
However, wide adoption will depend on educating designers, expanding service networks, and proving lifecycle cost advantages.
Cooling towers are critical to HVAC and process cooling plants. But how we control the speed of those massive fans can make the difference between an efficient system—or wasted energy. Because fan power scales roughly with the cube of speed, small reductions in rpm can produce outsized kW savings. This article breaks down your control options—constant speed, two-speed, dual-motor arrangements, and variable frequency drives (VFDs)—then compares efficiency when staging multiple towers or cells.
So, if you run a fan at 50% speed, airflow drops to ~50%, but power drops to ~12.5% (0.5³).
Control Options
A. Constant Speed (On/Off)
How it works: These fans are either on or off. It’s the simplest and lowest-cost method, but it comes with drawbacks—coarse temperature control, higher average power, and more wear from frequent starts and stops.
Motor runs at synchronous slip speed via across-the-line starter or soft-starter. Capacity is controlled by cycling the fan on and off and/or using basin bypass or waterflow modulation.
Pros
Lowest first cost, simple controls
Robust and familiar
Cons
Coarse control, temperature “hunting”
Highest average kW to meet setpoint
Frequent starts increase mechanical/electrical stress (unless mitigated with a soft-starter)
Noise fluctuates during cycling
When to use
Small towers with permissive temperature deadbands
Facilities with tight budget and low run hours
B. Two-Speed Motor (Pole-Changing, e.g., 1200/600 rpm)
How it works: One motor with two synchronous speeds via pole switching (two windings or Dahlander). Control steps: OFF → LOW → HIGH.
Pros
Low/medium first cost
Meaningful energy reduction at LOW (power ≈ (N_low/N_high)³)
Fewer starts than pure on/off
Cons
Only two capacity steps; still coarse
Requires interlocks and proper sequencing to avoid switching under load
Less precise approach control than VFD
When to use
Moderate load variability where three steps suffice
Retrofit where VFDs are impractical
C. Dual Motors / Dual Fans per Cell
How it works: One tower cell with two smaller fan-motor assemblies instead of one large unit (or two cells run in parallel). Control by staging motors: 0, 1, or 2 fans (and possibly with two-speed/VFD on each).
Pros
Redundancy: one fan can be down while the other maintains partial capacity
Finer staging than single constant-speed fan
Can combine with VFDs for very fine turndown
Cons
Higher mechanical complexity
More drives/starters and controls
Slightly higher static/system effects at multiple inlets/outlets depending on geometry
When to use
Mission-critical plants (data centers, hospitals)
Plants needing N+1 redundancy at the cell level
D. Variable Frequency Drive (VFD)
How it works: Electronic speed control with continuous rpm modulation based on condenser-water (CW) leaving temperature or approach to wet-bulb.
Pros
Best energy performance (precisely exploit the cube law)
Smooth ramping: reduced inrush, less mechanical stress
Tight temperature control and quieter operation at part load
Higher first cost (drive + filters/harmonic mitigation as needed)
Requires attention to motor insulation (inverter duty), cable length, and minimum speed limits for gear/motor cooling
Potential for VFD harmonics—consider line reactors/filters and coordination with the utility
When to use
Almost always the lifecycle-cost winner for medium/large towers with variable loads
Facilities with demand charges, long operating hours, or noise constraints
Efficiency Comparison: One Fan at Full vs. Two Fans at Half
A simple illustration using the cube law:
Assume each fan at 100% speed draws 50 kW.
Option 1: One fan at 100%, the other OFF → Total 50 kW.
Option 2: Two fans at 50% speed each → Power per fan = 50 × (0.5³) = 6.25 kW → Total 12.5 kW.
For roughly the same net airflow (0.5 + 0.5 = 1.0 “unit”), two at half speed can use ~75% less power than one at full speed.
Why it works in towers (often even better than in ducts):
Distributing water over more fill area at a lower air velocity often improves heat transfer effectiveness (more contact time, better wetting), so you may achieve the same or better leaving CW temperature at even lower fan speeds.
Noise drops dramatically at lower speeds.
Caveats: confirm minimum motor/gear speeds, bearing lubrication needs, and avoid water maldistribution at very low air velocities.
Rule of thumb for multi-cell towers:
Run the maximum number of cells you can at the lowest possible fan speed to meet setpoint, subject to water distribution limits, freeze/plume management, and pump energy trade-offs.
4) Multi-Tower / Multi-Cell Control Strategies
A. Common Sequencing Priorities
Meet LWT setpoint (e.g., 85°F / 29.4°C) with a small deadband.
