Air conditioning in the region of Madrid, Spain: An approach to electricity consumption, economics and CO2 emissions

doi:10.1016/j.energy.2010.12.068

Energy

Volume 36, Issue 3, March 2011, Pages 1630-1639

https://doi.org/10.1016/j.energy.2010.12.068 Get rights and content

Abstract

An understanding of electricity consumption due to residential air conditioning (AC) may improve production and environmental impact strategy design. This article reports on a study of peak and seasonal electricity consumption for residential air conditioning in the region of Madrid, Spain. Consumption was assessed by simulating the operation of AC units at the outdoor summer temperature characteristics of central Spain. AC unit performance when operating under part load conditions in keeping with weather conditions was also studied to find cooling demand and energy efficiency. Likewise final electricity consumption was computed and used to calculate energy costs and greenhouse gas emissions (GHGs). Cooling demand, when family holidays outside the region were factored into the calculations, came to 1.46 × 10⁹ kWh. Associated seasonal electricity demand was 617 × 10⁶ kWh and seasonal performance of AC units around 2.4. Electricity consumption in the whole region was observed to peak on 30 June 2008 at 5.44 × 10⁶ kW, being the load attributable to residential AC 1.79 × 10⁶ kW, resulting about 33% of the total peak consumption. The seasonal cost per household was about €156 and the total equivalent warming impact was 572 × 10³ t CO₂. The method proposed can be adapted for use in other regions.

Research highlights

► The residential demand of AC in the Region of Madrid is studied including the effect of family seasonal holidays. ► A simulation of the air-cooled mechanical compression cycle was performed and several results were obtained such as a seasonal COP of 2.4. ► Some air-cooled AC apparatus marketed were studied and a “Commercial COP” was obtained. ► Electricity consumption and equivalent CO₂ emissions were also assessed and the seasonal COP was compared with commercial COP. ► Finally, influence of residential AC on electricity consumption of the whole region is analyzed, including also consumption peaks.

Introduction

Greenhouse gas emissions (GHGs) resulting from electric power generation have risen sharply in Spain in the last 12 years. According to the Spanish Ministry of the Environment’s GHG inventory [1], total equivalent warming impact emissions grew from 250 million to 380 million tonnes, i.e., by 149.5% between 1996 and 2006.

However, as a result of lower demand due to the economic crisis and the increase in the amount of electricity produced in combined cycle (around 30% of the total) and renewable energy plants, between 2007 and 2009 emissions declined by around 10%, to 350 million tonnes of CO₂. Spanish emissions per capita in 2009 came to 9.5 t.

A population’s consumption of electricity is associated with its standard of living. But it is well known that such consumption has adverse consequences for the Earth’s environment. Ensuring the supply of electricity and environmental quality is the responsibility of public authorities. Therefore, their objective is to implement efficient energy models that also ensure excellent air quality as stated in the Community of Madrid’s Energy Plan, 2004–2012 [2].

In high temperature climates, residential sector air conditioning (AC) generates power needs that these authorities prefer not to leave unmet. Moreover, as a recent report about the Spanish electric system shows [3], temperature extremes concur with yearly peak demand or peak consumption. This fact, which represents a serious problem for the stability and reliability of electricity distribution systems, was also observed in [4]. In such interesting study it was concluded that temperature is one of the most important factors affecting the electricity demand of a population. Knowing the actual energy consumption generated directly by AC may therefore help policy makers plan power generation and environmental impact strategies.

The region of Madrid, where this study was conducted in 2009, is a densely populated area with around 2.3 million primary residences and a population of 6.2 million, i.e., a mean of over three occupants per household, according to the Spanish National Statistics Institute, [5]. The region’s gross domestic product per capita is 133% of the national mean and slightly higher than the European average. Energy consumption per inhabitant is 1.8 t of oil equivalent (TOE), compared to 2.5 TOE in the European Union. The region’s energy-related CO₂ per capita, at 6.1 t, is much lower than the European mean of 8.2 t. The transport industry at 51%, the residential and commercial sector at 24.5%, and manufacturing at 12%, account for the largest share of final energy consumption. Ten percent goes to the service sector and just under 2% to farming. The energy sources include petroleum derivatives, which cover 62% of the demand, electric power, 21%, natural gas, 15% and other sources nearly 2% [2].

To the authors’ knowledge, no data have been published on electricity consumption by or the resulting TEWI attributable to residential AC units in the region of Madrid. The present study aimed to assess both as accurately as possible.

The only technical information available for buyers of AC units is contained in the user’s instructions booklet furnished with the facility, which includes the manufacturer’s power consumption and energy efficiency estimates. This information does not suffice, however, to evaluate the power consumed or the emissions generated by AC units.

