Heating, Ventilating, Air-Conditioning (HVAC)

The two main groups of heating are direct sys-tems, in which the heating is realized directly within the space to be heated, and indirect

sys-tems, in which heating energy is produced outside the space to be heated and then transferred to equipment in that space for use. The nature of the energy source may be solid, liquid, gaseous, or electrical. The terminal heating elements may be primarily radiant or primarily convective.

The leading trends in HVAC are: spreading of cen-tral heating (including district and city heating), the switch from some types of fuel (wood) to others (oil, gas and electricity), energy conservation and protection of the environment (reduction of air, water and soil pollution/contamination), introduction of up-to-date control devices and systems (con-densing boilers, thermostats, programmable elec-tronic control), automation and integration of sys-tems, reduction of the size of equipment (smaller boilers and boiler rooms), more efficient appliances (consuming less water and electricity). All this is manifested in the cost increase of HVAC equipment relative to the total cost and a need for more intel-lectual concern in its design, realization and opera-tion. CO₂emissions and, consequently, energy con-sumption, may for example be reduced by:

• more effective heat insulation of buildings, including walls, windows and other building parts

• better airtightness and ventilation

• improving the performance of glazing

• enabling façades to react to weather changes by increasing or reducing heat insulation (and daylighting)

• more efficient hot water boilers and household appliances

• use of solar energy (Hestnes et al., 1997)

• economic incentives and management mea-sures (certification of energy consumption, billing of energy on the basis of actual con-sumption, regular inspection of boilers, energy audits and third-party financing for energy-effi-cient investment) (Fee, 1994).

The selection of an HVAC system depends on the type of the climate and of the building (Boben-hausen, 1994, Faber and Kell, 1989). Houses usu-ally have individual systems. Large residential buildings may have a central heating plant with individually controlled and metered HVAC systems including mechanical ventilation for interior kitchen

and bath areas, or small systems for each residen-tial unit. The heating may be provided by warm or hot water, steam, air, electricity. Ventilation, cool-ing and air-conditioncool-ing systems may or may not be required. Open fires and closed stoves provide solid-fuel direct heating. Closed stoves and indus-trial air systems provide primarily convective direct heating. Luminous fires, infra-red heaters and radi-ant tubes provide primarily radiradi-ant gaseous fuel (or radiant electrical direct) heating. Natural convec-tors, forced convecconvec-tors, domestic and industrial water air systems are primarily convective gaseous fuel heatings. Quartz lamp heaters, high- or low-temperature panels, ceiling and floor heating are primarily radiant electrical direct heating. Finally, natural convectors, skirting heaters, oil-filled heaters, tubular heaters and forced convectors may serve as primarily convective electrical direct heating. Electrical off-peak storage systems do not fall within the category of either direct or indirect heating systems.Indirect systems comprise a heat distribution system and terminal equipment. Low-, medium-, or high-temperature hot water and steam indirect heating systems have as terminal equipment exposed piping, radiators, metal radiant panels or strips, natural or forced convectors, pipe coils embedded in the structure, metal panels in suspended ceilings, skirting heaters, unit heaters, air/water or heat/air heat exchangers for ventilation systems. Any decision on these will affect the design of buildings.

In order to assist in the design of energy-conserv-ing buildenergy-conserv-ings, various methodologies and com-puter-based design programs have been worked out. One of these is the Energy Performance Indoor Environmental Quality Retrofit. This was worked out within the framework of a European research programme, supported by the European Commission. Whilst primarily aimed at diagnosing and retrofitting existing buildings, it may also be used in the design process of new buildings (Jaggs and Palmer, 2000) with the objectives to produce a good indoor environment, optimize energy con-sumption, use renewable (solar) energy and be cost-effective.

A new approach to increasing heat insulation is transparent heat insulation that utilizes the energy of sunshine (Wagner, 1996). It is applied on the

external façade side, its material is polymethyl-metacrylate (PMMA, Teflon, acryl- or plexiglass) and polycarbonate (PC). A honeycomb or capillary structure made of extruded clear acrylic tubes serves to capture the sunshine’s heat.

