Mini-Space Series Installation, Operation & Maintenance Manual

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Mini-Space Series Installation, Operation & Maintenance Manual2.9.3 Water/Glycol SystemsIn water/glycol cooled units the refrigerant system isalready charged with R22 or R407C. The followingprecautions must be observed when installing andfi lling the water/glycol loop:• The piping system must be cleaned prior toadding wate/glycol to the system.• Glycol must be mixed with water before it isadded to the system. All air must be bled from thepiping system. Use only water/glycol solution withinhibitors for corrosion protection.1. Open the vent valve at highest point of the system.2. Fill the system until the solution is dischargingfrom the vent with minimal signs of foaming due toair in the system.2.9.3.1 PumpIf a pump is to be used, ensure the system is filledbefore turning the pump on. The pump is not selfprimingso it is important that there is a pressure onthe suction inlet.CAUTIONDo not run the pump dry.If the pump has no pressure on the discharge side,leave the discharge valve partially shut to create aback pressure in the pump so that liquid can build upin the impeller housing to keep the impeller housingfrom getting too hot. Make sure there is always liquidfl owing through the pump to cool the impeller andhousing. If there is no liquid leaving the pump, shutthe pump off immediately to prevent damage to thepump. Check for proper rotation of the motor observingthe arrow on the side of the impeller.2.10 System Settings and Adjustments2.10.1 Low/High Pressure Limit SwitchAir conditioning systems utilizing thermal expansionvalves are equipped with hermetically sealed highpressureand low-pressure switches. These switchesare preset by the manufacturer and cannot be adjusted.The high-pressure switch opens at 410 psigand has a manual reset. The low-pressure switchopens at 10 psig (± 4) and closes at 32 psig (± 5) andhas an automatic reset.2.10.2 Head Pressure Controls-Air Cooled Systems2.10.2.1 Condenser Fan Cycling(Condenser Model SCS-AA, 0°F)Used for outdoor installations where ambient condenserair inlet temperatures are 0°F or higher, thismethod utilizes a high-pressure differential controlswitch with SPST (Single Pole, Single Throw) contactsand an automatic reset. The switch activatesthe condenser blower contactor when the dischargepressure reaches 275 psig to maintain the condensingtemperature.Factory setting: Switch contacts are set to close ona pressure rise to 275 psig and open at 205 psig.Setpoint range is 170 to 375 psig. The differential isnon-adjustable and set at 70 psi.2.10.2.2 Condenser Multi-Speed Fan Switch(Model HES-CAA , 0°F)Used for indoor installations where ambient condenserair inlet temperatures are 0°F or higher, thecondenser fan speed switch senses refrigerant dischargepressure and changes the condenser blowerspeed to maintain proper condenser pressures. Thecondenser fan speed switch changes the fan (blower)from low to high speed at approximately 325 psig andreturns the fan (blower) from high speed to low speedat approximately 255 psig.Factory setting: On pressure rise, the high fan speedcontacts are set to close at 325 psig. This will increasethe condenser fan speed. A pressure drop to 255 psigwill close the low fan speed contacts and reduce thefan speed. Set point range is 170 to 400 psig. The differentialis nonadjustable and set at 70 psi.NOTEThis switch and settings does not apply to unitsdesigned for a power supply greater than 277V.2.10.2.3 Variable Condenser Fan Speed(Condenser Model SCS-SA, -20°F)Used for outdoor installations where ambient temperaturesmay fall to -20°F, a variable speed condensermotor control is used to maintain head pressure. Thevariable speed motor is located closest to the headerend of the condenser. The fan speed control is a continualmodulation of the motor’s speed. The controller is2-17(©April, 2008)Air Technology Systems, Inc.
Mini-Space Series Installation, Operation & Maintenance Manualfactory installed in the outdoor condenser/condensingunit. The fan speed controller requires no adjustment.The fan speed controller will automatically control thehead pressure. On systems with more than one fanon the condenser, the remaining motors cycle on andoff based on pressure.2.10.2.4 Intelligent Control(Condenser Model SCS-EC only, -20°F)Used for outdoor installations where ambient condenserair inlet temperatures may fall to -20°F, intelligentpressure control is designed to maintain dischargepressure by constantly modulating condenserfan speed. SCS outdoor condensers are equippedwith highly efficient, electronically commutated (EC),axial fan(s). The EC fan speed is infinitely variableup to full speed. The control system utilizes refrigerantpressure transducer(s) to monitor refrigerantdischarge pressure and control the EC fan(s) to theprecise speed needed to maintain design refrigerantdischarge pressures.2.10.2.5 Flooded Head Pressure Control(Condenser Model SCS-AA with FanCycling, -30°F)Used for outdoor installations where ambient condenserair inlet temperatures may fall to -30°F, fl oodedhead pressure control is designed to maintainhead pressure during low ambient conditions. A headpressure control valve and a receiver are used in therefrigeration circuit to back up liquid refrigerant intothe condenser coil. The head pressure control valveis a 3-way modulating valve controlled by dischargepressure.When the A/C unit begins to operate, the dischargepressure rises to 275 psig and the condenser fan iscycled on, as described in Section 2.10.2.1. Whenambient temperature drops, the discharge pressuredrops also. When the discharge pressure drops toapproximately 180 psig, the head pressure controlvalve diverts discharge gas away from the condenserto the receiver. Liquid flow from the condenser isrestricted, causing liquid to back up in the condenser.Flooding the condenser reduces the area availablefor heat transfer. The desired result is to increase thepressure into the condenser, maintaining a minimumdischarge pressure during low ambient operationthus ensuring proper condensing temperature. Thehead pressure control valve requires no adjustment.This method of controlling head pressure allows thecondenser fan to run continuously. While the fan isrunning, the fl ooded head pressure control valvemodulates the amount of discharge gas entering thereceiver. As the pressure increases, the valve divertsmore discharge gas to the condenser, allowing moreliquid to fl ow from the condenser to the receiver.When using this method of head pressure regulationthere must be enough refrigerant in the system to ensureadequate charge at the lowest expected ambienttemperature in which the system will be operating. Areceiver is used to store the extra refrigerant when thecondenser is not using it.NOTESystems utilizing air cooled condensers must nothave a refrigerant line pressure drop over 14 psigacross the condenser and the interconnectingpiping to the condenser sections.2.10.2.6 Flooded Head Pressure Control(Condenser Model HES-CAA , 30°F)Used for indoor installations where ambient condenserair inlet temperatures may fall to -30°F. First, familiarizeyourself with Flooded Head Pressure Control asdiscussed in Section 2.10.2.5. Instead of cycling thefan on and off, the condenser fan speed is continuous.The head pressure control valve diverts discharge gasto the receiver causing liquid to back up in the condenser,as described in Section 2.10.2.5, while the fancontinues to run.2.10.3 Head Pressure Controls-Water/Glycol Cooled SystemsIn a water/glycol condenser, condensing temperatureis maintained by the liquid fl owing through a regulatingvalve and then into a liquid-cooled condenser. Theregulating valve opens to increase the liquid fl ow asthe refrigerant pressure rises (or closes as the refrigerantpressure falls). The regulating valve is factory setfor the correct condensing temperature however, it canbe adjusted to increase or decrease the condensingtemperature.Head pressure regulating valves are available in 2-wayor 3-way configurations. Refer to the piping diagram to(©April, 2008)2-18Air Technology Systems, Inc.
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Mini-Space Series Installation, Operation & Maintenance Manual

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