The Green Consideration - Energy Efficient Windows

“Better Than The Standard”

BFRC Energy Rating for Windows

In accordance with the described methodology, the Bygone Collection of sash windows has been simulated under the BFRC calculation method. The Bygone window loses just 20KW / per square metre / per year.

Putting this into Perspective

In order to put this into some meaningful numbers we must first set the calculation criteria.

This paper is calculating the costs and CO² during the winter months, when heating would be required. For most households, our figures show that an average household has their heating on for, a period of 191 days, just over 6 months, taking into account increased usage for the colder days of the season, and shorter lengths of time for the Autumn / Spring days, and the difference between week days and weekends, and for an average of 8 hours a day, with a temperature difference between outside and inside of 15 degrees

It is also necessary to understand how the heat loss is calculated. What does W/m2K actually mean, let me explain.

A Watt is a unit of measure for energy, it is 1 Joule per second. is the area of the window, width x height, and Kelvin is the difference in temperature from the inside to the outside, the rest is just mathematics.

The Energy Loss Explained

To benchmark the Bygone window, lets first calculate how much money is lost in heat through a old single glazed timber window at 5.8W/m²K

Using the CEN standard size window as the standard size this would mean that the total heat loss would be 242 KW

(5.8 joules per second x 1.82m² x (191x8) x 15 =241.94KW )

Our average order quantity is 7 windows, and therefore the heat loss through the windows of an average house would be in the region of 1,693.58KW

(242KW x 7 = 1,693.58KW)

The costs

Based upon an average cost of 10 pence per KW (1000 Watts) per hour, the average single glazed timber sash window would lose the equivalent of £24.20 each year.

(241.94KW x £0.10 = £24.20)

However most boilers are only 70% to 80% efficient, consuming energy in the boiler itself and therefore the output cost should be factored by an average 25%

Saving Energy Saves Money

Meaning the average property with 7 timber sash windows, spends approximately £211.25 every year replacing the heat that is lost through the windows.

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