Glazing

A key component of the Integrated Greenhouse project is the provision of a highly efficient building envelope both to increase energy efficiency and to assist harvesting of excess solar gain.

The current glasshouses at The Living Rainforest are almost entirely single glazed, with a high U factor (see Energy Efficiency in the Integrated Greenhouse) and consequent high energy demand, even with the use of thermal screens. The design target for the Integrated Greenhouse project is to at least halve the energy demand in the final building complex.

Two glazing options for the Green Greenhouse have been investigated to achieve this:

  • double glazing units; and
  • triple layer polycarbonate sheeting

During initial research, the concern arose that the extra weight of double glazing would reduce robustness of the structure needed to support the glasshouse envelope, which would have deemed the project not replicable in a commercial environment. Consequently, investigations were initiated into the use of polycarbonate sheeting. However, it was later found that these early concerns were unfounded, as design limits imposed by other considerations (wind, snow loading etc) result in structures that could accommodate the increased weight of double glazed units with incorporation of minimal extra rigidity.

Polycarbonate sheeting and similar products have the advantage of a lower weight/m2 than double glazing, even when multilayered. They also have design values that match glass in terms of energy efficiency and although the embodied energy of polycarbonate is higher than that for glass (per kg), due to its lower density, calculations suggest no significant difference in embodied energy per m2 when comparing the two materials. The two glazing options would therefore be fairly equal choices were it not for considerations that need to be made at The Living Rainforest regarding the effect of ultraviolet (UV) light filtering and the behaviour of butterflies.

UV light appears to act as a trigger for butterflies to fly and as free flying butterflies are integral to rainforest exhibits at the centre, this needs to be taken into consideration. Manufacturers currently incorporate a UV filter in the production of polycarbonate sheeting that has consequences for some growers and centres like The Living Rainforest, where UV sensitive plant and animal collections are held. As Pilkington UK are able to supply specialist coverings to manage light penetration and emissivity of double glazing, overcoming the potential UV problem, double glazing is consequently the preferred option for the Integrated Greenhouse project.

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