Carrier Touch Pilot Control Series Control Manual

% Building loadReset value8 - STANDARD CONTROL OPERATIONS AND OPTIONS8.4.2 - ResetReset means that the active control point is modified so that themachine capacity required is adjusted to be as close as possibleto the demand.The reset source can be provided by one of the following:■ Outdoor air temperature that gives a measure of the loadtrends for the building. This reset source is applicable only tounits with option 154 (see section 8.15).■ Return water temperature (heat exchanger ΔT gives anaverage building load). Delta T (ΔT) is the difference betweenleaving and entering fluid temperatures (LWT minus EWT).When the load is light, temperature difference across theexchanger will be relatively small. The reset value should beconfigured by the user and its configuration may differdepending on the size of the water exchanger.■ 4-20 mA reset signal provided by an active sensor connectedto the input: If the reading of the 4-20 mA signal/externaltemperature value increases (load is lighter), then the currentsetpoint will be lowered.■ Space temperature reset based on the space temperaturesensor reading.The source of the reset can be configured in the Reset Configurationmenu (RESETCFG). In response to a change in delta T, 4-20 mAreset signal reading, or space temperature, the control point isreset to optimise unit performance.To set the source of the reset1. Navigate to the Configuration menu.2. Select Reset Configuration (RESETCFG).3. Set Cooling Reset Select [cr_sel] or Heating Reset Select[hr_sel].Cooling Reset Select [cr_sel]Heating Reset Select [hr_sel]0 = none1 = OAT *2 = delta T3 = 4-20 mA4 = Space Temp* OAT reset applies to units with option 154 (see section 8.15).The unit normally uses two control point reset types, cooling controlpoint reset or heating control point reset.Dry cooler condenser option has condensing setpoint reset whichcan be applied if the condensing setpoint control depends onoutdoor air temperature reading (reset source = OAT). See alsosection 8.15.Reset is a linear interpolation function based on the followingthree parameters:■ A reference at which reset is zero (OAT / delta T / 4-20 mAsignal / space temp. – no reset value).■ A reference at which reset is maximum (OAT / delta T / 4-20 mAsignal / space temp. – full reset value).■ The maximum possible reset value: The difference betweenthe lowest reset value (no reset value) and the highest possiblereset value (full reset value). Cooling / Heating Reset Deg.Value represents the maximum possible reset.Reset parameters, i.e. slope, reset, and maximum value, areconfigurable in the Reset Configuration menu (RESETCFG).Cooling mode: Cooling control point reset is used to control theevaporator water temperature reset.Heating mode: Heating control point reset is used to control thecondenser water temperature reset.Heating reset may be used to reset the condensing setpoint foroptimised condenser operation. This is only possible on the outsidetemperature. Delta T is not used.Reset example in Cooling mode for the space temperatureLegendA: Maximum reset valueB: Space temperature for zero resetC: Space temperature for maximum resetD: Building load8.5 - Ramp loadingThe control provides the ramp loading function used to minimisethe rate at which the water temperature changes. The minimumspeed is calculated based on saturated condensing temperatureand saturated suction temperature. Ramp loading sequence canbe enabled by the user (Ramp Loading Select, GEN_CONF –General Configuration).8.6 - Capacity controlThe unit is fitted with oil-free centrifugal compressors with magneticbearings. Each circuit may have one or two compressors installed.Compressors are controlled in such a way in order to provide thebest possible COP. Variable-speed centrifugal compressors exhibitbetter performance at part load conditions; therefore, the controlsystem would normally start both circuits as soon as needed.The Touch Pilot control adjusts the compressor capacity to keepthe heat exchanger water temperature at its setpoint.8.7 - Demand limitThe demand limit functionality is used to limit the unit powerconsumption whenever possible.The control allows limitation of the unit capacity:■ By means of user-controlled volt-free contacts: The unit capacitycan never exceed the limit setpoint activated by these contacts.The limit setpoints can be modified in the SETPOINT menu.■ By setting DEM_LIM when the unit is in Network mode.■ By lag limit set by the master unit (master/slave assembly).If the unit is not in the Master/Slave assembly, the lag limit valueis equal to 100%.■ By night capacity limitation. The limit can be modified in theGEN_CONF menu.Capacity limitation is expressed in percentage, where a limit valueof 100% means that the unit may run with its full capacity (nolimitation is implemented).27