HVAC Ductwork Design

Have you ever wondered how HVAC ductwork is designed?

There are actually six methods for designing low, medium, and high-pressure HVAC systems:

  • Equal Friction Method
  • Static Regain Method
  • T-Method
  • Extended Plenum Method
  • Velocity Reduction Method
  • Constant Velocity Method

The most commonly used method is the Equal Friction Method. This method is typically used for low-pressure systems found in commercial buildings and is distinguishable by the fact that the pressure loss in the duct system per every 100 feet of duct is designed to be the same for the entire system. A well-designed system is typically designed to have an average friction rate of about 0.1” of water column per 100 ft. of duct length.

After the desired friction rate and cubic feet per minute (CFM) of airflow is determined for a system, an air duct calculator is used to properly size the ductwork that can support these requirements. The major disadvantage for the Equal Friction Method is that there is no provision for equalizing pressure drops in duct branches unless the duct layout is symmetrical.

Air Duct calculator for HVAC ductwork design

Why Is Duct Design Important?

HVAC systems are comparable to cardiovascular systems; rooftop or air handling units are like the heart, and ductwork is similar to the body’s arteries and veins. Taking this example further, if arteries or veins are too big or too small, issues (such as high blood pressure or a stroke) can start to arise.

Similarly, if ductwork is incorrectly sized, vital issues to the units can arise. Having ductwork that is too large can lead to a low CFM (Cubic Feet per Minute) of air flow in a given space, which could cause the unit to run longer in order to properly heat or cool a space. Inversely, having ductwork that is too small can lead to high velocities and static pressures, creating a loud environment and putting unnecessary stress on the system.

Either direction you go — too big or too small — the system’s life span and energy expenses are both negatively impacted by having incorrectly sized ductwork. Having properly sized ductwork can lead to lower energy expenses, longer unit lifespans, and comfortable environments.

How Does a Melink Technician Verify Ductwork Installation?

While on site performing a Test & Balance, Melink technicians are trained to question if duct systems are installed correctly in the situation where proper airflow is unattainable, unless unit total speeds are further adjusted to deviate from the design.

When occurrences such as this happen, Melink technicians can reference the mechanical plans, a duct design table, or an air duct calculator to verify what the proper duct size should be for a given amount of air flow and compare that with the installed ductwork.

A close up of a device

Description automatically generated
This picture represents how air moves in ducts. Areas that are red have high static pressure, and areas that are green are showing high velocity.

Melink technicians are also trained to look for and identify areas of dynamic losses, which are portions of ductwork that have high friction rates and high static pressure.

Examples of dynamic losses due to installation errors are incorrect duct take offs, failure to include duct turning vanes, long runs of flex duct, or crimped flex duct. These issues, if not corrected, can shorten the lifespan of the unit and cost the owner upwards of $1,200 per year extra in energy expenses. Any duct design discrepancies found in a Melink Test & Balance will be reported and photographed for the customer to reference.


Contributed by Andy Austin, Jeremy Neff & Anna Rusconi

COVID-19 and Building Ventilation

Keeping your HVAC breathing through the Covid-19 pandemic.

As the United States continues the fight against COVID-19 and many reopened businesses are concerned about indoor air quality, new requirements are being implemented for the public’s safety.

Recently, New York allowed for the reopening of shopping malls but with a mandate from Gov. Andrew Cuomo: Update HVAC filters with at least a MERV-11 rating to capture the potentially airborne coronavirus particles. Likewise, Colorado’s Denver Public Schools unanimously approved Denver schools to get ventilation upgrades to help stem the spread of coronavirus. So what do these guidelines mean, and could other states follow these policies?

HVAC Filters

Minimum Efficiency Reporting Value (MERV) is used to measure the effectiveness of air filters on a scale of 1 to 16. The higher the MERV rating, the greater the filtration, i.e. the smaller the particles it can catch. The Centers for Disease Control and Prevention (CDC) recommends to improve central air filtration to the MERV-13 level (or the highest compatible with the filter rack) and to seal edges of the filter to limit bypass.

