AHU Casing and Filter Standards as per EN 1886

EN 1886 standard is a part of a series of standards for Air Handling Units used for ventilation and air conditioning of buildings for human occupancy. It considers the mechanical performance of an Air Handling Unit as a whole and will be supported by a standard for sections and components. 

This standard specifies test methods, test requirements and classification for Air Handling Units which are supplying and / or extracting air, via duct work for ventilating / conditioning a part or the whole of the building. Except for the thermal and acoustic performance of the casing, the test methods and requirements are applicable to both complete units and any separate sections. 

Filter bypass test is not applicable to the testing of HEPA filters. The test method for the thermal performance of the casing is applicable to the comparison of different constructions but not to the calculation of thermal losses through the casing or the risk of condensation.

Similarly, the test method for the acoustic performance of the casing is applicable to the comparison of different constructions but not to the provision of accurate acoustic data for specific units.

Mechanical Strength of the casing shall be categorized into classes as shown below:

Mechanical Strength	Max. Relative Deflection mm/m
D1	4
D2	10
D3	>10

Casing Air Leakage of AHU tested at 400 Pa & 700 Pa negative pressures shall not exceed values as shown below:

Casing Air Leakage	Max. leakage rate (f400) l/s/m2	Max. leakage rate (f700) l/s/m2
L1	0.15	0.22
L2	0.44	0.63
L3	1.32	1.9

Filter Bypass Leakage Rate - Air bypass around filter cells will decrease with effective efficiency of the filter. This bypass air is not filtered. Air tightness and area of casing between filter and fan are the factors that can affect the filter bypass leakage rate. Filter Bypass Leakage Rate classifications for are as shown below:

Filter Bypass Leakage	Max. leakage rate k in % of the volume flow rate
G1-F5	6
F6	4
F7	2
F8	1
F9	0.5

Thermal Transmittance (U) shall be determined when the steady state temperature difference is 20 K. Classification of U is as shown below:

Thermal Transmittance (U)	w/m2/K
T1	U < 0.5
T2	0.5 < U ≤ 1.0
T3	1.0 < U ≤ 1.4
T4	1.4 < U ≤ 2.0
T5	No requirements

Thermal Bridging Factor is determined by the Ratio between lowest temperature difference and mean air to air temperature difference. Thermal Bridging Factor classification is shown below:

Thermal Bridging Factor	kb
TB1	0.75 ≤ kb < 1.00
TB2	0.60 ≤ kb < 0.75
TB3	0.45 ≤ kb < 0.60
TB4	0.30 ≤ kb < 0.45
TB5	No requirements