Top 6 HVAC Control Strategies to Save Energy

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October 10, 2022

Top 6 HVAC Control Strategies to Save Energy. In this video we’ll learn the top 6 Control Strategies for reducing energy consumption. These are control strategies to reduce cost and save energy. The control strategies are programmed into the sequence of operation for the control of HVAC systems.

We’ll learn about using trim and respond (T&R) setpoint reset logic for controlling chillers and air handlers. The energy savings from these strategies vary by geographical area and building types.

If you prefer to watch the YouTube Video of this presentation, then scroll to the bottom or click on this link. Top 6 HVAC Control Strategies to Save Energy

#6 Supply Air Temperature Reset

To save energy the supply air temperature can be reset higher when the demand is reduced. This will save on compressor energy use and allow more time for the use of the air side economizer.

Using Trim and Respond control logic if no request for cooling is sent to the air handler controller, than the supply air temperature is trimmed by a set value that is determined by the programmer. Let’s say that if no request is made the supply air temperature is reset 0.2°F, this would move our setpoint to 55.2°F. Every two minutes or whatever duration is set by the controls programmer the trimming of the supply sir temperature will occur until a request is made from a zone.

HVAC Controls Strategy - Supply Air Temperature Reset — HVAC Controls Strategy – Supply Air Temperature Reset

The VAV zone boxes can be programmed to make a request when any VAV box damper reaches 90% open. When the request is sent, the supply air temperature will respond by decreasing by a certain value, chosen by the programmer, let’s say by 0.3°F. If our temperature was trimmed up to 58°F, before a request was made, the request would decrease our supply air temperature to 57.7°F.

If multiple VAV boxes send request at the same time, then the value is multiplied by the number of request. If 4 VAV Boxes sent a request for more cooling, then the Supply Air Temperature could be reset by 4 times 0.3°F, for a total of 1.2°F decrease. The controls programmer will limit how much the supply air temperature can be decreased at any one time, no matter how many request are sent for additional cooling. This allows system stability.

Systems using an air-side economizer will have more time when the economizer is in use because of the supply temperature being set higher. This allows the outdoor air to be used instead of the compressor to provide cooling, which saves on energy.

#5 Demand Control Ventilation

The reason it’s called Demand Controlled ventilation is that it controls the amount of ventilation based on the demand. Demand changes with occupancy levels, so some form of occupancy monitoring will be used as the control strategy. Ventilation air is required by ASHRAE standard 62.1, but providing ventilation air is energy intensive and costly. Providing only what’s needed can save on energy and money.

With ASHRAE 62.1 the ventilation requirements or outdoor air is increased based on the number of occupants and square footage of the space. Demand controlled ventilation is based on providing outdoor air in proportion to the occupancy level.

Energy is wasted in the form of conditioning excessive amounts of ventilation air when the occupancy level is less than the design maximum. By using demand-controlled ventilation, the occupancy level can be monitored, and the quantity of ventilation air adjusted downward according to actual occupant levels. Tracking the occupancy level with DCV reduces energy consumption by only bringing in enough ventilation air to satisfy the current level of occupants, not the design maximum.

Using a conference room for our example. If the meeting room was designed for 125 people, but only the presenter is currently in the room waiting for attendees. The CO2 monitor would pick up the low quantity of carbon dioxide and close the outside air damper to match the occupant level. As more attendees arrive to the meeting, the level of CO2 increases, and the CO2 Monitor picks up this increase and sends a command for the Outside Air Damper to open wider, allowing more outside air into the space. As, the occupants leave the system will begin to close the outside air damper. This is a basic explanation of how DCV works, for a further explanation see our video on Demand Controlled Ventilation.

#4 Optimal Start

HVAC equipment has often been setup to use a time clock or time-of-day schedule to turn the system on and off based on a proposed occupancy schedule. The time clock will be set to start the HVAC system equipment before the occupants arrive and to shut it off at a preprogrammed time when the building is scheduled to be vacant. The schedule of when to turn on the HVAC equipment in the morning to ensure the space is comfortable for the occupants is often based on the worst summer or winter conditions. This creates an opportunity to save energy by providing an optimal start time when conditions are not at these peak conditions.

