Glossary of Terms

AMP Draw
Amp draw (Amperes) is the rate of flow of electricity required to operate a device. Using amp draw and time, amp hours can determined. For example, a compressor could draw 6 amps for 30 minutes. This is three amp/hrs. Amps must be qualified with a voltage for comparison. Amp hours equal time in hours at a specific amp draw.

A British Thermal Unit or BTU is the amount of heat needed to raise one pound of water 1 degree F. The practical equivalent is the heat of a burning a wooden kitchen match. 

Capacity is the amount of work that can be done over time. Capacity is not to be confused with efficiency.

The compressor is a refrigerant pump. It can be an open drive pulley driven affair, direct drive, or a motor and pump sealed in a steel canister. A compressor has an intake or low side inlet and a discharge or high pressure outlet.

Compressor Electronic Module
The Danfoss compressors have an electronic control that is attached to the compressor that controls the operation of the compressor. This black box is commonly called the compressor module.

A condenser is the heat exchanger in a refrigeration system. It can be air or water-cooled.
An air-cooled condenser in most systems looks like a radiator having tubes and thin metal fins. Water cooled condensers are most often a coaxial copper and copper nickel tube construction where water is pumped into the center copper nickel tube and the refrigerant is cooled in the space between the outside and inside tube. Copper nickel (cupronickel) metal alloy is used to make a condenser. The alloy is 90 percent copper and 10 percent nickel. Nickel strengthens the copper and allows the copper to remain a good anti-fowling surface.

Condensing is the phase in the refrigerant cycle where pressure raises the boiling point allowing air or water cooling to condense the high pressure refrigerant vapor to liquid. The hot refrigerant releases heat when condensing.

Condensing Unit
A condensing unit refers to the section of a refrigeration system that includes the compressor and condenser, either air cooled or water cooled or both and sometimes packaged with the receiver and drier. The condensing unit is providing pressure and heat.

Cooling rate
Cooling rate is the speed of cooling. A large displacement compressor with a big motor will cool faster doing more work in a shorter period of time than a smaller one if all other factors are the same.

Direct Evaporator Plate
A direct evaporator plate is the cold device associated with smaller DC systems. Refrigerant evaporation is the cooling process. Highly conductive thin plates allow the refrigerant to rapidly cool the plate surface, cooling the air in the cabinet directly.

Ducted Air Cooling
Ducted Air cooling is a method of controlling air flow to an air cooled condenser to avoid re-circulation of air and to allow the coolest air available to enter the condenser. Ducted air cooling allows the best possible operation of an air cooled unit in a closed space. Air forced through the condenser is constantly removing the heat before it can build up like it does in a static air cooled device.

Efficiency relates to the input power verses output (amount of cooling) of a compressor. This is in electrical terms BTUs of heat moved per watt. To compare compressor efficiency the refrigerant temperatures and conditions must be the same for each compressor tested. Using efficiency data total amp hours per day can be calculated for a given heat load.

Buy controlling the pressure of refrigerant the boiling point or evaporation temperature can be assured. Refrigerant R-134a will boil at – 15 degrees F. at sea level or 0 pressure. This boiling process is the heat gathering property of refrigerant.

Expansion Valve
An expansion valve is a pressure control. The valve lowers pressure by restricting flow to the low pressure side of the system created by the compressor suction. At the expansion valve low pressure liquid refrigerant starts to evaporate, cooling. Expansion valves can thermally adjust the pressure or be manually set at a fixed pressure.

Holdover Plate
A holdover plate in contrast to direct evaporator plates contain a solution that freezes. Holdover plates have much greater mass and heat content. Holdover plate systems must use a large (1/2 to 1 HP.) compressors that can freeze them quickly. Think of them as thermal batteries that can be charged in an hour and that will cool for a day. Running the compressor makes a captive block of blue ice.

Quick Connect Fittings
Quick connect or quick disconnect fittings are sealed connectors that when assembled, open to each other allowing refrigerant to flow. They can be connected and disconnected without loss of refrigerant.

SAE R-134a Service Ports
SAE R-134a service ports are quick connect fittings designed by the Society Of Automotive Engineers for use as a dedicated fitting for R-134a. Dedicated service gauges with the SAE ball chuck design can be snapped on these service ports for leak free no loss testing and system service.

Static Air Cooling
Static air cooling is air cooling with no fan to move the air. The item needing cooling creates air flow by heating the air in contact with it. A statically cooled device will be much hotter than a fan cooled unit.

Static Water Cooling
Water cooling by immersion of the radiating surface with no forced water flow is static water cooling. Keel coolers and through hull coolers are static devices. Boat motion can add the very effective scrubbing effect to strip the hotter water layer away for efficient operation however static water cooling looses effectiveness when the boat is not in motion.

Swagelock Fittings
Swagelok fittings are a high tech compression fittings featuring a double ferrule design that compensates for temperature and vibration. They can be connected and re-connected may times but they do not seal the tube ends when disassembled like quick connect fittings.

A thermostat is a switch that is controlled by temperature. A mechanical thermostat uses refrigerant pressure and it’s pressure change with temperature to control the switch. An electronic thermostat senses a resistance change at it’s probe with temperature change. It then electronically operates a switch.

Thermostat Range
Thermostat range is the lowest to highest temperature a device can control.

Thermostat Dead Band
The dead band is the differential where the switch turns off and turns back on.

Temperature Differential
The number of degrees between the off point and the on point is the temperature differential of a thermostat.

Watts are a measurement of energy. In electrical terms voltage multiplied by amps equals watts. Amp draw can be determined by dividing watts by the measured voltage.