MERV filter rating for HVAC systems
Model of MERV filter ratings. (Source)

However, updating an HVAC system’s air filters may not be as simple as it sounds. For instance, a common factor that will get overlooked is that most HVAC systems that were designed for lower MERV filters (likely most of them) will need to be rebalanced for the new filters. The higher the MERV rating, the better the filtration but also the higher the static pressure (or resistance) that the fan must work against, resulting in a drop in airflow. The reduced airflow could cause comfort problems and even frozen coils. To prevent these issues, the airflow will need to be measured with the new filters installed, and then the fan speed will need to be increased to achieve the designed airflow.

Yet this is still not a “one size fits all” solution for all. Many HVAC units cannot handle the higher-rated filters. Using a filter with a higher MERV rating may cause the motor to burn out. This is why it is important you have a trained technician review your unit before making any changes.

Other Building Ventilation Recommendations

In addition to replacing filters, ASHRAE recommends the following actions, with the ultimate goal being consistent and frequent air changes:

  • Increase outdoor air ventilation (use caution in highly polluted areas); with a lower population in the building, this increases the effective ventilation per person.
  • Open minimum outdoor air dampers, as high as 100%, thus eliminating recirculation. (During mild weather, thermal comfort or humidity within a facility normally wouldn’t be affected. During extreme weather, this clearly becomes more difficult to control.)
  • Consider portable room air cleaners with HEPA filters.
  • Consider Ultraviolet Germicidal Irradiation (UVGI), protecting occupants from radiation, which is particularly in high-risk spaces such as waiting rooms, prisons and shelters.

Developing Solutions

While the experts are recommending the above items, they are not mandatory across the country. States’ policies vary. Not to mention that COVID-19 research is still developing.

COVID-19 changing building ventilation

The result, in the near term, is likely to be a patchwork — some commercial buildings, schools, colleges, and other facilities will make investments, while others will not. One example of an organization making the investment to fight COVID-19 is KIPP DC, a publicly funded and privately operated network of seven school campuses with 1,200 employees and 7,000 students. KIPP DC has taken huge measures, working to find the ideal system optimized to filter the coronavirus.

KIPP DC’s Coronavirus Filter System (Source)

Hire Melink to Help

Overwhelmed and not sure where to begin? Melink employs a 100% self-performing, NEBB-Certified national network of Test and Balance (T&B) HVAC technicians that can quickly deploy to assess mechanical systems, verify airflow rates in accordance with ASHRAE 62.1 standards, and perform any traditional T&B work. 

We have multiple, long-standing relationships with some of the largest national restaurant, retail, hotel, and supermarket chains. These relationships began because those partners liked the idea of having just one third-party company to coordinate. Melink handles all their properties by objectively verifying that the HVAC systems were installed and are working as expected.

We are here to help you navigate the ever-changing recommendations and regulations of the pandemic. Let us help you keep your doors open while helping protect your employees, customers, and equipment. Contact us.

Indoor Dew Point: Maintaining Thermal Comfort, Avoiding Building Damage

Condensation, moisture absorption and, subsequently, mold or organic growth are often a result of high indoor dew point combined with cool surface temperatures. For example, if a facility’s indoor dew point is above 60oF, it is possible that moisture will begin to condense on cool surfaces like ductwork, chilled water supply lines, windows, or refrigeration systems. This collection of moisture can cause damage to the building, as well as to merchandise. It can even promote organic growth over time.

In addition to the risk of moisture accumulation, ASHRAE recommends maintaining a dew point below 62 oF to meet thermal comfort for approximately 80% of occupants; a dew point of 45 oF is recommended to maintain summertime humidity comfort levels.

Monitoring Dew Point

Consider this: You are a kid in a candy store with a plethora of delicious options in front of you. You sort through the store and boil your decision down to two candy bars.

