Combining ground source absorption heat pump with ground source electrical heat pump for thermal balance, higher efficiency and better economy in cold regions

• GSEHP and GSAHP have opposite features on thermal imbalance and energy efficiency.
• Hybrid GSAHP-GSEHP can counteract the disadvantages and combine the advantages.
• Various GSAHP-GSEHP combinations keep soil temperature changes within 0.2 °C/year.
• Energy efficiency improvement is 10.9–34.6%, and energy saving rate is 9.8–25.7%.
• Lifecycle cost reduction is 3.7–22.0% for coal and 4.1–12.1% for gas in 20 years.

Ground source electrical heat pump (GSEHP) and ground source absorption heat pump (GSAHP) have opposite characteristics on thermal imbalance and primary energy efficiency (PEE) in cold regions: (1) GSEHP leads to cold accumulation while GSAHP may cause heat accumulation in the warmer part of cold regions; (2) GSEHP has higher PEEs in cooling mode while GSAHP has higher PEEs in heating mode. The hybrid GSAHP-GSEHP is proposed to counteract the disadvantages and combine the advantages. Different combinations of heating and cooling supply ratios contributed by GSAHP in a hybrid GSAHP-GSEHP can maintain good thermal balance with soil temperature variations within 0.2 °C/year. The influence of supply ratios on thermal imbalance ratio (IR), annual primary energy efficiency (APEE) and economy are investigated to select some preferred configurations of GSAHP-GSEHP, which will be modeled and dynamically simulated over 20 years. Results show that a bigger heating supply ratio of GSAHP and a more negative IR contribute to higher APEEs and fewer boreholes within acceptable IRs of ±20%. Compared with GSEHP, the APEE enhancement is 10.9–34.6%, the energy saving rate is 9.8–25.7%, the lifecycle cost (coal) reduction is 3.7–22.0%, and the lifecycle cost (gas) reduction is 4.1–12.1%. The GSAHP-GSEHP maintains good soil balance with high PEEs in cold regions.