Fabric and services unite!
Passive design approaches blur the distinction between fabric and services. The fabric becomes part of the services, and vice versa. So while cibse's publications are directed first to services engineers, over recent years they have become increasingly relevant to architects - particularly because the riba does nothing similar for its members. The five cibse publications reviewed here exemplify this.
Architects would expect to use the first two publications as working documents. The first, on lighting for communal residential buildings, is a thorough round-up of the state of the art. The second, on non-domestic natural ventilation, covers the range of recent developments. The other three publications are more specialist, but still informative.
Lighting for Communal Residential Buildings1 is a straightforward, workmanlike guide to lighting buildings for the elderly, for students and the like. It is very much concerned with the quality as well as the quantity of lighting, whether trying to reduce the institutional feel of lit spaces, addressing privacy or arguing for curtains rather than blinds as more congenial.
It covers site planning, windows and natural lighting, exterior and interior artificial lighting. This includes corridors, stairs, kitchens and bathrooms as well as principal spaces. The chapter on colour and decoration is useful, though the level of concepts is sometimes a bit basic for architects. There are notes on lighting particular buildings, for example for the elderly, school dormitories and secure accommodation. The guide finishes with energy management, emergency lighting and a round-up of legislation and standards.
Ventilating non-domestic buildings
Mentioned when it came out last year, it is worth spelling out the content of this manual. Natural Ventilation of Non-Domestic Buildings 2 is the best overview so far of developments in natural ventilation. Recent examples cited throughout the text and informative illustrations enhance the sense of a synthesis of projects in progress.
The manual begins with the paramaters, from basics such as overheating to more subtle ideas such as adaptive opportunities - designing in opportunities for occupants to change the building which do have a significant effect on the acceptability of environmental conditions. Basics established, it goes on to selection of a ventilation strategy. It covers planning flow paths through the building, offers rules of thumb on room dimensioning and explains wind and stack performance, use of atria, double facades and mixed-mode approaches (combined natural and mechanical systems). Then, in more detail, it looks at windows as ventilation openings, inhibitors of air flow like partitions, control and the integration of other design factors such as lighting, fire and heat-gain control.
The chapter on design calculations can be skimmed to get a sense of what can be calculated. The manual finishes with case studies of buildings such as the University of East Anglia (ecd/Arup) and Inland Revenue, Nottingham (Hopkins/Arup). The descriptions are informative but performance data are lacking. The most recent references to the aj and others are from 1995, suggesting a book long in the making. This is disappointing, but at least the descriptions are clear on the design intentions.
Hot off the press is Building Energy and Environmental Modelling3. Mainly for committed building modellers, it concentrates on dynamic rather than steady-state computer modelling, focused on the indoor environment. It covers what modelling can currently achieve as part of design, the criteria for selecting software and its generic capability, the management issues of setting up an in-house modelling capability, and general guidance on application. That is, on turning a design question into a problem that can be modelled. Case studies illustrate this design process in action.
Chilled Ceilings and Beams4, and the next document, are photocopy-quality research reports on the state of their respective arts. This one is mainly about the risk of 'office rain', the concern that condensation might occur on chilled beams and ceiling panels, forming water droplets that rain down on office occupants. Generally the conclusion is that the risk has been overstated. Even when calculation suggests some risk of condensation, other factors may come to the rescue.
However, condensation is reasonably predictable. Where there is a risk, either dehumidification can be introduced, or the chilled surface temperature can be increased, though this inevitably reduces cooling capacity. For example, in summer 'chilled' water temperatures of 18degreesC rather than 14- 15degreesC can be effective. The report emphasises the need for good sensors and for good commissioning and facilities management, otherwise energy use may run out of control.
Thermal Storage: Environmental Benefits5 focuses on the co2-saving potential of a wide range of thermal storage options - the building fabric, ice, rocks and more. It is early days for most of this technology in terms of there being clear performance data and readily available design methods. The report itself is episodic, working through many examples, which are presented mainly in terms of the available performance data. Based on this evidence, what does emerge is an overview of the current viability of thermal storage technologies.
Building fabric storage - Useful for dissipating heat gains in summer and for heat recovery in winter. Most of the data for fabric storage with night cooling apply only to offices. There, the approach has been used successfully to avoid air conditioning, and significant amounts of co2 have been saved. Though design methods are not fully established, the normal area of exposed mass, such as a floor soffit, is usually enough. A simple exposed soffit can deal with heat gains of the order of 20W/m2. With night cooling the capacity can rise to around 60W/m2.
