http://www.legislation.gov.uk/id/uksi/2012/2999

Calculation of reckonable energy from combined heat and power stations7

1

Reckonable energy from a combined heat and power station must be calculated by reference to the gross calorific value of the commodity burned to produce it.

2

Where part of the energy from a combined heat and power station is used in a place, the formulae set out in paragraphs (3) to (5) must apply for calculating the reckonable energy from the station in relation to that place.

3

The following formula applies in respect of electricity from the combined heat and power station which is used in that place—

R E = \frac{2 E C \times E P}{2 E T + H T}

where—

RE is the reckonable energy in respect of electricity from the combined heat and power station which is used in that place;
EC is the total energy content of the relevant commodities burned in the combined heat and power station calculated by reference to the gross calorific value of each commodity;
EP is the quantity of electricity produced by the combined heat and power station which is used in that place;
ET is the total quantity of electricity produced by the combined heat and power station which is used in that place and elsewhere; and
HT is the total quantity of heat produced by the combined heat and power station which is used in that place and elsewhere.

4

If no electricity from the combined heat and power station is put into public supply, the following formula applies in respect of heat which is used in that place—

R H N = \frac{E C \times H P}{2 E T + H T}

where—

RHN is the reckonable energy in respect of heat from the combined heat and power station which is used in that place;
EC is the total energy content of the relevant commodities burned in the combined heat and power station calculated by reference to the gross calorific value of each commodity;
HP is the quantity of heat produced by the combined heat and power station which is used in that place;
ET is the total quantity of electricity produced by the combined heat and power station which is used in that place and elsewhere; and
HT is the total quantity of heat produced by the combined heat and power station which is used in that place and elsewhere.

5

If electricity from the combined heat and power station is put into public supply, the following formula applies in respect of heat which is used in that place—

R H S = [\frac{E C \times H P}{(2 E T + H T)}] - [\frac{H P \times E S}{H T} (2.6 - \frac{2 E C}{2 E T + H T})]

where—

RHS is the reckonable energy in respect of heat from the combined heat and power station which is used in that place;
EC is the total energy content of the relevant commodities burned in the combined heat and power station calculated by reference to the gross calorific value of each commodity;
HP is the quantity of heat produced by the combined heat and power station which is used in that place;
ES is the quantity of electricity produced by the combined heat and power station and put into public supply;
ET is the total quantity of electricity produced by the combined heat and power station which is used in that place and elsewhere; and
HT is the total quantity of heat produced by the combined heat and power station which is used in that place and elsewhere.

6

For the purposes of paragraphs (4) and (5), electricity is put into public supply when it is supplied to an electricity utility.

7

Where absorption cooling is used to produce a cooling supply for use in the installation, installations or parts of installations on a site and the heat for the absorption cooling is from a combined heat and power station—

a

the heat used to provide the cooling supply must be treated for the purposes of paragraphs (1) to (6) as used in the place where the cooling supply is used; and

b

the quantity of that heat must be estimated by dividing the output of the cooling supply by the coefficient of performance of the cooling system.