HOLISTIC

GAINS A

Electrical building services engineers can help cut CO2 emissions, energy use and costs by applying a ‘whole-life total ownership cost’ approach, write Tony Sung, Ya Ping Du, Marty Barrett and Laurie Brady

1 x 2 x3 DNO-2 11KV supply

lthough many buildings use electricity for 24 hours every day of the year, the price of electricity that the building user pays to a

supplier may be different depending on the time the electricity is being used. In some countries, the price of electricity during peak time may be 150% of the price of electricity at off-peak. There is also a difference in the content of CO2 emissions between peak and off-peak periods. Soon it may be possible to apply smart

meters in conjunction with a good energy management system to optimise the energy benefiting from the least expensive tariffs at the time of the demand. In the form of a generalised but simplified form of optimisation equation, this would be to minimise, say, the objective function1 Ξ( )y :

Ξ( )y = f x( , , , ..., ) n x

where y = maximum energy efficiency % of the electrical distribution system

Figure 1: Three-transformer (150% rated) dual primary dual secondary supply DNO-1 11KV supply Subject to:

m number of relationships governed by ≤ inequalities 11 1 12 2 13 3

a x + a x + a x a x p a x + 22 2

...+ 1n 21 1 … m1 1 a x + a 2m x2 + a 3m x amn n m

a x + a x a x p2 x ≤ p

23 3...+ 2n 3...+

n ≤ 1 n ≤

r number of relationships governed by ≥ inequalities

b x +b x b x b x q b x +b x +b x b x q

11 1 12 2 13 3...+ 1n 21 1 22 2 23 3...+ 2n

+ … b x +b x b x b x pr r1 1 r2 2 + r3 3...+ rn n ≤

s number of relationships governed by = equalities

c x + c x + c x c x e 21 1 22 2 23 3...+ 2nxn = e2

11 1 12 2 13 3...+ 1n c x + c x + c x c

… c x + c 2s x2 + c x c x e= s s1 1 s3 3...+ sn n

We need to apply some non-negativity restriction, for example, 1

x is the

professional fees of the electrical building services engineer, 2

G1 ( , , , ..., ) 0 x x 2 x3 x ≥ n transformer, 3x is installation cost etc. These x is the size of an HV/LV

variables should not have a negative value: 1

The above generalised equations are G2 400/230V Bus

Connection point for mobile genset

all-encompassing for the whole electrical installation. By breaking it down into smaller manageable chunks, electrical building services engineers can offer a best- value engineered whole-life building carbon and energy ownership system to the client. This article analyses the supply arrangement for a fictitious building to illustrate how to carry out this best-value engineering design exercise using the whole-life total ownership cost (WLTOC) design approach.

48 CIBSE Journal June 2011 www.cibsejournal.com n = 1 n ≤ 1 n ≤ 2

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