Optimal Start of HVAC Air Conditioning Equipment

With an Optimal Start strategy the building automation system will select the best, or optimal start time based on the conditions existing for that day. The buildings control system will determine how much time, or how early the HVAC equipment needs to be started to ensure the space is comfortable for the occupants when they arrive. The building automation system will prevent the HVAC equipment from starting too early, which is a waste of energy. The controls will ensure that the system is started with just enough time to have the space conditioned when occupants arrive, no sooner.

Using the capabilities of a building automation system to track historical data and use that data for current conditions is how this strategy is implemented. The controls system receives input from space sensors on the current temperature and compares this to the setpoint temperature. With historical trending data the building automation system can determine how long the HVAC equipment needs to run to make up the difference between this setpoint and the current space temperature. The greater the Delta-T, the earlier the HVAC equipment will be started.

This control strategy saves energy by optimally starting equipment and avoiding conditioning spaces to setpoint temperatures earlier than required. This saves on operational hours of the HVAC equipment, allowing the equipment to last longer.

#3 Shorten HVAC Schedule

Often HVAC schedules are set for longer time durations then the actual occupants require. Shortening the HVAC schedule works well with an optimal start and stop control strategy. This strategy avoids turning on HVAC equipment before they are needed and quickly turns them off when occupants are not scheduled to be in the building. The building automation system learns with historical trending data when it’s the best time to turn equipment on. The controls system uses outdoor air conditions, indoor temperatures and set points for heating and cooling during occupied mode.

There may be spaces within the building that operate only on specific days of the week. If this space is on the same system as the regularly scheduled equipment, it might payoff to provide a separate system or method of controlling the conditioning of this space.

HVAC Equipment operating Schedules - Separate System for irregular Scheduled Spaces — HVAC Equipment operating Schedules – Separate System for irregular Scheduled Spaces

Working with optimal start to determine the best time to start the equipment, including night setback temperatures, this strategy ensures that the equipment is only running when the building is occupied.

#2 Minimum VAV Box Damper Flow Reductions

Systems using Variable Air Volume boxes have their dampers set to a minimum open position to ensure that there is always ventilation air per ASHRAE 62.1. Often this minimum open setting is greater than the actual CFM required of the space, as the space will most likely be influenced by the internal load which will drive the damper wider open, negating the minimum setpoint. Set the VAV box damper open to the minimum mandated to meet ASHRAE standard 62.1 for ventilation and no more. See ASHRAE 62.1 Appendix “F” for a Simplified Ventilation Rate Calculation for multiple zone recirculating systems.

When the minimum damper position is set too high, then fan and cooling energy is wasted. Too much cold air is being sent into the space, requiring additional energy to reheat the air. This can be avoided by reducing the minimum setpoint, and by using this Minimum VAV Box Damper Flow Reduction strategy. This will of course depend on the space type and usage.

#1 Wider Dead Bands and Night Setbacks

On average, this was the #1 way to save energy.

DeadBand

The deadband is the temperature range when the HVAC system is neither calling for heating or cooling.

By widening the dead band, the amount of time that the HVAC system would save energy would increase. In California zonal thermostats that are used to control both heating and cooling shall be capable of providing a deadband of at least 5°F.

Night Setback

When the building is unoccupied during the nighttime hours, the HVAC system temperature can be setback in the range of 6° to 10°F. This allows the building to become warmer or cooler at night then during the day, but avoids letting it get too far from setpoint. By allowing the HVAC system to increase or decrease from the setpoint, depending on whether in cooling or heating mode, the system will come on less during the night when the building is unoccupied, thereby saving energy.

The system will come on only to avoid extreme temperature conditions. For instance, if your normal daytime setpoint for cooling is 76°F, you could program the DDC system to bring on the HVAC equipment to cool the space after hours or off schedule if the building temperature reached 86°F.

You can see that this works directly with the Optimal Start Control Strategy which is to ensure there is enough time in the morning to cool the space down to its normal setpoint. This is because it was prevented from maintaining normal setpoint temperature of 76°F during the night, hence night setback.

