Heat pumps convert heat from a lower temperature to a useful higher temperature. The heat is used for space, water and manufacturing process heating. The low temperature heat source can be air, water, ground or low temperature waste-heat. Heat pumps make use of the refrigeration cycle. They rely on the specific refrigerant properties including performance and safety. According to the European Heat Pump Association (EHPA), for each kW of electricity consumed by a heat pump, about 4kW of thermal energy is generated. This corresponds to a 300% efficiency whereas all direct heating methods are less than 100% efficient. EHPA reports that there were 10.7 million heat pumps in the Europe in 2017. Heat pump tumble dryers are electric powered and are typically 40% to 50% more efficient than the most efficient condenser electric tumble dryers, contributing to reduced greenhouse gas emissions. Heat pump water heaters for domestic or other hot water systems raise the temperature to higher temperatures (>60°C) compared to space heating requirements (25-40°C). Due to its non-flammability and properties, R-134a is used as refrigerant for some heat pump water heaters. For combined space/water heaters R-32 is being implemented for some systems.
The majority of heat pumps use fluorinated hydrocarbons. The HFCs, R-410A and to lesser extent R-407C are used in most heat pumps, with R-134a and R-407C being used in heat pump tumble dryers. R-32 is replacing R-410A for air- or water-to-water heat pumps, which is facilitated due to the water circuit transferring the heat. R-32 has higher efficiency than R-410A and a lower GWP (675 compared to 2088 for R-410A) contributing to lower over greenhouse gas emissions. R-407C is typically used for water- or ground-water heat pumps. The mildly flammable HFC/HFO blend refrigerants R-454C or R-455A refrigerants with GWPs less than 150 have properties that may make then suitable as alternatives to R-407C but only in new equipment. The non-flammable HFC/HFO blend R-450A is being used for heat pump tumble dryers as an alternative to R-134a as it has similar properties and a GWP of 605 (compared to 1430 for R-134a).
The Renewable Energy Directive sets a new, binding, renewable energy target for the EU for 2030 of 32%, including a review clause by 2023 for an upward revision of the EU level target. Heat pumps can contribute to achieving this target as they are included in the directive as sources of renewable energy:
‘ambient heat’ means heat energy at a useful temperature level which is extracted or captured by means of heat pumps that need electricity or other auxiliary energy to function, and which can be stored in the ambient air, beneath the surface of solid earth or in surface water. The reported values shall be established on the basis of the same methodology used for the reporting of heat energy extracted or captured by heat pumps;
Regulation 517/2014 on Fluorinated Greenhouse Gases contains measures that apply to heat pumps containing HFCs. These are all the measures that have the objective of reducing emissions through leakage checking, recovery, and training and certification. While the HFCs used in heat pumps and, from 2017, for imported pre-charged heat pumps must be within the HFC quota system, there are no placing on the market restrictions for heat pumps (see also the stationary air-conditioning applications page). This recognizes the valuable role of HFCs as refrigerant for heat pumps7.
The possible leakage of refrigerants from heat pumps is overcompensated by their benefits of reducing emissions due to their energy use, meaning that heat pumps using HFCs blends are appropriate applications to contribute to a reduction in overall GHG emissions when compared to conventional heating technologies. The adoption of lower GWP HFCs, HFC/HFO blends or HFOs, compatible with safety requirements and performance together with well-designed systems and leak prevention will reduce emissions further.
A report for the UK Department of Energy and Climate Change addresses the net benefit of heat pumps in the UK, taking into account the environmental costs associated with refrigerant leakage. The primary research and modelling indicated that whilst leakage led to significant CO2 emissions, this was nonetheless a small proportion of the total reduced emissions associated with heat pump technologies. It also highlights that there is scope to reduce leakage further, thereby increasing the net benefit associated with heat pumps.
It was determined from analysis of F-gas log books that annual leakage rates from operation of heat pumps were of the order of 3.8% of installation charge for non-domestic applications and 3.5% for domestic applications. However, these log books were generally of poor quality, leading to significant uncertainty within the modelling of this data.
Optimum charging has an impact on energy efficiency performance. Tests suggest that a refrigerant charge reduction of 10% would lead to a relative coefficient of performance (COP) reduction of about 3% in heating and 15% in cooling operation respectively. Undercharging the heat pump by 40% would reduce the relative COP by around 45% in heating mode and 24% in cooling operation. For the heating mode in particular this is a very significant reduction in performance.
The roll-out of heat pumps provides benefits in terms of their replacement of existing fossil fuel heating technologies. This benefit is determined by calculating the reduction in CO2 emissions compared to these counterfactual technologies. The results of this analysis show that for the UK the level of benefit is an order of magnitude greater than the emissions associated with refrigerant loss.
European Heat Pump Association Heat Pump website https://www.ehpa.org/
2018 AFCE Final Report Energy Efficient State of the Art of Available Low-GWP Refrigerants and Systems. This report can be downloaded from the AFCE (Alliance Froid Climatisation Environnement) website at http://www.afce.asso.fr/wp-content/uploads/2018/10/Final-rapport-energy-efficiency-GWP-2018.pdf
Impacts of Leakage from Refrigerants in Heat Pumps, Eunomia Research & Consulting Ltd and the Centre for Air Conditioning and Refrigeration Research (London Southbank University) March 2014
Proposal for a DIRECTIVE OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL on the promotion of the use of energy from renewable sources (recast) COM/2016/0767 final/2 – 2016/0382 (COD)