Shape of things to come

It seems almost inevitable when it comes to creating sustainable buildings that they set out to save the planet, but often end up costing the earth. Many of the finest examples of ultra-environmentally friendly buildings are statements made by clients who have the money to back up their eco-principles.

This is all very well, but unless sustainability can be seen to be cost-effective from the outset, then a lot of clients may decide against trying to achieve it. The question is, how to make sustainable building available to all levels of client?

The newly built Environmental Building at Plymouth College set out to achieve just this, balancing capital cost with an eye to being environmentally friendly, client and consultant alike have created the kind of pragmatic sustainability which others may find less daunting to emulate.

The building itself is a 2 500 m2 four-storey extension to Plymouth College to provide additional teaching areas and a student refectory in this rapidly growing centre of further education.

The original client brief was for a development that was low-energy, low-emission and low-maintenance, but fell within the constraints of the £850/m2 budget. The college were insistent that the building should be seen as an environmental exemplar, displaying design methods that other developers could adapt to future projects at a cost that would be comparable with conventional construction methods.

The college demanded that the building's four floors were all to serve different purposes. The basement was to provide a proposed 24-hour distance learning facility, where lecturers would be on round-the-clock call to students with queries. The ground floor would be the refectory and kitchen with teaching areas on the upper levels.

Appoint to prove
The design team appointed to achieve these demands consisted of Hoare Lea as the m&e consultant engineers with Kay Elliot as the main architect and Airey & Coles as the structural engineers.

It was decided that the extension would be connected to the existing tower block that was currently used for housing the college's IT equipment. The original design of the tower block had led to complications with its ability to cope with the college's IT demands. Jerry Barnes, partner at Hoare Lea explains: "The problem was that the tower was built back in the early 60s and building design and requirements were far different. The building was naturally ventilated with lots of glazing, which has led to problems with high solar gain on the south-west side from direct sunlight and glare problems on computer screens."

As a result the college looked to put a new building on to the end of the tower block that would address these issues, rather than simply expanding the existing block.

During the initial design stage there were a number of integrated meetings between the design team and the client. The very fact it was to be an extension to an existing building combined with the variation in facilities proposed for the new structure provided a number of challenges for the design team.

Interestingly, as the college was insistent that the project costs were kept to a minimum whenever possible, one of the key processes in the design development was to take the unusual step of employing the m&e consultants on a time-charge basis right up to the scheme design stage. Barnes says: "We felt this was the best way for the college to achieve its objectives. Employing the m&e consultants on a time-charge basis until such a late stage is not common practice, but we felt that if the building was to be seen as an exemplar then it was the way to go."

The engineers and architects working in tandem with the client produced a final triangular shaped plan that at first glance may not be considered as the ideal shape for a building that was supposed to save costs by maximising space. Yet it proved to be the ideal shape.

Barnes explains the thinking behind the design: "At first we looked at how the sun travels round a building and how there can be problems with solar gains on the south-east, south and south-west facades. Because of the requirements for IT we wanted to minimise solar gains. Secondly, we wanted to make maximum use of natural north light, which provides savings on energy costs and gives glare-free light."

The design team considered an L-shaped building, but discounted it on the basis that it would suffer with high solar gains from the south. They then considered adapting the L-shape, by moving the building around and attaching a south facing high-mass wall with minimal glazing, creating the triangular design and also incorporating an atrium feature. The theory is that the thermal mass of the wall will soak up the solar energy, while maximising north light on the adjacent sides. The building also has two stairtowers at either end which utilise the otherwise redundant corner space.

The internal structure of the building has been extensively exposed to take advantage of the building's thermal mass and help control the internal environment. There are no false ceilings in any of the classrooms which helps to aid night-time cooling. The building is steel frame with concrete plank flooring and high mass concrete block walls. All cavity walls comprise of a conventional outer leaf facing brickwork, partial fill cavity wall insulation and inner leaf insulating plastered blockwork. As a result the building can return U-values of 0·35 W/m2K for the walls and 0·25 W/m2K for the roof.

Bright idea
The creation of an atrium allows natural ventilation of the classrooms from the external perimeter windows and also brings in light. With the college's desire for the use of natural over mechanical ventilation wherever possible, the atrium has proved to be highly effective.

Night-time cooling is achieved by the installation of vents in the north-west and north-east facades, which open automatically under the control of the building management system, and cross-ventilate with the atrium area. On the top of the atrium there are mechanical extract fans that draw air from the atrium at times when the passive ventilation system is not sufficient.

The sub-basement area houses the college's 24-hour distance learning facility and an abundance of IT equipment. It is a totally enclosed central space and requires an under-floor displacement ventilation system, which is connected to an exterior air to water heat pump. Using an earth coupling system would have undoubtedly been more environmentally sound, but the college's sensible approach of balancing cost with eco-friendly systems meant a heat pump was the ideal solution. Jerry Barnes comments: "The building is not totally green and the whole point of the exercise was to show that you can be both environmentally aware and still come up with a sustainable, good example of a passive building within a reasonable cost."

During the winter heat generated from the sub-basement area is redirected to the atrium via vents providing a simple and economical form of additional heating to the large atrium space. Additional heating is supplied through radiators, which source hot water from the boiler systems in the main college building.

On the ground floor level there are the main refectory and kitchen areas. The plantrooms are located adjacent to the existing building so services can be picked up. In the refectory area there is mixed mode ventilation, this keeps the central space under a slight positive pressure, while the kitchen is kept under a negative pressure, effectively producing a balanced system and stopping smells from the kitchen emanating up to the classrooms.

On the first and second floors are the teaching areas, which are all naturally ventilated with manually opening windows. Inside the teaching labs the lighting is connected in parallel rows away from the windows. By arranging the lighting in this way, and with the use of automatic photocell control, it has been possible to achieve an economic and effective lighting control solution. It means the bank of lights nearest the windows can be automatically switched off when there is sufficient natural illumination in the space, with artificial light supplementing the inner classroom area. Internal windows in the walls between the classroom and the atrium bring in additional light.

Collection point
Solar thermomax collectors are positioned for hot water heating on the south façade. The tubes are used as a canopy on the entrance area. This serves the dual purpose of protecting the building from solar gain and also absorbing this energy and using it to heat the building's domestic water requirements.

There is also a rainwater collection system that collects all the water from the roof and redirects it to a central collection tank, which is then used for flushing the wcs. Unfortunately, this eco-friendly method cannot be relied upon all year round, therefore during the summer, when water levels may drop, the system is backed–up with a mains cold water system.

The designers of Plymouth College's extension are the first to admit that it is not the greenest building around today. So, the question is – how can it been seen as an exemplar building? The key lies in the principles behind the project of balancing costs with environmental awareness. By using a sensible yet innovative approach client and consultants were able to meet the environmental demands and also keep the price down – the final cost came in under budget at £802/m2. The designers set out to show that it is possible to create a sustainable building at a reasonable cost and the Environmental Building at Plymouth College is their proof that it can be achieved.