It’s important the system be put in the unoccupied mode; this is to ensure that the outside air dampers are closed. Bringing in ventilation air in unoccupied mode can increase energy consumption unless outdoor conditions are in the economizer range for free cooling of the space in summer.

Top 6 Control Strategies to save Energy

Water Coils Explained

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MEP Academy Instructor

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October 2, 2022

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Water Coils explained Coil rows, passers, circuits, headers, fins, materials, etc.

Water Coils Explained. In this presentation we’ll learn how coils are constructed and how to select coils for optimizing energy and performance. We’ll learn all the parts of the coil assembly so that you can discuss coils with anyone including engineers. We’ll look at Chilled water and Heating Hot Water coils. Coils can be found in Air Handling Units, Fan Coils, VAV Boxes and Induction coils to name a few.

If you prefer the YouTube Video of this presentation then scroll to the bottom or clink on this link. Water Coils Explained.

Coils are used to transfer heat between two mediums, often water and air. Air passes over a coil and the water passing through the coil either absorbing or giving up its heat. The greater the temperature differential between the air and water, the greater the potential heat transfer.

Coils can be installed with just one or multiple coils in a stacked or side by side configuration within HVAC equipment or as part of a built-up system. Built-up systems are used on large projects and require special structural supports to hold them in place.

First we’ll cover coil construction. Most coils used in the HVAC industry are constructed using copper tubing ranging in size from 5/16” up to 1” O.D. You may find 5/8” to be the most commonly used size. The tubes go back and forth from one end and back again, each time they go up and back that is considered 2 passes, as the coil has traversed the face of the coil twice.

Rows of Coils

The tubing can have anywhere from 1 row of coils which is common in small VAV Boxes using reheat coils, all the way up to 12 row coils for larger chilled water systems.

By adding additional rows to a coil, you can increase the heat transfer capabilities if the fins per inch remain constant. But by increasing the number of rows in a coil, the pressure drop across that coil will increase also, causing the fan to work harder, we’ll discuss more about this later.

HVAC Coil Construction - Rows of Coils and Number of Tubes on Face of Coil — HVAC Coil Construction – Rows of Coils and Number of Tubes on Face of Coil

To count the rows of coils there are several methods, first look at the end of the coil without the header and count the return bends or hairpins. The hairpins are 180-degree fittings that turn the flow back into the coil. Each hairpin accounts for two rows if aligned horizontally, so if you have two hairpin turns horizontally aligned, then you have a 4-row coil. If looking at the header, there would be one row for each header, which isn’t visible when looking directly at the end.

The coil will be housed in a casing often constructed of galvanized sheet metal. Coil casing material can be galvanized steel, carbon steel, stainless steel, copper, or aluminum. Typical casing thickness for galvanized steel is 16 or 14 gauge. The casing is the structural support frame that holds the tubing.

Coil Fins

The coil tubing is covered with fins which increase the heat transfer surface to improve energy transfer from the air to the water in the coil.

In the HVAC industry coil fins are customarily made using aluminum, but are also available in copper, and in restricted sizes for stainless steel and carbon steel. The fins surface area increases the contact area of the air passing through the coil. This increases the efficiency of the coil. The thickness of the aluminum fin material is very thin and can range from 0.0045 to 0.016”.

The tubing slides through the openings in stamped sheets of metal that comprises the fins, acting as a guide. The fins are spaced close to one another, and the quantity is referred to as the fins per inch (FPI), or fins per foot (FPF). Coils can be provided with anywhere from 4 to 20 fins per inch.

Remember the increased surface area, meaning more fins per inch, or more rows will increase the heat transfer capabilities but at the cost of fan energy. Coil manufactures software will pick the best coil, with the least number of rows to meet the project requirements.

The fins are provided in various patterns and configurations. The fins are attached by forcing a mandrel through the copper tubing, causing the tubing to expand and tighten against the fins.

This ensures a good bond between the tubing and the fin which creates good thermal conductance for heat transfer.

The fins surrounding the coils can be configured in various shapes from flat to corrugated.

