A fresh look at building automation and air filtration.
Ken Bloom,
President, Precision Air Technology, Inc.
The issue of regular replacement of air filters is not exclusive to any modern ventilation and air conditioning (HVAC) system. Perhaps, not much attention was paid to this issue before. However, there is a growing understanding that it is the fulfillment of this condition that determines the ability of the ventilation and air conditioning system to provide indoor microclimate quality and the necessary energy savings within the framework of the functioning of building automation systems.
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The operation of any modern HVAC system is based on monitoring the condition and maintenance of the air filter system. Without this, it is difficult to guarantee the required level of indoor air quality. Methods of monitoring and maintenance of air filters are very diverse.
Some installations use differential pressure gauges along the entire length of the ducts. Filters are changed when the differential pressure drops to near zero. In other cases, trained technicians visually determine the need for filter replacement during periodic inspections.
Some organizations replace filters on a schedule without evaluating their condition. If the evaluation is based on the difference in pressure drops before and after the filter, then a very simple rule of thumb is often used to monitor filters: they are replaced if the outlet air pressure is half the inlet air pressure.
This method gives a relative indication of the filter resistance, but often does not provide the level of accuracy required for a building control system. Based on the constant air flow, monitoring air filters in HVAC systems is limited by the fact that less air flows through the ventilation system as the filters become clogged.
In the absence of means for monitoring and adjusting the fan speed, it is difficult to establish a connection between the degree of filling of the filter and the pressure drop on the supply line. And according to experts, due to the increase in air quality requirements, a monitoring system is needed that would allow for a more accurate analysis of the condition of air filters.
Modern energy saving requirements
As we move towards more efficient and environmentally friendly architecture of engineering solutions in buildings, reliable operation of air filters comes to the fore. In our opinion, engineering systems of buildings are required not only to have good functionality, but also the necessary level of standardization of operating parameters, which are controlled by the building management system (BMS). To an increasing extent, the building automation system takes on the function of energy saving.
The use of energy saving technologies is related to the economic aspects of the operation of facilities. One of these technologies is the use of a frequency-controlled electric drive. It is considered to be one of the most effective strategies for reducing electricity consumption in air conditioning systems.
According to research by the U.S. Department of Energy, the use of variable frequency drives significantly reduces energy consumption. For example, a textile mill, through the utility company Pacific Gas and Electric, replaced fixed-speed motors in its ventilation system with a variable frequency drive. The reduction in energy consumption was 59%. However, the main limitation preventing the adoption of this technology in HVAC systems is the fact that variable frequency drives create changes in the pressure difference of the air passing through the filter.
The traditional method of monitoring the condition of air filters is based on measuring this value. Such pressure fluctuations can lead to failure of traditional air filter monitoring systems. Accordingly, the adoption of this technology as a tool for energy saving makes it impossible to determine the state of contamination of the filter, since the parameters of the air flow change.
Building automation experts recognize this incompatibility between proven energy-saving technology and the required accuracy of air filter monitoring systems within building management systems.
Another air filtration technology that can bring significant energy savings is the use of low-pressure filters in HVAC systems. Such filters are already being manufactured in industry.
The use of low-pressure filters reduces the resistance of the system, and the economic effect is that, to ensure the required air exchange in buildings, less powerful fans are required. To adapt this technology, it is necessary to include a reduced pressure value in the system in the ventilation and air conditioning system project. Here, as in the case of a frequency-controlled electric drive, the problem is the same. Difficulties arise in assessing the condition of air filters by the air pressure drop.
Possibilities of modern technologies
Modern building management systems allow for more flexible monitoring of a range of environmental parameters, such as temperature, humidity, air flow and energy consumption. Air filtration affects all of these parameters to some extent. The amount of heat or cold that must be supplied to the system depends, among other things, on how the air passes through the filters. Clogged filters provide less air flow, meaning that it will take longer to heat or cool the air in the room.
By maintaining the air conditioning system with the correct air filtration parameters, it is possible to achieve better results in related areas: reducing excess humidity, creating a comfortable microclimate and reducing the effect of accumulation of mold and other microorganisms.
Proper ventilation operation is determined by the calculated amount of air that can be passed through the filter package, and energy efficiency in air conditioning systems depends on the use of new technologies (e.g. frequency drives and low-pressure air filters). In any case, for the proper functioning of the ventilation system, it is necessary to have an accurate and flexible building management system.
Until recently, there were relatively few innovations in air filtration technology that could provide sufficient monitoring of the condition of filters and, accordingly, their maintenance. Now, any team of engineers monitoring the condition of buildings can arm themselves with the latest technology and gain previously unimagined building automation capabilities. However, monitoring an air filtration system is still “more art than science.” As for the economic consequences of the current status quo, the real costs cannot yet be fully assessed.
A Step Forward in Air Filter Monitoring
To bridge the gap between the capabilities of building automation systems and the required accuracy of air filter condition assessment, Precision Air Technology Inc. decided to apply innovative microprocessor-based air filter monitoring technology. This modern approach to filter condition assessment can provide accurate filter resistance measurement at both constant and variable air flow.
Unlike the traditional method of monitoring the condition of air filters (based solely on differential pressure), the developed device measures both pressure and air velocity. The monitoring process begins with calibration on a clean filter pack. One push of a button and the alarm warning system is programmed to a resistance level of 1.5, 2.0 or 2.5 times higher than the initial filter resistance.
As soon as the filter resistance increases to a preset level, a signal is sent to the relay (type “dry contacts”) and the LED indicates that the filters need to be replaced.
In this way, the limitations imposed by traditional methods of controlling air filtration systems are removed and the system is harmoniously integrated into the overall building management system. With this new tool, the building automation system can integrate air filter monitoring to a greater extent.
The 3200 Filtrometer microprocessor system offers the following features:
• Microprocessor technology accurately monitors the status of individual air filter units under both constant and variable air flow.
• The air filter monitoring system is calibrated from the keypad.
• Filter change alarm levels can be adjusted in increments.
• 24V AC power makes the system compatible with other low-current systems.
• A locally mounted LED not only indicates filter status but also signals when it needs to be replaced.
• Optional dry contact relay, 4-20mA current source, and analog output.
• All versions are easy to install between fan and filter unit.