ASHRAE 70-2023
Method of Testing the Performance of Air Outlets and Air Inlets

Standard No.

ASHRAE 70-2023

Release Date

2023

Published By

American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)  US  /  ASHRAE

Latest

ASHRAE 70-2023

Introduction

Standard Revision Background and Technological Evolution

ANSI/ASHRAE Standard 70-2023, the latest standard replacing the 2006 version, reflects significant evolution in ventilation testing technology. Jointly approved by ASHRAE and the American National Standards Institute on February 28, 2023, this standard marks a significant update to test methods for air distribution equipment.

Major technical evolutions in this revision include: the addition of definitions and test methods for displacement ventilation; supplementary test procedures for underfloor air supply applications; updated references in Appendix A; and the addition of Appendix E (Risk Assessment of Draught Sensation for Displacement Ventilation Inlets) and Appendix F (Rotating Vane Anemometer Flow Measurement Systems). These updates reflect recent advances in ventilation technology and shifting market demands.

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Analysis of Standard Core Content

Test Purpose and Scope

This standard defines laboratory test methods for evaluating air inlet and outlet equipment used for building air distribution and return air that terminate in ducted and non-ducted systems. The scope of testing includes specifications for test instruments, facilities, installations and procedures, as well as calculation methods for determining the aerodynamic performance and sound generation of air inlet and outlet equipment. Feet (m) Drop The maximum distance that the vertical velocity line of the horizontally projected (non-isothermal) airflow drops below the centerline of the outlet ft(m) Terminal Velocity The maximum specified air velocity sustained in the mixed airflow at the air outlet fpm(m/s)

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Test Instrument and Facility Requirements

Temperature Measurement Specifications

Temperature measuring instruments must comply with ANSI/ASHRAE Standard 41.1, with an accuracy of 0.2°F (0.1°C), and the smallest scale division must not exceed 0.2°F (0.1°C). The instrument must be calibrated against an accredited standard or have its own annual accuracy certification.

Pressure Measurement Standards

Pressure measuring instruments must meet the requirements of ASHRAE Standard 41.3, with different scale accuracy requirements corresponding to different ranges. Atmospheric pressure shall be measured using a barometer accurate to within 0.05 in. Hg (169 Pa). The temperature shall be maintained within ±2.0°F (1.0°C) during pressure measurements.

Airflow Measurement Accuracy

Airflow measurements shall be made using a rotating vane anemometer system in accordance with ASHRAE Standard 41.2 or Annex F of the Code, with an accuracy of ±3.0% of reading or 2 cfm (0.5 L/s), whichever is greater. Air leakage in the duct or plenum setup shall not exceed 2% of the target airflow or 3 cfm (1.5 L/s), whichever is greater.

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Test Procedure Details

Static and Total Pressure Tests

The test system shall consist, at a minimum, of the fan, airflow control device, airflow measurement device, and duct or plenum test setup. Pressure measurements shall be made at a minimum of three evenly distributed airflow rates, with explicit reference to the position or adjustment of any flow equalization, damping, or deflection components.

Isothermal Air Test

When tested under isothermal conditions, the supply air temperature shall not vary more than 2°F (1°C) from the average room air temperature. The airflow rate shall not vary more than the greater of ±5% or 1 cfm during the air velocity measurement period. Air velocity measurements shall be made at sufficient locations to determine projection, spread, and drop distances to the nearest 1 foot (0.3m) increment.

Non-isothermal Air Test

Non-isothermal testing requires a supply air temperature difference of 5°F (2.5°C) or greater from the room temperature, with no more than a 10% variation during the measurement period. A heat load shall be provided to maintain steady-state conditions, but the airflow generated by the heat source shall not directly affect the test data.

Displacement Ventilation Test

The displacement ventilation test must be conducted under a Diffuser Class V positioning. The heat source must not be closer to the air outlet than the radius of the farthest wind speed measurement point, and the height above the ground must not be less than 30 inches (0.75m). The wind speed at different distances and heights above the ground in the airflow, as well as the local temperature at each wind speed point, must be measured.