Right-Handed or Left-Handed Coils

Coils are considered left-handed or right-handed. The reason this is important is that when the coil is installed you want to make sure that the piping connections to the coil are on the correct side of the equipment to avoid extra piping.

This can be determined by standing in front of the coil looking in the direction of the airflow, with the air at your back. If the connection is on your right, then it’s considered a right-handed coil connection, and if it’s on the left, than its left-handed.

Coil Headers

Headers are provided for the supply and return connections to the coil which can be provided in materials such as copper, carbon steel, stainless steel, and red brass. Piping connections can be provided in both male or female threads, grooved, welded, or brazed/sweat. Male threaded connections are common up to 2-1/2”.

Coil Header Pipe Connections (Threaded, Grooved, Welded, Brazed/Sweat)

The header serves several purposes, one is to provide a method to connect all the individual tubes in the coil to one larger pipe, that can then be used to connect the system piping to one or more inlet and outlet connections. The header allows the water to be distributed to the smaller connecting tubes.

The term coil passes refers to the number of times water traverses from one end of the coil to the other, starting at the inlet. Going up and back would be one round trip and considered a 2-pass coil, once across and then the second pass would be returning.

The face area is considered that portion of the coil which air passes through. This would exclude the casing area. To calculate the face area of a coil you would measure the height and length from the inside of the coil casing. This is the area that the air travels across and is often referenced by the square feet of face area.

Coil Circuiting

Circuiting refers to the path of travel from when the water enters the coil until it leaves the coil. Starting where the tube or circuit attaches to the supply header and then travels back and forth through the coil until it attaches to the return header is considered a circuit.

The longer the path for the water, the greater the pressure drop and the lower the flow rate, which gives the water more time to absorb or reject heat to the air blown over the coil.

Coil Air velocity

The air velocity over the coil will affect the size of the coil and the HVAC equipment cabinet that the coil is installed in. The slower the velocity, the larger the coil and cabinet that houses the coil. The reason for slower velocities might be for energy savings by reducing fan size, but there will be a slight offset in additional pump and chiller energy.

The air velocity is indicated in feet per minute (FPM) across the face area of the coil. This can easily be calculated if the CFM and the Face Area of the Coil is known. The following formula can determine the velocity.

Velocity = CFM (Ft3) / Face Area of Coil (Ft2) = FPM

Velocity = 10,000 CFM / 20 Ft2 = 500 FPM

We can also use this formula to determine the required face area of the coil. Taking our CFM and dividing it by our velocity.

Face Area of Coil (Ft2) = CFM (Ft3) / Velocity (FPM) = Ft2

10,000 CFM / 500 FPM = 20 Ft2 Face Area of Coil

Water Coil Comparisons and the effects of Air Velocity on Coil Area

If the velocity is too high then condensate can be blown downstream of the drain pan. Moisture carryover can leak out of the ductwork and cause damage to the building or within the air handler.

Coil Velocity and Flow

Water coils control capacity by modulating the flow or the temperature of the water entering the coil. When the temperature of the water is adjusted to track demand then the velocity or flow remains relativity constant. When flow is used to control capacity the velocity through the tubes will change when the control valve modulates the quantity of water through the coil. Some coil manufacturers suggest velocities from 1 to 12 feet per second.

When water velocities are too high there can be tube erosion, noise and high pressure drops. If velocities are too low, there could be tube fouling, air trapped in the coil, poor water distribution and the risk of freezing.

Less water is usually flowing in a Heating Hot Water coil as compared to a Chilled Water coil due to the different delta-t temperatures used in each system. Heating hot water systems use higher Delta-T’s allowing for lower flow volumes (GPM)

Water Coil Coatings

Coatings are provided to protect the coil from harsh environments, such as that encountered near coastal areas or offshore where the equipment is exposed to salt water. They’re also beneficial for harsh industrial environments such as oil refineries and electrical generation facilities.

