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HVAC Low Ambient Controls

Industry standard option for applications faced with low ambient conditions.

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Specific Systems offers control packages for low and ultra low ambient conditions. Most HVAC units operate to approximately 55 °F (13 °C). However, standard Specific Systems InPac units operate effectively down to 35 °F (2 °C).

  • Low ambient package allows mechanical cooling at temperatures to -35 °F (-37 °C)
  • Ultra low ambient packages work down to approximately -75 °F (-59 °C).

Specific Systems’ optional low ambient control package includes

  • Crankcase heaters
  • Head pressure control valves
  • Receivers, and
  • Freezestats.

How does it work?

  • Crankcase heaters are used to prevent refrigerant in the system from reverse migrating back into the compressor and mixing with the oil. This is especially an issue if a compressor is used in a low ambient condition, because during the off-cycle the oil inside the compressor cools off. This cooled oil has a higher propensity to attract refrigerant because of the pressure difference between it and the vaporized refrigerant in the cycle. When the compressor is started during the next cycle, the oil, now attached to the refrigerant, flows out of the compressor and toward the condenser, leaving less oil to effectively lubricate the compressor. The compressor could then experience immediate or eventual failure.
  • Use of head pressure control valves contributes to low and ultra-low ambient stability in the refrigeration systems. Head pressure control valves help maintain suction pressure when the unit is operating at ambient temperatures below about 40°F (4.5°C), keeping the evaporator coil from freezing over due to lack of refrigerant flow.
  • Receivers work as essentially a holding tank for the extra refrigerant needed to maintain pressures at low ambient temperatures. The receivers are sized specifically to fit the refrigeration systems in individual units.
  • Freezestats are temperature sensors for the coils that keep them from icing over. When a freezestat senses a temperature predetermined by the customer or Specific Systems, it sends a signal to shut off the compressor, thereby keeping water from condensing on the coil and freezing it.

Ultra Low Ambient Upgrade

The ultra low ambient package adds and upgrades several items, allowing mechanical cooling down to -75°F (-59°C):

  • Time delay function on the low pressure control
  • Thermostatically controlled heater for the receiver
  • Insulation for the receiver
  • Steel-blade condenser fan
  • Custom built low-temperature motors

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