Could it be possible to put more than 18 at equipment list?

edit

80 seems unrealistic and I think the same type of equipment should be combined first, but anyway you can edit Energy+.idd file in your local folder to extend the limitation.

If you are using EnergyPlusV22-2-0, probably the location of your idd file is C:\EnergyPlusV22-2-0

You can use any text editor tool and open the idd file. If you search "ZoneHVAC:EquipmentList", you can find the following description:

!*****************ZONE EQUIPMENT SPECIFICATION*********************
!Zone Heating and Cooling Equipment are attached to zones by the following statements:

ZoneHVAC:EquipmentList,
       \extensible:6 Duplicate the six fields Zone Equipment Object Type through Sequential Heating Fraction

This class is extensible. You can copy from A3 to A6.

  A3 , \field Zone Equipment 1 Object Type
       \begin-extensible
       \type choice
       \key ZoneHVAC:TerminalUnit:VariableRefrigerantFlow
       \key ZoneHVAC:AirDistributionUnit
       \key ZoneHVAC:EnergyRecoveryVentilator
       \key ZoneHVAC:EvaporativeCoolerUnit
       \key ZoneHVAC:HybridUnitaryHVAC
       \key ZoneHVAC:ForcedAir:UserDefined
       \key ZoneHVAC:FourPipeFanCoil
       \key ZoneHVAC:OutdoorAirUnit
       \key ZoneHVAC:PackagedTerminalAirConditioner
       \key ZoneHVAC:PackagedTerminalHeatPump
       \key ZoneHVAC:UnitHeater
       \key ZoneHVAC:UnitVentilator
       \key ZoneHVAC:VentilatedSlab
       \key ZoneHVAC:WaterToAirHeatPump
       \key ZoneHVAC:WindowAirConditioner
       \key ZoneHVAC:Baseboard:RadiantConvective:Electric
       \key ZoneHVAC:Baseboard:RadiantConvective:Water
       \key ZoneHVAC:Baseboard:RadiantConvective:Steam
       \key ZoneHVAC:CoolingPanel:RadiantConvective:Water
       \key ZoneHVAC:Baseboard:Convective:Electric
       \key ZoneHVAC:Baseboard:Convective:Water
       \key ZoneHVAC:HighTemperatureRadiant
       \key ZoneHVAC:LowTemperatureRadiant:VariableFlow
       \key ZoneHVAC:LowTemperatureRadiant:ConstantFlow
       \key ZoneHVAC:LowTemperatureRadiant:Electric
       \key ZoneHVAC:Dehumidifier:DX
       \key ZoneHVAC:IdealLoadsAirSystem
       \key ZoneHVAC:RefrigerationChillerSet
       \key Fan:ZoneExhaust
       \key WaterHeater:HeatPump:PumpedCondenser
       \key WaterHeater:HeatPump:WrappedCondenser
       \key HeatExchanger:AirToAir:FlatPlate
       \key AirLoopHVAC:UnitarySystem
       \required-field
  A4 , \field Zone Equipment 1 Name
       \required-field
       \type object-list
       \object-list ZoneEquipmentNames
  N1 , \field Zone Equipment 1 Cooling Sequence
       \required-field
       \type integer
       \minimum 0
       \note Specifies the zone equipment simulation order
       \note when the zone thermostat requests cooling
  N2 , \field Zone Equipment 1 Heating or No-Load Sequence
       \required-field
       \type integer
       \minimum 0
       \note Specifies the zone equipment simulation order
       \note when the zone thermostat requests heating or no load
  A5 , \field Zone Equipment 1 Sequential Cooling Fraction Schedule Name
       \note The fraction of the remaining cooling load this equipment will attempt to serve
       \note if the load distribution scheme is SequentialLoad, otherwise ignored.
       \type object-list
       \object-list ScheduleNames
  A6 , \field Zone Equipment 1 Sequential Heating Fraction Schedule Name
       \note The fraction of the remaining heating load this equipment will attempt to serve
       \note if the load distribution scheme is SequentialLoad, otherwise ignored.
       \type object-list
       \object-list ScheduleNames

By default, the last line of ZoneEquipmentList is A74. You can paste the copied A3 to A6 after the line A74, and please change the line number of the pasted lines accordingly i.e. A3→A75, A4→A76, N1→N37, N2→A38, A5→A77 and A6→A78.

Besides, you should change "Zone Equipment 1" in the pasted lines to "Zone Equipment 19".

And the most important thing is that you need to change comma (,) and semicolon(;). By default, the last line is as follows.

  A74; \field Zone Equipment 18 Sequential Heating Fraction Schedule Name
       \note The fraction of the remaining heating load this equipment will attempt to serve
       \note if the load distribution ...