In automatic changeover, the zoning system works on a first come first serve basis. If 1 zone is calling for heating and the other for cooling, the zone which sent its demand to the I/O center first will operate the equipment in that mode until that zone is satisfied.
→Step 5ÐDuct Temperature Optimizer (DTO) For Monitoring Leaving Air Temperature
As the WeatherMaker Two-Zone System operates through a heating or cooling cycle, the zone demands will change. This changes actual load that is applied to the HVAC equipment. If the zone airflow decreases, the cooling equipment will tend to lower supply-air temperatures which could tend to exceed the LAT trip limits. Conversely, the heating equipment will tend to raise the supply-air temperatures which could exceed high trip limits. In cooling, when the LAT reaches the non-adjustable low tempera- ture trip limit (50°F) the LAT algorithm begins operating, closed dampers are initially opened 3 positions, then 1 position every 20 sec there after until full open. WeatherMaker Two-Zone will not shut down second-stage cooling (if used); however, if temperature continues to drop to 45°F, the zoning system will turn off both stages of cooling. If the temperature improves, the system will stay in the duct temperature optimizer mode until the LAT reaches 55°F or higher. At 55°F the LAT algorithm will reset and return dampers to their original position. In the heating mode, Weather- Maker Two-Zone will perform the same duct temperature optimi- zation. The trip limits will be determined by the jumper setting. (See Fig. 12.) This will continue until the LAT problem is corrected.
This control helps WeatherMaker Two-Zone System cope with installations where the air conditioning system may suffer from poor ductwork, improperly sized heating or cooling equipment, and/or improper settings of the barometric bypass damper. This control is especially useful in retrofit applications where the size and routing of the ductwork may not be entirely known or satisfactory.
The duct temperature optimizer works by controlling how cold or hot the air inside the supply-air duct gets by monitoring the temperature of the air inside the supply-air system.
Whenever WeatherMaker Two-Zone is providing heating or cool- ing, the zone within the home that is asking for conditioned air will always have its damper fully open. The other zone in the system may or may not have an open damper depending upon its particular needs. If the ductwork is too small (or the air conditioner/heater is too large), then the zone requiring condi- tioned air may not be able to take enough air to allow your equipment to operate properly. WeatherMaker Two-Zone will detect this, and open up the closed damper allowing the equipment to continue to operate.
The duct temperature optimizer may be disabled on the control center. A 10k resistor can be installed in place of the duct sensor at the terminal block. By disabling the duct temperature optimizer, the LAT safety algorithm is removed from the system.
It is highly recommended that you use this control option. The
heating LAT is adjustable for the duct sensor. In this Installation Instruction, you will find the section showing an adjustment for the heating LAT. (See Fig. 12.) It is very important that this tempera- ture is properly set. For gas or oil furnaces, the temperature limit will be in the higher temperature range. For heat pumps the temperature setting should always be in the lower temperature range.
If you encounter a situation where 1 zone seems to have poor ductwork, then the WeatherMaker Two-Zone system is capable of reverting back to a fully open, constant-volume system. If this condition persists, it should always be looked upon as an indication of a HVAC problem, not a WeatherMaker Two-Zone problem.
Step 6ÐElectronic Thermostat Connection with WeatherMaker Two-Zone Control
Carrier electronic non-programmable and programmable thermo- stats can be connected to the WeatherMaker Two-Zone. See pre-sale literature for thermostat part numbers.
NOTE: The zone control board is only capable of 2-stage heat and 2-stage cool operation. Fig. 13 and 14 will reflect these applications only. Review and understand the following items before installing.
THERMOSTAT SETUP
1.Thermostat will not operate unless both R and C are connected to zone module input.
2.If selected thermostat is a heat pump (HP) or 2-speed (2S) model, convert thermostat to air conditioning operation. This will assure that Y signals are generated for cooling, and W signals are generated for heating from thermostat to zone module input. The thermostat O/W2 output will now be the second-stage heat call. If installation is a heat pump system, the zone control board will provide proper output signal to heat pump.
3.Select "Zoning" option on thermostat. This will disable the Timeguard and 4-cycle per hr (cph) protection built into thermostat. Let zone control board perform the Timeguard and cycle protection. Refer to thermostat Installation Instruction under Zoning for more detail.
4.The zone 1 thermostat is the only thermostat that can control continuous fan operation with zoning. Connect G between zone 1 thermostat and zone 1 input on zone control module.
5.Follow all safety and installation considerations outlined in the thermostat Installation Instructions.
ZONE CONTROL BOARD SETUP
1.Configure zone control board jumper for Tstat (thermostat) Fnc option only. Do not use Tstat HP option. When Tstat Fnc is selected this will setup control inputs to recognize Y1 and Y2 for first- and second-stage cooling, W1 and W2 for first- and second-stage heating.
2.Configure zone control board for either Equipmt (equipment), HP or Fnc. When a heat pump system is used, Equipmt HP mode should be selected. The zone control board will provide the proper output signal to the heat pump. When a gas/electric furnace is used, Equipmt Fnc mode should be selected for proper output signal.
3.Configure zone control board for either Fnc Ht, w/f (with fan), or w/of (without fan). With Fan mode should be selected when a heat pump is installed and fan is needed to come on immediately with demand. Without Fan mode should be selected when fan is controlled by gas/electric furnace.
4.Configure zone control board for either DTO On or Off. When DTO On is selected (Factory default) and if a LAT trip occurs, closed dampers will begin opening to try and keep equipment running by maintaining proper air temperatures. However, if LAT temperatures exceed their limits, equipment will start staging down. When DTO Off is selected, equipment will stage down. Closed dampers will not open on inial trip, however if LAT temperatures exceed their limits, control will lockout and damper will open.
