Performance Evaluation of Hybrid Earth Pipe Cooling with Horizontal Piping System

S.F. Ahmed, M.M.K. Khan, M.T.O. Amanullah, M.G. Rasul and N.M.S. Hassan,    School of Engineering and Technology, Higher Education Division, Central Queensland University, Rockhampton, QLD, Australia

Earth pipe cooling technology is a building design approach for cooling a room in a passive process without using any customary units. It can reduce energy consumption of the buildings for hot and humid subtropical zones. This chapter investigates the performance of horizontal earth pipe cooling (HEPC) in combination with a green roof system. To measure the performance, a thermal model was developed using Fluent in ANSYS 15.0. Data were collected from three air-conditioning modeled rooms installed at Central Queensland University, Rockhampton, Australia. One of the rooms was connected to a HEPC system, the second to a green roof system, and the third standard room had no cooling system. The effect of air temperature, air velocity, and relative humidity of the hybrid earth pipe cooling performance were assessed. A temperature reduction of 4.26°C is predicted for a combined HEPC and green roof system compared to the standard room, which will assist the inhabitants to achieve thermal comfort and save energy in the buildings.

Keywords

Passive air cooling; earth pipe cooling; horizontal piping system; green roof; air temperature; air velocity

1.1 Introduction

A significant amount of energy is consumed by buildings today and buildings are accountable for about 40% of world annual energy consumption [1]. There has been an enormous increase in energy demand worldwide in recent years due to industrial development and population growth. World energy use is projected to rise from 524 quadrillion Btu in 2010 to 630 quadrillion Btu in 2020 and 820 quadrillion Btu in 2040 as shown in Figure 1.1 [2]. This represents an energy consumption increase of 56% during this period. More than 85% of this growth in global energy demand is predicted to occur among the developing nations outside the Organization for Economic Cooperation and Development (OECD) nations, where demand is driven by strong long-term economic growth and expanding populations. In contrast, the greater part of OECD member countries are now more established energy consumers with slower expected economic growth and particularly no foreseen population growth [3].

Energy use in non-OECD nations will increase by 85% compared to an increase of 18% for the OECD economies. Country-wise world energy consumption over this period of 2010–2040 is summarized in Table 1.1.

Almost all of the world population uses energy at some point for their own needs and the greater amount of this energy is used in buildings for cooling, heating, and lighting. The building sector consumes a lot of energy which is responsible for more than 40% of global energy use [4] and 40–50% of the total delivered energy in the United Kingdom and the United States [5,6]. In 2010, the sector accounted for more than one-fifth of global energy consumption [2]. Ventilation, cooling, and heating in buildings can be responsible for as much as 70% of the total energy use in buildings [7]. This growth, along with unprecedented changes in the underlying living standards and economic conditions, will make developments within the building sector. Total world delivered energy demand for buildings shown in Figure 1.2 increases from 81 quadrillion Btu in 2010 to nearly 131 quadrillion Btu in 2040 at an average annual growth rate of 1.6%.

Energy consumption in Australia has also been increasing rapidly with the rest of the world. This energy is used for residential, commercial, agricultural, and industrial purposes. The energy consumption for the Australian residential sector in 1990 was about 299 petajoules (PJ) and that by 2008 had grown to about 402 PJ and is projected to increase to 467 PJ by 2020 under the current trends [8]. This represents a 56% increase in residential sector energy consumption over the period 1990–2020. The contribution of electricity to this residential energy consumption is predicted to increase from 46% of total energy consumption in 1990 to 53% in 2020 as shown in Figure 1.3. Gas consumption is also expected to increase from 30% in 1990 to 37% in 2020, while wood is predicted to decrease from 21% to 8% over the same period [8]. Liquefied petroleum gas use in the residential sector remains unchanged and is expected to contribute to 2% in 2020.

Residential electricity consumption grew 1.5% per annum at a compound rate between 2008 and 2011 [9]. Energy consumption in this sector has been less responsive to electricity price increase since 2008 than before 2008. Per capita residential energy consumption was nearly static between 2003 and 2012, suggesting higher consumption due to population growth rather than higher spending per capita. In Australia, this residential energy consumption varies state to state as shown in Figure 1.4.

Victoria, NSW, and Queensland show steady growth of residential energy consumption over the period of 1990–2020 as shown in Figure 1.4. This energy consumption is primarily due to extensive use of gas for space heating and cooling. Australian homes use 38% of their total energy consumption on heating and cooling [10]. Moreover, the average annual temperature in Australia has increased by 0.9°C since 1950 [11]. Projections from Commonwealth Scientific and Industrial Research Organization (CSIRO) indicate an increase of average annual temperature by a further 0.6–1.5°C by 2030 and 1–5.0°C by 2070, depending upon the levels of global emissions [12]. According to this projection, more energy will be needed to achieve the same level of thermal comfort. It is essential to save energy today in the Australian residential sector, as well as globally, for the betterment of the world economy and environment. This residential energy consumption can be reduced significantly by employing energy-efficient technologies.

There has been renewed interest toward building energy efficiency because of environmental concerns and the high cost of energy in recent years. Energy efficiency in building might be enhanced by adopting either active or passive energy-efficient methods. Upgrades to heating, ventilation, and air conditioning frameworks, lighting, and so on might be dealt with as active strategies, while the changes to building envelope components could be classified under passive strategies [13]. Among these passive strategies, passive air cooling of the earth pipe cooling strategy is an appealing choice to reduce the energy consumption in buildings for all...