Arrowform have released the following report on thermal performance of insulated ceilings with/without using Isolite or Flexi downlight enclosures that can help to determine the AS/NZS 4859.1:2002/Amdt 1 2006 Total R-Values of insulated ceiling systems incorporating an Isolite or Flexi downlight enclosure around each recessed downlight. The report can also help to determine the thermal insulation benefit as compared to downlights not enclosed by Isolite or Flexi downlight enclosure.
These installations are assessed as subject to the installation requirements of AS/NZS 3000:2007 Clause 126.96.36.199 options b, or d.
This insulation study report excludes analysis of additional benefits of the unventilated Isolite or Flexi downlight enclosure in eliminating air leakage when installed over ventilated downlights. Arrowform undertook this calculation.
Calculations: The following calculations are based upon AS/NZS 4859.1:2002/Amdt 1 2006 materials for the thermal insulation of buildings, the Australian Institute of Refrigeration Air-conditioning & Heating (AIRAH) Handbook Millennium Edition 2000, Section 6.
The results reported are per AS/NZS 4859.1:2002 Clause 188.8.131.52 – ‘Total thermal resistance - A total resistance associated with a material or a system or construction of materials, specified as a Total R, including surface film resistances. Air space calculations are iterative and only the converged results are shown. In accordance with AS/NZS 4859.1:2002/Amdt 1 2006 Clause K3.1, results are presented for indoor air temperatures of 24°C (summer) and 18°C (winter).
Conclusion: The Isolite/Flexi downlight enclosure was estimated to have negligible thermal resistance (R0.1m²K/W). However it allows insulation to abut the downlight, significantly reducing the thermal bridging through the normal significant area cleared, uninsulated, around a downlight.
If the Isolite/Flexi downlight enclosure had significant thermal resistance, it would overheat the downlight it enclosed. Its effectiveness relies on enhancing the surface area through which a downlight releases lamp heat into the attic while having minimal interruption to ceiling insulation.
If a downlight is ventilated (gimballed), the fitting of an Isolite/Flexi downlight enclosure eliminates that ventilation. This reduces the convective heat transfer through the ceiling. The Isolite/Flexi downlight enclosure thus improves the efficacy of the heating and cooling systems of the conditioned room. The benefit cannot be calculated as it depends on too many variable factors (wind, ambient temperature and attic construction).
In conclusion, the use of an Isolite or Flexi downlight enclosure significantly reduces thermal bridging, and restores ceiling insulation effectiveness.