Natural ventilation will generally be effective if up to four air changes/hour can be achieved reliably. Otherwise mechanical night ventilation is likely to be more effective. However, where mechanical ventilation is used, control is essential to avoid the risk of large energy use for fans.
It has to be accepted that the internal environment will be less well- controlled than in a well-working air-conditioned building.
Since during night cooling a considerable quantity of relatively low- temperature external air is driven across the soffit within the working space, this may have to be curtailed if working hours are extended into the night.
Where a building is only used intermittently, say for three or four hours a day, a lightweight building will usually require less heating energy than a thermally heavyweight one.
Hollow-core systems - The best known system is Termodeck, well-established particularly in Scandinavia, and with a few examples in other countries such as the uk. Air is mechanically driven through the voids in hollow- core concrete floor planks, with the soffit left exposed to the space below. This achieves significantly greater cooling or heating capacity and greater environmental control than the systems noted above. Unlike with air-conditioning, window opening should not be a problem. And 24- hour working can be accommodated. The extra co2 cost comes from energy for fans. Some early uk examples were saving little energy when first installed, but subsequent attention to commissioning and building management has brought down performance to at or below target energy consumptions, saving considerable co2 compared with air conditioning.
Bunding (part-burying) buildings - Bunded buildings can offer temperature stability through contact with the earth and the potential to cool ventilation air by drawing it through tubes buried in the ground. However, the capital costs and the difficulties of planning permissions make this approach of little general relevance.
Air-earth systems - A variant on the above; a normal building but with the tubes in the ground to cool ventilation air in summer, or to partly pre-warm it in winter. Only a few experiments have been done, for houses, saving around 10 per cent of total energy consumption. Capital costs and fan energy use are disadvantages, as is the need to keep air paths clean.
Water-earth systems - Contamination risk can be avoided if water is circulated through the earth and the heat input or output to the building via a heat pump (for summer cooling or winter heating). It is early days for these systems. The long-term effects on soil temperature, and thus the earth's capacity compared with the building's footprint, are unclear. Groundwater movement will help locally in evening out temperature differentials in the ground, but this may not work well in dry summer conditions. Overall the report feels this is an approach well worth pursuing
Packed beds - Beds such as rock stores can act as heat sinks and sources. They can save on space heating. But cost, space requirements and fan energy are disadvantages.
Phase-change materials - These exploit the heat storage capacity of phase change, normally between liquid and solid, typically at around 25degreesC. This provides a much greater density of thermal storage than simple (sensible) heating or cooling, as in packed beds. Phase change materials may be in dedicated stores or encapsulated in building materials. Work is still at the research stage.
Off-peak heat stores - Storage radiators save money through tariffs but not co2.
Solar energy stores - Solar panels on roofs connected to hot-water systems are still not cost-effective. For space heating, the problem is that they work best in summer when you need them least, and vice versa. This has been addressed by a number of continental housing schemes, using seasonal rather than daily heat storage. The costs of such heat stores are high and have worked better when provided centrally for a group of houses. Monitored schemes have provided 40-100 per cent of district heating requirements. As the systems use solar energy, their potential to save co2 is very great. But fuel costs will have to rise greatly before they are cost-effective.
Ice storage - Some commercial systems use energy to create ice for later cooling (exploiting sensible and latent heat storage). These can make sense in engineering terms but do not save co2 emissions.
Hydrogen-based thermal storage - One approach to using hydrogen is to begin by storing electricity generated by photovoltaics. Some electricity is used for electrolysis of water, creating hydrogen and oxygen as required.
The battery, or using stored hydrogen in a fuel cell to create electricity, could be used to power lights and appliances. Hydrogen could be used directly in heating and cooling and for powering vehicles.
Again, this is attractive because it begins with a renewable energy source and also uses a not-very-scarce main resource, water. Today the combined system efficiency of the photovoltaics and the water conversion and storage is about 7 per cent. The technology is in the research phase. There are also safety concerns (remember the Hindenberg airship). Even so, the report sees medium-term promise for group and district schemes.
All publications available from cibse Publications Sales, 0181 675 5211.
1 Lighting for Communal Residential Buildings. Lighting Guide LG9: 1997. 55pp. £35.
2 Natural Ventilation in Non-domestic Buildings. Applications Manual AM10:1977. 102pp. £45.
3 Building Energy and Environmental Modelling. Applications Manual AM11:1988. 96pp. £48.
4 Chilled Ceilings and Beams. cibse Research Report RR5. 128pp. £31.
5 Thermal Storage: Environmental Benefits. cibse Research Report RR6. 150pp. £34.