Impact of Air Density Variation on a Simulated Earth-to-Air Heat Exchanger’s Performance

Abstract

Due to their simple design and reliable operation, earth-to-air heat exchangers (EAHE) are used in modern buildings to reduce ventilation heat losses. EAHE operation in atmospheric conditions results in variation in ambient air temperature and pressure affecting air density. The paper presents the study on the impact of ambient air density variation on the calculated hourly air temperature at the EAHE outlet and the resulting energy use for space heating and cooling of an exemplary residential building. The ground temperature was computed from the model given in EN 16798-5-1. Then, air density was obtained using five various methods. Energy use for space heating and cooling of the building was computed using the 5R1C thermal network model of EN ISO 13790. Depending on the chosen method and concerning the base case without EAHE, a reduction in annual heating and cooling needs was obtained from 7.5% to 8.8% in heating and from 15.3% to 19% in cooling. Annual heating and cooling gain from EAHE were 600.9 kWh and 628.3 kWh for heating and 616.9 kWh and 603.5 kWh forcooling for the Typical Meteorological Years (TMY) and International Weather for Energy Calculation (IWEC) files, respectively. Unit heating and cooling gains per heat exchanger area were from 34.9 kWh/m2 to 36.8 kWh/m2 and from −35.1 kWh/m2 to −36.3 kWh/m2. Density variation with temperature from the relevant typical Polish meteorological year at constant pressure, in comparison to the method of EN 16798-5-1, resulted in an hourly difference of that unit gain up to 4.3 W/m2 and 2.0 W/m2 for heating and cooling, respectively. The same was true inthe case of IWEC files that resulted in differences of 5.5 W/m2 and 1.1 W/m2.

Simulation and Experimental Study on the Use of Ventilation Air for Space Heating of a Room in a Low-Energy Building

“…with the volumetric heat capacity of air is assumed to be constant at a c a = 1200 J/m 3 K according to EN ISO 13790. However, both ventilation air density and specific heat capacity may vary following outdoor environmental conditions [68,69]. Finally, average hourly values of nodal temperatures are as follows:…”

Heat Transfer and Heat Recovery Systems

“…Michalak analyzed the impact of air density variation on the operation of earth-to-air heat exchangers (EAHE) coupled with the ventilation system of a residential building [13]. The analysis took into account air density variation with ambient air temperature as Polish hourly typical meteorological years do not contain atmospheric pressure.…”

Numerical and Experimental Analysis of an Earth–Air Heat Exchanger

“…Although the variation of air properties with temperature could affect the performance of the EAHE [23], in this study, the air was considered incompressible and with constant properties. Therefore, the continuity equation, obtained from Tannehill et al [24], is expressed in Equation ( 1…”