In the effort to de-carbonize the building stock, heat pumps are increasingly utilized in Switzerland, with 70% of the fast-growing heat pump market using ambient air as heat source. Inexpensive and easy to implement, these heat pumps are, however, less efficient than their ground- or water-source counterparts. In this modeling study, we aim at increasing the efficiency of air-source heat pumps using domestic greywater-contained heat. We assess the performance improvement relative to standard heat pump configurations across various climates, seasons, building envelopes, and domestic hot water consumption patterns. The results show that the annually-averaged coefficient of performance improves by 4.1% on average – ranging from 0.6% to 7.5%. This efficiency gain translates on average to 1.8 kWh/week of compressor electricity savings. Although attractive due to its simplicity, the proposed open-loop configuration – preheating of an external heat source – only leads to moderate performance improvement of air-source heat pumps. Based on these results, we extensively discuss and compare alternative system configurations and identify several fundamental differences in the heat recovery dynamics of each configuration. We show that closed-loop systems – using greywater as direct heat source – show the largest performance improvement potential, although being more expensive and complex to implement.

为了使建筑材料脱碳，瑞士越来越多地使用热泵，快速增长的热泵市场中有 70% 使用环境空气作为热源。然而，这些热泵价格低廉且易于实施，但效率低于地源或水源热泵。在此建模研究中，我们的目标是提高空气源热泵使用家用灰水所含热量的效率。我们评估了在各种气候、季节、建筑围护结构和生活热水消耗模式下相对于标准热泵配置的性能改进。结果表明，年均绩效系数平均提高了 4.1%——范围从 0.6% 到 7.5%。这种效率提升意味着压缩机每周平均可节省 1.8 千瓦时的电力。尽管由于其简单性而具有吸引力，但所提议的开环配置——外部热源的预热——仅导致空气源热泵的适度性能改进。基于这些结果，我们广泛讨论和比较了替代系统配置，并确定了每种配置的热回收动力学的几个根本差异。我们表明，使用灰水作为直接热源的闭环系统显示出最大的性能改进潜力，尽管实施起来更加昂贵和复杂。我们广泛讨论和比较了替代系统配置，并确定了每种配置的热回收动态的几个根本差异。我们表明，使用灰水作为直接热源的闭环系统显示出最大的性能改进潜力，尽管实施起来更加昂贵和复杂。我们广泛讨论和比较了替代系统配置，并确定了每种配置的热回收动态的几个根本差异。我们表明，使用灰水作为直接热源的闭环系统显示出最大的性能改进潜力，尽管实施起来更加昂贵和复杂。