Refrigeration – Processes – Defrosting or frost inhibiting
Reexamination Certificate
2000-03-15
2001-11-27
Wayner, William (Department: 3744)
Refrigeration
Processes
Defrosting or frost inhibiting
C062S156000, C062S175000
Reexamination Certificate
active
06321543
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to the field of compressors used in chillers and/or heat pumps, and in particular, to protecting the compressor by keeping the compressor within its proper operating parameters.
BACKGROUND OF THE INVENTION
Heat pump systems use a refrigerant cycle to transfer heat (or energy) from a relatively cool side to a hotter side. At the cooler side, evaporation of the refrigerant occurs at a relatively low pressure. As a result, liquid is turned into vapor and heat is extracted from a media that can be air, water, brine, or even the ground. The generated vapor flows through one or more compressors where its pressure is raised. After leaving the compressor, the high pressure vapor flows into a condenser where it is turned into a liquid. At this stage, heat is released by the refrigerant into another media that can be air, water, brine, or the ground. The amount of heat released is roughly equal to the amount of heat extracted at the cooler side plus the amount of energy needed to drive the vapor refrigerant from the low pressure side (cool side) to the high pressure side (hotter side).
Because the refrigerant cycle in a heat pump can be reversed, the unit can be used for either heating or cooling. In principle, the refrigerant cycle for the two modes are comparable.
For heat pumps to operate efficiently, an adequate temperature difference must exist between the refrigerant and the medias (air, water, brine, or ground). From an efficiency standpoint, it is desirable that the heat pump deliver more energy (thermal) than it uses (electrical).
The heart of a heat pump or chiller system is the compressor. Each compressor type has an associated compressor map, i.e., an area function of saturated suction temperature and saturated discharge temperature. Manufacturers typically guarantee the reliability of the compressor if the compressor is operated within its compressor map. Unfortunately, compressors can operate outside their compressor map, unbeknownst to the user, until the compressor fails suddenly.
SUMMARY OF THE INVENTION
Briefly stated, a controller monitors the saturated suction temperature and the saturated discharge temperature of a system that includes a compressor operating as part of a chiller and/or heat pump. When the compressor operates outside its compressor map, the controller takes action to ensure the compressor operates only within its compressor map. Such actions include defrosting the compressor coil if the system is in heating mode or unloading the unit.
According to an embodiment of the invention, a method for protecting at least one compressor used in a heat pump or chiller system includes the steps of (a) determining a saturated suction temperature (SST) for the at least one compressor; (b) determining a saturated discharge temperature (SDT) for the at least one compressor; (c)providing first and second limits for the at least one compressor; (d) providing first and second specified performance margins for the at least one compressor wherein the first and second performance margins are related to the first and second limits; (e) determining, based on the first and second limits and the first and second performance margins, whether the at least one compressor is operating in a preferred zone, and if not, performing a subsequent action.
According to an embodiment of the invention, a method for protecting at least one compressor used in a heat pump or chiller system includes the steps of (a) determining a saturated suction temperature (SST) for the at least one compressor; (b) determining a saturated discharge temperature (SDT) for the at least one compressor; (c) providing first and second limits for the at least one compressor; (d) providing first and second specified performance margins for the at least one compressor wherein the first and second performance margins are related to the first and second limits; (e) comparing the SST to a specified temperature, and if the SST is less than the specified temperature, unloading, if present, one compressor from the system, and if the SST is not less than the specified temperature, comparing the SST to a sum of the first limit and the first performance margin; (f) determining, if the SST is not greater than the sum of the first limit and the first performance margin, whether the SST is greater than the first limit; (g) determining, if the SST is greater than the sum of the first limit and the first performance margin, whether frosting of a condenser coil is greater than a specified percentage, and if so, defrosting the coil, and if not, unloading, if present, one compressor from the system; (h) determining, if the SST is not greater than the first limit, whether a rate of change of the SDT is greater than a specified amount, and if not, periodically determining whether the rate of change of the SDT is greater than the specified amount, and if so, determining whether frosting of the coil is greater than the specified percentage, and if so, defrosting the coil, and if not, unloading, if present, one compressor from the system; and (i) determining, if the SST is greater than the first limit and the SST is not greater than the sum of the first limit and the first performance margin, whether the SDT is greater than a difference between the second limit and the second performance margin, and if so, forbidding compressor loading, and if not, allowing compressor loading if necessary.
REFERENCES:
patent: 4831834 (1989-05-01), Yoshida
patent: 5797729 (1998-08-01), Rafuse, Jr. et al.
patent: 5806327 (1998-09-01), Lord et al.
Chavagnat Hippolyte
Said Wahl
Carrier Corporation
Wall Marjama & Bilinski
Wayner William
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