Taking the PV out of the total consumption brings down the energy intensity to 25 kWh/m² per annum. While not zero carbon, this means that the total annual CO2 emissions are below 3 tonnes a year or 13.4 kgCO2/m² per annum. The Zero Carbon Hub has best practice benchmarks of 10 kgCO2/m² per annum for regulated loads in detached houses, while data from DECC’s housing energy fact file produced benchmarks of 12.7 kgCO2/m² per annum for appliances and 2.2 kgCO2/m² per annum for cooking. This would give a combined total benchmark for regulated and unregulated loads of 24.9 kgCO2/m² per annum. This means that the vicarage is performing at just over half the benchmark for emissions.
The areas performing above the SAP predictions are the energy consumption of both the ground source heat pump and the MVHR unit. This is not the first site to experience difficulties with these technologies. Looking through the back catalogue of a number of journals, magazines or news websites, it isn’t difficult to find a story about nonperforming installations. But what is the problem? Well for the vicarage this isn’t known without further investigation, but typically it is related to incorrect operation or commissioning issues.
One issue that can be confirmed is the additional energy consumed by the electric heater within the heat pump. The monitoring has shown that this is coming on over significant portions of the year, mainly in the colder months. Why is this? Well there are a number of possible reasons, such as controls, sizing of the heat pump, storage size. As can be seen in the graph of instantaneous power, the heater mainly comes on during the heating season.
A building is a sum of its parts, hard materials and services. But a home is a place where people feel comfortable. So, naturally occupant comfort is an important factor in producing a sustainable home. A vicarage is not typical in terms of home occupancy patterns as it is a work-live set-up, leading to higher than average occupancy hours. This may have led to part of the difference between the SAP calculation energy usage and the actual consumption.
Temperature measurements show that the internal temperatures remained relatively stable at around 24°C. During the warmer periods of the summer the internal temperatures never reached the highs of the external temperatures, but still increased. Conversely during the cold spell at the beginning of 2013 internal temperatures remained comfortable, and only dropped below 20°C in the study and bedroom during periods when the building was unoccupied. This was confirmed by the occupant interviews. When asked about the temperature in winter the response was: “excellent, we never feel cold in the house.” They also felt that the air quality was “definitely better than average.” They do however like to open the windows both in summer and winter. “In summer we needed to open the windows as we feel we need more fresh air in the house,” the vicar commented. But added, “with the windows open we felt the air quality was sufficient.” Talking about colder times of year he said, “I think overall in the winter it is a very comfortable place to live.” The amount of natural light was also a positive point for the occupants, as was the image. “Most people who come to the ground floor think it is the best house they have ever been to. It has a very good image to visitors. Sometimes people even take pictures of the house.”
The biggest complaint from the occupants is the lack of storage space and shapes of some of the bedrooms. The master bedroom is too long and narrow and doesn’t work very well.
But the real positive aspect has been how moving into the new vicarage has affected the way the vicar and his family think: “if you live in this house you become very sensitive about how much water and electricity you are using. It really makes you think about what you are using”.
The overall view
So while the building has not matched the predictions of the assessment software, this is not an uncommon occurrence. SAP makes many assumptions, which do not necessarily match the operational nature of the building. Other teething problems, such as issues with the heat pump, can compound the increase in energy consumption over the predicted values.
But is the project a success? Well from the occupant point of view it is a building they like. It has made them more aware of their energy consumption, and is a pleasant environment to live and work. These positives can be built on to help drive the energy consumption down, and learn lessons for future developments.