A second aim of the present study, then, was to compare electricity consumption and CO₂ emissions, found using manufacturer’s specifications, to the consumption and emission values obtained with a numerical simulation based on the refrigerant cycle. In the present study, a simulation was run based on outdoor summertime temperature characteristics of the area. Assumptions were made with respect to the standard building envelope and the location and total number of AC units installed in the region. Coefficient of performance (COP) was determined by applying energy balances to the refrigeration cycle in terms of isentropic, mechanical and electrical efficiency. Part load operation and the electricity consumed by auxiliary elements were also taken into consideration. Other results of interest, such as the comparison between electricity consumption obtained from the simulation and manufacturer’s specifications, were also recorded. Furthermore, taking into account real information on electric power consumption in the region of Madrid furnished by Iberdrola Distribución, S.A.U [6], the influence of cooling demand on the electricity peak consumption was obtained.

Section snippets

Methodology

The methodology followed to meet the paper’s aims is discussed in this section. To begin with, information about number of dwellings and population of Madrid, Spanish standard dwelling size and construction materials, and the amount of air-conditioned homes are taken from the Spanish National Statistics Institute [5].

Next, by using meteorological data from the weather station of the Eduardo Torroja Institute’s Solar Energy Experimental Plant at Arganda del Rey, 22 km far from Madrid, seasonal

Standard air-conditioned home

According to the Spanish National Statistics Institute [5], the mean net size of Spanish homes is 80 m² and the distance between structural floor and ceiling slabs is usually 2.5 m. Not all rooms are air-conditioned; units are generally installed in the living-dining room and bedrooms, which account for around 60% of the total area. The standard home chosen for the present study was assumed to be oriented north–south, located at mid-height in the building and occupied by three people. The

Thermal load and demand

The first step in AC design is to calculate cooling load, which has a significant effect on AC unit efficiency. Thermal load depends on:

1-
heat transfer coefficient of the building envelope;
2-
weather conditions;
3-
internal loads; and
4-
external loads.

Refrigeration cycle

For the analysis of AC energy efficiency discussed below, units were studied by capacity and type of refrigerant. Another simplifying assumption made to calculate operating parameters was that all units were fitted with low capacity (up to 7 kW), electrically powered, air-cooled, mechanical compression chillers.

The information needed on the type of refrigerant used was drawn from the statistics published by the national manufacturers’ association on the number of units installed in recent years

Performance of commercial AC units

This section discusses the main operating parameters and curves for the units presently used in residential AC. Two models applying variable flow technology were chosen.

The efficiency curves for two AC units marketed by a well known manufacturer, referred to here as models (I) and (II), used to air condition homes of different sizes, are plotted below. Both units use refrigerant R410A. Table 1 gives the refrigeration capacity and power consumption values furnished by the manufacturer in 2008 at

Electricity consumption

From the thermal demand on the three representative days and the performance values found in Section 5, electricity consumption results were calculated and plotted in Fig. 15. The maximum values observed were 2.9 kW on 2 August, 1.4 kW on 11 July and 0.7 kW on 13 June. All these peaks were recorded between 1:00 and 4:00 p.m. The daily electricity consumption was 24.7 kWh on 2 August, 10.2 kWh on 11 July and 1.8 kWh on 13 June. The value for the entire summer came to 919.9 kWh per home. Note that the

Environmental impact

The environmental impact of the refrigerants used in AC units and the emissions generated in electric power production is evaluated below. The parameter used for this purpose is the Total Equivalent Warming Impact (TEWI), which represents the amount of associated CO₂.

To begin with, TEWI can be broken down into two parts. The first, GWP (Global Warming Potential), takes account of the refrigerants that leak directly into the air, while the second, IGWP (Indirect Global Warming Potential), refers

Conclusions

AC unit efficiency under different outdoor conditions is an important consideration, for it provides insight into the optimal capacity to be installed and the effect on demand of connecting AC at one or another outdoor temperature.

The demand for electricity in Madrid generated by residential AC was calculated on the basis of data from the Spanish National Statistics Institute and an analysis of the thermodynamic AC cycle. This calculation was performed via numerical simulation, using

Acknowledgements

This study was funded by the Spanish Ministry of Science and Innovation under Projects INVISO, sub-project SP3 “Sustainable power generation in housing” and ENE2010-20650-C02-01. Author A. Gonzalez-Gil is grateful to the Spanish National Research Council (CSIC) for its support while he worked toward his PhD. The authors also wish to thank J. Cabetas from Iberdrola de Distribución Eléctrica S.A.U. for the information furnished.

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Air conditioning in the region of Madrid, Spain: An approach to electricity consumption, economics and CO2 emissions

Abstract

Research highlights

Introduction

Section snippets

Methodology

Standard air-conditioned home

Thermal load and demand

Refrigeration cycle

Performance of commercial AC units

Electricity consumption

Environmental impact

Conclusions

Acknowledgements

Energy

Appl Therm Eng

Energy

Int J Refrigeration

Appl Therm Eng

Int J Refrigeration

Int J Refrigeration

Appl Therm Eng

Inventario de Gases de Efecto Invernadero de España

Plan Energético de la Comunidad de Madrid 2004–2012

Informe del sistema eléctrico español en 2008

Air conditioning in the region of Madrid, Spain: An approach to electricity consumption, economics and CO₂ emissions