Roof top HVAC fans

Commercial Building Pressurization – Air Pressure

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Why Building Pressurization Matters

In commercial construction, one often overlooked aspect of planning and design is keeping a building in a homeostatic state in terms to air pressurization. The reason for this is simply that, there are a lot of variables that can affect a building’s air pressure that can not be accounted for.

There exists many unaccounted for variables that affect a buildings air pressure which can cause it to function much differently than the way it was originally designed or engineered. Abnormal foot traffic patterns, causing doors to be opened more than anticipated is one of the more obvious ways. Natural degradation of building materials and/or poorly functioning HVAC systems is another; albeit this may take years to be noticible. Even something as simple as not changing air filters in the HVAC blowers can affect the pressurization of a building. In any case, the inability to create or maintain a homeostatic building pressurization can cause a multitude of issues.

Poor Building Air Pressurization = Poor Air Quality

Most buildings attempt to maintain an environment of positive air pressure. In short, this means there is greater or “higher” pressure inside the building than that of the outside atmospheric resting pressure. This serves a few basic functions. It ensures that dust, dirt and debris introduced into a building is “pushed” back out once a door or window is opened.  You probably experience this when you enter a commercial building.  In most commercial buildings, when the automatic door opens you typically feel a rush of air exiting the building. That air can be likened to deflating a balloon – the pressure in the balloon seeks to deflate to an area of lower pressure – so the balloon air rushes out.

This air moving into or out-of a building is due to the pressure differential.  If the air pressure in the building is greater than the air pressure outdoors, it is called a “positive pressure room” or “positive air pressure building.” Conversely, if the pressure inside the building is less than the pressure outdoors, the room or building is said to have “negative pressure.”  Generally it is not desirable to have negative pressure inside a building.  The problem with negative pressure is that once a door or window is opened – any exterior air is permitted to enter the building. That unfiltered air brings with it pollen, dust, dirt, biological and chemical particulates, etc. These particles entering the building and affect the people working in the building and the general cleanliness of the building.

Filtration For Cleaner Air

Keeping the air fresh in a positive pressure building requires precise engineering.  To keep a building pressurized requires air to be drawn into the building to create the positive pressure.  Since it is not being pulled from undesirable sources like unfiltered air via doors and windows – it must be pulled from an outside source across a filtration system.

HVAC systems pull air from a fresh air duct and through various types of filters. The more fine the filter media the more force required to pull the air across it.  So the more robust the HVAC system will need to be.  This is like sucking a milkshake through a straw with a tiny diameter. Now, let’s imagine a person sucking the same milkshake through a very large straw. Same concept – more suction/blowing power is needed to pull more air through more filters or finer filters.

And how tight or leaky a building is will determine the amount of air per cubic foot per minute to inflate the building envelop (balloon). Some buildings require as little as 45 CFM per 1000 SqFt. Other, more drafty or leaky buildings may require up to 300 CFM. The amount of air needed to positively pressurize and maintain pressurization will initially affect the  design of the building HVAC system, and after the building is completed, the energy costs.  It is much better to seal up air leaks in a building than to use larger fans to ‘push’ more air into a leaky building to maintain a positive pressure.

Negative Pressure Areas

Even in the most strict of positive pressure room and building environments you will want areas of negative pressure. These include maintenance closets, bathrooms, food prep areas, areas where chemicals are used, etc. In these areas, it is important to create negative room or area pressure so the fumes exit these areas quickly.  To create they localized areas of negative pressure exhaust fans can be used very effectively.  Once installed they will function to relive the area of polluted air, and at the same time, allow an equal volume of clean air to constantly flow into the area.

It is important from an engineering perspective to refill the area of negative pressure with an equal volume of clean air. This air is called “make up air” – or “air that makes up for the deficit of air created by the exhaust.” The overall building HVAC system must be engineered and calibrated to account for these deliberate breeches in positive air pressurization.

Monitoring results

Because there are areas of positive and negative pressure inside a building it is not possible to measure “building pressure” at any one spot.  Different rooms and areas have different pressures – some positive and some negative.  It is much more important to think of local pressure.  In a hospital, for example, it might be important to have negative pressure in patient’s rooms but positive pressure in lobby areas.  It is critical, in fact even mandated by federal laws and local codes, to have negative pressure in areas of nuclear medicine.  The system of maintaining positive and negative air pressure is a very complex process, more art than science in many cases.  However, it is an important concept to understand. Just because a building “feels” like it has positive air pressure in no way means it is acting the way it should. This is where it is critical to ensure absolute certainty that a each area of a building’s air pressurization system is functioning properly. in fact, if it is not working properly – it can cost hundreds or even hundreds of thousands of dollars in operating costs, depending on the size of the building.

