Tag: commercial hvac

If you are primarily a residential technician working on equipment under 5 tons, there is a lot of similarities between the systems you are used to and 5 – 20 ton rooftop units that are common to the light commercial market. There are some additional things to consider on larger equipment and here are just a few of many.

Wash Fresh Air Filters

While fresh air intake is becoming more common across the entire industry, it has been most common in commercial environments. Fresh air filters are often metal mesh and should be washed regularly with a hose and maybe some degreaser when they are in an environment near exhaust hoods.

Check and Adjust Belt Tension 

When I was a new commercial maintenance tech I used to get belts far too tight. This would result in high amperage on the blower, belt breakage, stretching and excessive bearing wear. You want the belt to be tight enough that it doesn’t slip or vibrate excessively but no tighter. In most cases, the tension is adjusted by moving the position of the motor itself, either by way of adjusting the height of the motor base plate or sliding the base plate back and forth. In some cases, the tensioning will be done with a tensioner pulley like the one shown below.

Many techs will use the 1/2″ deflection rule or something similar to guess at belt tension. The trouble is this rule doesn’t account for the length of the belt or the amount of pressure used for deflection. Many experienced techs have a good “feel” for proper belt tension, but even that can be pretty far off at times.

Browning Belt Tension Tool

Browning makes a belt tension tool that you can use to ensure that the best has the proper tension for the application. Here is a quick video showing how it works.

You can read the full guide on using the tool as well as proper deflection force HERE 

Keep in mind that belts do need to be replaced regularly. If a belt begins to loosen significantly due to stretching after the initial break-in period, it is often best to replace it rather than to keep tightening it.

Align Pulleys 

When aligning pulleys keep in mind that you need to align the pulley centers with one another both right to left as well as the “camber” or angle of the pulleys themselves. Often pulley misalignment can happen when one of the bolts holding the motor base in place begins to slip or if a pulley has been adjusted or replaced. Misaligned pulleys and result in thrown or damaged belts, damaged bearings and noise.

In addition to aligning pulleys, keep in mind that pulleys can become worn over time and lose the deigned shape or wear grooves in the sides. If a pully becomes worn it will lead to improper airflow, noise and shorter belt life.

Clean Condensers, Split as Needed 

Many commercial units have multirow condensers that will need to be split from time to time to get them completely clean. The frequency that this will be required is dependant on the location of the unit and the amount of debris in the air. Here is a video showing the process.

Checking Phase Balance 

Many 3-phase systems will already have phase monitoring controls installed that check for voltage imbalance and dropped legs of power. This is important on 3-phase systems because even small imbalances can result in motor heat and failure. Check voltage from leg to leg on all three legs on the equipment. Any imbalance of more than 2% is considered detrimental and an imbalance of over 4% is totally unacceptable. To learn more about exactly how to measure voltage imbalance read this excellent article by John Tomczyk

— Bryan

This article was written by Gary McCreadie from “HVAC know it all”. You can learn more about Gary and his tips and growing community on Facebook and on LinkedIn

What is an economizer?  Simply put, it is a mechanical device that is designed to reduce the consumption of energy, whether it be fuel, electricity, or other. According to Wikipedia, the first economizer was patented by Edward Green in 1845.  It was used to increase the efficiency of stationary steam boilers.

