Could the Benefits of Future Building Standards be Affected?
It’s not a recent study, but its contents may have become newly relevant. In March 2014, the then Department for Energy and Climate Change (DECC) published the results of a study commissioned from Eunomia Research and London Southbank University - “Impacts of Leakage from Refrigerants in Heat Pumps”.
Governments are looking for a huge increase in the number of heat pump installations in an attempt to decarbonize the heating of buildings. Leading the charge will be developers of new homes, since these are the easiest to legislate for. The UK government has unveiled its Future Homes Standard and Scottish Government is consulting on a New Build Heat Standard. Neither of these regulations would force developers to install heat pumps in the homes they build, but the standards will be set in such a way that fossil-fuel powered boilers will not comply - the clear intention is to use regulation of the new-build sector to scale-up the heat pump industry.
The approach being considered by Scottish Government is to require heating systems to emit no carbon dioxide at the point of use. Technologies considered to meet this requirement are direct electric heating (panel heaters, underfloor electric, electric boilers), heat pumps and also heat networks (where you could be burning coal at the far end of the pipe but this doesn't count as point of use).
But since the goal of all of this is to reduce global warming, then surely the emissions of other gases that cause global warming should also be considered. It turns out that the refrigerant gases used inside some heat pumps are greenhouse gases that are thousands of times more powerful than carbon dioxide. So long as they stay safely inside the heat pump during its life and are collected up at end of life, there is no problem, but the question the report set out to answer was how much of this refrigerant gas is lost to leaks, and how big an issue could that be?
The researchers examined the logbooks of heat pumps to see how often they had to be re-charged with refrigerant, and also conducted experiments where heat pumps were emptied and then recharged with refrigerant gases and the amount lost in the process was measured.
How Much Refrigerant is Lost?
The report found that:
- 10% of domestic heat pumps experience a leak of refrigerant in any given year
- The median amount lost was 35% of charge (the total refrigerant gas in the system)
- So the equivalent annual leakage rate was 3.48% of the charge
- The mean refrigerant charge for a domestic heat pump was 3.3kg
- So the mean annual leakage for a domestic heat pump is 0.114kg of refrigerant
- Decommissioning losses at end of life were 15% of charge
- Commissioning and recharging losses were around 0.06kg
So if we assume a 20 year life for the heat pump, a charge at commissioning, one recharge and decommissioning at the end of life then the total losses are:
Filling: 0.06kg
Recharge: 0.06kg
Leakage: 10% x 35% x 3.3kg x 20 years = 2.31kg
Decommissioning: 15% x 3.3kg = 0.495kg
Total Refrigerant Losses over 20 year life: 2.925kg
Refrigerant loss per year: 0.146kg
Does it Matter?
At the time of the report, R410A was the most used refrigerant. It has a Global Warming Potential (or GWP) of 2,088, which means that 1kg of R410A released into the atmosphere has the same effect on global warming as if 2.088 tonnes of carbon dioxide were emitted.
So, a refrigerant leakage of 0.146kg per year from a heat pump is like it emitted 305kg of CO2 per year. This is expressed as 305kgCO2e (CO2 equivalent)
The authors of the report compared the impact of refrigerant leakage to the benefits of the low-carbon energy delivered by the heat pump. The annual heating load for a domestic property was assumed to be between 10 and 25 thousand kWh and it was concluded that the impact of leakages was small.
However, the leakage losses from the heat pump does not vary with the amount of heat it supplies. The more heat the heat pump delivers, the less of a penalty the refrigerant leakage is per unit of heat delivered. Conversely the more energy efficient is the building and the lower its heat demand, the more of a penalty the leakage becomes per unit of heat.
Since the regulations are aimed at new homes, perhaps we should instead consider refrigerant emissions in relation to the heat demand of these.
Homes that are built today have very much higher levels of airtightness and insulation than the average building stock. Based on energy calculations we see in our design team, an average sized new build house (say 85m2 total floor area) will have space heating demand around 3,300kWh per year to which you can add 1,600kWh per year for domestic hot water. The proposed standards envisage tightening rules on insulation too, so by then buildings will have an even higher level of thermal efficiency than this.
Many houses are now being built to ‘passivhaus’ standards which remain at a comfortable temperature most of the year without heating, so the annual heating demand approaches a minimum which is that needed for hot water for showers and baths.
