Birchensale School 2

The PROBE Team has maintained a watching brief with the designers of the extension building – ECD Architects and m&e engineers Whitby Bird. The PROBE Team's role has been to help fine-tune the design based on the findings from PROBE post-occupancy studies. This has ranged from proffering advice on a wide range of issues, from lighting controls and acoustics, to the amount and location of storage spaces.

In this context the researchers have been acting purely as passive commentators and information providers rather than formal consultants. The Team has identified potential pressure points, related instances of problems in similar buildings studied in the PROBE project, and monitored the usefulness of those lessons to the Birchensale design team.

The first article in this series of three was published in the June 2000 issue of Building Services Journal. Readers should read that article for full details of the project. What follows is an analysis of the building prior to the tendering process which began on 19 February. Start on site is scheduled for 14 May 2001.

Matters arising
The extension building and refurbishment works will double the school's accommodation, from 300 to 600. The budget is £1.35 million, which equates to around £740-750 m2. It will house classrooms, an IT room, laboratories, communal spaces and circulation corridors.

The building's brief was well advanced by the time the PROBE Team became involved, so it was only possible to suggest modifications to the extension rather than have a major influence on its structure, form and internal layout.

After the first round of PROBE Team discussions (June 2000), the Council put the project on hold to deal with more immediate needs. Work began again in September 2000, but in the interim the original m&e engineer on the project had moved on to other duties, and the architectural team had also changed with Peter Stokes at ECD picking up the reins.

These changes highlight a problem faced by professional teams everywhere, namely how "intelligence" gained during the gestation of a project can survive changes in personnel. While physical records – drawings, specifications and the results of modelling – can easily be archeived and retrieved, the thought process that drove development is more difficult to preserve.

The PROBE Team considered, en passant, that this could seed problems that arise later in a project or even during handover when it is too late to make changes. For example, a contractor might not appreciate the importance attached to a detail – the quality of opening window mechanisms for example – or a user might find that the storage space requested for a specific location has been moved somewhere else.

Here, the design team's principal point of contact has been the school headmaster. ECD Architects has also presented its scheme to the school governors, and two governors have had involvement in the scheme development (one governor is a teacher, and another is the school manager).

This helped them decide optimal location for those elements most crucial to the users of the building, such as teachers' white boards. Worcester County Council has also employed a consultant, Graham Parker, to advise on the layout of laboratories and typical classrooms, and these have also been discussed extensively with the head of science at the school.

Design issues
The extension of Birchensale School was one of a number of projects on the County Council's books. Given the strong environmental agenda local authorities are required to follow, the Council considered how its purchasing power might help it procure low energy products and materials more cost effectively.

Unfortunately the volumes involved – roofing materials for example – were not large enough to obtain significant price reductions. The same was true of the designers' preference for Velfac windows. Other project tenders have come in high, with structure being one factor and the other being preliminary costs (especially the health and safety costs associated with working on a live site with children running around).

ECD Architects has tried to lighten structure and feel that the approach they have taken to containing the extension works during construction should mean they won't suffer to the same extent on high prelim costs. Clearly it is helpful to have other tenders in for similar building works in the locality.

The budget for the Birchensale School extension is quite tight. The design team had to consider reducing structural costs and programming the works. Primarily this involved keeping the extension separate from the existing school building, and only connecting the two late in the project along a designated service route.

Ventilation and acoustics
Given the tight budget, mechanical ventilation was out of the question, save for a landlocked information technology classroom. The perimeter classrooms will therefore be naturally ventilated with cross-ventilation via openable fanlights above the classroom doors.

It was agreed that there were three important issues that needed to be addressed in the specification of the ventilation:

• the importance of positive-friction window mechanisms to ensure windows stay open at different degrees of travel
  
• signage near the fanlights above the doors that reinforce the need for the vents to be normally open
  
• A method by which the users of the building know when ventilation is necessary.

This is because the key to good natural ventilation is not just one of free area, but more to do with the usability and accessibility of the windows and the ability of the hinges to keep the window open at all stages in its travel, particularly in breezy conditions. The preferred windows should provide this, but the PROBE Team thought it important to word the specification in such a way that the contractor is forced to preserve the functionality of the windows irrespective of who supplies them.

The PROBE Team pointed out the lack of robust guidance on default-to-open windows. ECD thought that clear and robust signs, located either by the windows themselves or within the classrooms generally, would help maintain understanding among the teachers and pupils as to the appropriate default settings. There is also the need to ensure that classrooms are "purged" between classes to reduce CO2 levels.

While ECD felt, not unreasonably, that users will have to learn to use and control their spaces more effectively, the PROBE Team thought it would be optimistic to expect teachers to manage the classroom environment at the same time as educating pupils. Teachers may also not perceive the classrooms to be stuffy until levels of CO2 are quite high1.

