Conference Agenda

The potential for improved performance for variable-speed heat pump systems is resulting in their widespread adoption globally. Conventional heat pump and air-conditioning rating methods, such as AHRI 210/240-2023 (2020), were originally developed to characterize the performance of fixed-speed heat pumps, and have been modified over time to include variable-speed equipment. Recently, load-based testing methods such as CSA SPE07:23 have been developed as a response to evidence that fixed-speed tests are inadequate to represent field performance of variable-speed systems. These methods test the heat pump along with its built-in controls, imposing loads that scale with outdoor conditions and allow the heat pump to respond and control the indoor temperature. Laboratory testing has shown that SPE07 results (using the previous edition, EXP07:19) differ substantially from AHRI 210/240 results, raising the question: does SPE07 do a better job representing in-field performance than AHRI 210/240?

This paper presents preliminary results from a study in which six variable- or multiple-speed heat pumps were installed in three unoccupied, calibrated test houses in Lincoln, Nebraska. Lincoln has a wide range of weather conditions, with heating and cooling design temperatures of -17 °C and 34 °C. Each house had both a ducted and a ductless system installed, which alternated operation throughout the heating and cooling seasons. The systems and houses were instrumented to collect detailed performance data. After the field testing, the same units were tested in a certified laboratory using both the AHRI 210/240 and SPE07 test procedures. This allows a direct comparison of results between the laboratory rating methods and in situ performance, and thus a fair assessment of the representativeness of each rating method using the same tested units.

Each set of test results from the field and the lab are mapped to a range of climates, from Hot-Dry to Subarctic, to compare the rating methods to the in-field performance. The objective of load-based testing and rating is to inform heating and cooling efficiency metrics that may prove valuable to consumers, utility programs, and design professionals, and to improve design practices, performance-based modeling and code compliance. They may also be useful to manufacturers in improving their products’ performance and comfort. Previous lab results have established the merits of the procedure and suggest the value of stakeholder adoption of SPE07, with the goal of improving state and utility program design, home energy ratings, performance-based code compliance and other voluntary activities that support energy efficiency and carbon reduction. To that end, the field and lab data from this project will provide a clear comparative evaluation demonstrating the relevance and potential value of load-based testing to predict real-world performance of variable-speed heat pumps and air conditioners.

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Dynamic load-based testing methodologies allow for the evaluation of air conditioner and heat pump performance in a laboratory setting, taking into account realistic operating conditions. In order to improve the load-based testing methodology's repeatability and reproducibility, it is important to understand the effect of sensor accuracy and dynamic response on load-based test results. This paper presents a systematic approach to quantify the uncertainty in dynamic load-based test results for residential air conditioners and heat pumps. The proposed uncertainty quantification approach employs statistical techniques to consider both systematic and random uncertainties. It builds upon existing uncertainty quantification methods that were primarily developed for steady-state tests and are not applicable to dynamic tests. Furthermore, this paper presents a method to assess the impact of sensor dynamics on load-based test results using a simulation-based approach. For demonstration and quantifiable results, the proposed methodology is employed to estimate the uncertainty in load-based test results of a variable-speed heat pump for both cooling and heating modes, as well as the overall uncertainty in seasonal performance. The results suggest that the measurement uncertainty in seasonal performance is reasonable when using sensors that meet the required accuracy according to current standards. However, there are still aspects that could be improved. In addition, the impact of sensor dynamics on overall performance is insignificant compared to measurement uncertainty and the results suggest that accurate sensors with reasonable time response should not introduce significant variability in dynamic test results. This work contributes to improving load-based testing methodologies by offering a comprehensive framework for quantifying uncertainty and assessing sensor dynamics.

The existing testing and rating procedure for split-type residential heat pumps in the United States is based on AHRI 210/240, which provides a standardized metric for assessing equipment performance that is based on steady-state tests where the equipment native controls are overridden. In an effort to improve testing and rating of heat pumps, a load-based testing methodology has recently been developed that accounts for the effect of the integrated controls and thermostat. In this approach, a test unit with its thermostat dynamically responds to emulated building loads in real-time, continuously adjusting indoor test room conditions based on a virtual building model, while the outdoor test conditions are maintained at a steady state. For typical load-based testing, two psychrometric chambers are used and only one unit can be tested at a time. Load-based testing can be time-consuming and expensive, particularly for residential split systems when different combinations of indoor and outdoor units need to be tested. Additionally, implementing load-based testing in psychrometric chambers necessitates controller and software upgrades for the rooms to enable virtual building emulation. To address these issues, this paper proposes a closed-loop apparatus (CLA) featuring integrated controls and automated software for load-based testing. In this setup, the indoor unit is installed in the CLA, while the outdoor unit is installed in a single psychrometric chamber. The CLA maintains indoor test unit return air (RA) conditions in real-time based on the virtual building temperature and humidity set points during load-based tests. Test unit performance is measured in real-time, and the indoor unit supply air is reconditioned with an electrical heater, cooling coil, and humidifier in the air loop. In this setup, multiple outdoor units could be positioned within a single psychrometric chamber, and multiple CLAs could be coupled with various indoor units. This configuration would allow for the simultaneous testing of multiple units, streamlining the testing process.

A load-based testing methodology has previously been developed for estimating representative seasonal performance of residential cooling and heating equipment based on dynamic performance measurements in a test laboratory. This method captures dynamic interactions of the test equipment with its embedded controls and building dynamics by continuously updating the indoor psychrometric chamber temperature and humidity based on a virtual building model. During load-based tests, it is critical to provide representative and reproducible test conditions over the thermostat since variations in airflow and temperature distribution across an environmental chamber can affect the thermostat sensing dynamics and can lead to differences in test equipment dynamic performance between different laboratories at the same test conditions. To address this, a thermostat environment emulator (TEE) has been developed. Cheng et al. (2021a) suggested an initial design concept using an air-to-air thermoelectric cooler heat exchanger (TECHX) and investigated its performance. Kim et al. (2021) improved the TEE performance and applicability across different test facilities and investigated seasonal performance ratings determined from load-based testing using the TEE. In this paper, a 3^rd generation TEE is introduced that has lower cost and improved cooling performance. An overview of the 3^rd generation TEE design and its performance evaluation across varying test conditions is presented. In addition, load-based testing results obtained using the TEE in combination with a closed-loop apparatus are presented for a 2-ton variable-speed heat pump.