Dominic Miles-Shenton

Quantifying the domestic building fabric ‘performance gap’

In the UK, there is mounting evidence that the measured in situ performance of the building fabric in new build dwellings can be greater than that predicted, resulting in a significant building fabric ‘performance gap’. This paper presents the coheating test results from 25 new build dwellings built to Part L1A 2006 or better. Whilst the total number of dwellings reported here is small, the results suggest that a substantial ‘performance gap’ can exist between the predicted and measured performance of the building fabric, with the measured whole building U value being just over 1.6 times greater than that predicted. This is likely to have significant implications in terms of the energy use and CO2 emissions attributable to these dwellings in use. Practical application : This paper describes an aggregate approach (coheating test) that has been applied to a small sample of dwellings to quantify the size of the ‘performance gap’. The results suggest that this ‘gap’ can be large (>100%) and can vary depending upon form and construction type. The results also illustrate the importance of developing a larger, more representative whole dwelling heat loss data set. This could be used by industry to apply a suitable performance factor (note 1) to the nominal performance of new build that accounts for the ‘performance gap’. This factor could be specific to form and main construction type.

Bridging the domestic building fabric performance gap

It is recognized that there is often a discrepancy between the measured fabric thermal performance of dwellings as built and the predicted performance of the same dwellings and that the magnitude of this difference in performance can be quite large. This paper presents the results of a number of in-depth building fabric thermal performance tests undertaken on three case study dwellings located on two separate Passivhaus developments in the UK: one masonry cavity and the other two timber-frame. The results from the tests revealed that all the case study dwellings performed very close to that predicted. This is in contrast with other work that has been undertaken regarding the performance of the building fabric, which indicates that a very wide range of performance exists in new-build dwellings in the UK, and that the difference between the measured and predicted fabric performance can be greater than 100%. Despite the small non-random size of the sample, the results suggest that careful design coupled with the implementation of appropriate quality control systems, such as those required to attain Passivhaus Certification, may be conducive to delivering dwellings that begin to ‘bridge the gap’ between measured and predicted fabric performance.

Adding value and meaning to coheating tests

Purpose – The coheating test is the standard method of measuring the heat loss coefficient of a building, but to be useful the test requires careful and thoughtful execution. Testing should take place in the context of additional investigations in order to achieve a good understanding of the building and a qualitative and (if possible) quantitative understanding of the reasons for any performance shortfall. The paper aims to discuss these issues. Design/methodology/approach – Leeds Metropolitan University has more than 20 years of experience in coheating testing. This experience is drawn upon to discuss practical factors which can affect the outcome, together with supporting tests and investigations which are often necessary in order to fully understand the results. Findings – If testing is approached using coheating as part of a suite of investigations, a much deeper understanding of the test building results. In some cases it is possible to identify and quantify the contributions of different factors wh...

Quantifying the aggregate thermal performance of UK holiday homes

In the UK, there are approximately 330,000 holiday homes spread across a large number of mainly privately owned sites. These homes are often sited in exposed locations, are poorly insulated and are generally heated using expensive fuels, such as electricity or LPG. There is also a lack of empirical evidence available on the in situ energy performance of these homes. Consequently, it is not possible, given the existing evidence base, to determine whether these homes suffer from the same scale of building fabric thermal ‘performance gaps’ (between assumed and realised in situ performance) that have been documented for newbuild UK housing. This paper presents the results obtained from undertaking detailed in situ thermal fabric tests on five new holiday homes. Whilst the size reported here is small, the results indicate that a ‘performance gap’ exists for all of these homes. Results obtained indicate that this gap appears narrower than that documented for newbuild UK housing. The results also suggest that the scale of the ‘gap’ may be more a consequence of the way in which the design intent of these homes has been determined, i.e. a ‘prediction gap’. Practical application: This paper presents the results obtained from undertaking detailed building fabric thermal performance tests on a small sample of new holiday homes. The results of these tests indicate that although a building fabric thermal performance ‘performance gap’ exists in all of the holiday homes tested, the results suggest that the ‘gap’ is much smaller than that documented for new build UK housing and may be more of a consequence of the way in which the design intent of these homes has been determined, i.e. a ‘prediction gap’, rather than a ‘performance gap’ between assumed and realised in situ performance. These results could be used by industry to develop more appropriate prediction tools that are relevant to holiday homes.