For this, ECD is investigating simple passive CO2 detectors that darken when CO2 levels are high. These should be located where they provide a fair representation of CO2 levels in the classrooms (ie not subject to draught dilution), while being both tamper-proof and accessible. The PROBE Team felt that, together, these measures could go a long way to ensuring that ventilation effectiveness is maintained.

ECD Architects is investigating simple passive CO2 detectors that darken when CO2 levels are high

The architects are considering fan lights over the classroom doors to create cross ventilation. If these are introduced, some way needs to be found of informing the teachers when the fan lights should normally be open, along with an appropriate percentage of the perimeter windows. The question is: how can that be addressed in the specification? To address the potential problem of noise break-in from corridors into classroom via the fanlights, ECD have designed them as bottom-hinged units that open out into the corridor, which would help to bounce noise back down.

While this was thought worthwhile, the PROBE Team was not sure how effective it would be. The degree of noise intrusion is a function of many variables, such as the proximity of the teaching areas to the noise source, the level and frequency of the noise and the reverberation qualities of the circulation spaces.

For the internal IT room, the designers are considering either making the room's clerestory windows openable or putting in some cassette air conditioning units. The m&e engineers are keen to use the cassettes, first because they will work, and second because they will introduce some cooling into the space. Experience shows that gains in IT space are often higher than anticipated and there is a problem with dissipating the heat, particularly by the often less-than-optimal location of cassette devices.

While low-energy flat-screen monitors are expensive, they may be a worthwhile investment by the school and will serve to reduce the cooling load. The school should be informed about the use of energy-saving screensavers and the need to switch off computers out of hours.

In any case, the controls for the cassettes will need to be easily understood, and this should be made explicit in the specification.

Lighting and solar shading
The design team is keen to reduce reliance on electrical lighting by maximising daylight and reducing glare. The architects and engineers have introduced a fixed, aluminium louvre on the south-west elevation which is designed to protect the bottom two-thirds of the three-element window.

The PROBE Team pointed out that external shading can protect against solar gain but still leave the potential for glare. The design team has recommended blind installation, but funds are not sufficient for incorporating them within the main contract. That means the blinds will be installed under the fit out budget.

If internal blinds are not provided, the occupants will find other ways of obscuring the glass, particularly with classwork. This could mean the lighting may tend to stay on. To reduce the risk of windows acting as postboards the architect has given specific roles to classroom walls. For example, one wall is a traditional teaching wall, another houses storage space while the third will be kept clear for display purposes. "This gives a simple, reasonably clear and understandable structure for the use of the classrooms", said Brendan O'Neill.

The PROBE Team believe that the teaching wall design should work very well and is only likely to be subject to glare in two of the classrooms that face South West, and this is where the internal blinds are likely to be needed most.

The designers have been investigating the use of automatic lighting controls to reduce lighting energy consumption of the standard linear fluorescent fittings. The client has favoured presence detection with daylight sensing for the classrooms, but not for corridors, science labs, workshops or kitchens. The scheme proposed by Whitby Bird will incorporate a 32 minute delay plus manual override.

The PROBE Team's experience is that absence detection can be better than presence detection. With absence detection systems, the lights are switched on manually but go off automatically. This has proved a very robust method of operation in other buildings.

With presence detection, lighting comes on when human movement is detected, and stays on for a programmed period after people have left the space. The problem with presence detection is that the programmed periods can become very long. All lights will tend to come on even when occupation is momentary.

The architect is favouring display panels by the manual light switches which rely on weather symbols – such as sunny, partly sunny and overcast – to tell the users when lighting should be switched on and off. The PROBE Team was open-minded about the usefulness of such panels, but believe that the effectiveness of these and the lighting controls are bound up with the quality of the glare control method. Electric lighting could easily default to on, despite the best intentions of the lighting designers.

The PROBE Team think it beneficial for manually controlled lighting to be controlled in rows parallel to the windows, with the light switches arranged in separate panels next to the icons on the display panel. This could help prevent "sweep of the hand" light switching.

Metering and energy management
The design team is aiming to monitor the energy consumption of the new extension, and this led to a discussion on energy monitoring and targeting methods, and the appropriate number and location of energy meters.

Sub-metering on this project will be needed, mainly because some of the primary services, like the boilers, will be shared between the existing building and the extension.

For the electricity consumption, monitoring will be easier if the sub-circuits (lighting and small power) in the extension can be monitored separately, with meters on the main lv panel monitoring the site's total electricity consumption. By logging the energy consumption on spreadsheets contained in the Energy Analysis Reporting Method of CIBSE TM22, the loads can be easily broken down and analysed.

The PROBE Team suggested that energy metering will need to be installed in such a way that they are useful on a regular basis. This would also be useful to the client in specifying future school projects.

"With all the effort that has gone into designing the windows, the lighting and control systems," said Paul Ruyssevelt, "it would be interesting to compare the electrical demand on this site to an existing demand on another site. If someone could be persuaded to read a couple of the meters on a weekly or monthly basis, then that could be quite useful.