If we divide our 305kgCO2e figure by these lower figures for annual energy demand, the contribution to global warming per unit of heat delivered looks very different.
Table 1: Release of refrigerant gases per kWh heat delivered (CO2e)
|
Annual
Heating Budget (kWh) |
2,000 |
3,000 |
5,000 |
10,000 |
25,000 |
Gas Heating CO2 emissions for
comparison |
|
Annual
Emissions from Refrigerant Leakage per kWh of heat delivered (kgCO2e) |
0.152 |
0.102 |
0.061 |
0.031 |
0.012 |
0.208 |
The table shows the global warming impact of refrigerant leakage for each unit of heat provided by a heat pump running R410A for different levels of annual heat demand.
It can be seen that for buildings with high heating demand (such as the levels assumed by the report authors), the CO2e figure is very low compared to delivering the same heat with gas heating. However for very highly energy efficient properties the penalty from the refrigerant leakage rates is very significant – approaching that of gas heating.
Current Refrigerants in Use
Of course, we would expect heat pump technology to have moved on in the last six years and with regulations aiming to phase out the use of the refrigerants with the highest GWP, maybe R410A is no longer in use?
I did a quick straw-poll of the products available today from a range of heat pump manufacturers. As you can see from the table below, there are clearly now models available that work with refrigerant with much lower GWP than the R410A used in the calculation above. Notable leaders are products from Vaillant using R290 (which is propane gas and has a GWP of 3) and from Mitsubishi using R744 (which is carbon dioxide and so has GWP 1) - although both these manufacturers still offer models with the much higher GWP refrigerant for some reason, perhaps cost or efficiency?
It is also clear that there are also many, many models still being sold today that are using refrigerants with GWP above 1,000 and that R410A is still very popular.
|
Company |
Model |
Refrigerant
|
GWP |
Source |
|
Daikin |
Altherma 3 H HT - EPRA014-018DW |
R32 |
675 |
|
|
Daikin |
Altherma 3 R - ERGA04-08EVA |
R32 |
675 |
|
|
Daikin |
Daikin Altherma - EDLQ-CV3 |
R410A |
2,088 |
|
|
Daikin |
Altherma R - ERLQ-CV3 |
R410A |
2,088 |
|
|
Kensa |
Shoebox |
R134A |
1,430 |
|
|
Kensa |
Evo |
R407C |
1,774 |
https://uh8ex3jph2xqg0pb4bs7if12-wpengine.netdna-ssl.com/wp-content/uploads/2017/02/TI-EVO-v6.0.pdf
|
|
Mitsubishi |
Ecodan R744 |
R744 |
1 |
|
|
Mitsubishi |
Ecodan R32 |
R32 |
675 |
|
|
Mitsubishi |
Ecodan R410A |
R410A |
2,088 |
|
|
Panasonic |
Aquarea HT Bi-bloc F Generation |
R407C |
1,774 |
|
|
Panasonic |
Aquarea T-CAP Bi-bloc H Generation |
R410A |
2,088 |
|
|
Panasonic |
Aquarea High Performance All in One Compact J Generation |
R32 |
675 |
|
|
Vaillant |
Arotherm plus |
R290 |
3 |
|
|
Valillant |
Arotherm Split |
R410A |
2,088 |
https://www.vaillant.co.uk/for-installers/products/arotherm-split-heat-pump-58752.html
|
|
Valillant |
Arotherm |
R410A |
2,088 |
https://www.vaillant.co.uk/for-installers/products/arotherm-air-source-heat-pump-2944.html
|
Conclusions
Based on the report, it appears to me that the level of “Fugitive emissions” from heat pumps is significant enough that heat pumps with refrigerant of high GWP should not be considered as zero carbon (equivalent) at the point of use.
This is especially the case when the heat pump is providing heat to a highly energy efficient new building and the emissions ‘cost’ is spread over a much smaller heat ‘benefit’.
Perhaps legislators should consider the global warming potential of refrigerant in heating systems when they create new building standards? Since heat pump models are available with improved refrigerants, perhaps they should consider applying a ceiling GWP value to the refrigerant in use?
I would be interested to hear from colleagues in the heat pump industry about whether this issue has been much discussed, and what the future direction of travel in heat pump technology is to address the likelihood or impact of leakage of refrigerant - please comment below!