Simple yet effective systems exist that can either be integrated with existing building management and control systems and/or act as standalone monitoring systems for room air pressure. Some of these systems are capable of monitoring both negative and positive air pressure and in multiple rooms simultaneously. Even further, some systems allow for monitoring of temperature and humidity – both of which are complimentary variables in overall environmentally controlled rooms and especially in positive and negative air pressure rooms.

Installing many of these systems requires little or no technical experience and can be set up and running out of the box in a few minutes. The advantage of using some of the more reliable systems on the market is the ability to alerting one or more building maintenance personnel of issues before they are in a “no turning back” scenario. In such systems, authorized building personnel can receive alerts via test/SMS messaging, email alerts, and even phone calls. In essence, if there is too little pressure in a controlled environment, it means the company is spending more money in wasted energy to maintain positive pressure. If a system were put into place to monitor positive pressure, there would be no more doubt and even better – no more wasted money.

Keep this in mind next time you receive your heating and cooling bill. It may well be that lowering energy cost is a simple fix – but one you’ll be able to realize unless  you are certain what your current environmental conditions are.

 

Preventing Mold In Hospitals

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Mold in Hospitals?

Mold is a collective term which refers to fungi that grows in the form of multi-cellular thread-like structures called hyphae as opposed to fungi that exist as single cells are called yeasts.  Some molds as well as yeasts cause disease or food spoilage while others are beneficial and play an important role in biodegradation or in the production of various foods, beverages, antibiotics and enzymes. Ironically, while most mold types are potentially harmful to patients, penicillin is a mold used in hospitals that is used to actually treat patients!

In a healthcare setting, it is important to prevent mold growth of any kind where possible; even the most harmless types can cause health issues for patients with serious illnesses and compromised immune systems. A patient with a compromised immune system can be especially at risk.

Although hospitals are generally considered to be clean and sterile environments, a closer look tells us there is actually a greater potential for problematic viral, fungal and bacterial threats due to the very nature of hospitals. Think of it this way, hospitals typically house patients with severe illnesses. These illnesses can be transferred to the garments, linens, walls and floors of the hospital. This is in addition to the obvious blood and other bodily fluids transferred from patient to hospital assets. Basically, there is a lot of fluids in one form or another being transferred from patients to the hospital itself. Where there are fluids, there is the potential for mold growth.

Keeping the hospital clean for patients and preventing cross-contamination is a full-time job, usually for several personnel – and can be a real challenge.

In all hospitals, heavy cleaning agents along with water as a dilutant are used to launder linens, clean surfaces and for general-purpose sanitizing. As you probably know, where there is water, there is a potential for mold growth. Additionally, some hospitals may be older structures with leaky roofs, and foundations; allowing for even greater potential for mold growth.

In any case, prevention is key. Once mold starts to grow, it can become a devastating and never-ending cycle of growth and remediation. Keeping mold growth to a minimum requires monitoring temperature and relative humidity effectively. It may also be beneficial to monitor and correct for undesirable differential air pressures in patient rooms and entire floors. A patient room with a positive air pressure will expel air along with any pollutants in the air every time the door is opened.  So any mold spores quickly move in the hall ever time someone enters or leaves the room.

Sources of Mold

Mold growth can originate in places where standing water is present or in use such as bathrooms, showers, laundry areas and kitchens. Moisture, temperature and humidity are usually monitored in these locations. However, it is usually places that are not monitored effectively where mold can start growing and thrive.

Mold in ceilings

Most hospitals have drop-tile ceilings in rooms and hallways. These are usually made of mold-resistant materials and a general inspection of these tiles usually indicates a water or moisture problem because the ceiling tiles will have visible brown or discolored areas. These may appear as circular, and start from one corner or from the middle of the tile. Sources for the water leak may be the roof (if on higher floors) or from fresh water pipes, sprinkler systems or other plumbing. The problem is, by the time you can see evidence of water leaks it is too late to prevent mold growth.  You are unfortunately just seeing the “tip” of the iceberg.

