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BER numbers not adding up

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  • 08-10-2020 10:00pm
    #1
    tails_naf
    Registered Users Posts: 861 ✭✭✭


    My parents had an assessment done and got a D2, 284 Kwh/m2. It also said thr floor area is 147m2. This means their house consumes 40,000 kwh of energy per year. The thing is, they use about 1000L of oil a year, (=10,000 kwh) and about 5,000 units of elec. This is 15,000 kwh per year, plus some sticks for the fire. It's hard to see them anywhere near the 40,000 number. Does this indicate the assessment was pessimistic?


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    #2
    Str8outtaWuhan
    Registered Users Posts: 968 ✭✭✭Str8outtaWuhan


    tails_naf wrote: »
    My parents had an assessment done and got a D2, 284 Kwh/m2. It also said thr floor area is 147m2. This means their house consumes 40,000 kwh of energy per year. The thing is, they use about 1000L of oil a year, (=10,000 kwh) and about 5,000 units of elec. This is 15,000 kwh per year, plus some sticks for the fire. It's hard to see them anywhere near the 40,000 number. Does this indicate the assessment was pessimistic?

    My house is a B3 updgraded from D1 but it my utilities come to same amount that a typical A3 house has. Reason is simple , im tight and refuse to let the heating go on before 1st november. Maybe your parents are the same?


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    #3
    tails_naf
    Registered Users Posts: 861 ✭✭✭tails_naf


    Str8outtaWuhan wrote: »
    My house is a B3 updgraded from D1 but it my utilities come to same amount that a typical A3 house has. Reason is simple , im tight and refuse to let the heating go on before 1st november. Maybe your parents are the same?

    Well it's a 3 bed house and they only have heating on in one, as all kids have moved out, so they are not wasting energy heating unused rooms, but the house is comfortable to be in, not cold.


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    #4
    Metric Tensor
    Registered Users Posts: 3,724 ✭✭✭Metric Tensor


    The BER is based on standardised profiles and assumptions.

    There could be a miser living in the house who never turns on the heat and one uses one thirty watt lightbulb and it would get the exact same result if a family of 8 lived there with heat on day and night and a growhouse in the attic.

    In order to be able to compare like with like the calculation decides upon occupancy and how much heating, hot water and lighting is used based solely on the parameters of the house and pays no attention to the actual occupants or how they use the house.


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    #5
    sydthebeat
    Subscribers Posts: 40,981 ✭✭✭✭sydthebeat


    tails_naf wrote: »
    My parents had an assessment done and got a D2, 284 Kwh/m2. It also said thr floor area is 147m2. This means their house consumes 40,000 kwh of energy per year. The thing is, they use about 1000L of oil a year, (=10,000 kwh) and about 5,000 units of elec. This is 15,000 kwh per year, plus some sticks for the fire. It's hard to see them anywhere near the 40,000 number. Does this indicate the assessment was pessimistic?

    You make the fundamental mistake of thinking the BER system is a method to measure the specific energy usage of your house.
    It isnt.

    Its a system designed to compare the energy usage of like with like dwellings.
    In order to do this (as MT says above) it must make many assumptions in order to standardise the results so they can be used to compare.

    but anyway.... lets discuss the energy usage in the BER system...
    the BER takes "primary" energy into account in its algorithms... this means it includes the energy losses in the processing system, to get that energy to your dwelling.

    currently for electricity the grid system is considered to be 48% efficient... so you can practically double your electricity units when assessing BER.... so 5,000 kwhrs usage is 10,000 kWhrs in the BER

    On oil, you get about 12 KWhrs per litre of oil... and a standard oil boiler will be running at about 85% efficiency. You also need to account for energy losses in the transportation of the oil from the refinery to your door, so oil is given a conversion factor of 1.1.......... so 1000 litres equates to:

    1000 x 12=12,000 / 85 x 100 = 14,117 x 1.1 = 15,500 kwhrs

    so while that doesnt add up to 40,000 (its about 25,000), it is a small sample showing how losses are accounted for within the algorithms. There are many others.

    1000 litres and 5000 units would be considered on the low side for a 150 sq m D2 rated dwelling. Im sures that's reflected in the fact that theres only 2 people living in the house?


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