What is the most efficient way to heat the vast spaces of sports halls, which may be in use for extended periods, for a variety of activities? Andrzej Krawecki outlines the options

Indoor sports facilities for combined school and community use are a growing trend. They often operate well beyond the school day, and these long hours of operation mean the selection and design of the heating system is critical if it is to produce a satisfactory environment for users while keeping energy costs to a minimum.

According to the Scottish Sports Council’s Technical Digest 203, Sports Halls Heating and Ventilation, 1995, energy can account for 25-30% of the overall operating cost of a dry sports facility and is often the next largest cost after staff.

Services design for sports buildings should incorporate four important factors: accessibility, attractiveness, functionality and manageability.

The designer must also bear in mind the fact that there are many sports disciplines, each with their own requirements.

The first thing an engineer must do is to establish the design conditions for the facility. Sport England produces two useful guides to help designers do this: Village and Community Halls, 2001, and Sports Halls: Design, 1999.

These give more specific information than CIBSE guides B1 and B2. If a sports governing body funds the hall, it may have its own performance criteria which need to be factored into the heating system selection.

These criteria may include temperature, lighting levels, space requirements, etc. In some cases, a specialist consultant may become involved in checking the design of building services.

Table A (attached) summarises the most important comfort requirements for dry sports halls from various guides.

The mechanism of heat transfer is fundamental to the selection of heating systems for sports halls. Heat transfer is possible in three ways: conduction, convection and radiation.

Because of the large air volumes of most halls, convective methods of heating are generally less efficient than radiant methods so it is worth having a closer look at heat transfer via radiation.

Normally, environmental conditions in a sports hall need only be maintained in the occupied zone, in other words up to 2m above floor level. Every heating system considered needs to fit into the previously mentioned criteria of accessibility, attractiveness, functionality and manageability. The system is likely to be controlled by the sports hall staff, so simplicity of operation must be considered.

The pros and cons of the six main types of heating system are listed below.

Warm air system

This is a complete ducted system providing both heat and ventilation. The air-handling unit is usually fairly big because of the large air volumes required.

The system can include air recirculation options and a heat exchanger to help capture heat gains from occupants. Heat is usually from an LPHW system fed from a gas boiler, although direct gas-fired heating can be used.

Some sports halls may not be suitable for radiant heating. In such cases ducted warm air systems can provide both heating and ventilation to a space.

For smaller community halls, with heights not exceeding 5m, and for larger multi-use halls, where students may sit exams, a ducted warm air system may be the most appropriate solution.

In the case of smaller halls, running costs can be minimised by careful control of the ventilation rate. Also, it may be easier to maintain a ventilation unit located in a plantroom rather than at high level in the sports hall where an access platform will be needed.

Factors to consider: there is the possibility of temperature stratification or a large temperature gradient in a room with a high ceiling. If the air velocity is too high, draughts within playing zones may affect games such as table tennis or badminton and the high levels of noise produced through the air supply may be distracting for some participants.

Advantages: good-quality ventilation. It is possible to fit all heat and ventilation plant into one room. The system can be designed to be relatively attractive or its visual effect can be minimised by integration in the hall finishes. Can be flexible if fitted with efficient controls.

Disadvantages: installation and running costs can be expensive. The preheat periods prior to occupancy mean it is less efficient than some instantaneous systems. Large plant items need to be properly maintained.

Fan convectors

These units can be built into a facility’s walls at low level. They require protecting in a way that does not to affect their output, for example by using bulkheads. Fan convectors can also be hung from the ceiling. As their name implies, they give out heat mainly as convection.

Factors to consider: same as warm air system.

Advantages: can be connected to the rest of the LPHW system and zoned appropriately.

Disadvantages: often relatively bulky and their appearance can be an issue. Noise can sometimes be a problem, especially when the units are installed at low level. The protection which is required may affect the unit’s performance to an unacceptable extent.

Unit heaters

Fan-operated unit heaters are usually hung at high level. The units can be gas-fired or operated from an LPHW system. They have an industrial aesthetic which limits their application.

Factors to consider: same as warm air system

Advantages: cheap to install with no plant space required.

Disadvantages: noise may be a problem. Also, fan-operated units may create significant air turbulence which could affect some games. Flues need to be provided for the gas-fired units.

Radiant panels

• LPHW-operated units, fed from an oil or gas boiler, are usually suspended at high level.

Factors to consider: the system should be sized for the resultant temperature within the occupied zone and should take account of the ventilation losses and the effectiveness of panel construction. Protective guards may be required for the heaters and sensors. Access will be required for installation and maintenance.

