Energy efficiency I would attempt to minimise the number of spaces where conservation and preservation conditions are required and employ a separate HVAC system for areas where conservation isn’t needed. Zoning the building according to variations in environmental requirements of different exhibits and functions (vulnerable objects should be placed together) and the creation of smaller spaces separated by doors reduces the volume of air that needs to be heated/controlled. A correctly sized and highly efficienct plant with a condensing boiler provides reheating for dehumidification, which substantially reduces dehumidification energy costs.
Relative Humidity Relative humidity poses the greatest potential risk to the collection. Control of relative humidity is crucial to the sensitivity of some objects and the potential for fluctuation in an occupied gallery space. High relative humidity encourages mould growth in organic materials or corrosion of metals, or changes in physical size such as the expansion of wood. Low relative humidity can cause shrinkage or brittleness in some materials. Rapidly fluctuating relative humidity can therefore cause damaging cycles of expansion or contraction, particularly in objects of mixed materials with differential rates of movement. The recommended humidity range is 45-60 (±5)% provided the “buffering effect” of the building’s thermal mass and porous finishes can be utilised to dull short term fluctuations. Close control with a narrower band of RH of 50-55% (±3)% is a prerequisite for international artefact loan. This applies to all areas where the loaned item or its packing may be located, such as display, shipping, storage, conservation and circulation areas. Environmental techniques such as heavy building construction, hygroscopic materials, high ceilings, thermal buffering and window sealing can be employed to help stabilise relative humidity. Utilising display cases create stable microclimates with much closer control.
Temperature CIBSE recommends 20°C for galleries and museums. Lower temperatures results in lower level of moisture in the air and reduces dehumidification loads, operational cost and potential damage to artefacts and the building fabric. Relaxing the temperature level required also reduces the need for complex servicing, thus reducing the energy required for heating and humidification. Many objects are tolerant to changes in temperature within the typical range for human comfort (18-25°C), provided they are not subject to rapid fluctuations or exposed to direct sources of heat, which can cause localised dryness. Specification of lower temperatures in storage spaces also aid conservation by slowing down the speed of any chemical reaction. The strategy to minimise solar gain in unwanted parts of the building primarily is to simply protect the centralised exhibition spaces with service, private and ancillary spaces that wrap round the south face. The addition of double glazed low e glazing prevents unwanted solar gain in the sensitive exhibition spaces.
Lighting Lighting levels and the effects of ultraviolet and infra-red radiation need to be controlled to minimise damage to artefacts. The effects of exposure are cumulative, and so the risk of damage can be minimised by reducing the length of exposure to visible light and by screening from ultraviolet radiation. In display areas, all luminaires that emit UV would be fitted with filters or secondary sheeting. UV filter films or interlayers to laminated glass would be used on all external windows including roof lights. Artificial lighting whould be fitted with filtering diffusers or secondary glazing. Exhibits with drawings, watercolours and inks are particularly sensitive to light damage and the recommended light level is 30 Lux. Levels up to a maximum of 200 lux are generally accepted for moderately sensitive items, such as oil paintings and wood. A balance is important between lighting levels for good viewing and the conservation needs of the exhibits.
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