Too cool for school

Heating for educational buildings must cater for the special needs of such premises. As well as ensuring the correct temperature levels are achieved and maintained, it is necessary to consider the safety aspects of radiator design and positioning. Other considerations include energy efficiency, ease of use, maintenance and aesthetics.

The design of heating systems in educational buildings is dictated by a combination of regulations and best practice. Guidance on minimum temperatures is provided by the Education (School Premises) Regulations 1996. This states: “Each room or other space in a school building shall have such a system of heating, if any, as is appropriate to its normal use.” This means that the heating system needs to achieve the minimum temperatures (shown in table 1, below) and take account of the duty of care to the staff and pupils.

The minimum temperatures required for different areas of an educational establishment are as outlined in table 1. In each case the temperature is measured at a height of 0·5 m above floor level when the external air temperature is -1°C.

Most educational buildings use a conventional wet heating system served by central boiler plant, with radiators in most rooms. For spaces with high ceilings, such as halls and gymnasia, underfloor heating may be the best solution, but in all other areas radiators are generally the most cost-effective and efficient option.

However, standard radiators and associated pipework can reach a temperature as high as 75°C, hot enough to cause serious burns within seconds. For this reason, it is important to ensure that children cannot come into contact with these hot surfaces.

The Education (School Premises) Regulations 1996 includes provisions relating to risks from hot surfaces, especially those catering for younger children. The Regulations dictate that in special schools, nursery schools and teaching accommodation used by nursery classes, radiators and exposed pipes that are located where pupils might touch them must not become hotter than 43°C.

The most practical way to prevent children from coming into direct contact with hot surfaces is to use radiators that are designed to eliminate this possibility by incorporating a casing that covers such surfaces. Low surface temperature radiators are designed to do just that, providing a safe, cool-touch solution.

The casing covers the pipework as well as the radiator, so all hot surfaces are concealed. For areas where very young children may be crawling, a bottom grille is also required to ensure that hot surfaces cannot be accessed from below.

Design considerations

In most schools it will be necessary to take measures against tampering and vandalism. Radiator casings should therefore be resistant to physical abuse and use tamper-resistant fixings so the casing can only be removed with special tools.

In areas such as corridors where there is the possibility of collision with cleaning trolleys etc, the casings should be specified for extra strength and impact resistance.

Another consideration is the likelihood of children falling onto the radiator and injuring themselves from the impact. Conventional radiators tend to have sharp edges that can cause serious injury. The outer casing of a low surface temperature radiator must be designed to avoid sharp edges, using rounded corners and edges to minimise the risk of injury.

There is a clear correlation between the attitude and motivation of pupils and the interior design of the educational environment. As a result, there is now considerably more thought given to the décor of schools, with greater emphasis on creating a pleasant, stimulating environment that is conducive to learning.

As a highly visible element of a room, radiators need to be designed to complement the rest of the décor. Low surface temperature radiators offer a high level of flexibility in this respect as the casing can be adapted to a wide range of spaces and shapes and supplied in a diversity of colours. The casing can also be designed to blend with other decorative or architectural features so that it is barely visible.

Positioning of radiators

With any type of radiator its positioning is important in achieving optimum performance. The standard approach is to position radiators below windows, as this is the area of maximum heat loss from a building. This also helps to prevent condensation forming on cold windows.

As insulation standards improve with the use of the latest thermally efficient double and triple-glazing, in line with Approved Document L2 of the Building Regulations, this is less of a consideration. Positioning needs to be considered in relation to the thermal insulation of each building.

Educational buildings must also provide easy access for disabled people. This is covered in Approved Document M of the Building Regulations, which states: “Corridors and passageways in the entrance storey should be sufficiently wide to allow convenient circulation by a wheelchair user. Consideration should be given to the effects of local obstruction by radiators and other fixtures.”

This condition is satisfied if “elements such as columns, radiators and fire hoses, do not project into the corridor, or where this is unavoidable, a means of directing people around them, such as a visually contrasting guard rail, is provided.”

Greater flexibility in the positioning of radiators is achieved through the use of slimline radiators that protrude only a short distance into the room or corridor. Low water content radiators are particularly compact and therefore more versatile from a positioning perspective.

Sizing of radiators

Choosing the right size of radiator is essential for optimising performance. A radiator that is too small for the space will not achieve the required temperature on cold days. One that is too big will achieve the required temperature more quickly but could waste energy doing so if the thermostatic controls do not react quickly enough or the radiator is a high mass unit that reacts slowly.

The size of radiator is determined by the volume of the room, the desired temperature and the level of insulation – the latter determining the heat output in watts per cubic metre required to maintain the temperature. Table 2, left, gives a rough guide to the watts per cubic metre (W/m3) needed relating to different levels of insulation.

Using these figures is clearly illustrated by a worked example for a room with excellent insulation, measuring 3 m long x 3 m deep and 2·5 m high. The desired temperature is 24°C and the water temperatures are 80°C flow and 60°C return.

Calculate the volume of the room by multiplying length x depth x height:

3 x 3 x 2·5 = 22·5 m3

For excellent insulation and a desired temperature of 24°C, the W/m3 = 55

Multiply the room volume by the W/m3:

22·5 x 55 = 1237·5 W

Thus the required output is 1237·5 W. However, a correction factor needs to be applied to take account of the water temperatures being used in the building, in this case 80°C flow and 60°C return.

The correction factor is determined by the Euronorm standard EN442, which provides a table of average correction factors. For these flow and return temperatures it is 0.9. To determine the final output of the radiator the figure derived above (1237·5 W) is divided by the correction factor (0·9), giving an output of 1375 W. A radiator with this output is then selected.

If necessary, the radiator manufacturer will be able to assist with these calculations.

Maintenance

Once an efficient system has been designed and installed it will require regular maintenance to ensure that efficiency continues. As well as servicing of boilers, radiators should be bled annually and visibly inspected for leaks or damage. Because of thermal air currents, there will also be a build-up of dust on grilles and these will require regular cleaning.

The chosen radiators should therefore be easy to access and maintain. With low surface temperature radiators, access should be as easy as possible without compromising on security. Useful features to look for are the ability to remove grilles separately from the casing for cleaning and the facility to remove the casing without needing to drain the central heating system. The latter feature will also be useful when decorating is carried out.