There are other instances where pipes may sweat because of temperature changes and relative humidity. This creates a humid environment which facilitates mold growth, even though there may be no visible sign of water leakage. HVAC and AC systems can be an especially common source for mold growth and increased relative humidity – heated air mixed with condensation; creating an environment that is relatively tropical. As a note, tropical climates are know to exponentially increase mold, bacteria and viruses.

It is advantageous and advisable for all hospitals to install temperature and relative humidity sensors in ceilings to constantly monitor humidity and temperature.  Any temperature fluctuations can lead to greater condensation and relative humidity.

For many hospitals, installing a complete system would be a challenge because of having to install wire throughout a facility to a centralized location or trying to integrate it with an existing BACnet or other building management system. Fortunately, there are wireless systems that allow hospital administrators to monitor relative humidity, differential air pressure and temperature in ceilings throughout the entire hospital without construction costs. In fact, some systems even allow for automated email alerts, text/SMS alerts with automated phone calls to management personnel or maintenance staff long before a environment becomes too humid.

Can you prevent mold growth?

Mold can grow in obvious areas like hospital kitchens, bathrooms, showers, laundry, etc. Keeping these areas dry and properly ventilated is key. It requires more than just drying up the water; the room temperature may naturally increase the relative humidity – creating an environment for mold growth. An often overlooked way to combat this higher relative humidity is by using proper ventilation via exhaust systems and monitoring differential air pressure between common “wet” areas and dryer areas. Keeping a wet area under constant positive air pressure will allow the room to “push” the damper air to areas of dryer air. As the air mixes, it will become more homogeneous and stable.

If wet areas have negative air pressure, and inadequate exhaust, the air can become overly humidified and stale. The key takeaway is “Do you actually know for sure if you have adequate pressurization and ventilation between rooms?” If not, finding out the hard way can cost millions and even result in the potential loss of life.

While mold is less common in modern/new construction hospitals, it can still happen. Simple engineering and construction inconsistencies can allow for water to slowly trickle in from outdoors or allow for unwanted condensation in plumbing and HVAC systems. The problem is, no one really knows there is a problem – until there is a problem.

After all, how many hospital staff have the job description requiring them to physically inspect all plumbing, wet walls, and wet areas, ceilings, roof, etc.? Fortunately, there are automated systems that can monitor just about any area within fractions of a degree in temperature and relative humidity and provide advanced warning in the instance of environmental instability.

Note: If you are a hospital administrator and would like additional information on ways to keep mold and bacteria growth to a minimum with automated instrumentation, call   (877) 241-0042 and ask for Rick Kaestner.

Laminar Flow hood with equipment

Laminar Air Flow Systems Explained

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Laminar Air Flow Systems – General Terminology

Laminar air flow principles and Laminar air flow systems are commonly used in cleanrooms, positive and negative pressure rooms and other sensitive controlled environments. The best way to understand laminar air flow is to first differentiate between laminar air flow as a principle and laminar air flow in use as a system.

Laminar air flow: principle – Laminar air flow is a process where air is manipulated to force air to move at the same speed and in the same direction, with no or minimal cross-over of air streams in a given space.

“In laminar flow, the motion of the particles of the fluid is very orderly with particles close to a solid surface moving in straight lines parallel to that surface. Laminar flow is a flow regime characterized by high momentum diffusion and low momentum convection.” – Wikipedia

Laminar air flow systems – these are mechanical systems manufactured to provide laminar air flow in a large or small area to perform certain tasks in an environment of constant non-turbulent air flow.

Laminar air flow systems are usually cabinet-based, but may be designed to be a booth or work bench or even a room as well. Some common designs are:

  • Vertical Laminar Flow Cabinets – Vertical Laminar Flow Cabinets function much like horizontal Laminar Flow Cabinets, however, in vertical setups the laminar air is directed vertically downwards onto the working area. The air can leave the working area via holes in the base. Vertical flow cabinets typically provide more protection for the booth/cabinet operator because the air can be directed away from the operator.
  • Horizontal Laminar Flow Cabinets – Horizontal Laminar Flow Cabinets where air flow originates from above the work area but then changes direction and is processed across the work area in a horizontal direction. The constant flow of filtered air provides material and product protection.
  • Laminar Flow Cabinets and Hoods – these are the housings manufactured to create the controlled air environment.
  • Laminar Flow Benches and Booths – these are larger designs; typically designed for larger manufacturing processes.