Maximize active cells, then modulate all fans down together (with VFDs).
Respect minimum fan speed (e.g., 20–25%) for motor/gear cooling and to maintain water distribution.
If you hit minimum speed on all active cells and are still below load → deactivate one cell (to keep others above their minimum and maintain water distribution quality).
In cold/wet conditions, include plume and icing logic (bypass, basin heaters, intermittent reverse jog if manufacturer allows).
B. Pump & System Interactions
If pumps are constant speed and head doesn’t change much when enabling extra cells, the fan-energy benefit typically dominates.
If enabling more cells adds significant hydraulic head (uncommon), re-evaluate the fan vs. pump energy trade-off.
With variable-flow condenser pumps, coordinate VFD setpoints: unnecessary high waterflow can offset fan savings.
C. Practical Limits
Minimum waterflow per cell: stay within manufacturer’s turndown for proper fill wetting.
Freezing risk: winter operation may require cycling fans off, bypassing fill, or minimum speeds to prevent ice.
Water treatment/plume: more cells at low speed can increase plume risk in certain ambient conditions—use plume abatement strategies if required.
Option-by-Option Energy & Control Summary
Option
Energy at Part Load
Control Resolution
Reliability/Stress
First Cost
Best Use Case
Constant Speed
Poor (cycling)
Coarse (on/off)
More starts; simple
Low
Small/simple towers, low run hours
Two-Speed
Fair
Medium (low/high)
Fewer starts; still stepped
Low–Medium
Moderate variability; simple upgrades
Dual Motors/Fans
Good (with staging)
Medium–High (0/1/2 fans)
Redundancy; more components
Medium–High
Mission-critical; N+1 needs
VFD
Excellent (∝ N³)
High (continuous)
Soft starts; least wear
Medium–High
Most variable-load plants
6) Control Set Points & Tuning Tips
Primary loop variable: Leaving CW temperature (or approach to ambient wet-bulb).
Setpoint strategy: Fixed setpoint (e.g., 85°F) or reset based on chiller efficiency (some chillers prefer warmer CW at light loads to reduce lift; always coordinate tower and chiller curves).
PID tuning: With VFDs, use slow integral action to avoid oscillation; apply a small deadband (e.g., ±0.5–1.0°F).
Starts per hour: Enforce maximum starts if any staged (non-VFD) fans remain.
Minimum speed: Honor manufacturer minimum (often 20–30%) for gear/motor cooling and ensure adequate airflow through the motor.
Safety interlocks: High/low basin level, vibration switch, gear oil pressure/temp (if applicable), fan contactor/VFD status, freeze protection, and motor space heaters.
7) Reliability, Maintenance, and Noise
VFD benefits: Soft starts reduce mechanical shock on gears, couplings, and blades; lower average speed reduces wear and noise.
Two-speed motors: Check contactor and interlock sequencing; avoid switching between speeds under load.
Dual-fan cells: Plan for access, vibration monitoring per fan, and balanced staging to equalize wear.
Noise: Since acoustic power falls sharply with rpm, low-speed multi-cell operation is typically the quietest strategy.
8) Quick Worked Example (Energy)
Goal: Deliver “1.0 unit” of airflow.
One fan at 100%: 1.0 airflow → 1.0³ = 1.0 power unit (e.g., 50 kW).
Two fans at 50% each: 0.5 + 0.5 = 1.0 airflow → 2 × (0.5³) = 0.25 power units (e.g., 12.5 kW).
Savings: 75% fan power reduction, often with better heat transfer due to more wetted fill area at lower face velocity.
9) Commissioning Checklist (Field-Ready)
Verify rotation, tip clearance, blade pitch, and vibration cutouts.
Confirm minimum VFD speed and motor/gear cooling requirements.
Calibrate LWT sensor; confirm wet-bulb source if using approach control.
Test multi-cell sequence: enable extra cells before increasing speed, and shed cells last.
Validate freeze protection logic (bypass, heaters, reverse-jog if specified).
Trend fan kW, LWT, ambient WB; verify stable control and expected cube-law savings.
10) Bottom Line
If you can only pick one upgrade, choose VFDs—they offer the largest, most controllable energy savings and better temperature stability.
In multi-cell towers, operate more cells at lower speeds rather than one cell at full speed, subject to manufacturer turndown, plume, and freeze constraints.
For critical facilities, consider dual-fan/cell redundancy, ideally each on a VFD, to combine reliability with ultra-low kW/ton of heat rejection.
