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VAV Laboratory Fume Hood Control

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VAV Laboratory Fume Hood Control

In this article, we’ll explore one effective method for managing VAV systems in laboratory settings, focusing on the sequence of operations that ensures a safe and energy-efficient environment.

If you prefer to watch the video of this presentation, then scroll to the bottom.

A common strategy for addressing exhaust and supply requirements while minimizing energy consumption is to implement a variable air volume (VAV) lab control system. This system can be as straightforward as a single exhaust fan connected to two variable-volume fume hoods, or it can scale up to include multiple fans that activate based on laboratory demand. 

VAV Laboratory Fume Hood Exhaust System
VAV Laboratory Fume Hood Exhaust System

No matter the size of the lab, each VAV fume hood is equipped with an exhaust airflow control valve to regulate airflow through the hood. Typically, hoods used for standard research are connected to a manifolded exhaust duct that leads to roof-mounted fans. Additionally, the laboratory space is supplied with fresh air through a duct with a modulating damper to control the air’s volumetric flow.

A VAV lab system is managed to maintain a safe environment by use of the following.

Space Pressurization

Laboratories typically operate under negative pressure to contain fumes and odors. To achieve this, the control system is configured to exhaust more air than is supplied. The amount of exhaust air required is directly related to the Air Changes required, Fume Hood airflow capacity, and or the amount of conditioned supply air needed based on heat gain driven labs.

Chemical Fume Hood Flow

The VAV fume hood is equipped with a fume hood monitor, sash position indicator, controller and an airflow control valve that adjusts the airflow based on the position of the sash. While exhaust velocities vary by application, the use of 100 feet per minute is often used. If you have a 6-foot fume hood with an open sash height of 24 inches, then the volume of air would be 6-feet times 2-feet equals 12 square feet times 100 feet per minute, equals 1,200 CFM. An 18-inch open sash would equal 900 CFM. In a lab that measures 64 feet in length by 32 feet wide with a 10-foot ceiling at least 2,048 CFM would be required to achieve the 6 air changes required for this lab. If you want to learn more on how to calculate air changes per hour see our other video.

Laboratory Fume hoods with Venturi type airflow Valves
Laboratory Fume hoods with Venturi type airflow Valves

Lab Airflow Valves

A VAV laboratory controller maintains negative pressure by dynamically adjusting the fume hood exhaust valves, general airflow exhaust valves, and supply airflow valves in response to real-time conditions.

Fume Hood Exhaust Valves

The controller modulates the fume hood exhaust valves based on the sash position. When a sash is opened, the valve opens further to increase the exhaust airflow, ensuring that fumes are effectively captured and removed.

Laboratory Airflow Valve - Phoenix Style Lab Airflow Valve
Laboratory Airflow Valve

General Airflow Exhaust Valves 

These valves control the overall exhaust from the lab space, beyond just the fume hoods. The controller adjusts these valves to maintain the desired negative pressure in the lab, ensuring that air flows from adjacent areas into the lab, preventing contaminants from escaping. If the fume hoods are not being used, then the General Exhaust valve will increase its airflow to maintain a negative pressure based on the position of the supply valve.

Supply Airflow Valves 

To maintain balance, the controller also modulates the supply airflow valves. As exhaust airflow increases or decreases, the supply airflow is adjusted to ensure that the lab remains at a slightly negative pressure. This ensures that the lab draws in clean air from adjacent spaces, rather than allowing potentially contaminated air to escape the lab.

By coordinating the adjustments of these three types of valves, the VAV laboratory controller effectively maintains a consistent negative pressure, ensuring a safe and controlled lab environment.

Sash Position

As the sash opens, the sash sensor detects the change and signal the fume hood controller to adjust the exhaust airflow control valve to open, ensuring the desired airflow and maintaining a safe hood velocity. When the sash closes, the valve adjusts to a specific level to sustain the required face velocity. As the sash is moved to a new position the controls will respond within seconds to reposition the exhaust airflow control valve to maintain the required face velocity. This requires that the exhaust airflow control valve be able to adjust flow (CFM) from full load to the minimum required. The valves are pressure independent and will maintain the required flow when the overall system pressure fluctuates.