Underfloor Air Supply Application Test

The underfloor air supply test requires the test static pressure box to have a minimum size of 96×96 inches (2.4×2.4m) and a minimum internal height of 14 inches (0.35m). The sample is located at the center of the upper surface of the test static pressure box, and the static pressure box pressure must be measured at three specified points. All measurements must be within ±0.01 inches of water column (2.5Pa).

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Acoustic Test Specifications

Sound power level measurements must comply with the requirements of NAIS Standard 12.51 and be conducted at least in the 125, 250, 500, 1000, 2000, and 4000 Hz octave bands. Testing must meet Engineering Class 2, but the test room must meet Precision Class 1 requirements. The test equipment must be installed in accordance with the manufacturer's recommendations, and all connecting pipes must be covered with sound insulation material to prevent sound from escaping and affecting the measurement.

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Standard Implementation Recommendations

Test Equipment Selection Recommendations

When selecting test instruments, priority should be given to equipment with NIST traceable certification. For rotating vane anemometers, system calibration must be performed in accordance with the requirements of Appendix F to establish an empirical mathematical relationship between wind speed frequency and flow rate. It is recommended to use multiple flow meters with different ranges to cover the entire measurement range.

Test Environment Control

Test room environmental control is critical and requires ensuring that surfaces are smooth and flat and that return air exhaust outlets are away from the supply air path and measurement plane. The maximum airflow rate should be such that the maximum jet velocity at a distance of 3 feet (1m) from the vertical boundary in the direction of investigation does not exceed the end velocity of the investigation.

Data Recording and Reporting

Test data should record all settings and adjustments in detail, including equipment positioning, adjacent side wall location, distance to ceiling or floor, etc. For non-isothermal testing, the temperature difference must be specified to determine the non-isothermal projection, diffusion, or drop. Displacement ventilation tests must also provide a detailed description of the heat load maintenance method.

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Technical Comparison Analysis

Test Type	Temperature Requirements	Installation Requirements	Measurement Focus
Isothermal Test	ΔT≤2°F(1°C)	According to Location Class IV	Projection and Diffusion Distance
Non-Isothermal Test	ΔT≥5°F(2.5°C)	Installation according to Usage Orientation	Descent/Rise Distance
Displacement Ventilation	ΔT ≥ 5°F (2.5°C)	Class V Positioning	Air Velocity Distribution at Different Heights
Underfloor Air Supply	ΔT ≥ 5°F (2.5°C)	Dedicated Plenum Installation	Vertical Projection and Horizontal Diffusion

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Application Cases and Best Practices

Commercial Office Environment Applications

When using displacement vents in open office areas, pay special attention to the draft risk assessment outlined in Appendix E. Test data indicates that air velocity exceeding 40 fpm (0.2 m/s) at 4 inches (0.1 m) above the floor may cause ankle discomfort. Adjusting air velocity and temperature differentials is recommended to optimize comfort.

Data Center Cooling Applications

Underfloor air systems are widely used in data centers, and the new standard's underfloor airflow test procedures provide an accurate performance assessment method for these applications. Test results show that horizontally configured outlets (maximum terminal velocity not exceeding 50 fpm measured 12 inches above the floor) effectively avoid localized overcooling.

Acoustic Requirements for Healthcare Environments

Noise-sensitive environments such as hospital wards require particular attention to acoustic test results. Converting sound power levels to noise criteria (NC) curves according to the method in Appendix D can assist in selecting appropriate outlet types and airflow rates to ensure that ambient noise levels meet healthcare standards.

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Standard Implementation Challenges and Solutions

The main challenges in implementing the new standard include upgrading test facilities, increased accuracy requirements for instrumentation, and increased complexity in the test procedures. A phased implementation strategy is recommended, prioritizing the most critical testing capabilities, such as displacement ventilation and underfloor airflow test equipment.

For existing laboratories, the accuracy of test results can be verified by comparing them with certified laboratories. It is also recommended to participate in standard training and technical exchange activities organized by ASHRAE to keep abreast of the latest information on standard interpretation and implementation guidelines.

The normative and informative annexes provided in the standard provide important references for implementation, especially the projection data analysis method in Appendix B and the flow measurement system calibration procedure in Appendix F, which are worthy of in-depth study and application.