The carbon performance rating and the wholebuilding method CPRhlac

The whole-building CPR takes account of heating, lighting and air conditioning. In principle it is calculated in the same way as the CPR for air conditioning and mechanical ventilation, but with three additional sets of data, two for the heating system and one for the lighting. The equation for CPR(HLAC) is:

CPR(hlac) = (PD x HD x CD x FD) + (PR x HR x CR x FR) + (PB x HB x CB x FB) + (PH x HH x CH x FH) + (PL x HL x CL x Fl)

As before, the terms PD, HD, CD and FD refer to the mechanical ventilation system, and the terms PR, HR, CR and FR refer to the refrigeration plant. The additional terms are defined as follows:

• PB The total installed capacity of the heat raising plant, kW/m2

• HB The typical annual equivalent hours of full load operation

• CB The carbon emission factor, in kgC/kWh, for the fuel used in the heat raising plant

• FB A plant management factor for the heat raising equipment.

• PH The total installed capacity of the heat distribution system, kW/m2

• HH The typical annual equivalent hours of full load operation

• CH The carbon emission factor, in kgC/kWh, for the fuel used by the heat distribution system

• FH A plant management factor for heat distribution equipment

• PL The total installed power of the lighting system, kW/m2

• HL The typical annual equivalent hours of full load operation

• CL The carbon emission factor, in kgC/kWh, for the fuel used by the lighting system. This is nearly always electricity for which CL = 0.113

• FL A plant management factor for the lighting system.

Values for PD, HD, CD, FD, PR, HR, CR and FR are as before. Values of PB, PH and PL are obtained from the ratings of the installed equipment, and the carbon emission factors CB, CH and CL are obtained from Table 3.5. For HB, HH and HL, typical annual equivalent hours of full load operation are:

HB = 1250 hours per annum HH = 2500 hours per annum HL = 2000 hours per annum

Values for the remaining parameters, FB, FH and FL are given in Tables 12.3, 12.4 and 12.5 respectively.

Table 12.3 The factor FB.

Monitoring and reporting features

Plant management features

Provision of energy metering of plant and/or metering of plant hours run, and/or monitoring of internal temperature in zones, plus the ability to draw attention to out-of-range values

Provision of energy metering of plant and/ or metering of plant hours run, and/or monitoring of internal temperature in zones

No monitoring provided

Controls which restrict the hours of operation of boiler plant

0.75

0.80

O.85

Efficient capacity control of boiler plant

0.75

0.80

O.85

Controls to prevent simultaneous heating and cooling in the same zone

0.90

0.93

O.95

Adapted with permission from BRE Digest 457 [44]

Adapted with permission from BRE Digest 457 [44]

The three time and occupancy factors, TOF, are obtained from the following formulae:

TOF(A) = 1 - 0.15(TC + 2 x OC - TC x OC) TOf(b) = 1 - 0.10(TC + 2 x OC - TC x OC) TOf(c) = 1 - 0.05(TC + 2 x OC - TC x OC)

where TC is the fraction of building fitted with time-based control

OC is the fraction of building fitted with occupancy control, i.e. either with sufficient zonal switching to allow occupants to control lighting in their own workspace, or with occupancy-sensing control.

The daylight management factor, DMF, is obtained from:

Table 12.4 The factor FH.

Monitoring and reporting features

Plant management features

Provision of energy metering of plant and/or metering of plant hours run, and/or monitoring of internal temperature in zones, plus the ability to draw attention to out-of-range values

Provision of energy metering of plant and/ or metering of plant hours run, and/or monitoring of internal temperature in zones

No monitoring provided

Controls which restrict the hours of operation of heating system

0.85

0.90

0.95

Efficient capacity control of distribution system

0.90

0.93

0.95

Adapted with permission from BRE Digest 457 [44] Table 12.5 The factor FL.

Monitoring and reporting features

Plant management features

Provision of energy metering of lighting systemand/or metering of hours of use, plus the ability to draw attention to out-of-range values

Provision of energy No monitoring metering of lighting provided system and/or metering of hours of use

Time-based lighting control and occupancy based lighting control

TOF(A)

TOF(B)

TOF(C)

Daylight-based lighting control and ability to utilise daylight

Daylight management factor, DMF

Adapted with permission from BRE Digest 457 [44]

Adapted with permission from BRE Digest 457 [44]

where DC is the fraction of building fitted with daylight control

DA is the fraction of building which falls within the definition of a daylit space, i.e. any space within 6 m of a window wall provided that the glazed area is at least 20% of the internal area of the window wall, or a roof-lit space with a glazing area at least 10% of the floor area.

As with FD and FR, the final value of FB, FH or FL is found by multiplying together all applicable factors in the relevant column.

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