Tag Archives: commercial

Controlling Building Pressure

Welcome to All Sensors “Put the Pressure on Us” blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities and you. In this blog we’ll discuss proper indoor versus outdoor pressure in commercial buildings.

Controlling Building Pressure

Proper indoor versus outdoor pressure is important in commercial buildings. When indoor pressure is less than the outside pressure, outdoor air leaks, or infiltrates into the building. In addition to impacting heating, ventilation and air conditioning (HVAC) effectiveness, excessive infiltration can also cause uncomfortable drafts, especially in stairways, as well possible odor migrations and even encourage microbial growth depending on the outside weather conditions.

The opposite pressure condition, exfiltration, occurs when indoor pressure is greater than the outside pressure, indoor air leaks out of, or exfiltrates from the building. Excessive exfiltration negatively impacts temperature control by reducing supply airflow into occupied spaces, makes opening and closing doors difficult and creates noisy high-velocity airflow around doors and windows.

In addition to the operation of its mechanical ventilation system, a building’s pressure can be positive or negative due to the impact of wind and weather. Using either a return fan or a relief fan, for direct control of building pressure, manages the combined effects of weather, wind, and mechanical ventilation. This control requires pressure sensors mounted inside and outside of the building to determine the actual pressure difference. Depending on the desired exfiltration and infiltration goals, the pressure difference is typically less than 0.1-inch water gauge (wg) and can be either positive or negative.

What do you think/Comments?
Do you have a pressure sensing question? Let me know and I’ll address it in an upcoming blog.
-Dan DeFalco, Marketing Manager, All Sensors Corporation (ddefalco@allsensors.com)

Pressure Sensing and Improved HVAC Efficiency

Welcome to All Sensors “Put the Pressure on Us” blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities and you. In this blog we’ll look at pressure sensing and how it improves HVAC efficiency.

Pressure Sensing and Improved HVAC Efficiency

Clean air in heating, ventilating and air conditioning (HVAC) systems requires filtering to eliminate dust, pollen and other airborne contaminants in residential, commercial and industrial buildings for the health of occupants and equipment. Some locations such as clean rooms in semiconductor and other manufacturing operations as well as hospital operating rooms and research laboratories have very special requirements. Clean air depends on the filter’s initial efficiency and the pressure drop across it, which increases with usage. The pressure drop is also called the air filter resistance.

The National Air Filtration Association (NAFA) says, “Most large HVAC commercial grade systems are designed to handle pressure drops of one inch, possibly more, for the air filter resistance. Matching filter initial, final and average resistance to the system is critical for proper air filtration and air exchange rates. Also, providing pressure drop reading devices such as manometers or electronic pressure sensors is an absolute requirement.”

According to the Lawrence Berkeley National Laboratory (Berkeley Lab or LBL) Design Guide for Energy-Efficient Research Laboratories – Version 4.0, for HEPA filters, the “pressure drops can be as low as 0.1 inches water gage (w.g.) (24.9 Pa) and as high as 1.0 inches w.g. (249 Pa), with significant energy use impacts resulting from the nonlinear power use requirements of higher pressure drop filters.”

Filters are rated in static pressure at a specified cubic feet per minute (CFM) air flow. In 103 – Filtration Fundamentals, one company states that most heating /cooling systems in the residential and light commercial markets are designed to move 900 CFM to 2000 CFM at a total system static pressure of approximately 0.5″ to 0.7″ total pressure drop including the resistance through the ductwork and the filter.

With usage, the total pressure drop increases causing the filter to draw more power and increase the stress on the air handling equipment. The point where the pressure drop increases the electrical power consumption and overtakes the initial cost of the filter indicating that a filter change is required is called the optimal change-out point and is shown in Figure 1.

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Figure 1. The optimum final pressure drop across an air filter.

The equation used to determine the energy cost based on the final pressure drop is:

Energy Consumption (in kWh)= Q ∆P t / η 1000

Where:

Q = airflow (m3/sec)

ΔP = avg. pressure loss (Pa)

t = time in operation (hours)

η = fan efficiency

In the summary for pressure drop considerations for air filters, NAFA concludes, “Pressure drop reading devices are essential to determine optimum performance results and filter change-out frequency.”

Achieving the optimum performance leads to efficient filter operation and safe, clean air.

What do you think/Comments?
Do you have a pressure sensing question? Let me know and I’ll address it in an upcoming blog.
-Dan DeFalco, Marketing Manager, All Sensors Corporation (ddefalco@allsensors.com)

Another Pressure Sensor Possibility: A Vacuum Cleaner

Welcome to All Sensors “Put the Pressure on Us” blog. This blog brings out pressure sensor aspects in a variety of applications inspired by headlines, consumer and industry requirements, market research, government activities and you. In this blog we’ll look at a pressure application for vacuums.

Another Pressure Sensor Possibility: A Vacuum Cleaner

In hotels and several other types of commercial buildings, you have good chance of seeing a maintenance person using a Sensor S12 or S15 vacuum cleaner (or in this case, waiting to be put away). The industrial service vacuum cleaner has a bag full light that comes on when there is a reduction in airflow in the system from a clog or full bag; the machine has a 99.6% filtration rate at 0.3 microns. After 45 seconds to a minute, the machine shuts down to prevent excessive loading of the motor and ineffective cleaning. While a pressure sensor could be used to provide this functionality, an alternate technique is currently used.

 

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In fact, measuring the pressure drop in many airflow situations that need to be monitored and controlled for proper operation are a perfect application for low pressure sensors (frequently less than 1-inch of water such as the 1 INCH-D1-4V-MINI or 1 INCH-D2-BASIC) that can measure and accurately detect small pressure variations. With the right resolution pressure sensor, even more functionality can be provided to vacuum cleaners and critical airflow applications.

What do you think/Comments?
Do you have a pressure sensing question? Let me know and I’ll address it in an upcoming blog.
-Dan DeFalco, Marketing Manager, All Sensors Corporation (ddefalco@allsensors.com)