Friday, May 6, 2011

Certified Data can Optimise your BER Value

Casa Bui has written before about how to retrofit to Passive House Standard, but even if you are not trying to reach this level of energy performance for your dwelling, you will want to get the best possible energy value from your investment in improving your home.

Casa Bui has much experience of BER assessments that have been delayed or impacted negatively by the lack of certified evidence of the energy performance of different building elements that have been incorporated into a home, often times with the best of intentions, and at significant cost. The BER Assessment is carried out per the DEAP procedure which requires certified data for all building elements. In the absence of the satisfactory certifications, default values must be taken which can lead to a significant negative impact on your BER value.

It is an altogether more thorny process to try and get these certifications retrospectively when the elements have been purchased and installed or integrated into your dwelling. Casa Buí recommends that obtaining these certifications be part of your planning and materials selection process.
Outlined below is a list of items that we recommend you take into account if included in your home energy performance upgrade.

Heating System Efficiency

The heating system efficiency plays a significant role in determining your BER value so your aim should be to maximise the certified seasonal efficiency of this system. You should verify that your proposed boiler is listed in either the SEAI HARP database or the UK SEDBUK system. Heat Pumps are especially problematic in this regard as there are only a handful of systems added to the SEAI system at this stage. Currently there is an interim method in place for determining the Coefficient of Performance of the Heat Pump but this data needs to be certified as tested to EN14511-2 by an accredited laboratory or organisation. Manufacturer declared data is insufficient and the default value of 250% must be taken in the absence of actual values that can be the range of 300-350%.

Potential Impact 5 to 10 kWh/m2/yr

Windows and Doors

If you have invested significantly on state of the art windows with high solar gains and very low u-values, you want to ensure that you are getting credit in the BER Assessment for these. Once again Manufacturer declared data needs to be backed up with certificates of testing carried out as per ISO 10077 by an accredited laboratory or organisation. These tests will most likely have been carried out on windows (1.48 high * 1.23 wide) and doors of standard dimensions. For your build, you will require these certificates, and also declarations from the Manufacturer that the u-values claimed for your windows are based on the Test Certificates, and have been calculated per ISO 10077.

Potential Impact 3 to 5 kWh/m2/yr

Thermal Bridging

Default value for existing house is 0.15 W/m2K  whereas new build can be taken as 0.11W/m2K. However a value of 0.08 W/m2K if your architect/builder can certify that the construction meets ‘Limiting Thermal Bridging and Air Infiltration - Acceptable Construction Details’’ ( ) as referenced in Building Regulations 2008 TGD L.

If you have invested heavily in state of the art technology to get the thermal bridging in the region of 0.03 W/m2K, the actual value for Thermal Bridging may also be calculated using numerical modelling or measurement. You will need the relevant certifications from your architect or builder in order to obtain full credit for your efforts in minimising thermal bridges in your home.

Potential Impact 5 to 10 kWh/m2/yr

Hot Water Cylinder

If the manufacturer of the cylinder can certify the cylinder heat losses in kWh/day, there can be a benefit accruing as against the default values

Potential Impact 1 to 2 kWh/m2/yr

Solar Thermal Panels

Solar panel performance can be taken from the HARP Database or from certification of testing to IS EN 12975-2 Thermal solar systems and components – Solar collectors – Part 2: Test methods.

Potential Impact 3 to 5 kWh/m2/yr

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