One should keep in mind that objectives and mea-sures to achieve these may be complex and inter-related. The shading of façades is contributing towards protection against excessive sunshine, to enhancing human comfort by limiting the warming of internal spaces, to reducing disturbing glare and to energy conservation by eliminating or reducing air-conditioning requirements. These objectives are attained by adequate sunshading devices (see also below, under Daylighting). They may be placed on the outside of the façade as independent devices or internally, linked to the windows or as indepen-dent curtains or shutters. This exemplifies the complexity of the architect’s task in making a deci-sion that will have a profound effect on the look of the building.

Transparent heat insulation equally affects the façade design. The use of translucent fabric roofs has an overall impact on the internal ambience of buildings. Another new factor in the architecture of the exterior of buildings is the use of sunshine for

Figure 4.3 External sun-shading elements rotating around vertical axis (Mesconal, Germany). a) rotating mechanism at the bottom, b) rotating mechanism at the top, c) and d) countersunk layout with the rotating mechanism at the bottom and the top respectively. © Sebestyen: Construction: Craft to Industry, E & FN Spon.

Figure 4.4 Vertically mounted external sun-shading structure rotating around a horizontal axis, with 180 mm wide extruded aluminium lamella.

© Sebestyen: Construction: Craft to Industry, E & FN Spon.

energy conservation and energy production through the application of solar collectors or photo-voltaic cells.

Photovoltaic cells usually produce expensive energy but intensive research promises to improve this. In Japan the application of photovoltaics is increasing and it is expected that by 2020 10 per cent of all energy will be produced by photovoltaics (Yamaguchi, 2001).

The solar collectors may be arranged vertically on the façades, on high- or low-pitched roofs or sepa-rated from the plane of the façades and roofs. Solar collectors usually have a black colour all over their surface and the resulting contrast between the black colour of the solar collectors and the enve-lope’s differently coloured surfaces again provides new potentials for architectural design.

Solar systems may be:

• individual collector panels assembled on the roof

• prefabricated large collector modules assem-bled into complete roofs or other components of the external envelope.

The solar systems may be combined with heat storage systems, which store heat in water or solids (gravel or concrete).

Natural and artificial ventilation are sometimes underestimated because it is assumed that they do not exert any major impact on architectural design and that, being mostly concealed behind surfaces and ducts, their design is primarily the responsibil-ity of mechanical engineers. In real life, however, they may be closely linked to lighting, energy con-servation, heat and noise insulation and therefore their technical solution may have important reper-cussions on overall design. Various solutions may comprise natural or mechanical or combined sys-tems depending on specific circumstances. For example, the Yasuda Academia Building in Tokyo, Japan (architect: Nihon Sekkei Inc., 1994) has an atrium that is naturally ventilated. In warm weather air enters at ground and intermediate levels, rises in the atrium and is expelled through the atrium roof. Air is also drawn to the atrium from the upper-floor bedrooms. A heat-reclaiming plant is located at the top of the atrium (Jones, 1998). A very

pecu-liar solution has been applied to traditional Baghdad homes: inclined towers direct air into the heart of the buildings (Jones, 1998). In the Vice Chancel-lor’s Office, Académie des Antilles et de la Guyane, Martinique, French West Indies (architect: Christ-ian Hauvette and Jérôme Nouel, 1994) the strong winds of the hot, humid climate were utilized for natural ventilation (Jones, 1998). The high-tech Commerzbank Headquarters building in Frankfurt am Main (architect: Norman Foster, 1997) has been mentioned. Where heating requires energy, heat recovery from used air is a resulting economy.

An innovative ventilation system is displacement ventilation, usually combined with cooled ceilings.

In this, fresh air is supplied at the lower part of the rooms. Displacement ventilation ensures good ventilation levels, low cost and adequate human comfort and affects the interior design of the build-ings. Displacement ventilation may be designed by other arrangements: in Hall 26, Hanover Messe (architect: Herzog and Partner, 1996) the air is introduced via large glazed ducts 4 metres above the ground floor. The fresh air flows downwards distributing itself evenly over the floor. The air then rises upwards transported by the effect of the heat generated in the hall space.

The above examples demonstrate the attention that architects must devote to matters of ventila-tion. HVAC and other technical services are increasingly integrated into a system, which requires a careful supervision during the design process in order to integrate the technical system with the architectural concept. We will revert to this in Chapter 5.