In other words, AHUs remove polluted air from indoor spaces - either actually polluted air or air that is simply uncomfortably hot or cold - and replace it with clean, fresh (and sometimes humidified) air at the correct temperature. Not only the right temperature and humidity are a must, but even more the purity of the air we breathe when we are indoors. In recent years, society has become increasingly aware of the negative health effects of particulate matter (PM).
Air Handling Units matter
The functional design of the AHU was closely related to the design of the building. In winter, the AHU recirculates the most air - only a small part was the external air supply. Humidification of the supply air was initially introduced in the AHU primarily by spraying water into the ventilation system.
The basics
Traditionally, an air handling unit (AHU) is classified as a complex device designed to handle and condition the air processed in heating, ventilation and air conditioning (HVAC) systems. Today, air handling units on the EU market usually consist of fans, energy recovery units, filters, heating/. Air handling units are usually located in utility rooms or outdoors (mostly on the roof).
Application areas
Swimming pools require ventilation to reduce humidity in the building for comfort reasons, but also to protect the building structure from moisture damage. This means that the particles are eliminated and the air is thermally treated for the specific application. The air is then transferred to a duct system, which distributes the air to different parts of a building.
Functions and components
As a result, the need to heat the heater behind the supply air is much less. Recovery systems have less cross-contamination of air streams compared to rotary heat exchangers. The water content in the supply and outside air is similar, no condensation occurs.
To increase energy efficiency, the pressure drop on the air and water sides of the heating and cooling coils should be as low as possible. The way to lower the water content in the air is by using the cooling coil to cool the air so that it reaches the saturation temperature. Downstream of the heating coil will heat the air to the required supply air conditions.
Indirect adiabatic cooling can be installed before the energy recovery system, on the exhaust air side. The annual energy consumption for air heating and cooling is usually very high. The amount of power used to process the ventilation air increases the enthalpy change (excluding the ERS effect) and the air flow rate.
The energy used by the fans to distribute the air increases with the airflow, pressure and efficiency of the fan and its drive system.
Energy Efficiency and Life Cycle Costs
It depends on several factors such as indoor climate requirements, ambient climate, the design of the system and the way it is operated. Within the European Union, air handling units must meet the requirements of Ecodesign Regulations, which stipulate that energy recovery must be included where appropriate. The main characteristic of energy recovery for comparison and evaluation is the dry air temperature efficiency.
It is recommended to establish a holistic analysis, which evaluates all costs during the lifetime of the ventilation system by means of a Life Cycle Cost (LLC) analysis. The energy costs are dominant as they can account for up to 80% of the total costs. However, the investment cost of an AHU with an optimized energy recovery system is likely to be higher.
Another important issue to consider is the possible impact of each air conditioner on other elements of the investment. As a result, a more expensive unit with a better energy recovery capacity will reduce the investment for thermal energy supply. The experience gained on the fundamental characteristics of the AHU is transferred by the manufacturer to intelligent integrated control functions.
In addition, pre-configured controls that take into account the exact specifications of the AHU enable quick and reliable commissioning.
Control system
Correct commissioning of the AHU and its control system has a substantial impact on the correct and energy efficient operation of the plant. In addition to all these technical advantages, the integrated control system in the AHU simplifies its subsequent operation by limiting unit servicing and controls to a single contractor. Proper predictive maintenance is essential for the undisturbed and failure-free operation of the system during its lifetime.
When a building management system (BMS) is implemented, it is crucial that this system can communicate with the AHU's factory-installed control system. However, it can also change set point and device states to influence the behavior of the AHU to its requirements. By using a factory-fitted intelligent control system for the AHU, reliable and energy-efficient operation of the AHU is guaranteed.
A zone unit with its controller will use the primary air from the AHU to heat or cool it to the required temperature level in the connected room(s). Maintenance intervals depend on the dust holding capacity of the filters and are adjusted by monitoring the pressure drop. The length of the AHU must accommodate enough space for filters, heat exchangers, access sections for maintenance and fans.
Detailed 3D or BIM views of the unit design can be used when planning and designing buildings and ventilation systems.