Off-the-Shelf Solutions to the Retrofit Challenge: Thermal Performance

The potential to reduce energy demand and thus carbon emissions from the built environment is considerable. As well as benefitting the environment, good energy efficient retrofits can reduce energy bills and improve thermal comfort; however, the discrepancy between expected and actual performance can mean the anticipated benefits are not fully realised. If thermal upgrades are to be accepted and adopted the retrofit solutions should be simple and effective and deliver the performance expected. This paper summarises part one of a two-stage Saint-Gobain funded research project which investigated the change in thermal performance resulting from a number of ‘off-the-shelf’ thermal upgrade measures applied to a circa 1900 solid wall end terrace house situated in an environmental chamber. The project involved a phased programme of upgrades to the thermal elements of the test house; thermal upgrades were applied either individually or in combination. Presented are the quantitative measurements of thermal performance at each test phase which are compared against baseline values measured while the test house was in its original condition. The heat loss coefficient (HLC) of the fully retrofitted dwelling was 63 % lower than the dwelling in its baseline condition. 72 % of the HLC reduction was attributable to the application of a hybrid solid wall insulation system. The fully retrofitted test house had a measured air permeability value that was 50 % lower than in its baseline condition. There was close agreement between the calculated upgrade U-value and that measured in situ for most thermal upgrade measures. The primary conclusion of the paper is that dwellings of this type, which represent a significant proportion of the UK housing stock, have the potential to be retrofitted using off-the-shelf thermal upgrade measures to a standard which meets design expectations and can significantly reduce their requirement for space heating and currently associated CO2 emissions.

The airtightness and air leakage characteristics of new UK holiday homes

It is estimated that in the UK, 200,000 residents live in park and holiday homes all year round, the majority of which are elderly and on low incomes. As these homes are often thermally inefficient and leaky, these residents are some of the most susceptible in society to fuel poverty. Despite this, there is a dearth of empirical data available on the in situ fabric performance of these homes. This paper presents the results obtained from undertaking a series of pressurisation tests and leakage identification on new build holiday homes. While the sample size reported is small, the results indicate almost a factor of two variation in the airtightness performance of the homes. In spite of this, all of the homes achieved an air permeability significantly lower than the default value incorporated within the industry standard Energy Efficiency Rating Calculator, suggesting that a much lower figure may be more appropriate. The results also suggest that the use of the air permeability metric within the calculator potentially biases the performance of holiday homes due to their particular form factor, and that this bias could be mitigated against by adopting the air leakage metric within any future revisions to the calculator.

Assessing the quality of retrofits in solid wall dwellings

Purpose The purpose of this paper is to provide a detailed appraisal of the quality of domestic retrofits. Design/methodology/approach This paper presents the results of technical surveys on 51 retrofits undertaken before, during and after the retrofits. Findings Failures are observed to be endemic and characterised into five themes: 72 per cent showed moisture issues pre-retrofit, 68 per cent had moisture risks post-retrofit, 62 per cent did not adopt a whole house approach, 16 per cent showed inadequate quality assurance protocols and 64 per cent showed evidence of insufficient design detailing. Each theme is further subcategorised with a view to identifying implications for future policy. Research limitations/implications The findings suggest the 10 per cent Ofgem retrofit failure rates predictions are an underestimate and so there may be a need for additional investigations to understand the trend across the UK. Practical implications Recommendations to reduce the failure rates may include making changes to the current inspection regime, widening understanding among installers; providing standard repeatable designs for repeated features; and empowering occupants to trigger inspections. Social implications The sample is representative of a substantial proportion of the homes in the UK suggesting that retrofit quality may in many instances be below the required standards. Originality/value Risks of moisture issues and underperformance in domestic retrofit are a concern for government industry and households. This research shows that many installation failures are the result of not implementing existing guidelines and a change to the enforcement of standards may be needed to enact a fundamental change in installer practice and process control.

Quantifying the performance of a passive deaerator in a gas-fired closed loop domestic wet central heating system

In the UK, approximately 16% of the energy use can be attributed to domestic wet central heating systems. Government financial support and advances in technology have led to boilers becoming more efficient and a range of technologies are now available that claim to be able to improve the efficiency of domestic wet central heating systems. One such low cost technology is a passive deaerator. This article presents the results obtained from installing a passive deaerator on the closed loop of a gas-fired wet central heating system, under controlled conditions in the Salford Energy House. The results indicate that although marginally less heat output was required from the boiler when the passive deaerator was operating, these savings are more or less out weighted by the boiler short cycling more frequently. Consequently, the overall reduction is gas consumption achieved by utilising the passive deaerator device is only of the order of 0.5%; this scale of savings may just be a consequence of measurement noise. The implications are that although a marginal benefit may be attributed to these products, if short cycling takes place, then these savings may become insignificant. Practical application: This article describes a test method that has been used to quantify the energy savings that could be achieved by installing a passive deaerator on the closed loop of a wet central heating system. Although the results indicate that the energy savings associated with using such a device are likely to be marginal, the test method described could be used to test a range of other devices that claim to improve the performance of domestic wet central heating systems, to directly compare before and after performance.