Elsevier

Energy

Volume 91, November 2015, Pages 1009-1017
Energy

Performance analysis of a thermoelectric air duct system for energy-efficient buildings

https://doi.org/10.1016/j.energy.2015.08.102Get rights and content

Highlights

  • Examines the performance of TE-AD (thermoelectric air duct system) on building load for tropical region.

  • Performance of TE-AD system has been analyzed by supplying different input current.

  • Provides comparative analysis between TE-AD system and traditional air conditioning system.

  • Optimum operating conditions of TE-AD system has been determined.

Abstract

This paper describes experimental and simulation study results of an air duct system that cools down airflow by using TEMs (thermoelectric modules). This system is designated as TE-AD (thermoelectric air duct) system which consists of twenty four TEMs along with heat sink and fan for circulation of air. Both experimental and simulation results were in good agreement with each other and showed that the TE-AD system reduces room temperature in the range of 1.2–5.3 °C and humidity in the range of 5–31%. The COP (coefficient of performance) of the system ranges from 0.392 to 0.679 under different operating input current for Malaysian weather conditions. By comparing TE-AD system with conventional air conditioning system, energy saving of 38.83% and CO2 emission mitigation of 38.81% was achieved with additional benefits of high reliability and refrigerant free system.

Introduction

Presently, maintaining thermal comfort has been a challenge for most of the developing countries, as the process of air conditioning in large buildings can lead to excessive use of energy [1]. Energy requirements for air conditioning will escalate from 300 TW h in the year 2000, to around 4000 TW h in the year 2050 and a further expected to increase around 10,000 TW h in 2100 [2]. One of the main reasons for higher energy requirement of an air conditioning system is 25–40% energy lost in an air duct system while channeling conditioned air inside the building [3]. Approaches to deal with the current situation are to utilize alternative energy sources and thus reduce the usage of regular power technologies and air conditioning system.

Thermo-electric effect was discovered at the beginning of the 19th century by Thomas Seebeck, and among the latest potential technologies being researched in compliance with the requirements of space conditioning [4]. TE materials are solid-state energy converters that can create a temperature difference when an electric potential is applied to the material (Peltier effect) or generates the electric potential by introducing a temperature difference (Seebeck effect) [5]. TE materials arranged in a certain configuration are called TEMs (thermoelectric modules) and it can be classified into either TEGs (thermoelectric generators), which directly convert heat to electricity, or thermoelectric coolers (TECs), which directly convert electricity into a temperature gradient [6]. Previously TEMs are limited only to small applications due low COP (coefficient of performance), but over the past few years researchers have identified its potential for building applications.

Stockolm et al. [7] in 1982 used TEMs for cooling small cabs of railroad and submarines. Lertsatitthanakorn et al. [8] investigate TE air-conditioning unit installed on the celling. Two heat exchanger one attached on the evaporator side were used to dissipate thermal energy from the source and other attached on the condenser side were used to discard heat to the surrounding environment. Result shows that at input current intensity of 3 A, cooling capacity of 169 W was achieved. Maneewan et al. [9] develop TE air conditioning system by implementing three TE modules for small space conditioning application. At operating current of 1 A, COP of 0.34 and cooling capacity of 29.2 W was achieved. Cosnier et al. [10] investigated air heating and cooling capacity of TEMs both experimentally and numerically. It was found that when the TE module was operated at the input electrical current supply of 4 A, cooling capacity of 50 W per module, with a temperature difference of 5 °C between hot and cold side and COP range between 1.5 and 2 was achieved. Li et al. [11] experimentally studied TE module application in cooling or heating of airflow for small envelope. Results showed that COP greater than 1.5 can be achieved with a small temperature difference of (5–10 °C) in cooling mode. Totala et al. [12] also attempted to study the effect of thermoelectric cooling in a 1 m3 box using a single TEM and found that their design was able to cool the ambient air temperature from 32.5 °C to 22.1 °C using 4 TEMs, each providing 37.7 W of cooling power. Gillott et al. [13] investigated the effect of TEMs on small scale building space conditioning application. Results showed that maximum cooling capacity of 220 W and COP of 0.46 was achieved when TE cooling unit was operated at input electrical current supply of 4.8 A to each module. Shena et al. [14] use TEM as radiant panels instead of conventional hydronic panels to develop TE-RAC (thermo-electric radiant air-conditioning) system. This system can be used for both heating and cooling purpose and optimum results were obtained when the system operates at current 1.2 A. A Maximum COP of TE-RAC in the cooling mode was 1.77 and the minimum temperature achieved at cold side was 20 °C. Performance of TE air-conditioners were compared with conventional vapor compression air-conditioners by Riffat and Qiu [15]. Results showed that the COPs of TE air-conditioner was in the range of 0.3–0.45 while vapor compression air-conditioner was in the range of 2.6–3.0 respectively. However, Hermes and Barbosa [16] concluded that present TEMs was having only 1% thermodynamic efficiency as compared to Stirling and reciprocating vapor compression refrigeration systems which was having a 14% thermodynamic efficiency. So in order to improve performance of the TE air-conditioning system, Tipsaenporm et al. [17] applied direct evaporative cooling techniques in TE air-conditioning system, which enhances the cooling power from a value 53.0 W–74.5 W. Cherkez [18] develop a novel TE air-conditioning unit by combining TE and the Joule–Thomson effects. The results show that COP of system improves by a factor of 1.6–1.7 as compared to existing TE systems.

Different studies have shown that the application of TEMs for small scale air-conditioning system application has been achieved, but the application of same in an air duct for space conditioning of buildings has not been researched. The main significance of this paper is to study the application of TEMs in an air duct system for developing novel TE-AD (Thermoelectric air duct) system for large scale application. TE-AD system provides cool and dehumidified air to the test room and thus reduces cooling load and energy requirement. The prospect is not to have a fully air conditioned test room, but rather to have a thermally affordable house in the tropical climate of Malaysia without consuming excessive energy and refrigerants. In the present study, an experimental system containing TE-AD system was set up that cools down an airflow circulated through it. A simulation model using TRNSYS software that calculates the system's thermal performance was compared with the experimental system. First a description of the experimental setup, simulation model and results are presented followed by energy consumption, CO2 emission and carbon credit potential by TE-AD system are illustrated.

Section snippets

Test room description

The experiment and data collection was conducted from 1 January to 31 January 2015 using the single-room house facility equipped with TE-AD system located in the campus of Universiti Teknologi PETRONAS (4°23′11″N and 100°58′47″E, Perak, Malaysia). The test room is of dimensions 2.8 m (width, X) × 2.7 m (depth, Y) × 2.5 m (height, Z) as shown in Fig. 1 and its thermo-physical properties are presented in Table 1. All the external walls are three-layered with a middle layer composed of 20 cm thick

Results and discussions

In this section, findings of implementation of the TE-AD system in the test room, operated at different input current are presented. The detailed discussion and comparison of experimental and simulation results are given in the subsequent subsections. Carbon credit potential and CO2 emission mitigation by implementing the TE-AD system are also discussed.

Conclusions

A novel TE-AD system was successfully installed and tested for the test room. Major conclusions can be drawn as follows:

  • 1.

    COP over 0.679 and cooling power, Qc up to 499 W could be achieved in an air-cooling mode with the system operated in the range of 5–6 A, and 5 V.

  • 2.

    Temperature difference between indoor and the outdoor of the test room can be reach up to 3.0–5.3 °C while operating at 6 A current intensity. Fan and heat sink attached to the hot side of TEMs plays an important role in maintaining

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