IEA EBC ANNEX 88: “Evaluation and Demonstration of Actual Energy Efficiency of Heat Pump Systems in Buildings”

This short summary is about an international R&D project on the evaluation and demonstration of actual energy efficiency of heat pump systems in buildings. The project is within the framework of the EBC TCP on Energy in Buildings and Communities (EBC).

Why this project was started

Certain heat pump systems in buildings have previously been found to exhibit relatively low energy efficiency under low partial load conditions, while other heat pump systems have been able to maintain higher energy efficiency under the similar conditions. Therefore, technical guidance on how to improve the overall energy efficiency of such heat pump systems is critical information for many engineers and HVAC system designers. Public policy and decision makers require support on how requirements to follow such technical guidance can be implemented within building energy codes and regulations.

A first state of the art report has been published

1. Testing Methodologies

·         Category A Standards: Current testing methods focus on steady-state conditions, often overriding native controls, which may not represent real-world performance.

·         Category B Standards: Emerging load-based testing methods evaluate heat pumps under real-world conditions using native controls, improving representativeness and accuracy.

·         Challenges: Existing standards often fail to account for part-load operation and dynamic conditions, leading to discrepancies between lab and field performance.

2. Monitoring Methods

·         Field monitoring methods for air-to-air and air-to-water heat pumps include air-specific enthalpy difference and refrigerant-specific enthalpy difference methods.

·         Monitoring standards exist, such as ASHRAE Standard 221-2020 and CSA SPE-17:23, but challenges remain in achieving high accuracy in field measurements.

·         Figures show an example of field monitoring for room air-conditioners in a research house built in Tokyo area (Figure 1). The sizing of room air conditioners followed a standard recommendation of rated cooling capacities for each range of room floor area. Distribution of part load ratio (PLR) and the relationship between PLR and COP (EER) are shown for cooling (Figure 2) and for heating (Figure 3). This kind of monitoring result contributed to the validation of the energy calculation method for room air conditioners in the Japanese Building Energy Conservation Standard.

3. Energy Calculation Methods

·         Energy performance calculation methods vary widely across regions, with different approaches to modelling heat pump efficiency.

·         Common challenges include sensitivity to operating conditions, part-load operation, and limited availability of standardized product data.

·         Methods reviewed include EN standards (EN 15316-4-2, EN 16798-13), EnergyPlus, NECB, BECS, UNI TS 11300-4, SAP 10.2, SBEM, DIN V 18599, and RE 2020.

4. Design Guidelines

·         Design guidelines aim to optimize heat pump performance, ensure occupant comfort, and comply with regulations.

·         European guidelines (e.g., EN 15450, VDI 4645) focus on heat pump sizing, operating temperature, and environmental impacts.

·         Canadian guidelines (e.g., CSA SPE-17:23, NRCan Toolkit) emphasize integrated design, proper sizing, and performance verification.

·         U.S. guidelines (e.g., ACCA Manuals, NEEP guides) provide detailed procedures for load calculation, equipment selection, and installation.

·         Japanese guidelines (e.g., LEHVE, ISO 13153) offer validated energy-saving strategies for residential buildings.

5. Challenges and Recommendations

·         Heat pump performance is highly sensitive to operating conditions, requiring accurate testing and calculation methods.

·         Coordination between product testing standards and energy performance calculation methods is essential to bridge the gap between lab and field performance.

·         Future guidelines should focus on improving design practices, addressing low partial load conditions, and providing clear design strategies.

6. Future Directions

·         Development of load-based testing standards and their integration into energy calculation methods.

·         Enhanced field monitoring to validate energy performance and refine calculation models.

·         Collaboration among manufacturers, designers, and policymakers to ensure reliable data and effective design practices.

7. Global Collaboration

·         Annex 88 involves international experts from various countries, aiming to harmonize standards and improve heat pump systems' energy efficiency globally. It collaborates with IEA HPT TCP (Heat Pumping Technologies) and its Task Force.  Its participants are from Australia, Brazil, Canada, China, Germany, Irland, Italy, Japan, Netherlands and Philippines.

References

[1]     IEA EBC Annex 88., https://annex88.iea-ebc.org/

[2]     Building Research Institute (2011). Report of Committee for Actual Energy Performance of Room Air Conditioners, 28th February 2011 (in Japanese).

Figure 1. Plan of the research house and positions of monitored room air-conditioners. [2]

Figure 2. Monitoring results of room air-conditioners in cooling operation. The monitoring was carried out in a research house with mechanically simulated occupant behaviour such as use of equipment and heat emissions (see Figure 3). The part load ratio is defined as the ratio of capacity at each period (10 min.) to the full capacity. [2]

Figure 3. Monitoring results of room air-conditioners in heating operation in the same research house. [2]