Fume Hood Monitor

The fume hood monitor will indicate the current velocity. There may. be a green light indicating normal operation, and a yellow light when the velocity drops below normal. Once the velocity drops too low or there is a system failure the fume hood monitor will show a red light and produce an audible alarm to alert the room occupants of a potential unsafe condition and to close the sash.

Fume Hood Monitor
Fume Hood Monitor

If the user spills a toxic or hazardous substances within the hood, the user can push the purge button on the hood monitor. This will close the sash to contain the contaminants.

Duct Pressure and Bypass Air

Monitoring duct pressure between chemical fume hoods or other exhaust points ensures the system maintains the appropriate negative pressure. This is to keep the lab space negative, even when VAV hood sashes open suddenly. This pressure monitoring also prevents excessive negative pressure, which could damage the exhaust valves or ductwork.

A crucial aspect of controlling duct pressure is adjusting the capacity of the exhaust fan(s) that draw air from the system. While there are various methods to regulate fan capacity, including variable frequency drives. The most common approach is to use a bypass air plenum with a modulating damper.

The bypass air plenum is located either beneath an inline fan or next to a scroll-style centrifugal fume exhaust fan. It includes a modulating isolation damper that disconnects the fan from the duct system when not in use. When sashes are closed and duct negative pressure increases, the bypass damper allows outside air to flow into the fan. This reduces the amount of air pulled from the exhaust system when hood demand is low. The benefits of this setup include:

Laboratory Exhaust Fan with Bypass Damper control
Laboratory Exhaust Fan with Bypass Damper control

Lab Exhaust Fan

Stable operation of the exhaust fan, ensuring consistent nozzle velocity and plume rise. Exhaust fan stack velocity is crucial in laboratory fume hood exhaust systems because it ensures that hazardous fumes and contaminants are effectively dispersed into the atmosphere, away from building occupants and nearby areas. A sufficient stack velocity creates a high-velocity plume that carries pollutants to a safe height.This minimizes the risk of re-entrainment into the building’s air supply and reducing the exposure of nearby personnel to harmful chemicals. This helps maintain a safe and compliant laboratory environment.

Quick response to changes in duct pressure.

Energy savings, as reduced exhaust from the lab lowers the demand for tempered supply air

The opposite occurs when the sashes begin to open. As the VAV hood valve opens, the duct pressure becomes less negative, and the bypass dampers begin to close. This adjustment draws more air from the lab exhaust system, while the make-up air increases to maintain proper system pressure.

Summary

Lab exhaust systems are essential for ensuring a safe environment in and around laboratory facilities. However, managing chemical fume exhaust, creating high-velocity plumes, and handling 100% outside air can result in significant energy consumption. By implementing a VAV lab system and providing proper training for lab users to close their sashes when not in use, it is possible to maintain a safe environment while also reducing overall energy usage.

VAV Laboratory Fume Hood Control

Construction Estimator

MEP Academy Instructor
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Construction Estimator

Welcome to our article on the exciting field of construction estimating! If you’ve ever wondered what goes into determining the cost and planning of construction projects, you’re in the right place. In this article, we’ll dive into the essentials of becoming a construction estimator, including the educational background you’ll need to get started, the salary you can expect, and the current job market outlook. Whether you’re considering a career change or just curious about the role, stay tuned to learn everything you need to know about this vital profession in the construction industry.

If you prefer to watch the video of this presentation, then scroll to the bottom.

A construction estimator plays a crucial role in the planning and budgeting stages of construction projects. The first thing most candidates want to know is how much does a Construction Cots Estimator make?

Expected Pay

As of May 2023, non-residential construction cost estimators in the United States earn a competitive salary, with the U.S. Bureau of Labor Statistics reporting an annual mean wage of $94,430. This figure reflects the critical role these professionals play in accurately forecasting the costs of large-scale construction projects, ensuring that budgets are realistic and that projects are completed efficiently. With experience and expertise, many estimators can expect to earn well above this average, particularly in regions with high demand for construction services. What does an estimator do every day?