This article will revolve around air side economizers.  You will typically see them as an accessory built into rooftop units used for the purpose of “free cooling”.  Free cooling is a funny term because it’s not actually “free”, the fan motor and economizer controls must be powered in order to operate, which consumes energy.  The term merely demonstrates the fact that less power consumption is taking place due to the fact we are utilizing outdoor air to cool a space rather than the use of a compressor or compressors.  Economizers also offer the added feature of providing fresh air to the building and it’s occupants.  A carbon dioxide sensor can be integrated into the set up.  As CO2 levels increase within the building, the outdoor air dampers are commanded to open, filling the space with fresh air.  As CO2 levels drop off, the dampers return to their minimum position.
The Guts of an Economizer
The economizer set up employs several parts in order to operate correctly.
1) A set of outdoor air dampers that are directly linked to the return air dampers are used to control air flow.  They move together as one, as the outdoor air dampers begin to open, the return air dampers begin to close and vice versa.
2) An outdoor air sensor.  This sensor is responsible for determining if the outdoor air is acceptable for free cooling.  In most cases, there will be an option between a sensible temperature sensor or an enthalpy sensor.
Sensible Temp Sensor – Measures dry bulb temperature of the air
Enthalpy Sensor –  Measures heat content within the air measured in btu/lb.  This sensor takes dry bulb temperature and wet bulb temperature into account for total heat content.
3) An indoor air sensor, this sensor reads sensible temperature and is responsible for maintaining mixed or discharge air temperature.  The damper assembly will modulate according to feed back from this sensor to maintain a pre-determined mixed or discharge air set point.  On newer economizer controls, like the Honeywell Jade for example, you are able to set the mixed or discharge air temperature as desired.
4) The damper actuator, which receives a signal from the economizer control board and moves to the assigned position to maintain the mixed air or discharge air set point.
5) When using free cooling you must remember that you are introducing fresh air, this added air into the space can cause positive pressure issues within a building.  To eleviate this problem economizers in most cases will have a built-in barometric relief damper or power exhaust system.
6) The control board is the heart and soul of the operation.  The control board receives sensor input signals, internally calculates the next step and relays the output signals to the damper actuator and power exhaust motor if utilized.
Order of operation
To keep it simple, the following example will be based on a single stage cooling rooftop unit complete with an economizer package.
On a call for cooling from the thermostat or BAS (building automation system), the Y1 terminal will be powered.  In most cases, the signal will first move through the rooftop control board and over to the econmizer control.  At that point, the econmizer control will then decide whether to proceed with free cooling or mechanical cooling based upon the outdoor air conditions either using sensible temperature of the air or the heat content of the air measured in enthalpy.  If the outdoor air is not suitable for free cooling, the control signal will be then relayed back to the main control board of the rooftop and initiate mechanical cooling (compressor operation).  If the outdoor air is suitable for free cooling, the outdoor air dampers will modulate from their minimum position (damper minimum position is set up during commissioning to maintain constant fresh air to the building and occupants) to maintain the mixed air or discharge air set point until the space temperature is reached.  Once the thermostat or BAS has been satisfied, the call for cooling will cease.
Most air side economizers in general, work as explained above.  It is best to contact the manufacturer of the equipment you are working on for technical advice or when issues pertaining to that system arise.
— Gary McCreadie

This article was written by Christopher Stephens, he is a commercial HVAC/R service manager in the greater Los Angeles area. Thanks Chris.



Let’s start by covering the three elements that are needed for a Fire-  Fuel, Air, and Heat (spark). With those three elements in the right condition you can start a fire. So, with if we reduce the oxygen to an existing fire we can slow it down until the Fire Department can arrive to extinguish the fire.

In a restaurant, we use exhaust fans to remove unwanted smoke and heat produced by cooking appliances from the kitchen, however we also need to add makeup air to the restaurant to compensate for the exhausted air. If we didn’t than the exhaust fans would create a negative air pressure that would make it very difficult to open the doors to the restaurant. (I always like to use the paper bag analogy here if you put a paper bag over your mouth and suck the bag will collapse, but if you cut a hole in the bag the air will pass right thru the bag) This makeup air can be delivered back into the building by a dedicated supply fan unit or by using fresh air dampers on the air conditioning units. Now let’s move to some safety devices.

Air conditioning units move large amounts of air, so for safety reasons we install duct smoke detectors in the ductwork to “detect” smoke. if they sense smoke they shut down that air conditioning unit to eliminate the oxygen source and to stop the spread of the fire. At the same time they also send a signal to the fire alarm company that there is a fire. Most duct smoke detectors have two alarm functions. They can detect a Fire condition and they can detect a trouble condition. A fire condition is obvious the detectors sensor is sensing smoke so it triggers a direct short (closed) in a relay and sends a signal to the fire alarm company. Now a trouble condition can be several issues all depending on how the detector is configured. We can configure a Duct smoke detector to signal a trouble condition if someone has taken the cover off the duct detector, if the detector has lost power, or if there is a malfunction in the smoke sensor.

It’s important to note that most fire alarm companies monitor a duct detector with an 18/2 thermostat wire, a fire condition is sensed when there is a direct short between those two wires, and a trouble condition is sensed when a resistor that is placed between those two wires disappears from the system by means of a normally open contact closing. So, on a properly operating duct smoke detector without a fire condition if we place an ohm meter across the alarm terminal we should read the resistance of the resistor (the resistance value is determined by the fire alarm panel manufacturer) If we have a trouble condition we will read open line across the alarm terminal and if we have a Fire condition we will have a direct short across the alarm terminal. This is designed so the smoke alarm system can ensure that the circuit is intact at all times, otherwise the circuit could be broken (open) and when a fire occurs the alarm wouldn’t trigger. The resistor helps the fire system prove that the circuit is intact and ready to rock.

Now let’s talk about exhaust fans as stated above they remove smoke and heat from the building during normal operation. But if there is a fire in the restaurant they can aid in slowing down the fire until the fire department arrives to extinguish the fire. We can do this by turning on the exhaust fans and turning off all supply air to the building (makeup air and/ or air conditioners) and by doing this we will be reducing the oxygen in the building to suffocate the fire. We accomplish this task by using relays built into the exhaust control system. These relays open and shut off all of the A/C systems and makeup air while closing to turn on exhaust. This reduces the exposure of the flame to oxygen and therefore reduces the spread and intensity of the fire.

— Christopher

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