Post-Occupancy Evaluation

Post-Occupancy Evaluation (POE)

Posted by on Aug 13, 2014 in Post-Occupancy Evaluation | Comments Off on Post-Occupancy Evaluation (POE)

Post-Occupancy Evaluation (POE)

We are interested in how Passivhaus buildings actually perform and we thought you might be, too. We want to understand how occupants are finding living in low-energy homes and whether their Passivhaus homes are living up to their (and our) expectations. The following graphs present the first stages of our analysis.  They cover a number of certified Passivhaus dwellings that we have had involvement in over the last couple of years. Read more about: The performance gap Energy benchmarks & targets Comfort The houses measured Carbon Emissions CO2 emissions take account of all energy used by the household. Standard national conversion factors are applied to the different fuels used by the building occupants, and these factors also take account of energy consumed/lost in generation and transportation.  As carbon emissions consider all energy used by the occupants, and not just the energy that can be influenced by the building design, the final value depends a lot on occupant lifestyle, which is reflected in the data below. We have plotted an equivalent value for the “primary energy” upper limit, which is what the building was designed to use.  As well as this, we’ve plotted the UK 1990 average, the 2012 average (which is interesting because of the increase), and the Government’s 2050 target, which is 80% of the 1990 level. The Passivhaus primary energy limit is pretty close to the 2050 target, although further work would be required (e.g.  in appliances and lighting) to achieve the target consistently. The design primary energy limit of ~18 kg/m2 of CO2 compares fairly well with the average of our houses at 21 kg/m2 of CO2.   Heating Energy We wondered what the performance gap was between the heating energy predicted in each PHPP and the reality, and how this compares to some other well-known targets.  Nearly all the buildings perform better than the PHPP prediction. Generally, the average internal temperature is comparable to the PHPP prediction of 20oC, but there are some oddities; house 12, for example, is using a lot of energy, but is on average fairly cool. Further investigation is needed to understand what’s happening here. It may be a building fault, or just that the windows are being left open. Note that most of these figures relate to heating season 2013-14, apart from house 23, which was 2011-12.  The data has not yet been corrected for the variation in weather. If you’ve got a project you’ve got data for and you’d like us to include it in this analysis, please...

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POE: The Performance Gap

Posted by on Aug 13, 2014 in Post-Occupancy Evaluation | Comments Off on POE: The Performance Gap

This post is part of a series on post occupancy evaluation (POE). Click here for the main article. The performance gap describes the well-recognised disparity between designed and in-use energy consumption. There is extensive interest in the performance gap right now; see Zero Carbon Hub’s work: http://www.zerocarbonhub.org/current-projects/performance-gap.  There are many examples that show that the performance gap observed when using complex technologies to make a building zero carbon is often greater than when a fabric first approach is used. Conversely, many traditional buildings use less energy in use than they do when simulated (usually because residents live in uncomfortable conditions). Passivhaus buildings in Europe have demonstrated in-use energy consumption very close to the simulated targets*. This is because the standard assumes a high level of comfort as standard and the assumptions within the calculations better reflect how low energy buildings really behave. We thought we would put this to the test and identify the performance gap for some of the Passivhaus buildings that we have been involved with.   * As pointed out by one of our blog readers, this statement is slightly misleading. The data we were referring to is presented on passipedia for those who can access it. The summary of the data on passipedia states “Different users, even if they live in identically constructed houses, frequently have very different consumptions: deviations of ±50% from the average value are not exceptional.”   A variation of ±50% from the simulated targets could be argued to be quite significant.  However we observed that, although there is variation amongst users in both Passivhaus and non-Passivhaus developments, the data suggests that the variation from the mean is lower in absolute terms in Passivhaus developments. Perhaps our statement above should be amended to ‘Passivhaus buildings in Europe have demonstrated in-use energy consumption close (±6kWh/m2.yr) to the simulated...

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POE: Energy Benchmarks and Targets

Posted by on Aug 13, 2014 in Post-Occupancy Evaluation | Comments Off on POE: Energy Benchmarks and Targets

This post is part of a series on post occupancy evaluation (POE). Click here for the main article. An energy benchmark provides a reference level of energy consumption, against which other buildings can be compared. An energy target provides a minimum aspirational level of energy consumption. Benchmarks are ideally based on data from a sample of real buildings and can be used to compare buildings in use (e.g. the low energy buildings database: http://www.lowenergybuildings.org.uk/).  Targets, on the other hand, are usually calculated from computer simulation or mathematical models and can be used to compare building designs (e.g. PHPP, SAP).  There is not much ‘in use’ benchmark data available worldwide as it is difficult and expensive to collect. To address this lack of data we have decided to collect data on a number of projects that we have been involved with over the last few years. In Passivhaus we normalise all data based on floor area.  This means that the energy limits do not reflect the number of occupants in the...

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POE: Comfort and Energy Consumption

Posted by on Aug 13, 2014 in Post-Occupancy Evaluation | Comments Off on POE: Comfort and Energy Consumption

This post is part of a series on post occupancy evaluation (POE). Click here for the main article. When assessing energy consumption it is critical that buildings are “normalised” for thermal comfort.  For example, if you keep your home at 15 oC throughout the winter then your energy consumption will be much lower than a house at 20 oC (if all other conditions were the same then this would represent a rough doubling in energy consumption). Typically, temperature and humidity are measured as a reflection of internal comfort. We have this data for most of the projects.  CO2 and VOC levels are useful to understand the air quality, but are more expensive to monitor, and we haven’t included this information here. In addition, measuring the in-use ventilation rate would be interesting, but is not often undertaken as it’s much harder to do, and whilst it does have an impact on the energy consumption it is not as significant as the internal...

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POE: The Houses Monitored

Posted by on Aug 13, 2014 in Post-Occupancy Evaluation | Comments Off on POE: The Houses Monitored

This post is part of a series on post occupancy evaluation (POE). Click here for the main article. All the houses are new-build and have been certified to the Passivhaus standard.  Some of the houses have been monitored by ourselves, and some by a third party. The houses that are heated with gas are a mixture of owner-specified detached dwellings and terraced social housing.  Some have solar hot water but most are fed from combi. boilers. The houses that are heated by electricity are all terraced social housing and have solar hot water...

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