Construction Estimator Job Duties

  • Review project plans, specifications, and drawings to understand the scope of work and project requirements.
  • Calculate the costs of materials, labor, equipment, and other expenses involved in the project. This often involves creating detailed cost estimates and budgets.
  • Prepare and submit detailed bids or proposals to potential clients or contractors. This includes gathering quotes from subcontractors and suppliers.
  • Measure and quantify materials, labor, and equipment needed for the project from blueprints or design documents.
  • Identify potential risks and challenges that could affect the cost or timeline of the project. Propose solutions or contingencies to address these risks.
  • Monitor and manage costs throughout the project lifecycle to ensure that the project remains within budget. This includes analyzing and adjusting estimates as needed.
  • Work closely with project managers, architects, engineers, and other stakeholders to ensure that estimates are accurate and reflect project requirements.
  • Stay updated on current market rates for materials, labor, and equipment to ensure that estimates are competitive and realistic.
  • Maintain detailed records of estimates, bids, and project changes. Prepare reports and documentation for review and approval.
  • Review and analyze contracts and agreements to ensure that they align with the estimates and scope of work.

Estimators need strong analytical skills, attention to detail, and a thorough understanding of construction methods and materials to perform their job effectively. What type of education is required?

Education

For those looking to break into the construction industry as a cost estimator, pursuing an expensive four-year college degree which can range from $30,000 to over $100,000 isn’t the only path to success. Instead, consider enrolling in the MEP Academy Construction Estimator course, which offers a targeted, practical education at a fraction of the cost and time commitment. 

This course can be completed in less than six months for around a thousand dollars. This will provide you with specialized skills that are directly applicable to the HVAC and piping industries. By focusing on the specific knowledge and tools needed for this niche, the course equips you to enter the workforce quickly and efficiently, without the burden of student debt. Additionally, the online, industry-specific training offered by the MEP Academy is designed to meet the current demands of employers, making you job-ready upon completion.

In contrast, a four-year degree often involves general education courses that may not directly contribute to your career as an estimator, extending your time in school and inflating costs. With the construction industry increasingly valuing practical experience and specialized skills, the MEP Academy course offers a streamlined, cost-effective alternative that prepares you for a high-paying, in-demand career in a fraction of the time. What are some of the qualities of a good estimator?

Construction Estimator Qualities

The following are some of the qualities of a good estimator.

Analytical skills: Cost estimators need strong analytical abilities to assess various construction and fabrication methods, identifying the most cost-effective options.

Attention to detail: Precision is crucial for cost estimators, as even minor inaccuracies can significantly impact the overall budget of a construction project.

Mathematical proficiency: Excellent math skills are essential for cost estimators to accurately calculate labor, material, and equipment costs for construction projects. While mathematical proficiency is important for cost estimators, the widespread adoption of advanced estimating software has significantly reduced the need for manual calculations. These tools automate many of the complex mathematical processes, allowing estimators to focus more on analysis and decision-making rather than number crunching.

Time management: Effective time management is vital for cost estimators, who must plan ahead and work efficiently to meet strict deadlines.

Writing skills: Strong writing skills are necessary for cost estimators to craft detailed proposals that aid upper tiered contractors or owners in making informed contractor selection decisions.

What is the current job prospect for Construction estimator?

Job Outlook

The job outlook for cost estimators is promising, with the U.S. Bureau of Labor Statistics projecting about 18,000 job openings each year, on average, over the next decade. The steady demand is driven by the ongoing need for accurate cost assessments in construction and manufacturing, as businesses strive to manage expenses and improve efficiency.

The profession offers strong opportunities for those with the right skills. As industries continue to grow and evolve, they require precise cost estimation to ensure project success. These figures are inclusive of other categories besides construction cost estimators. The construction industry is one of the largest contributing factors at about 51% of those employed as cost estimators.

Should you Oversize your Air Conditioner

MEP Academy Instructor
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Should you Oversize your Air Conditioner

The question customers often ask, is should I oversize my air conditioner? 

We’re going to show you the difference between an air conditioner that is correctly sized and one that is oversized. 

If you prefer to watch the video of this presentation, then scroll to the bottom.

Customers often think that a larger unit will cool their space more quickly, leading to immediate comfort. While it is true that an oversized unit will cool the air faster, it won’t run long enough to evenly distribute the cool air and effectively remove humidity, resulting in discomfort. 

