Our Glazing Systems app undertakes vision area System U-values and SHGC calculations in line with ISO 15099: 2003 - Thermal performance of windows, doors and shading devices — Detailed calculations.
The procedures within ISO 15099: 2003 give the actual thermal performance of fenestration products for use in building energy analysis and for the evaluation of products in specific building applications. These procedures are used to produce data to compare products by using standardised NFRC 100 boundary conditions.
This International Standard is also intended as a reference document for the description of models used in computer programs for a detailed calculation of the thermal and optical transmission properties of window and door systems.
Glazed Area Thermal Transmittance
Speckel uses an alternative method (ISO 15099: 2003 4.1.4) for calculating frame thermal transmittance. The glass area is divided into centre-glass area plus edge-glass area, and an additional thermal transmittance is used to characterise the edge-glass area, determined by a 1.4 uplift factor based on the centre pane thermal transmittance.
Thermal transmittance simulations are performed using NFRC Approved Software, NFRC Approved Simulation Documentation and NFRC technical documents (NFRC 100 + NFRC 200). Speckel is currently using THERM 7.6, developed at Lawrence Berkeley National Laboratory (LBNL). Using THERM 7.6, frame details model two-dimensional heat-transfer effects in building components. THERM's heat-transfer analysis allows Speckel to evaluate a product's energy efficiency under NFRC 100 winter boundary conditions.
Speckel encourages all parties to provide the required thermal models for inclusion in the Speckel database subject to a strict two-step audit procedure. Speckel does not undertake THERM calculations for third parties directly and does not provide this service. All THERM files used on Speckel are subject to a review of performance values and boundary conditions by means of an automated script. Once a review is undertaken, any anomalies are raised that may result in any inaccuracy against NFRC 100 + NFRC 200. Where parties are able to meet the requirements of the automated script, models are randomly reviewed upon upload to Speckel to identify any additional opportunity to enhance step 1. Therefore, all models are review twice.
Calculation of Total Product Rating
The total fenestration product System U-values shall be calculated to determine total product rating.
Ut = Total product U-factor
Apf = Projected fenestration product area
Uf = Frame U-factor
Af = Frame area
Ud = Divider U-factor
Ad = Divider area
Ut = Total product U-factor
Apf = Projected fenestration product area
Uf = Frame U-factor
Af = Frame area
Ud = Divider U-factor
Ad = Divider area Divider area