Option A: The tried and true milk chocolate bar. Nothing fancy but classically delicious.

Option B: Fluffy nougat topped with caramel and peanuts, coated in milk chocolate. An exciting snack bursting with flavor.

Did you choose Option A or Option B?

If I had to guess, you chose Option B as it gives you more variety with your purchase! Now, what if I told you that the decision you just made also can apply to thermal HVAC design and dew point monitoring principals?

Option A: A design principal of maintaining 60% relative humidity (RH).

Option B: A design principal of maintaining a 60oF dew point.

Both are similar and help maintain a healthy building, but maintaining a 60oF dew point (Option B) is inherently better and offers a more reliable risk indicator. Using 60% RH as an indicator (Option A) is unreliable as it creates needless concern when air temperature is cool. In the example below, you can see that the amount of water vapor in the air remains the same while relative humidity concentration varies depending on the temperature of the air.

Conversely, a facility manager or building owner may have a false sense of security when indoor air temperature is above normal levels because relative humidity will decrease as air temperature rises. These reasons are why dew point should be used as a threshold of concern. Dew point will not only factor in moisture content and temperature of the air but also provides a risk indicator for condensation and moisture absorption, which should be a facility manager’s primary concern.

Using Indoor Dew Point as a Risk Indicator

If you are already using indoor dew point as a risk indicator for indoor moisture activity, then continue to do so! Specifically, look to ensure that indoor dew point remains below 60 oF during cooling operations to reduce the risk of moisture absorption, condensation, and organic growth.

If you are not using indoor dew point as your risk indicator, now is the time to do so! You could be surprised to learn that measuring relative humidity alone may not be keeping your facility safe.

If you are already noticing signs of moisture accumulation, mold or organic growth, then ASHRAE recommends implementing the following HVAC factors to reduce your risk:

  • Ensure that ventilated air is dehumidified to a dew point below the indoor dew point when the building is in cooling mode.
  • Ensure that all condensation inside HVAC components is being properly drained.
  • Ensure that indoor surfaces are not cooled to temperatures below indoor dew point during occupied and unoccupied modes.
  • Keep indoor dew point low enough to ensure that condensation does not occur on cool surfaces of HVAC components, building materials, or building furnishings.
  • Ensure that humidifiers are sized, installed, and controlled properly to avoid the risk of overloading indoor air with humidity.
  • Ensure that cool HVAC and plumbing components are properly insulated to keep their surfaces about 10 oF above indoor dew point.

These simple steps — in addition to proper HVAC ventilation, indoor air monitoring, indoor air verification, and keeping an eye on seasonal changes — can help ensure that your facility is operating in a safe manner while reducing risk of mechanical damage, moisture accumulation, or organic growth.

If you would like to learn more about ways in which your indoor air environments can be improved, please reach out to us. Please complete our contact form or contact us by phone at (513) 965-7300.

COVID-19 Closures: Mitigating Damage to Unoccupied Buildings

As states across the U.S. are working to flatten the curve, many businesses are impacted by COVID-19 closures as a result of “stay at home” or “shelter in place” orders to limit human interaction and prevent the virus’s spread. Additionally, many companies across the country have opted to temporarily close facilities to prevent employees from contracting the disease. With these shutdowns, it can become increasingly difficult to determine the condition of a facility and repair any issues that could be developing while the facility is unoccupied.