Copper Tubing with Copper Fins for additional corrosion protection

After the coils are manufactured, they’re shipped to the coating factory where the coils are washed to remove any dust, dirt or residue from fabrication and transporting. Next, they’re rinsed in several baths of deionized water before they enter the coating tank. After the protective coating is applied the coil will go through several rinsing tanks or spray booths before entering a large oven to ensure that the coating is cured. The curing process ensures that the coating will adhere to the coil and prevent it from flaking off, pitting, while avoiding corrosion. The complete coil surface, fins and cracks and crevices will be covered with the coating, while still allowing air flow and heat transfer.

There is an option to provide an additional coating to protect against the UV rays of the sun, just like you might put on sunscreen before heading out for a day at the beach.

There is also the option of providing copper fins which adds another level of corrosion protection, but also adds additional cost. Another option for less sever applications would be to have just the fins precoated before assembling.

Bypass Air

A small percentage of air will bypass the coil and be untreated. This is a very small percentage that is based on how many rows and fins per inch the coil has. The amount of air that is bypassed is reduced when there is an increase in coil rows or fins per inch, or a reduction in air velocity. This accounts for less than 1% of the total air.

Coil Arrangement

Coils can be arranged within HVAC equipment or as stated previously, as part of a bult-up system. Coils can be before the supply fan which is called a Draw-Thru arrangement, or the coils can be after the fan in which it is referred to as a Blow-Thru.

Duct Mounted Coils

These coils are usually used for reheating and are installed in the ductwork feeding the zone. They can be attached to the ductwork with flanges or with a SMACNA standard S & Drive connection.

Venting and Draining

It’s important to provide a method of removing air from a coil and having the ability to drain the coil. A connection at the top of the header provides for the removal of air, while a connection at the bottom of the coil provides a method for draining.

Coil Selection

Most coil manufacturers have coil selection software to quickly provide coil options on the entered design parameters. If an increase in capacity is needed, there are four common ways to achieves this. The first would be to increase the face area of the coil, next would be to increase the number of rows of coil, another would be to increase the number of fins per inch, and lastly provide closer tube spacing.

Coil Flow (Counter Flow or Parallel Flow)

The counterflow coil arrangement is more efficient for a chilled water coil, with a supply temperature range of 42 to 44

HVAC Water Coils Explained

Calculating CFM or Velocity Across a Coil or in Ductwork

By

MEP Academy Instructor

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September 25, 2022

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How to calculate CFM or Velocity from Area — Taking the known values of 2,700 CFM and the new duct area of 36” x 12” we can find the new velocity. First the duct area needs to be converted to square feet.

In this presentation we’ll learn how to calculate the Total CFM in a section of ductwork or moving across a coil or other piece of equipment. Then we’ll learn what happens to velocity when we try to reduce our ductwork without reducing or CFM.

If you prefer to watch the YouTube Video of this presentation, scroll to the bottom or click the following link. Calculating CFM Video

Here is the formula that is used to calculate CFM or Velocity.

CFM = Velocity x Area

CFM, which is “Cubic Feet per Minute” = Velocity which is shown in “Feet per Minute” multiplied by the Area which is shown in “Square Feet.”

A cubic feet of air is a slice of air one foot by one foot, by one foot deep, which might look like this cube.

For example, to determine how many CFM were flowing through a duct section we can do the following. First we would measure the width and height of the duct. Let’s say it was 36” x 24”. Next, we could use some form of anemometer to get an average velocity reading across the duct section. Let’s say the velocity reading is 450 feet per minute. Now we can solve for the quantity of CFM flowing through this section of ductwork using the following formula.

CFM = 450 ft/min x the area, which is 36” x 24”

We’ll need to convert our duct dimensions in inches, into square feet, because we are looking to arrive at cubic feet per minute.

36” x 24” = 864 in2

864 in2 / (144 in2/ft2) gives us 6 ft2

Now we can enter the total square feet into our formula.

CFM = 450 ft/min x 6 ft2 = 2,700 CFM

Now we can use another version of this formula to calculate for velocity when the CFM and Area are known.

Solving for Velocity

For recommended velocities in ductwork see ASHRAE’s handbook of Fundamentals. Depending on the noise criteria and where the duct is located the velocity for rectangular duct could be from 950 to 3,500 feet per minute.