Design and selection
The calculated internal specific fan power (SFPint) is the ratio of the pressure drop across the internal ventilation components to the efficiency of the fan and should be low for energy efficiency. The overall energy efficiency of the building, on the other hand, is highly dependent on the efficiency of heat recovery from the exhaust air stream to the supply air stream – especially in colder climates. Using the cross-sectional area of the AHU to maximize the filter surface allows for high dust retention capacity and thus longer filter change intervals.
The desired airflow that the unit directs into and out of the building gives an idea of the size and capacity of the unit. The size of the AHU, in terms of external dimensions, allows transportation with standard trucks without the need for expensive special transports. When using bag filters, moving the bags over a long period of time will remove the protection of the inner sheet of the floor panels.
The mechanical strength of the casing is crucial for the reliability of the air conditioner. The AHU enclosure will reduce the transmitted fan noise inside the AHU. Both the sound insulation of the housing and the sound power in the duct are specified for air conditioners.
Hygienic air conditioners place special requirements on planning, manufacturing and shipping, as well as on unit design.
Certification
Due to the ever-growing environmental challenges, most of the global community is focused on improving energy efficiency, thus reducing the carbon footprint and air pollution. Efficiency of air handling and air transport processes is the most important parameter with regard to energy consumption attributable to ventilation and air conditioning. Even small differences between actual and declared energy performance can lead to essential differences in actual energy consumption, and consequently in a building's energy performance and operating costs.
Participation in the certification programs offered by Eurovent Certita Certification offers a solution for fair competition and reliable data. In addition, the certification assessment includes an energy efficiency label that helps planners, installers and end users choose the most suitable product for their application. Unlike in the past, one of the main goals of standards today is to provide industry with the right tools to ensure compliance with legislation (e.g. European Union Ecodesign).
CEN/TC110 (Heat exchangers)/WG6: EN308 - Test procedures for determining the performance of air-to-air and flue gas heat recovery devices. EN 13053 “Ventilation for buildings – Air handling devices – Rating and performance for units, components and parts”. EN 16798 "Energy performance of buildings - Ventilation of buildings" is a fairly new series of standards (issued in November 2017).
It is divided into 18 parts and includes, in addition to specifications on the energy efficiency of buildings, detailed specifications for the ventilation of buildings.
Standards
The European Commission provides, for example, CEN mandate to prepare technical standards that facilitate compliance with essential requirements. EU Directive 2009/125/EG (the Energy-related Products Directive), also known as the Ecodesign Directive, defines minimum requirements for energy-related products. The aim of the Ecodesign Directive is to reduce energy consumption and CO2 emission rates as well as an increase in the overall proportion.
This directive applies to all products placed on the market within the European Economic Area (EEA). Of importance for AHUs is the EU Regulation on Ventilation Units", which defines the requirements regarding the energy efficiency of AHUs. They regulate the minimum requirement of AHUs to reduce microbial contamination in hospitals or surgeries.
EN 308 describes "Test procedures for determining the performance of air-to-air and flue gas heat recovery appliances". Therefore, based on tests of filter effectiveness, the new standard includes 49 new filter categories instead of 9 in EN 779. Scan the QR code to download the latest version of Eurovent Recommendation 4/23 on how to select EN ISO 16890 air filter ratings for general ventilation applications.
Europe is home to more than 100 air handling unit manufacturers, ranging from small, family-owned businesses that usually focus on a particular country or region within a country, to large multinational corporations operating all over the world.
The European AHU industry
Eurovent and its members play a major role in jointly developing forward-looking European standards and industry recommendations. Eurovent Certified Performance" program for AHUs with the aim of ensuring a level playing field by allowing customers to compare performance values verified by a third party. All certification programs are managed by Eurovent Certita Certification in Paris, which is an independent sub-unit of Eurovent.
This also includes non-certified producers, as the certification programs are organized independently of association activities. Within the product group, manufacturers develop e.g. industry standards, define legislative positions, monitor the market and discuss recent developments of general relevance. The European Union (EU) is one of the largest markets for air handling units worldwide.
Eurovent recommends the code of good practice for the interpretation of Directive 2006/42/EC on machinery in relation to air handling units. Eurovent Symbols and units of physical quantities in the field of air handling and heating techniques.
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