COVID-19 closures of restaurants

Damage to Unoccupied Buildings

Consider these scenarios that could arise in an unoccupied facility…

  • A building in the coastal region may experience high humidity that is going unnoticed, which can in turn lead to mold growth. Imagine if the facility is a retail store; the end-result might mean thousands of dollars of damaged, unsalvageable clothing merchandise.
  • If indoor moisture levels drop too low — perhaps in a cooler climate that is shifting from winter to spring temps — it could lead to wood warping. For instance, the frames of wood windows can shrink in size, making them more difficult to open and potentially creating gaps that let in more cold, dry air.
  • Low indoor moisture can also lead to peeling or separated wallpaper, or cracked paint on plaster walls. What would you do if you come back to your facility, only to realize you need to bring in professional painting or remodeling services?
  • Think about a restaurant or bar. There may be hundreds (or thousands) of dollars of liquor or wine in stock, going untouched through the COVID-19 crisis. Corked bottles of wine are not exempt from the effects of dry indoor air. Extremely low humidity levels can slowly chip away at a cork, leaving room for air to get into the bottle and ruin the flavor. The ideal humidity level for wine storage is 60%.
  • Another thought for a restaurant facility: A humid environment allows mold growth to fester. The COVID-19 shutdowns came on suddenly for many facilities. Did kitchen staff have adequate time to scrub walk-ins, pots, and pans? Were grease traps thoroughly degreased? These are potential breeding grounds for mold during non-occupation.
  • Contemplate multi-purpose facilities, such as an apartment complex with retail or dining space on the first floor. Completely shutting down HVAC airflow to the unoccupied businesses could lead to uneven air flow and temperature throughout the larger building.

The bottom line: Scenarios like the ones above will go unnoticed and unrepaired until employees return to the facility to find the damage caused by an unoccupied month.

Preventing Facility Damage During COVID-19 Closures

While these issues may seem frightful, thankfully many state governments have kept issues like this in mind when mandating shelter-in-place orders. Seeing the value and necessity of essential services, many states are allowing skilled trades such as HVAC technicians to continue working. During quarantine, let these technicians be the eyes and ears at the facility to ensure that, when business returns, critical issues didn’t develop, delaying reopening.

In addition, this downtime can also be the ideal occasion to have technicians visit the facility to address any known issues or to perform preventive maintenance. Maybe there is a repair the facility manager has been putting off because its fix requires closing a typically busy corridor or lobby area. By addressing this work now while the facility is shut down, managers can limit future downtime, employee inconvenience, and lost profit.

And as a preventative measure for the duration of this closure or in preparation of future closures, consider installing sensors to remotely monitor a facility’s indoor air quality levels through relative humidity, temperature, building pressure, and CO2 checks. A system like Melink Corporation’s PositiV® building health monitor can remotely track and trend building health, plus send alerts to the facility owner or manager when the system detects measurements outside its set parameters. While a facility may not have this in place to combat the current COVID-19 closures, it can be installed now to prepare for future unplanned closures or even a vacation (Facility managers need a break at some point, right?!). 

How Do Seasonal Changes Affect Building Health?

As we transition from dry, cool winter months to hot, humid summer months, you may be saying to yourself, “Woohoo! Bring on the heat!” However, seasonal changes can affect building health. Specifically, the summer season can present major problems for facility managers and building owners as their buildings’ HVAC systems struggle to keep up with increasing cooling loads and extremely humid outdoor air.

Just as spring plant life sprouts, HVAC mechanical issues can pop up with warmer temperatures. Poor indoor conditions such as high indoor relative humidity, negative building pressure, CO2 buildup, or drastic temperature fluctuations are just a few examples.

Staying ahead of these issues before they become noticeable, costly problems is crucial when considering the overall health of your building and its HVAC systems.

Humidity: A Common Seasonal Issue

At various facilities, a common issue that comes with changing seasons is humidity. Specifically, humidity can be difficult to maintain at a comfortable level.

Condensation on building window, a seasonal building health issue.
Condensation in office building

In the winter, the heating mode on air handling equipment can heat or evaporate the existing moisture in the air to reduce the overall relative humidity as outdoor air is brought into the building. However, in the summer, the opposite occurs: the air handling equipment cools the building space and doesn’t heat or evaporate the moisture out of incoming air. This combination of high relative humidity and indoor dew point ultimately creates conditions that promote condensation or organic growth within the facility.

