Once the clash was discovered, post-handover, the venetian blinds were replaced with roller blinds only covering the main part of the window. This enables the fanlights to open and for the air to flow easily. Anti-glare film was fixed to the fanlights on the south-facing side (and all other glass panels above blinds) to reduce residual glare.
Surprisingly, given the problems caused by clashes of this nature, conflicts between openable windows and inappropriate blinds are widespread.
Getting a tick in the box for a BREEAM credit is all well and good, but implementation really does need to be thought-through. There is no way that BREEAM could assess for this kind of problem as it would become a huge unwieldy monster with very complicated ifs-and-buts type questions to get credits.
Energy is the main measure of a building's environmental footprint. A high BREEAM or LEED rating at the design stage is often held to be an accurate indicator of a building's operational energy use. While this might be the case, the two should not be confused. Not only is the association between design aspiration and in-use performance rather fragile, but energy is only one of several metrics in both BREEAM and LEED.
For the year to April 2009, VillageGreen used 530,000 kWh, or 260 kWh/m2 per annum, for electricity and fossil fuel. This is way above the ECON19 good practice benchmark for an open-plan naturally ventilated office (133 kWh/m2 per annum), slightly above the typical value (236 kWh/m2 per annum). However, against the Display Energy Certificate benchmark of 95 kWh/m2 per annum quoted in CIBSE TM46:2008, the building's performance looks rather worse.
Obviously this is disappointing for a building with strong environmental credentials. However, the building doesn't fit perfectly into TM46 and ECON19 benchmark peer groups, as it has a ground floor showroom and a data centre - things normally not associated with a naturally ventilated office.
Gas consumption for space heating and domestic hot water is 74 kWh/m2 per annum compared with the (good practice) benchmark of 79 kWh/m2 per annum, probably a reflection of higher insulation and airtightness standards in the Building Regulations. Electricity consumption over both floors comes in at 186 kWh/m2 per annum, which is high compared to the ECON19 good practice value of 54 kWh/m2 per annum, and also the typical value of 85 kWh/m2 per annum.
Although this performance looks poor, there are militating circumstances. For a start a data centre is not normal for a naturally ventilated office, and the one at VillageGreen serves more than one site. Meter readings from submeters to the data centre suggest electricity consumption of 123,500 kWh per annum, a sizeable chunk of the overall power consumption.
Then there is the ground floor showroom. The lighting here is manually controlled, and for aesthetic reasons is kept on for visitors or clients. In contrast, lighting in the first floor office space is much more energy efficient. Each individual luminaire has sensor control, detecting both lighting levels and movement. There is also a manual override for those times when light is absolutely necessary. The day of BSRIA's visit was bright, and while very few of the first floor lights were on, all of the showroom lights were on.
The difference in power consumption of the two lighting strategies is clear from the submeters. The first floor lighting consumes around 27,000 kWh per annum, while the showroom consumes 111,300 kWh per annum over a smaller floor area.
Even allowing for the age of ECON19 benchmarks, VillageGreen demonstrates the difficulties of benchmarking the energy performance of a building that doesn't quite fit in any of the benchmark peer groups. Benchmarking has to be done with great care. End-uses need to be separated out or at least highlighted.
If VillageGreen didn't have a showroom or a data centre, its performance would be more respectable. Fortunately the lighting and small power for the traditional office space on the first floor are metered separately. Lighting is about 27 kWh/m2 per annum, with the small power coming in at 34 kWh/m2 per annum. These compare to good practice benchmarks of 22 and 20 kWh/m2 per annum respectively in ECON19. The typical benchmarks are 38 kWh/m2 per annum and 27 kWh/m2 per annum. So lighting is within the right range and small power a bit high.
When the lighting and small power from the first floor is added to the energy use for heating and domestic hot water, this gives a rough value of 138 kWh/m2 per annum - very close to the good practice value in ECON19. While VillageGreen has room for improvement in comparison with the benchmarks, it's by no means the high energy consumer the headline figures suggest.