ASHRAE Recommended Maximum Airflow Velocities

What happens to the velocity if you reduce the size of the ductwork with the same CFM. Let’s say that we reduce the ductwork to 36” x 12” in order to get under a beam. The approximate velocity can be calculated with the same formula, except this time will keep the CFM constant and not worry about static pressure or other factors that may affect the outcome slightly.

Velocity = CFM (ft3) / Area (ft2)

Taking the known values of 2,700 CFM and the new duct area of 36” x 12” we can find the new velocity. First the duct area needs to be converted to square feet.

36” x 12” = 432” in2

432 in2 / (144 in2/ft2) = 3 ft2

The new duct is half the area of the previous duct size, but it is carrying the same CFM. So, what happens to the velocity going through the reduced duct size in relationship to the previous velocity. Our velocity was at 450 feet per minute, now with the same CFM but a smaller duct we get 900 feet per minute.

Velocity = 2,700 CFM / 3 ft2 = 900 FPM

The ductwork area was cut in half from 6 ft2 to 3 ft2, but the velocity doubled from 450 FPM to 900 FPM. You can see there is a direct correlation between CFM and Velocity when the size of the duct or coil is changed.

How to calculate CFM and Velocity

Outdoor Air Intake Locations & Air Classifications

By

MEP Academy Instructor

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September 18, 2022

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Outdoor Air Intakes and air classifications Class 1 through Class 4 Air

Outside Air Intake Locations and Air Classifications. In this presentation we’ll learn where outside air intakes can be located and why. We’ll learn what the four classifications of air are, and how they relate to outdoor air intakes, including their Minimum separation distances as shown in ASHRAE 62.1 Table 5-1.

If you prefer to watch the YouTube version of this presentation then scroll to the bottom or click on this link. Outside Air Intake Locations and Air Classifications

ASHRAE 62.1-2019 Air Classifications

ASHRAE ranks air according to the level of contaminants in the air and the level of sensory irritation. The classification extends from Class 1 which is considered low contaminant level, to class 4 which is highly objectionable. Class 1 is the cleanest air classification, while class 4 is the worst.

Class 1 Air with low contaminant concentrations, low sensory-irritation intensity, an inoffensive odor is suitable for recirculation or transfer to any space in classes 1 through 4.

Class 2 air can be recirculated within the same space of origin, or transferred to another Class 2 or 3 Space used for similar purposes or has similar pollutants. Class 2 air can be transferred to class 4 spaces. Class 2 air can’t be transferred to the cleaner class 1 air spaces. Air is almost always transferred from the cleaner space to the dirtier classification of air, unless some method of air cleaning is used.

Class 3 air can be recirculated only within the same space of origin, and can’t be recirculated or transferred to any other space. Class 4 air can’t be recirculated or transferred to any space.

According to ASHRAE 62.1 Table 5-1

Per ASHRAE standard 62.1 the following minimum distances need to be maintained from the location of any Outdoor Air Intake. A minimum distance of 25 feet (7.5 meters) needs to be maintained between an Outdoor air intake and locations where Buses park or idle. A minimum of 5 feet (1.5 meters) is required between intakes and driveways, streets or parking places.

Any Class 2 exhaust or plumbing vent terminating less than 3 feet (1 meter) above the level of the outdoor intake is required to be located a minimum of 10 feet (3 meters) away. Class 2 Air has moderate contaminant concentrations, mild sensory-irritation intensity, or mildly offensive odors. (Class 2 air also includes air that is not necessarily harmful or objectionable but that is inappropriate for transfer or recirculation to spaces used for different purposes.)

A plumbing vent terminating at least 3 feet (1 meter) above the level of the outdoor intake is required to be located a minimum of 3 feet (1 meters) away.

Continuing with ASHRAE Table 5-1, we have the requirement to keep Outdoor intakes a minimum of 25 feet (7.5 Meters) away from truck loading docks. A minimum of 25 feet (7.5 meters) must be kept between any highway with high traffic volume and an intake.

