Carrier WEATHERMASTER 48/50Z030-105 Operation And Service Manual

Also see for 48/50Z030-105: Installation instructions

Contents

Carrier WEATHERMASTER 48/50Z030-105 Operation And Service Manual Manual pdf 61 page image

61Setting up the System — The relevant set points for temper-ing are located at the local display under Setpoints:Operation — First, the unit must be in a vent mode, a low cool,or a high cool HVAC mode to be considered for a temperingmode. Secondly, the tempering mode is only allowed when therooftop is configured for staged gas or hydronic heating (Con-figuration→HEAT→HT.CF=3 or 4).If the control is configured for staged gas or hydronic heat-ing and the control is in a vent, low cool, or high cool HVACmode, and the rooftop control is in a situation where the econo-mizer must maintain a minimum position/minimum cfm, thenthe evaporator discharge temperature (EDT) will be monitored.If the EDT falls below a particular trip point then the temperingmode may be called out:HVAC mode = “Tempering Vent”HVAC mode = “Tempering LoCool”HVAC mode = “Tempering HiCool”The decision making/selection process for the temperingtrip set point is as follows:• If an HVAC cool mode is in effect, then the vent trippoint is T.CL.• If in a pre-occupied purge mode (Operating Modes→MODE→IAQ.P=ON), then the trip point is T.PRG.• If in an occupied mode (Operating Modes→MODE→IAQ.P=ON), then the trip point is TEMPVOCC.• For all other cases, the trip point is TEMPVUNC.NOTE: The unoccupied economizer free cooling does notqualify as a HVAC cool mode as it is an energy saving featureand has its own OAT lockout already. The unoccupied freecooling mode (HVAC mode = Unocc. Free Cool) will overrideany unoccupied vent mode from triggering a tempering mode.If OAT is above the chosen tempering set point, temperingwill not be allowed. Additionally, tempering mode is lockedout if any stages of mechanical cooling are present.A minimum amount of time must pass before calling outany tempering mode. In effect, the EDT must fall below thetrip point value –1° F continuously for a minimum of 2 min-utes. Also, at the end of a mechanical cooling cycle, there mustbe a minimum 10 minutes of delay allowed before consideringa tempering during vent mode in order to allow any residualcooling to dissipate from the evaporator coil.If the above conditions are met, the algorithm is free toselect the tempering mode (MODETEMP).If a tempering mode becomes active, the modulating heatsource (staged gas or hot water) will attempt to maintainleaving-air temperature (LAT) at the tempering set point usedto trigger the tempering mode. The technique for modulation ofset point for staged gas and hydronic heat is the same as in aheat mode. More information regarding the operation of heat-ing can be referenced in the Heating Control section.Recovery from a tempering mode (MODETEMP) willoccur when the EDT rises above the trip point. On any changein HVACMODE, the tempering routine will re-assess the tem-pering set point which may cause the control to continue or exittempering mode.Static Pressure Control — Variable air volume (VAV)air-conditioning systems must provide varying amounts of airto the conditioned space. As air terminals downstream of theunit modulate their flows, the unit must simply maintaincontrol over duct static pressure in order to accommodate theneeds of the terminals, and therefore to meet the varyingcombined airflow requirement. The unit design includes twoalternative optional means of accommodating this requirement.This section describes the technique by which this control takesplace.A unit intended for use in a VAV system can be equippedwith either an optional variable frequency drive (VFD) or inletguide vanes (IGV) for the supply fan. The speed of the fan orthe position of the IGV can be controlled directly by theComfortLink™ controls. A transducer is used to measure ductstatic pressure. The signal from the transducer is received bythe RCB board and is then used in a PID control routine thatoutputs a 4 to 20 mA signal to the VFD, or a digital LEN signalto the IGV.Generally only VAV systems utilize static pressure control.It is required because as the system VAV terminals modulateclosed when less air is required, there must be a means ofcontrolling airflow from the unit, thereby effectively prevent-ing overpressurization and its accompanying problems.The three most fundamental configurations for most appli-cations are Configuration→SP→SP.CF, which is the staticpressure control type, Configuration→SP→SP.S, used toenable the static pressure sensor, and Configuration→SP→SP.SP, the static pressure set point to be maintained.OPERATION — On units equipped with either VFD or IGVand a proper static pressure sensor, when SP.CF, SP.S andSP.SP are configured, a PID routine periodically measures theduct static pressure and calculates the error from set point. Thiserror at any point in time is simply the duct static pressure setpoint minus the measured duct static. The error becomes thebasis for the Proportional term of the PID. The routine also cal-culates the integral of the error over time, and the derivative(rate of change) of the error. A value is calculated as a result ofthis PID routine, and this value is then used to create an outputsignal used to adjust the IGV or VFD to maintain the staticpressure set point.Static pressure reset is the ability to force a lowering of thestatic pressure set point through an external control signal.Explained in detail further below, the control supports this intwo separate ways; through a 4 to 20 mA signal input wired toTB203 terminals 6 and 7 (thereby facilitating third partycontrol), or via CCN.In the latter case, this feature leverages the communicationscapabilities of VAV systems employing ComfortID™ termi-nals under linkage. The system dynamically determines andmaintains an optimal duct static pressure set point based onthe actual load conditions in the space. This can result in asignificant reduction in required fan energy by lowering the setpoint to only the level required to maintain adequate airflowthroughout the system.SETTING UP THE SYSTEM — The options for staticpressure control are found under the Local Display ModeConfiguration→SP. See Table 52.ITEM EXPANSION RANGE UNITS CCNPOINT DEFAULTT.PRG TemperingPurge SASP–20-80 dF TEMPPURG 50T.CL Tempering inCool SASP5-75 dF TEMPCOOL 5T.V.OC Tempering VentOcc SASP–20-80 dF TEMPVOCC 65T.V.UN Tempering VentUnocc. SASP–20-80 dF TEMPVUNC 50