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 ([email protected])

What does a psi matter anyway?

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 why a PSI or two matters.

What does a psi matter anyway?

Underinflated footballs created a viral controversy before Super Bowl 2015.  Measurements of air pressure of 10.5 pounds per square inch (psi) instead of the minimum 12.5 were the issue. Rather than just talk about the issue (a.k.a. Deflategate), engineers performed calculations and more. One company conducted experiments as well.

In its testing, HeadSmart Labs found that on average, footballs dropped 1.07 psi from temperature change in a 75°F room to a 50°F room. Exposing the football to water resulted in an additional 0.75 psi pressure drop. With the combined effects, the footballs’ pressure decreased by an average of 1.82 psi to a max of 1.95 psi.

Richard P. Binzel, professor of planetary science at MIT, calculated that a 5 to 10% drop in temperature could create a drop of 0.5 to 1.5 psi, in a football’s air pressure. Equally important, he noted that the accuracy of the meters used to measure the footballs is unknown.

The bottom line for this or any critical pressure measurement is that for accurate measurements, especially at lower pressures, temperature changes are among the operating environment aspects that should be taken into account and accurate meters need to be used.

footballPNG

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 ([email protected])