Solar-Driven Active Hydronic Cooling System for Permafrost Preservation

摘要

Active hydronic cooling systems have several advantages over passive cooling methods for preservation of thaw-susceptible permafrost soils in arctic regions. Currently, passive cooling systems are primarily used in maintaining the integrity of foundations in permafrost soils. Some limitations of passive cooling systems include high construction costs and reliance on weather conditions to operate. Passive cooling systems do not operate in the summer and allow the active layer to thaw each season. With the recent occurrence of more extreme weather events and wanning air temperatures throughout the arctic, passive systems do not provide sufficient cooling capacity for some applications. An active cooling system can be programmed to deliver energy during the summer months when it is needed and can be designed to prevent the active layer from thawing. By maintaining a frozen state for the site soils, the energy requirements of the system are greatly reduced due to the elimination of the phase change of moisture within the soil. When the cooling load is reduced to sensible heat only, the system can be powered by electricity produced from a small photovoltaic power plant. Other advantages of active cooling systems over passive cooling devices include lower material and freight costs, lower construction costs due to the ease of installation, and more flexibility in construction scheduling. In February of 2014, the Alaska Native Tribal Health Consortium installed an active cooling system under a lift station located in Old Kasigluk, a rural Alaskan village. The system consists of a low-pressure cooling coil made of cross-linked polyethylene tubing laid out in a grid above the existing permafrost. Coolant is circulated through the coil by a self-contained chiller. Heat is absorbed from the surrounding soils by the circulated coolant. Ground temperature data from this system were collected and are presented in this paper.