Thursday24 August 2017

Green Deal benefits overstated, study claims

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Study finds calculations used to work out benefits of retrofit work overestimates energy savings achieved by up to 77%

Heat sensitive house picture

The system used to calculate energy savings under the Green Deal, which is critical to the flagship energy efficiency programme’s success, is unreliable and inflates the savings a householder can expect to achieve from retrofit work to their home by as much as 77%, a study has found.

Social housing provider Affinity Sutton, which produced the study, monitored the effect of retrofit work carried out by contractor Keepmoat on 102 homes over the course of a year.

The data, analysed by consultants Verco, Baily Garner and Parity Projects, found that the SAP model, which is used to calculate building performance, on average predicted that tenants would save 77% more on their energy bills than they actually did.

The SAP model is central to the Green Deal assessment process and is used to ensure Green Deal packages meet the scheme’s “golden rule”, which states that measures must deliver more in energy savings than the cost of having them installed and financed.

But the report concluded that the “golden rule” calculation the Green Deal rests upon is “not entirely reliable”.

However, it said that the occupancy assessment, which also forms part of the golden rule calculation, would have a “mitigating effect” on the unreliability of the energy savings predictions under the Green Deal. But methodology for the occupancy assessment had not been put in place when the study was conducted.

“This makes the Green Deal a lottery for our residents. A few may benefit, and even fewer may do even better than expected, but the majority are likely to lose out with energy savings less than the annual Green Deal payments,” the report said.

It concluded that 61% of homes would make some sort of saving on their bills, but only one in four would save what was predicted through the SAP modelling.

However, the study also found that 73% of residents felt their homes were warmer after the works took place.

Jeremy Kape, director at Affinity Sutton, said the fact that the modelling was not reliable made the Green Deal particularly risky for low income households.

He said: “If [the modelling] is wrong, the impact on fuel-poor vulnerable households is more significant than those who have lower exposure to their fuel bills.”

He said Affinity Sutton would not be using the Green Deal to fund retrofit, but instead would look to treat all its lofts and cavity walls and fund other measures through the Energy Company Obligation, which funds energy efficiency measures for low income and vulnerable households.

Sustainability expert David Strong said he feared it could result in accusation that the scheme was “misselling”.

He pointed out that people’s energy usage patterns tends to change when heating becomes cheaper or homes become warmer.

“If you are being strictly theoretical about it, SAP is not probably far out [on savings].

The problem is when these other human factors come in,” he said.

The study also found that over half of properties experienced problems following retrofits many of which related to damp, ventilation, or residents not being able to work heating systems.

Kape said it was important that residents had extensive advice on how to use systems to avoid risks to health from damp homes. “It’s about making sure they adapt [the lifestyle] in their own homes,” he said.


Readers' comments (5)

  • This is selectively reported. From reading the actual document it’s apparent that the 77% discrepancy excluded the effect of both in-use factors (IUFs) and actual occupancy assessments (OAs). When Affinity Sutton included the Green Deal IUFs the 77% became 53%. Then they acknowledge that using an OA instead of 'standard occupancy' would further reduce the discrepancy, but they do not quantify it (presumably because they didn’t collect any actual occupancy data). Given the extent of under-heating in some poorly insulated homes, a 53% discrepancy wouldn’t surprise me at all – which is precisely why the OA is used for Green Deal.

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    I would agree with Neil Cutland's comments. The Occupancy Assessment (OA) in Green Deal is absolutely critical to give the householder a more bespoke calculation of their savings, based on their actual occupancy. 73% of residents said they were warmer after the work - demonstrating that they were under heating their homes in the first place. The OA would have been able to model this. The OA is a new concept and itself will need optimisation based on feedback. But it's a significant step forward compared with "standard occupancy" in SAP.

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  • Neil, I felt the significance of this finding about SAP warranted it being singled out from the rest of the report, which is why I reported it this way.

    However, I acknowledge the occupancy assessment is a crucial part of the Green Deal assessment methodology and you’re right, as the study says, it would have a mitigating effect on the level of energy savings expected. I have amended the story above accordingly.

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  • "We only want slam dunks."

    "The basket will be set at 17 feet."

    Hey, why is everybody on ladders?

    The "Golden Rule' must have been created by a bunch of people smoking pot, who failed high school math. The numbers don't line up. Energy Efficiency, even cherry picking energy efficiency is rarely free at the residential level. Just because they wave a magic spleef will not make it so.

    This is the same stupid presumption many programs are built upon in the US.

    So what happens? Cost effectiveness is lied about so it can be reached. 53% to 77% is about the lie in the US too:

    http://bit.ly/2007NYSERDAhpwesresults -The first report I found has program realization at .38 (see appendix page 13)
    http://bit.ly/NYSERDAandreattareport - the "we suck less" report - see conclusion at bottom
    http://bit.ly/2012HPwESImpact - didn't turn out as well as "we suck less" report projected

    Look, people want to fix their homes. Help them do that. Of course public money must be spent cost effectively, so pay incentive for the Energy Savings that meets the public value of the Negawatt, and leave decisions around "project cost effectiveness" to the people purchasing the projects.

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  • Simon Guy

    This article highlights the importance of human factors in the realisation of Green Deal savings. We agree, however, with the other comments above that it is very misleading as it relies on what is a flawed study.
    The Verco study is based on use of SAP 2005 which is not used in the Green Deal. It ignores the existence of an Occupancy Assessment methodology which was specifically developed to adapt SAP 2009 for Green Deal purposes, and highlight to home owners the importance of specific usage patterns on the potential savings that can be achieved.
    It also fails to apply in-use factors which significantly reduce SAP-predicted savings and uses bill data where only 41% is based on actual meter readings, with the rest based on energy company estimates, thereby rendering any conclusions based on the study highly dubious. In summary the Verco study uses a calculation that is significantly different to that which is embedded in the Green Deal system.
    There are also a number of points of accuracy to make on the related article by Rick Wheal of Arup on the calculations required for a Green Deal assessment. The algorithms in SAP have evolved considerably over time and they certainly do not rely on data from the 1980s as stated. For example the occupancy, lights and appliances and water heating procedures have all been thoroughly reviewed and updated in the past few years.
    Of course, SAP uses the same basic approach now as it always has done, and this is to be expected. The same would be true of any model with a similar purpose, including detailed building dynamic simulation models. Whilst human factors and lifestyle patterns may change over a period of time, the laws of physics do not change quite so often!

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