A Correctly Sized AC Unit versus and Oversized Air Conditioner

Comparison of Correctly sized to Oversized AC

Here we have two air conditioners, one that is sized correctly at 2-1/2 tons, and another that is oversized at 5 tons. When the thermostat calls for cooling, they both turn on. While the larger unit has the capacity to cool twice as fast, the correctly sized unit will run longer to satisfy the space. You may think this is where the advantage of oversizing makes sense by having a larger unit run for less time. We’ll show you why this is a bad idea.

We have added blue colored dots to represent the moisture level and what happens to the humidity or moisture in the conditioned space when the air conditioner is running. When the air conditioner is running, we can see that moisture is being removed from the air as water begins dripping out of the condensate drain line. The drain line is often out of sight of the occupant who is unaware of its existence unless it becomes clogged and causes a problem.

The oversized unit cools the space so quickly that the air conditioner shuts off before removing enough moisture. We can see the correctly sized unit keeps running while the larger unit has shutoff. The smaller unit runs longer, allowing more time for the moisture in the air to meet the cooling coil and condense out as water. The longer the unit runs the more moisture that is removed from the air, making the air less humid and stuffy.

There are many reasons why you shouldn’t Oversize your Air conditioner

Oversizing an air conditioner can lead to several issues that can negatively impact both the system’s performance and the comfort of the space being cooled. Here are some key reasons to avoid oversizing an air conditioner:

Short Cycling

An oversized air conditioner will cool the space too quickly, causing the system to cycle on and off frequently. This short cycling leads to increased wear and tear on the unit, reducing its lifespan and increasing maintenance costs.

Inadequate Humidity Control 

Air conditioners not only cool the air but also remove humidity or moisture. The air contains moisture that isn’t visible to the human eye. Proof of this moisture becomes visible on a hot day with a glass full of ice water. The moisture in the air condenses on the cool outer surface of the glass.

This moisture comes from the surrounding air and not from the ice in the glass. An oversized unit will cool the air so rapidly that it won’t run long enough to remove this moisture or dehumidify the space effectively, leading to higher indoor humidity levels. This can result in a clammy, uncomfortable environment and promote the growth of mold and mildew.

Why is removing moisture from the air so important?

The human body cools itself primarily through the process of sweating and subsequent evaporation of sweat from the skin’s surface. High humidity levels in the environment can slow down the evaporation process because the air is already saturated with moisture. This makes it harder for sweat to evaporate, reducing the cooling efficiency.

Increased Energy Consumption

Frequent cycling and running at a higher capacity than needed will consume more energy, leading to higher utility bills. An oversized unit is less energy-efficient compared to a properly sized one.

Uneven Cooling

Oversized air conditioners can create hot and cold spots within the space. The rapid cooling cycle may not allow the conditioned air to be distributed evenly, leading to some areas being too cold while others remain warm.

Higher Initial Cost

Larger units are more expensive to purchase and install. By properly sizing the air conditioner, you can avoid unnecessary costs and ensure you are investing in the right equipment for your needs.

Environmental Impact

Higher energy consumption results in increased greenhouse gas emissions, which contribute to environmental degradation. Properly sizing an air conditioner helps reduce the carbon footprint of the building.

To determine the correct size for an air conditioner, a detailed load calculation should be performed. Consider factors such as the size of the space, insulation levels, number of occupants, and local climate. This ensures that the system operates efficiently, provides adequate comfort, and maintains a healthy indoor environment.

Should you Oversize your Air Conditioner

Boiler Vent Categories

MEP Academy Instructor
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Boiler Vent Categories

All certified boilers have a uniform test procedure to evaluate the vent system. The vent categories are determined to be either under a positive or negative pressure. They are also categorized by their possibility to condense water from the products of combustion. The ability of the products of combustion to condense into a liquid is related to the efficiency of the boiler. As the efficiency of the boiler goes up, the temperature of flue gases becomes cooler, increasing the changes of condensation.

If you prefer to watch the video of this presentation, then scroll to the bottom of the page.

Boiler Flue Vent Chart

Here we put together a simple vent chart to help you envision the requirements.

