The Geothermal Heat Pump Unit
Direct Energy’s geothermal heat pump is a highly effective pump. It is supplied by EarthLinked and this article describes how it functions.
The use of small refrigerant tubes for heat exchange in the earth is made possible by the Refrigerant Management System which consists of the Liquid Flow Control (LFC) and the Active Charge Control (ACC). Together, they achieve high efficiency direct expansion and condensation of refrigerant in the earth through Direct GeoExchange.
EarthLinked® systems are the most effective method of harvesting the earth’s renewable energy for the purpose of providing domestic hot water and heating/cooling for buildings. Highly versatile, Direct Energy’s refrigerant flow controls have successfully operated commercial refrigeration systems, air source heat pumps from 3-50kWth capacity, a variety of GeoExchange systems produced by various manufacturers, closed-loop geothermal units , multi-compressor units, and radiant hydronic heating systems. These unique flow controls also make possible the inclusion of de-superheating or integrated water heating on any heat pump system without the need for electronic controls.
Until the development of EarthLinked’s Refrigerant Flow Controls, no simple controls or metering devices existed that could deliver refrigerant in the condition appropriate to each component throughout the entire operating cycle and continually maintain stable refrigerant conditions.
Special refrigerant flow controls were necessary to manage the refrigerant in the long evaporator-condenser which is buried in direct contact with the heat source. Direct Energy’s refrigerant management system serves this need and provides:
- Stable refrigerant management under all loading conditions.
- Continuous return of lubricating oil to the compressor without any liquid refrigerant.
- Improved system efficiency, reliability and serviceability.
To operate at optimum efficiency, the three major components of all heat pumps require the refrigerant to be in a particular physical state appropriate to each component (the compressor, condenser and evaporator). The compressor needs a dry refrigerant vapor from the evaporator, containing little or no superheat at the compressor inlet. The condenser needs its refrigerant outlet pressure to be just sufficient to cause the refrigerant vapor to complete its condensing just before it reaches the condenser outlet. This provides high pressure vapor to the entire condenser for maximum condensing with no uncondensed vapor passing through the condenser and no liquid refrigerant “backed up” in the condenser, thus eliminating sub cooling.
In contrast, the evaporator needs liquid refrigerant at its inlet. The liquid should then complete its evaporation just as it reaches the evaporator outlet. This is the optimum “flooded” evaporator condition which produces maximum system efficiency when no portion of the evaporator is wasted in producing superheat. Any un-evaporated refrigerant which passes through or out of the evaporator should not reach the compressor.
Conventional controls include thermostatic expansion valves (TXVs), electronic expansion valves (EXVs), automatic expansion valves (AXVs), fixed orifices, capillary tubes, and accumulators. No combination of these can assure simple, stable operation of a Direct GeoExchange system or achieve all the following conditions which our controls maintain in any standard air conditioning system, including:
- A fully condensing condenser (minimal sub cooling).
- A continuously flooded evaporator (no superheat).
- Dry vapor with no superheat at the compressor inlet.
- A simple, easy method of determining when the system is properly charged.
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