EnergyPolicy 1994 22 (8) 648-656 Calculating the energy requirements of household purchases A practical step by step method B C W van Engelenburg, T F M van Rossum, K Blok and K Vringer An accurate and fast method is presented for cal- culating the energy requirement of consumption items. The method combines process analysis and input-output analysis. The energy requirement of a particular consumption item is calculated in ten steps, each dealing with certain parts of the pro- duction network. Each step can be standardized to a large extent. The method is illustrated by apply- ing it to one product: a domestic refrigerator. Keywords: Energy analysis; Product energy requirement; Household consumption The domestic sector is an important consumer of ener- gy: households use natural gas for space heating, electricity for lighting and petrol for transport, This is called the direct energy requirement of a household. Energy is also needed for building houses, producing cars or growing tomatoes. The energy embodied in pur- chased products is called indirect energy requirement. The indirect energy requirements of households is cer- tainly not negligible: in the USA in 1986 ~ and in the Netherlands in 19872 this indirect energy requirement was about half the total energy requirement of the coun- try in question. Therefore, energy reduction strategies (eg by changing consumer behaviour) should also pay attention to the indirect energy requirement. A household has many different expenditures. Some of these expenditures interact. Drinking coffee, for in- stance, implies using coffee machines (1) and coffee cups (2) and consuming coffee filters (3), coffee (4) and drinking water (5). Drinking coffee is called a function The authors are with the Department of Science, Technology and Society (STS), Utrecht University, Padualaan 14, NL- 3584 CH Utrecht, The Netherlands. and each numbered object, which can be seen as an indi- vidual consumer purchase, is called a consumption item. 3 We should distinguish between functions and consumption items. Before calculating the energy re- quirement of a certain function and, for instance, be able to compare several ways of providing a function, we have to determine the energy requirement of the differ- ent consumption items which are necessary to fulfil a certain function. In this paper we present a new and practical method for calculating the energy requirement of consumption items. The method combines the best elements of two existing methods for determining the energy require- ment of goods and services: the physical approach provided by process analysis and the economic-statisti- cal approach provided by input-output analysis, We will first describe these two approaches and show how we combined them in the new method. Next, we will de- scribe the new method which consists of ten steps. The method will be illustrated by applying it to the produc- tion and use of a domestic refrigerator. Finally, the results of the research will be discussed. Methods for determining the energy requirement of a product There are two ways of calculating the energy require- ment of a consumption item: input-output analysis and process analysis. In input-output analysis the energy re- quirement is determined using an economic-statistical approach. The transactions between the various sectors of an economy are collected in an input-output matrix. 4 A certain direct energy requirement can be attributed to each sector in the input--output matrix, for instance on the basis of energy statistics. Subsequently, by applying some mathematical operations to the matrix, we can 648 0301-4215/94/080648-09 © 1994 Bunerworth-Heinemann Ltd