The report reveals that while leakage rates in the UK were generally low their effects on heat pump performance could be huge. Of the installations used in the survey, the standard of log book record keeping was also found to be poor.
The report from the Department of Energy & Climate Change recognises that heat pumps are a key element of the UK government’s drive to decarbonise the heat sector but the GHG emissions associated with refrigerant use will be increasingly important as deployment of heat pumps grows. It focusses on the impact of air to water heat pumps (AWHPs), ground source heat pumps (GSHPs), and exhaust source heat pumps.
The impact of a much larger number of existing air to air heat pumps (AAHPs) is also investigated. The analysis suggests that trying to reduce the level of leakage in the short-term whilst incentivising low GWP refrigerants in the longer term would be the most appropriate course of action to maximise the CO2e benefits associated with heat pumps.
Impacts of Leakage from Refrigerants in Heat Pumps, compiled by Eunomia Research & Consulting and the Centre for Air Conditioning and Refrigeration Research at London South Bank University, finds that whilst leakage led to significant CO2e emissions, this was nonetheless a small proportion of the total reduced emissions associated with heat pump technologies.
Based on the F-gas logbooks of six organisations and 528 unique installations, it was found that annual leakage rates from the operation of heat pumps were of the order of 3.8% of installation charge for non-domestic applications and 3.5% for domestic applications. Further analysis of this data suggest that 9% of non-domestic installations and 10% of domestic installations leaked each year.
While the median proportion of refrigerant lost was 42% for non-domestic installations and 35% for domestic installations occurrences of catastrophic leakage brought figures of 75% loss for non-domestic applications and a huge 92% for domestic installations.
The authors admit, however, that they were working with log books that were generally of poor quality. In particular they observed cases of refrigerant types and quantities not being recorded, along with no record of quantities of refrigerant being recovered and no dates or record of leakage checks. In some cases the type of installation was not recorded or the ID of the personnel performing the maintenance noted. In others the cause and location of a leak was not being recorded.
Impact on COP
Additional tests showed that a refrigerant charge reduction of just 10% would lead to a COP reduction of about 3% in heating and 15% in cooling operation. Leaks leading to undercharging by 40%, however, would reduce the COP by a hugely significant 45% in heating mode and 24% in cooling operation.
Modelling of leakage based on predictions of total heat pump installations shows an increasing overall refrigerant loss by weight from 14 tonnes CO2e in 2013 to 83 tonnes CO2e in 2020 for installations excluding AAHPs. When AAHPs are included, this becomes 103 tonnes CO2e in 2013 and 252 tonnes in 2020.
This was based on predictions of total heat pump installations reaching around 430,000 installations by 2020 (excluding AAHPs) and 2,700,000 installations when AAHPs are included. The vast majority (401,000) of the non-AAHPs are forecast to be in households, with only around 29,000 forecast in the non-domestic sector.
Based on the same predictions, the authors maintain that there will be significant growth in the total net CO2e benefit from heat pumps from around 0.35 million tonnes in 2013 to 2.07 million tonnes in 2020 ((excluding AAHPs). There is a similar pattern when AAHPs are included in the analysis, with net benefits of almost 6 million tonnes in 2020.
It is also suggested that a reduction in leakage rates would have a significant effect on the long-term net CO2e benefits of heat pumps.
Copies of the report are available here