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A two year Building Performance Evaluation Study, supported by the Technology Strategy Board and the University of East Anglia, has verified that the Wimbish Passivhaus development meets Hastoe’s objective of delivering very low heating bills that reduce the impacts of fuel poverty on their tenants, and that have the potential to reduce rent arrears. The development performs as designed. The occupants have homes that are economic to run, healthy to live in and feel comfortable and spacious. Some residents state that their heating bills are only £120 a year.
Wimbish Passivhaus was completed back in 2011, and was a first for all involved in creating the scheme. The development was the subject of a Building Performance Evaluation study supported by the Technology Strategy Board (TSB). All 14 units were equipped with sensors to log energy consumption, thermal comfort, and air quality.
Measured performance data and occpancy feedback from this study was presented at the 2014 UK Passivhaus Conference. The data proves that the housing is performing as predicted.
Findings
A Passivhaus is expected to be comfortable at all times. The mean temperatures in February 2013, the coldest month during the study, were within a degree or two of the Passivhaus design level of 20 °C. The residents reported “never feeling cold” and “hardly ever use heating”.
On average, the properties show a gas consumption saving from the Ofgem medium expectation of around £500 a year (excluding VAT). Electricity consumption in the houses ranges around Ofgem’s medium figure of 3,200 kWh a year.
This significantly exceeds the Passivhaus design expectation. The consequences of this ‘normal’ electricity use are ‘normal’ electricity bills, and an additional heat gain. In winter, this heat will reduce the gas demand, but in summer, it may need to be purged from the properties.
The mechanical ventilation with heat recovery delivers good air quality, thermal comfort, and heat recovery. But, the fans are generally working a bit harder than they should and using more electricity.
The annual cost of running the fans is about £50, this enables the gas bill saving. The Passivhaus approach sets high expectations for the build. Wimbish fabric tests returned slightly disappointing results; however, the extra cost of heating the largest 3-bed properties would only be about £10 a year, illustrating the resilience of the approach. Wall u-values from in-situ tests were worsethan the design and air permeability retests found some deterioration (though these results are still
much better than building regulations require).
The residents tell us they like the generally warm internal temperatures. However, this can make it easier for temperatures to rise during a hot spell. Some households accept feeling hot in a heat wave, but others do not. It seems that if residents know what to do to control the temperature then peaks are more acceptable.
Variations in summer warmth may be explained by many factors including excess heat gains from appliances, high occupation density, small properties, and residents not always behaving as expected. The study has confirmed that building to Passivhaus quality is the way to deliver excellent low energy homes at an affordable cost, delighting both residents and the housing association. This is remarkable because the development was a first for all involved and the experience will bring future improvements.
Copy of the Report can be downloded at Wimbish Passivhaus.
Source: Passivhaus Trust & Wimbish Passivhaus