Carrier 30XA080-500 Controls, Start-up, Operation, Service And Troubleshooting Instructions

Also see for 30XA325: Installation instructions Installation instructions

Carrier 30XA080-500 Controls, Start-up, Operation, Service And Troubleshooting Instructions Manual pdf 31 page image

4-20 mA Set Point ControlGOLI.O3o"on¢q90 (32.2)80 (26.7)70 (21.1)60 (15.6)50 (10)MI XlM JM40 (4.4) ....................... ;_41N MUr FI UD=1/30 (-1.1) /,,I20 (-6.7) fJ10 (-12.2) ..................................................................7fry INII4UIV FLLD=I'Jjr00 10 15mA SignalFig. 15 -- Set Point Control/20--Equation 1.............Medium Temperature Brine]- - Fresh Water ]--, Maximum Temperature ]Temperature Reset--Temperature reset is a valueadded to the basic leaving fluid temperature set point. The sumof these values is the control point. When a non-zero tempera-ture reset is applied, the chiller controls to the control point,not the set point. The control system is capable of handlingleaving-fluid temperature reset based on cooler fluid tempera-ture diffetence. Because the change in temperatute through thecooler is a measure of the building load, the temperature differ-ence reset is in effect an average building load reset method.The control system is also capable of temperature reset basedon outdoor-air temperature (OAT), space temperature (SPT), orfrom an externally powered 4 to 20 mA signal. An accessorysensor must be used for SPT reset (33ZCT55SP?). The EnergyManagement Module (EMM) is required for temperature tesetusing space temperature or a 4 to 20 mA signal.Under normal operation, the chiller will maintain a constantleaving fluid temperature approximately equal to the chilledfluid set point. As the cooler load varies, the cooler fluidtemperature difference will change in proportion to the load asshown in Fig. 16. Usually the chiller size and leaving-fluidtempet;tture set point ate selected based on a full-load condi-tion. At part load, the fluid temperature set point may be lowerthan tequited. If the leaving fluid tempet:_tute were allowed toincrease at part load, the efficiency of the machine wouldincrease.Delta T teset allows for the leaving temperature set point tobe reset upward as a function of the fluid temperature differ-ence ot, in effect, the building load.NOTE: Delta T reset should not be used with vtuiable CoolerFlow Rate Systems.To use Delta T Reset, four variables must be configured.They are: Cooling Reset Type (Configuration--eRSET_CRST), Delta T No Reset Temp (Setpoints_COOL_CRTI), Delta T Full Reset Temp (Setpoints_COOL--+CRT2) and Degrees Cool Reset (Setpoints_COOL--eDGRC). In the following example using Delta T Reset, thechilled water temperature will be reset by 5.0 ° F (2.8 ° C)when the AT is 2° F (1.1 ° C) and 0 ° F (0 ° C) reset whenthe AT is 10 ° E The variable (_RT1 should be set to thecooler temperature difference (AT) where no chilled watertemperature reset should occur. The variable CRT2 should beset to the cooler temperature difference where the maximumchilled water temperature reset should occur. The variableDGRC should be set to the maximum amount of resetdesired. To verify that reset is functioning correctly proceedto Run Status--eVIEW. and subtract the active set point(SETP) fi'om the control point (CTPT) to determine thedegrees reset. See Fig. 16 and Table 21.Other. indirect means of estimating building load and con-trolling temperatures reset ate also av_dlable and are discussedbelow. See Fig. 17.To use Outdoor Air Temperature Reset, four variables mustbe configured. They are: Cooling Reset Type (Cmlfiguration_RSET_CRST), ()AT No Reset Telnp (Setpoints--+COOL_CROI), ()AT Full Reset Temp (Setl_oints----_COOL_'R02) and Degrees Cool Reset (Setpoints--eCOOL--eDGRC). In the following example, the outdoor airtemperature reset example provides 0 ° F (0 ° C) chilled waterset point reset at 85.0 F (29.4 C) outdoor-air temperature and10.0 ° F (5.5 ° C) reset at 55.0 F (12.8 C) outdoor-air tempera-ture. See Fig. 18 and Table 22.To use Space Temperatute Reset in addition to the EnergyManagement Module and a space temperatute sensot: fourvariables must be configured. They are: Cooling Reset Type(Configuration--eRSET_CRST), Space T No Reset Temp(Setpoints_COOL_CRSl), Space T Full Reset Temp(Setpoints_COOL_CRS2) and Degrees Cool Reset (Set-points _COOL--eDGRC). In the following space temperaturereset example, 0 ° F (0 ° C) chilled water set point reset at 72.0 F(22.2 C) space temperature and 6.0 ° F (3.3 ° C) reset at 68.0 F(20.0 C) space temperature. See Fig. 19 and Table 23.31