Boiler Flue Category Chart - Type I, II, III, and IV, Negative, Positive, Condensing and Non-Condensing Boilers
Boiler Flue Category Chart – Type I, II, III, and IV, Negative, Positive, Condensing and Non-Condensing Boilers

Category I Vents

The most used vent category is category One, which is where you might find the use of Type “B” vent materials. This is considered a non-condensing, negative pressure or negative draft system. Since the products of combustion are hot enough to stay above the dew point temperature there should be no condensate.

Type B Vents

Type B vents are designed specifically for non-condensing appliances that produce high-temperature flue gases not exceeding 400 degrees Fahrenheit. These vents operate under negative pressure, relying on natural draft to expel combustion gases. They are usually used with gas appliances with draft hoods.

Category II Vents

Category II vents also operates under a negative pressure like category I, but the flue gases are much cooler than a category one vent. The cooler products of combustion make the gases susceptible to condensation, so they’re located under the condensing side of the chart. Since condensation is possible, the material of the flue must resist the corrosive nature caused by the presence of moisture.

Category III Vents

Category III vents are considered positive pressure because they use a power exhauster for combustion and venting. Positive pressure vents create a unique risk because they can push combustion gases, including potentially harmful carbon monoxide, into the occupied or living space if there are leaks in the venting system.

Unlike negative pressure vents, which rely on natural draft to pull gases out, positive pressure systems actively force gases through the vent, increasing the likelihood of leakage if the venting system is not properly sealed and maintained. Since the flue gas temperature is high enough to avoid condensation, category three vents are in the non-condensing section of the chart.

When replacing a non-condensing boiler with a condensing boiler, several critical considerations must be made regarding the existing flue system. Condensing boilers operate differently than non-condensing boilers, primarily because they extract more heat from the exhaust gases, causing the gases to cool and condense before exiting the flue. The cooler temperatures my cause water to condense in the vent. 

Category IV Vents

Category IV also uses a forced draft positive pressure vent, but since the flue gas temperatures can reach temperatures below the dewpoint they’re classified as condensing type. The flue will also require that the material resist corrosion caused by the presence of moisture.

Direct Venting

Specialized venting systems, such as direct venting, use sealed combustion to draw air from outside and expel exhaust gases directly outdoors, enhancing efficiency and safety. This system typically consists of two separate pipes for intake and exhaust. Direct vent systems improve efficiency by not using indoor air for combustion and minimize the risk of indoor air contamination. 

In addition to enhancing efficiency and safety, direct venting systems offer several other benefits. They reduce the risk of back drafting, which can lead to the infiltration of harmful combustion gases like carbon monoxide into the living space. Direct venting also allows for more flexible installation options, as these systems can be vented horizontally or vertically, making them suitable for a variety of building layouts.

Furthermore, by using outdoor air for combustion, direct vent systems help maintain better indoor air quality and reduce drafts, contributing to a more comfortable indoor environment. Lastly, these systems are generally quieter and more aesthetically pleasing, with fewer visible exterior components.

Flue Material

A category One vent with a non-condensing boiler flue typically use double-wall type “B” vent materials. The double-wall helps maintain the flue temperature above the condensing temperature.

Condensing Boiler Flues must be made from materials that can resist acidic condensate and moisture, such as PVC, CPVC, Polypropylene, or Stainless Steel. Check the boiler manufacturers data to determine the required material. If converting from non-condensing boilers to condensing boilers then the existing metal flues may corrode due to the acidic nature of the condensate produced by condensing boilers. 

Condensing boilers often require smaller flue diameters due to lower exhaust gas temperatures and higher efficiency. The existing non-condensing flue size may need to be reduced to maintain proper draft.

Condensing boilers produce significant amounts of condensate that must be safely drained away. The condensate is acidic and may require neutralization before being discharged into the drainage system to prevent damage to plumbing and the environment.

Summary

When replacing a non-condensing boiler with a condensing boiler, it is essential to thoroughly assess and potentially modify the existing flue system to accommodate the specific requirements of the condensing boiler. This includes using appropriate materials, ensuring proper sizing and configuration, managing condensate, complying with codes and regulations, and potentially insulating and sealing the flue system.

Boiler Flue Categories Positive and Negative, Condensing and Non-Condensing
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