Laminar air flow stations are built with respect to the type of process being performed. There are times when maintaining a very high level of cleanliness is desired, so a laminar air flow cabinet or bench may reside inside an existing cleanroom. Other times, a cabinet may be a standalone design in a facility without a cleanroom at all.

Laminar Flow Cabinets are typically designed to protect the working area only. They do not offer operator protection and are not suitable for working with bio-hazards.

Laminar Air Flow System Types and Uses

Depending on the goals of the company and operator of a laminar air flow system, there will exist certain “pro’s” and “con’s” of using one type over another. in fact, many larger facilities will take advantage of using both types.

Vertical Laminar Air Flow Systems

Let’s first look at some pros and cons of using a vertical laminar air flow system.

Pro’s

  • The hood/unit is not as deep as horizontal units, and thereby requires less floor space.
  • Best choice for compounding sterile products, consumables and pharmaceuticals.
  • Safer because the controlled air is not blowing directly towards operator, standard sash provides barrier between process and operator’s face.
  • The filter unit is located on top; which makes it easier to change without technical intervention.
  • Typically has less turbulent effects from air striking larger objects and equipment.
  • Less of a chance of cross-contamination between items positioned on the work surface.

Con’s

  • While filters are easy to access, most systems require a generous overhead clearance; changing filters or servicing unit may require a step-ladder and altered construction to provide ample overhead clearance.
  • Cannot place items (or hands) on top of other items: because or possible airflow obstruction.
  • Potential for increased turbulent effect at the work surface because of air striking the work surface.

Horizontal Laminar Air Flow Systems

Now, let’s take a look at some pros and cons of using horizontal laminar air flow systems:

Pro’s

  • Greatly reduced turbulent effect of air striking the primary work surface space.
  • No sash: may make it easier to work and position equipment.
  • Hands and gloves are generally less contaminating since they’re downstream of the primary work-space.

Con’s

  • Changing the filter and/or servicing the unit requires the hood be removed/re-positioned and may require technical expertise.
  • Large samples/objects may obstruct laminar air flow, and this may contaminate downstream objects.
  • Horizontal flow blows fumes and/or particles in operator’s face.

In addition to the primary differences in functionality and operation of both vertical and horizontal laminar air flow systems there are many sub-types of hoods and booths that may fall under each primary type. These may include:

  • Explosion proof laminar air flow systems
  • Biological protection laminar air flow systems
  • Ductless exhaust fume protection laminar air flow systems
  • Biomedical laminar air flow systems
  • Free-standing, portable, and built-in units
  • Units with high heat, or UV exposure
  • Clean benches

As a note of caution, neither vertical or horizontal laminar flow hoods are appropriate when operating in conditions where bio-hazards are present. Work with bio-hazards should only be carried out in an approved containment area. One such cabinet is a Class II, Type A2 Biosafety Cabinet; used in applications requiring Biosafety Level (BSL) 2 or 3 containment rating.

In essence, a laminar air flow system is a way of creating an ultra-clean work-space and environment for manufacturing a specific part of a larger process, or compounding a consumable/pharmaceutical compound. In a cleanroom or typical controlled air environment, there are too many factors that would negatively affect the process – the primary one being turbulence that can disturb processes on a microscopic level. Cleanrooms and controlled air environments can, in addition to improving the purity of a product, also protect operators and the general public.

Clean ratings for laminar flow systems, typically measured as an ISO class, varies, just as the rooms they are physically located in.

A large part of being able to control the environment inside of any laminar air flow system is the ability to control and monitor temperature, differential air pressure and relative humidity. Most modern units are manufactured with constant monitoring systems built-in to the laminar air flow unit. However, this is but one monitoring system. The drawback is potential instrument failure, and the fact that the builder of the laminar air flow system specializes in air flow, not necessarily in the monitoring and reporting of actual air conditions.

Many manufacturers of laminar air flow systems are turning to expert instrument manufacturers and creating OEM-based instrument inclusions.  Some operators are sourcing secondary monitoring and alerting systems irrespective of the laminar air system manufacturer for additional protection. After all, the operator stands to lose the most in terms of product efficacy, safety and operator safety.