Techniques for airflow measurements to determine the real efficiency of heat recovery in ventilation systems

Abstract

Heat recovery in ventilation is essential to reduce energy use and thus mitigate greenhouse gas emissions from the building sector. Heat recovery efficiency of at least 80 % in new buildings is required according to Norwegian standards. However, measurements show that the real heat recovery efficiency during operation is commonly 10-20 % lower. Measuring heat recovery efficiency in buildings is challenging, mainly due to difficulties measuring airflow rates close to the air handling unit (AHU). This study assesses the following duct airflow measurement techniques and equipment: pressure differential, velocity traversal technique, ultrasound and tracer gas. The pressure differential method can provide accurate flow rates and thus it is used as the reference measurement. However, it is not suitable for duct flow measurements due to its high pressure penalty and long straight duct requirement. Velocity traverse and tracer gas methods introduce less disturbance to the flow. Nevertheless, both methods require intensive labour work and cannot track quick changes of the airflow with time. The application of ultrasound to measure airflow is relatively novel and it can automatically measure constant and fluctuating airflows with low pressure drop and acceptable accuracy when the proper installation and minimum straight duct are provided.

Analisis Aliran Udara dan Kenyamanan Termal di Laboratorium Perpindahan Panas dan Massa menggunakan Metode Computational Fluid Dynamics (CFD)

“…Udara yagn yang digunakan pada proses simulasi diasumsikan sebagai fluida gas 1 fasa seperti Tabel 5. Selain propertis dari masing-masing material yang digunakan, pengaturan juga dilakukan terhadap boundary condition dari masing-masing inlet dan outlet, seperti kecepatan udara, tekanan, dan temperatur (Rønneseth dkk., 2019;Tanujaya dan Darmawan, 2021). Untuk kisi AC, digunakan kecepatan udara sesuai dengan variasi kecepatan udara pada kisi AC seperti yang dijelaskan pada Tabel 4 dengan temperatur sebesar 293 K (20 ºC) yang diukur berdasarkan pengaturan kecepatan AC, tingkat 1-4.…”

Development of an Airflow Monitoring System for Air Handling Unit using IoT

“…For example, a more recent method that has been used is the pressure differential method. Ronneseth et al (2019) used the pressure differential method to determine the airflow. This pressure differential method is relatively accurate and thus used as the reference measurement.…”