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How to measure and evaluate refrigerant cycles – in a representative, reproducible manner? An experimental case study for water-to-water heat pumps.

Number: 2492

Author(s) : GOBEL S., VERING C., MÜLLER D., WACHAU A.

Summary

Today, the testing and rating of heat pumps are based on steady-state measurements, which are very well established in standards worldwide and are considered reproducible. However, the high market penetration of inverter-driven heat pumps raised concerns among researchers and policymakers about whether fixed frequency testing is representative of real operation. Especially under low load conditions, inverter-driven heat pumps adjust the compressor frequency and thus affect the unit's performance. In addition, fixed frequency testing requires support from the manufacturer, and independent testing by market surveillance authorities is impossible. Recently, the Federal Institute for Materials Research and Testing (BAM) proposed a load-based test (compensation method) to be considered the new test standard for the EU-Energy Label, which is supposed to guide installers and consumers in their choice of an efficient heating technology. It has been shown by Palkowski et al. that the developed compensation method can overcome these issues in that the compressor speed is unfixed and the native control is active during the test. The repeatability and reproducibility of the compensation method have been studied through round-robin testing by the BAM (the results will be published elsewhere). Especially under low part-load conditions, higher deviations of the calculated coefficient of performances (COPs) were observed in the RRT, which are likely linked to the various test stand configurations of the participating labs. Thus, the reproducibility of more sophisticated testing methods could be limited due to different realization of heat sinks in the test setups. This work experimentally investigates the reproducibility of a load-based testing method and suggests solutions to ensure the reproducibility even over different heat sinks (thermal inertia) in test stand setups. The compensation method serves as the basis for all measurements, and the COP measurement of a 16 kW water-to-water heat pump serves as a case study. To investigate the reproducibility of load-based measurement methods through inertia, we emulate different inertias by PT1 behavior in a Hardware-in-the-Loop environment. The experimental results show that the COP varies by up to 45 % depending on the test conditions and the emulated inertia, emphasizing the need for sound test conditions and active heat pump controllers during testing. Therefore, future test procedures must take the test stand's inertia into account to achieve comparable, representative, and reproducible results.

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  • Original title: How to measure and evaluate refrigerant cycles – in a representative, reproducible manner? An experimental case study for water-to-water heat pumps.
  • Record ID : 30030749
  • Languages: English
  • Subject: Technology
  • Source: 2022 Purdue Conferences. 19th International Refrigeration and Air-Conditioning Conference at Purdue.
  • Publication date: 2022

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