Outdoor Air Intake Louver and Distances to Loading Dock, Trash, Parking and Heavy Traffic

All around the world offices, schools, homes, and hospitals are built near highways and major roadways. Pollution from traffic has been documented to cause serious health problems, from physical to cognitive. The level of pollutants from traffic varies based on proximity to road and level of traffic. There are two sources of contaminants from traffic, the tail-pipe emissions and the physical wear and degradation of brakes and tires. You could also include noise as having adverse effects on health.

Any locations where trash is stored or picked up, including dumpsters will need to be at least 15 feet (5 meters) away from any outdoor intake.

If you have a Outdoor Air intake near a cooling tower than the requirements are that the tower basin or intake to the tower needs to be a minimum of 15 feet (5 meters) away from the Outdoor Air Intake. The discharge of the cooling tower needs to be at least 25 feet (7.5 meters) away.

Potential contaminant sources are restricted on how close they can be to an air intake based on their classification. Air is classified based on the source of the contaminant, from class 1 to class 4.

Here is a Class 3 exhaust shown the minimum distance of 15 feet (5 meters) away from this air handlers outdoor air intake. Class 3 is Air with significant contaminant concentration, significant sensory-irritation intensity, or offensive odor that is suitable for recirculation within the same space. Class 3 air is not suitable for recirculation or transfer to any other space.

Class 3 and Class 4 Air allowable distances to Outdoor Air Intakes

There is a laboratory exhaust system in this building which is classified as Class 4 air, which means its minimum distance to intakes is 30 feet (10 meters). Class 4 Air has highly objectionable fumes, gases, or potentially dangerous particles, bioaerosols, or gases at concentrations high enough to be considered harmful. Class 4 air is not suitable for recirculation or transfer within the space or to any other space.

There is the requirement to maintain at least a 15 foot (5 meter) distance from a drive in queue to any outdoor air intake.

Outdoor Air Intake distance from Outdoor Air Intake Locations

When locating outside air takes its important to consider the possible sources of contaminants from the surroundings. ASHRAE 62.1-2019 4.3 requires an outdoor air quality investigation be conducted and documented. The survey should document any observation of odors, irritants, visible plumes, visible air contaminants, and include description of sources of vehicle exhaust on site and from adjoining properties.

ASHRAE Table 5-1 Air Intake Minimum Separation Distance

This table reflects the minimum distances that an exhaust or contaminant must be in reference to the outdoor air intake. There is an analytical method which can be used as an alternate procedure for determining separation distances between exhaust outlets and outdoor air intakes located in Appendix “B” of the standard.

Outdoor Air Intake Locations per ASHRAE 62.1 Minimum Separation Distances

Just because you maintain these distances doesn’t mean you will avoid entrainment, there is no magic to these distances. Other factors like wind direction and strength, building geometry and the exhaust design could have an adverse effect.

Roof, Landscaped Grade, or Another Surface Directly Below Intake.

If you live where snow is common, then the intake will need to be designed with the distances calculated from the average snow level. This snow average snow depth will be considered the ground level for distance calculations.

Summary

It’s important that air intakes be located safely away from sources of contaminants that could affect the occupant’s health. Outdoor air intakes provide fresh air for building occupants. The location and design of these intakes needs to include protection from contaminants, weather, such as rain, snow, puddling of water, wind-driven rain, and snow.

Outdoor Air Intake and Air Classification

#6 Supply Air Temperature Reset

#5 Demand Control Ventilation

#4 Optimal Start

#3 Shorten HVAC Schedule

#2 Minimum VAV Box Damper Flow Reductions

#1 Wider Dead Bands and Night Setbacks

Rows of Coils

Coil Fins

Right-Handed or Left-Handed Coils

Coil Headers

Coil Circuiting

Coil Air velocity

Coil Velocity and Flow

Water Coil Coatings

Bypass Air

Coil Arrangement

Duct Mounted Coils

Venting and Draining

Coil Selection

CFM = Velocity x Area

Solving for Velocity

ASHRAE 62.1-2019 Air Classifications

According to ASHRAE 62.1 Table 5-1

ASHRAE Table 5-1 Air Intake Minimum Separation Distance

Roof, Landscaped Grade, or Another Surface Directly Below Intake.

Summary

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