Variability of Soil Temperatures During 5 Years of a Horizontal Heat Exchanger Operation Co-operating with a Heat Pump in a Single-Family House

The paper presents the results of measurements of the temperature distribution of the ground source heat with the brine-water heat pump and a horizontal ground heat exchanger. The research was carried out for a period of 5 years. The horizontal ground heat exchanger is a ground source for a heat pump with the measured average heating output of 9.53 kW and cooling capacity of 7.8 kW, installed in a single-family house located in the north-eastern part of Poland. A heat exchanger with the area of 253 m² is located at a depth of 1.9 m in the groundwater layer being in hydraulic contact with the waters of Lake Elk. During the first four years, each year it can be observed that soil of the ground heat source is chilling at a depth of 1.9 m, due to working heat pump. Between January and April heat pump was working with the ground source frozen, where the temperature ranged from −0.6 to −2.1 °C. Subsidence and cooling of the soil was caused by a relatively small active area of ground source of heat which was 253 m² with the dimensions of 11 m × 23 m, as well as inadequate spacing between sections of the spiral heat exchanger amounting to 0.1 m. After operational testing of the heat pump and the ground source of heat, the “microBMS” a control and optimization system, working independently from the heat pump control was introduced into the building in January 2014. Its introduction has significantly increased that lower minimum flow temperature of the heat exchanger to +0.3–0.9 °C. There was also an increase of the minimum temperature of the ground source heat exchanger by the value of +1.3–3.0 °C and decrease in cooling of the soil in August—an increase of temperature by about 0.7 °C. Operational tests of heat pump system working with an unusual and original application of horizontal spiral heat exchanger have shown that in the first period introduction of an additional heat exchanger was considered. In subsequent years of heat pump operation and after the introduction of its independent monitoring and optimization, the study showed good properties of ground source and its complete recovery in the summer. Ground source, chilled properly to a temperature of about 0 °C became a very good cooling reservoir during periods of spring and summer heat. The use of the Earth’s heat helps to improve the environment, while in some way it violates the natural thermal and agrophysical condition of the ground. Operation of ground source heat pump affects the periodic changes of agro-thermal parameters of soil. The delay of the vegetation period above the horizontal heat exchanger of heat pump is about 13 days and is caused by postponed thawing of ground observed at 0.05 m.