Advantages: noise is not an issue; units can be unobtrusive. They can be connected to the LPHW system and zoned appropriately.

Disadvantages: the system is relatively inflexible. Access is required to a high level – the price of unobtrusiveness. Protective guards may be required even for units mounted at high level.

• Gas-fired radiant panels are constructed from a continuous black tube heated by gas burners (usually mounted on the top of the panel).

Some systems use a suction fan to pull the products of combustion through the tube. Heat reflectors are attached to this tube. These are usually made of stainless steel and are designed to maximise the reflected radiant heat output and to minimise convective losses. A flue is necessary.

Factors to consider: the system to be sized for the resultant temperature within the occupied zone and for the ventilation load. The unit’s effectiveness depends on the type of reflector used. They can be noisy. The flue needs to be carefully positioned. A balanced flue option could be considered. Protective guards may be required for both the heaters and sensors. Access is needed for installation and maintenance. It is important is to provide sufficient air for combustion – if wind stacks are included for ventilation, they can never be totally shut.

Advantages: the units are relatively lightweight and cheap to install. Control is straightforward from a simple modulated output. Units provide a good heat spread with the right type of reflector. The panels are away from playing the zone.

Disadvantages: the gas burners and vacuum fans can be noisy and acoustic treatment may be needed. Extra care should be taken when installing the temperature sensors or control interfaces in the playing zone to prevent them being tampered with or influenced by local heat turbulences.

Underfloor heating

An LPHW underfloor heating system consists of a set of pipe loops cast into the floor screed. The system is served by a conventional gas boiler with the distribution network consisting of flow and return manifolds.

Factors to consider: a decision on the floor construction must be made early in the project. Often sports halls have sprung floors on top of the floor slab, which may decrease the system’s thermal output. Also, the flexibility and response times are slow for applications where the system needs to cater for different activities within a hall.

Advantages: the pipework is embedded in the floor, making it totally unobtrusive. Manifolds can be located in ancillary storage spaces. The system’s lower temperature requirement means that more efficient condensing boilers can be used.

Disadvantages: lack of flexibility. Response times are slow. The construction system used must allow pipework to be embedded in the floor.

With electric underfloor heating, it is possible to use off-peak electricity to store heat in the floor slab. The environmental impact of an electricity-based heating system, however, precludes this method from most applications.

Low-level radiators

Old sports halls often use a system of tubular radiators mounted behind protective metal guards. This reduces the effective floor area of the hall and presents a risk of occupants colliding with the units, especially when playing ball games.

What is the answer?

The current default solution is often radiant heating. Table 4 from the Scottish Sports Council’s Technical Digest 203 (attached), compares various systems using 12 basic self-explanatory criteria.

It is important to re-emphasise that radiant heating is efficient because it heats the occupants rather than the large volume of air in the sports hall. Underfloor heating is also popular with architects because it is unobtrusive. Each project may have specific conditions to satisfy.

Ancillary areas

Social/administrative: spaces such offices, meeting rooms, bars or corridors can be heated by a standard LPHW radiator system, sized with addition of natural ventilation load.

Changing rooms: in small facilities, a conventional radiator system can be incorporated. However, warm air introduced at low level may give better results and maintain a dry floor surface. Underfloor heating could be considered in these cases when there is no space for radiators because of the layout of the changing lockers and if underfloor heating is used in the main hall.

Changing rooms also need to be maintained at a higher temperature than the hall, of approximately 25°C. For toilets, radiators are likely to be the best solution.

Activity areas: these may be a smaller version of the main hall that can be treated in the same way. In fitness rooms and gyms, a temperature of 18°C is sufficient. Combined heating and ventilation or a heat recovery variable refrigerant flow system can be used.

Radiant heating analysis

Thermal comfort is a balance between a person’s activity level, the dry resultant temperature and the relative air velocity. Dry resultant temperature is an average of air temperature and mean radiant temperature. To maintain the same comfort level, air temperature can be reduced as long as mean radiant temperature is increased to compensate. BSRIA application guide AG 3/96, Radiant Heating, states this in an equation:

dry resultant temp = mean radiant temp + air temp/2

This would mean less energy being used to get the same thermal comfort conditions. Also, people are likely to be running about, contributing to the air temperature by sensible heat gains. However, lower air temperatures can only be considered when the hall is used for sports-related activities; they would not be suitable for pupils sitting exams. Reduction of the internal air temperature also results in a reduction of ventilation heat losses.

A person in a radiant heated space receives thermal radiation directly from the source and from heat re-radiated from walls and floors. The warmed building fabric also contributes convective heat to the space, which can help thermal comfort. The BSRIA guide defines radiance as when at least 50% of total heat output is radiant.