Hourly Simulation of an Earth-to-Air Heat Exchanger in a Low-Energy Residential Building

Piotr Michalak

doi:10.3390/en15051898

Abstract

The earth-to-air heat exchanger (EAHE) is a well-founded and verified solution used in modern buildings both for heating and cooling purposes around the world. However, there is a lack of studies on operation of such devices cooperating with ventilation systems of buildings in hourly time step. In this study, the 5R1C thermal network model of a building from EN ISO 13790 was coupled with the EAHE model from EN 16798-5-1 to calculate hourly outlet air temperature. To improve the effectiveness of the considered solution, an additional algorithm was developed to choose between the EAHE outlet and ambient air as the source of ventilation air. Simulations were conducted in a spreadsheet for a low-energy single-family building. Ground temperature was compared with measurements taken in the considered location. The application of the EAHE with the proposed bypass resulted in a decrease in annual energy use for space heating and cooling from 14.82 GJ and 1.67 GJ to 12.74 GJ and 0.93 GJ, i.e., by 14% and 44%, respectively. Peak hourly heating and cooling thermal power decreased from 2.73 kW and 3.06 kW to 2.21 kW and 2.34 kW. Introduction of a bypass and switching between the EAHE and ambient air as the source of ventilation for the building resulted in annual energy savings of 123 kWh.

Highlights

Due to significant energy consumption by buildings [1,2], numerous efficiency-related initiatives have been launched recently in European countries [3–5]
To reduce ventilation heat loss various techniques of heat recovery are used [10,11], usually with cross-flow, counter-current or rotary heat exchangers [12,13]. These solutions, efficient, are rather difficult to apply in existing buildings that are considered for thermal modernisation. This is especially true in residential buildings, where the amount of available space rarely allows for installation of an air handling unit with necessary equipment
In such objects the heat transmission loss through external partitions is usually the most significant [7,14,15] and it can be efficiently minimised at relatively low cost by additional insulation. This approach to the required energy standards of a building can be achieved in a simple way without too much interference with the structure of the building and without costly installation work which is burdensome for the residents [16]

Summary

Introduction

Due to significant energy consumption by buildings [1,2], numerous efficiency-related initiatives have been launched recently in European countries [3–5]. To reduce ventilation heat loss various techniques of heat recovery are used [10,11], usually with cross-flow, counter-current or rotary heat exchangers [12,13] These solutions, efficient, are rather difficult to apply in existing buildings that are considered for thermal modernisation. In such objects the heat transmission loss through external partitions is usually the most significant [7,14,15] and it can be efficiently minimised at relatively low cost by additional insulation. This approach to the required energy standards of a building can be achieved in a simple way without too much interference with the structure of the building and without costly installation work which is burdensome for the residents [16]. In practice, in the case of residential buildings, reduction of a ventilation loss is not taken into account and typical modernisations are limited to the installation of new windows with diffusers [17,18]

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Conclusion