Description

Component Conditioning and Air Conditioning Technology

The goal for interior climate conditioning of exhibition rooms should be to maintain humidity levels and air temperatures as constant as possible over the long term.

Temperature 21° C throughout the course of the year +/- 3° C, relative humidity 55% +/- 5%

A variety of solutions have come into being in past years to fulfil these requirements. All the structural variations are based on the guidelines for technical installations that treat secondary air for places of assembly, without specifically addressing the special conditions obtaining in museums or fulfilling conservational requirements.

The essential differences between the individual climate-conditioning variants lie in the implementation of the different air handling components such as air warming/cooling, air humidification/dehumidification and the various types of air intake, as well as the air conveyance to the exhibition space and directional orientation of the flow of air. In the last ten years in particular, the point source air conditioning, which is often used for the useful areas of administrative buildings, has often been introduced into museums despite its unfavourable short term performance data. These very different approaches indicate a fundamental uncertainty as to whether it is even possible to treat secondary air adequately.

With the boom in museum building, the HVAC sector was given enormous impetus; the artificial ideal climate created by year-round climate-conditioning systems appeared to be the solution. However, doubts about this ‘solution’ are entirely justified. In spite of their high cost, such systems do not guarantee stable conditions, because constantly adjusting the control technology to the frequently changing climatic influences engendered by fluctuating quantities of visitors, the concentration of visitors in the space, and changes in the weather itself make climatic stabilisation impossible.

HVAC systems circulate large quantities of heated and humidified air or cooled and dehumidified air. They are very expensive to build, maintain and operate. The laws of physics demand that they have a high rate of air exchange per hour (usually of at least two or three times, and up to six times per hour and more). Draughts and stirring up dust in the rooms can hardly be avoided. With regard to the respective maximum cooling and warming load and with the enormous amount of air they put through, such systems are so large that they very quickly infringe on the space, altering it lastingly, and thus lead to a continuous load-following behaviour. Undoubtedly, if such a system were to break down, many modern museums would be forced to evacuate their art works, because they are compensating for unsuitable museum architecture by relying on the continuous operation of such systems.

The cooling load in a building should be kept as low as possible by means of passive measures such as using solid building components, solar protection, and maintaining a low lighting level. The cooling of the building by means of ductwork built into all building components to activate them by means of a geothermal installation is absolutely necessary; it forms the basis for the necessary climatic stabilisation to counteract the deviations from conservatorial temperature and humidity in the course of hours, days, and years. At the same time, building component activation serves to temper the surface of the envelope when it is heated; through the use of heat pumps during low temperature periods, all the surround­ing areas and the hanging areas warm up to the surface temperatures of the exhibits. Conventional heat distribution systems by means of heating the secondary air, like air heating, convectors, and floor heating, on the other hand, have to be ruled out for museums because of conservational disadvantages.

In winter, the task of air conditioning is limited to minimally heating and humidifying a reduced quantity of fresh air, and in summer, to cooling and dehumidifying it. The basis for calculating the necessary rate of air exchange should be determined by the number of visitors and the cooling load engendered by artificial light. Computer-supported building simulation calculation offers a means of significantly optimizing the determination of the rate of air exchange. When drawing up the climate control design, the benefits of thermal simulation already become evident with regard to homogeneous temperature distribution with varying visitor volumes and varying opening times at different times of the year. The flow simulation records the flow behaviour across the spatial cross-section and gives a visual representation of the rapidity of the flow.

Similarly, building simulation is appropriate for determining the optimum constitution of building component materials with regard to their heat and humidity storage capacity. The heating and cooling re­quirements of a museum building and the total energy requirement determined on the basis of an energy balance sheet offer both the client and the occupant a high degree of planning security for construction and operation.

The projection of the running costs taking into account rising energy costs is an important tool for establishing the economic efficiency of regenerative measures in building planning, for example, the increase of the energy storing masses, solar protection measures, the direction the building faces, intermediate climatic zones inside the building, using natural light, regulating the amount of artificial lighting, geothermics, photovoltaics, geothermal energy exchangers for pre-heating fresh air, etc. In­volving experts and ensuring that they play a part in the decision-making in the competition process in order to make the participating architects and the jury aware of the specification of the climatic requirements is another important step toward improving museum and conservational climate when planning new museums. The need for extensive renovation in modern museums – which often becomes apparent when they go into operation for the first time – does enormous damage both to the cultural and artistic property on display, and the reputations of these museums. The politico-economic loss is substantial and usually, the museum operators cannot finance the repairs.

Stringent limitations are placed on the implementation of conservational standards by museum architecture concentrating primarily on the exterior to the detriment of the interior – and thereby violating elementary laws of physics regarding buildings – and, as well, by the transformation of our museums into highly technicized “conservation machines” maintained at comfortable room temperatures and flooded with light. We will only be able to reduce the risk for the cultural assets entrusted to us if we abandon this concept – from an ecological perspective now outmoded – and recall passive preservation mechanisms. Experience has shown, however, that it is only with difficulty that such concepts can gain acceptance when they come up against the interests of the architects, planners and experts involved in competitions and planning practice; the latter will continue to be particularly problematic as long as their fees are calculated according to the amount of technology that is built in.

Climate control system for the new building of the Emil-Schumacher-Museum, Hagen, Germany

Architects: Lindemann Architekten, Mannheim

Climate control system: Ingenieurbüro Kahlert, Haltern

A three-storey reinforced concrete structure forms the core zone for the museum’s exhibition rooms. A supporting structure of steel trusses spans the entire museum and supports the glass roof as well as the accessible daylight-illuminating ceiling. A glass façade stiffened by steel cables on all sides forms an intermediate climatic zone between the outside skin and the museum itself. The southwest and the east zones serve exclusively as a climatic buffering zone to the exterior climate. The north façade forms the central access space.

Building component conditioning is installed in all of the concrete components as a passive basis for the climate control system. In order to avoid condensation of the secondary air humidity on the north façade, glass joint conditioning has been provided. For secondary air conditioning, an air distribution system has been installed in the peripheries of the daylight ceilings and artificial light-illuminating ceilings. The supply air flows into the exhibition rooms vertically via a surrounding wall/ceiling joint and is drawn off via a wall/floor joint. In combination with a foil dust ceiling, the daylight-illuminating ceilings and the artificial light illuminating-ceilings form their own air space, independent from the secondary air. The cooling burden arising from the lighting is drawn off directly in this intermediate climatic zone.

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Originally published in: Paul von Naredi-Rainer, Museum Buildings: A Design Manual, Birkhäuser, 2004.