A Year-Round Solution for Indoor Building Health

The most cost-effective solution to verifying and ensuring long-term indoor building health is with a sensor capable of measuring key building health metrics like differential pressure, relative humidity, dew point, temperature, and CO2.

Components of building health

By gathering data on these building health metrics, the facility manager, operator, and/or building owner can quickly verify on-site conditions in real-time, while also gaining peace of mind in knowing their buildings are meeting engineering specifications per design as seasons change. In addition to these benefits, sensors’ data gathering gives users the ability to track and trend building health over a long-term period.

Using Data to Plan for Seasonal Building Health Changes

Getting and staying ahead of maintenance doesn’t need to start with expensive truck rolls and frequent site visits. Instead, sensor solutions provide an inexpensive, effective avenue to implement a proactive mindset. The collected data can be aggregated to an easy-to-use online portal capable of summarizing, visualizing, and diagnosing issues on site, while also granting users the ability to trend and predict HVAC performance for a lasting solution.

Get ahead of the changing seasons by verifying your building is healthy today!

We are less than 12 months from the R-22 refrigerant phase-out: How can companies prepare?

What is R-22?

R-22 is an HCFC (Hydrochlorofluorocarbon) refrigerant found in older commercial and residential HVAC equipment, such as RTUs (roof top units), split systems and other equipment.  R-22 and other HCFC refrigerants are known to deplete the Earth’s protective ozone layer and contribute to harmful climate change.

The US has slowly been phasing out the use of R-22 per the following phase-out schedule:

  • 1/1/2010: The US government banned the use of R-22 in new HVAC equipment.
  • 1/1/2015: The US government bans the production and import of all R-22
  • 1/1/2020: The US government will ban the use of all R-22 (with a few exceptions).  This will be the end of the road for R-22 use in the US.

NREL (National Renewable Energy Laboratory) estimates 40 million commercial RTUs (roof top units) were installed in the US, in the decade prior to 2010.  The US Department of Energy also estimates that are at least 1.6 million old, low-efficiency RTUs in operation in the US.  This means there is a huge tidal wave of R-22 equipment in operation that will need to be replaced in the very near future.

How does the 2020 ban affect me?  R-22 costs have skyrocketed and are already more than 4X the cost/lb. of R410A. Older R-22 units have much lower EER ratings and are as much as 50% less efficient than current-day high-efficiency units.  In most cases, older R-22 RTUs cannot be converted to R410A refrigerant, and the older units will need to be replaced with a new, more energy efficient, more environmentally friendly RTUs.  It is already cost prohibitive to repair older R22 units, and the “fix-on-fail”, emergency replacement philosophy will be MUCH more expensive than a pro-active roof-sweep or planned equipment replacement program.

How can I best prepare for the phase-out, and where should I start?  I recommend companies start with an HVAC inventory of their older equipment, in addition to a detailed survey of all their facilities to verify the age and condition of all HVAC equipment, including newer and older HVAC equipment.  I also recommend involving a national or regional HVAC installation partner, and an independent, national testing, balancing and commissioning partner such as Melink Corporation to provide the unit data and a complete assessment of the entire mechanical system.  The survey should include duct-work inspections, inspection of the RTUs and exhaust fans.  Additionally, air-flow measurements should be recorded to verify proper building airflows and identify existing air-balance issues.  If the entire HVAC system is not inspected, the building will often continue to have comfort problems and building balance issues, even after the new equipment is installed.  The positive effects of the new, energy efficient HVAC equipment will not be fully realized, resulting in a lower-than-expected ROI.

  • For further information on HVAC surveys and other custom scopes of work, please e-mail [email protected] or call us at 513.965.7300.

