Abstract
Building foundation piles can be used as heat exchangers in ground-source heat pump (GSHP) systems to provide highly efficient renewable heating and cooling (H&C). Unbalanced H&C loads lead to heat build-up in the ground, decreasing the system's overall performance. In this study, the introduction of natural ventilation (NV) has been examined to decrease cooling load imbalance in cooling-dominated buildings to improve system efficiency. Building energy simulations estimated the H&C loads for an office building in three Portuguese cities: Lisbon, Porto and Faro, yielding heating loads of 0.2–3.6 MWh/year and cooling loads of 260–450 MWh/year. Four renewable H&C technology scenarios were used to assess energy performance: (1) an air-source heat pump (ASHP) system; (2) a GSHP system utilizing energy piles; (3) hybrid ASHP-NV and (4) hybrid GSHP-NV. Over 50 years of operation, in Scenario (1) COP values of 2.45–2.55 (heating) and 3.62–4.15 (cooling) were obtained. In (2), COP values increased to 4.15–4.34 (heating) but fell to 3.36–3.79 (cooling), which increased annual final energy needs by 7–8%. Unbalanced cooling loads increased the ground temperature by 21–24 °C, which is unlikely to be acceptable. Compared to (1), introducing NV reduced cooling loads by 65–90% in Scenarios (3) and (4), with the final energy needs decreasing by 59–80% and 62–88%, respectively. A further benefit of the GSHP-NV hybrid is that the ground temperature increase was limited to 8‑12 °C. For cooling, the COP in (3) decreased compared to (1) (3.14–3.69), while in (4), COP improved to 3.45–6.10. This study concludes that hybrid GSHP-NV systems should be considered in some cooling-dominated scenarios.
Highlights
In the modern world, people spend most of their time indoors, whether at work, at home or pursuing other activities [1], which has increased the use of energy by HVAC systems
Air-source heat pumps (ASHP) are one of the most common approaches to supply renewable heating and cooling (H&C). This system exchanges heat with the outside air, so changes in outdoor temperature will directly affect the coefficient of performance (COP)
The HVAC system was required to supply a very low albeit nonzero heating load during those time steps. This variation in heating load had no significant effect on the total electricity needs for heating and cooling and could be ignored
Summary
People spend most of their time indoors, whether at work, at home or pursuing other activities [1], which has increased the use of energy by HVAC (heating, ventilation and air conditioning) systems. Air-source heat pumps (ASHP) are one of the most common approaches to supply renewable heating and cooling (H&C). This system exchanges heat with the outside air, so changes in outdoor temperature will directly affect the coefficient of performance (COP). Hybrid natural-mechanical HVAC systems can significantly decrease overall HVAC energy needs by replacing mechanical ventilation and cooling with NV, whenever weather conditions allow its use [10,11,12]. A hybrid HVAC system (GSHP with piles) that uses NV is proposed This approach’s efficiency is compared, in a simulation environment, to that of other HVAC solutions for an office building model in three Portuguese cities: Lisbon, Porto and Faro
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