A Balancing Act: Air Balance is an important part of HVAC maintenance

When it comes to HVAC, no news is good news for restaurant facility managers. When you start hearing chatter about the building being hot and humid, drafty, smoky or uncomfortable, you know a problem has already taken root. It’s a lot like a piano being out of tune. In addition to unhappy customers and employees, these comfort issues typically are indicators of energy inefficiency within a system. So, what can facility managers do to prevent comfort and energy threats?

Identifying Common Problems

“Facility managers need to be trained on air balance and push it to their service contractors,” recommends Jeff Dover, resource manager at RFMA.

A good place to start is to gain a foundational understanding of building pressure and common HVAC deficiencies along with following seven easy steps to bring your restaurant back into tune. Most importantly, learn how to look for negative building pressure. Remember, the goal is to stay slightly positive in building pressure.

There are three methods to identify negative building pressure. The first and most reactive method is to monitor signals that your building is negative. These signs are hot/cold spots, entry doors that are hard to open, poor smoke capture, humidity, condensation dripping from diffusers and drafts.

Second, you can measure the building pressure yourself or with the help of your service contractor by using a pressure reading tool such as an anemometer to get a ballpark pressure reading. The third and most accurate method is to hire an air balance firm to check the facility’s building balance once a year. If comfort-related issues or a negative building pressure reading are observed, then an air balance needs to be scheduled.

Investigating the Cause

What causes a building to become negative or unbalanced? The usual offenders are equipment deficiencies, improper preventative maintenance programs, and adjustment errors such as kitchen staff fiddling with thermostats or service contractors opening or closing dampers.

 Here are 10 example deficiencies you or your service contractors should be on the lookout for:

  1. Exhaust fans in poor condition
  1. Supply air leaking above ceiling
  1. OA dampers improperly installed
  1. Exhaust fans not sealed to curb or hinged correctly
  1. Dirty compartment/coil in the RTU
  1. Tops of diffuser not insulated
  1. Filters improperly sized for hoods
  1. MUA not operating properly
  1. Dirty indoor/outdoor filters
  1. Worn/broken belts

7 Steps to HVAC Balance

Once you’re ready to bring a facility back into tune, there are seven easy steps to complete. These steps may be completed by the facility manager alone, but are more likely in partnership with a service contractor. To get started, pull out the facility’s previous balance report to use as a base line for data.

One Principal Engineer at a hamburger fast food chain overseeing thousands of locations explains how her team uses the air balance report to get started with troubleshooting comfort issues.

“The reports really are my first line of defense when someone says ‘Hey, my store is cold/hot/humid,’ ” she points out. “The first thing I do is pull out the T&B report and see what it says. I look at the punch list and ask was anything wrong? Not fixed? It helps when I have to remotely assess or diagnose problems.”

Whether the previous air balance report has been reviewed or not, proceed to the following steps:

  1. Ask the onsite restaurant managers what the complaints are from employees and customers.
  1. Turn on all HVAC equipment.
    • Verify thermostats are set to “FAN ON”
  1. Check building pressure with the flame test in different areas around the restaurant (Figure 3)
  1. Observe smoke capture
    • Is the hood in the correct overhang position?
    • Are there drafts along the cook line?
  1. Check for common comfort issues (hot/cold spots, entry doors that are hard to open, poor smoke capture, humidity, condensation dripping from diffusers and drafts).
  1. Inspect the equipment.
    • Are the filters clean?
    • Are the belts in good condition?
    • Are the exhaust fan wheels clean?
  1. Determine an intervention plan.
    • If some preventative maintenance actions and/or repairs need to happen, start with the service contractor.
    • If equipment is inoperable, have it repaired or replaced.
    1. If the preventative maintenance actions are in order and the problems persist, call in a certified air balance company that has experience with restaurants like yours.
Facility managers need to trust that their service contractors will notify them of airflow-related issues. Those technicians are out on the roofs and looking at the HVAC system components more than anyone else. If the restaurant has negative pressure or other out-of-tune symptoms, the service contractor needs to inform the facility manager right away. After all, you want your customers and employees to continue singing your praises.