Carrier 50PTH, PTV instruction

Auxiliary Modulating Hot Water/Steam Heating Reheat

—The control can modulate a hot water or steam valve con- nected to a coil on the discharge side of the unit and supplied by a boiler in order to maintain the desired heating set point should the compressor capacity be insufficient or a compressor failure occurs. Unless a compressor fault condition exists, the valve will only operate to supplement the heat provided by the compressor if the space temperature falls more than one degree below the desired heating set point. The valve will be con- trolled so the SAT will not exceed the maximum heating SAT limit.

Two-Position Hot Water/Steam Heating Reheat — The con- trol can operate a two-position, NO or NC, hot water or steam valve connected to a coil on the discharge side of the unit and supplied by a boiler in order to maintain the desired heating set point should the compressor capacity be insufficient or a com- pressor failure occurs. Unless a compressor fault condition ex- ists, the valve will only open to supplement the heat provided by the compressor if the space temperature falls more than one degree below the desired heating set point. The valve will be controlled so the SAT will not exceed the maximum heating SAT limit. The heat stage will also be subject to a 2-minute minimum OFF time to prevent excessive valve cycling.

Single Stage Electric Auxiliary Heat — The control can op- erate a field-installed single stage of electric heat installed on the discharge side of the unit in order to maintain the desired heating set point should the compressor capacity be insufficient or a compressor failure occurs. Unless a compressor fault con- dition exists, the heat stage will only operate to supplement the heat provided by the compressor if the space temperature falls more than one degree below the desired heating set point. The heat stage will be controlled so the SAT will not exceed the maximum heating SAT limit. The heat stage will also be sub- ject to a 2-minute minimum OFF time to prevent excessive cycling.

INDOOR AIR QUALITY (IAQ) AND DEMAND CON- TROLLED VENTILATION (DCV) — If the optional in- door air quality sensor is installed, the WSHP Open controller can maintain indoor air quality via a modulating OA damper providing demand controlled ventilation. The control operates the modulating OA damper during occupied periods. The con- trol monitors the CO2 level and compares it to the configured set points, adjusting the ventilation rate as required. The control provides proportional ventilation to meet the requirements of ASHRAE (American Society of Heating, Refrigerating and Air Conditioning Engineers) specifications by providing a base ventilation rate and then increasing the rate as the CO2 level in- creases. The control will begin to proportionally increase venti- lation when the CO2 level rises above the start ventilation set point and will reach the full ventilation rate when the CO2 level is at or above the maximum set point. A user-configurable min- imum damper position ensures that proper base ventilation is delivered when occupants are not present. The IAQ configura- tions can be accessed through the configuration screen. The following conditions must be true in order for this algorithm to run:

•Damper control is configured for DCV.

•The unit is in an occupied mode.

•The IAQ sensor reading is greater than the DCV start control set point.

The control has four user adjustable set points: DCV start control set point, DCV maximum control set point, minimum damper position, and DCV maximum damper position.

Two-Position OA Damper — The control can be configured to operate a ventilation damper in a two-position ventilation mode to provide the minimum ventilation requirements during occupied periods.

DEHUMIDIFCATION — The WSHP Open controller will provide occupied and unoccupied dehumidification only on

units that are equipped with the modulating hot water reheat (HWR) option. This function requires an accessory space rela- tive humidity sensor. When using a relative humidity sensor to control dehumidification during occupied or unoccupied times, the dehumidification set points are used accordingly. When the indoor relative humidity becomes greater than the dehumidifi- cation set point, a dehumidification demand will be acknowl- edged. Once acknowledged, the dehumidification output will be energized, bringing on the supply fan (medium speed), me- chanical cooling, and the integral hot water reheat coil. The controls will engage Cooling mode and waste heat from the compressor cooling cycle will be returned to the reheat coil si- multaneously, meaning that the reversing valve is causing the compressor to operate in the Cooling mode. During Cooling mode, the unit cools, dehumidifies, and disables the HWR coil; however, once the call for cooling has been satisfied and there is still a call for dehumidification, the unit will continue to op- erate using the reheat mode and HWR coil.

WATERSIDE ECONOMIZER — The WSHP Open control- ler has the capability of providing modulating or two-position water economizer operation (for a field-installed economizer coil mounted to the entering air side of the unit and connected to the condenser water loop) in order to provide free cooling (or preheating) when water conditions are optimal. Water econ- omizer settings can be accessed through the equipment status screen. The following conditions must be true for economizer operation:

•SAT reading is available.

•LWT reading is available.

•If occupied, the SPT is greater than the occupied cooling set point or less than the occupied heating set point and the condenser water is suitable.

•Space temperature reading is valid.

•If unoccupied, the SPT is greater than the unoccupied cooling set point or less than the unoccupied heating set point and the condenser water is suitable.

Modulating Water Economizer Control — The control has the capability to modulate a water valve to control condenser water flowing through a coil on the entering air side of the unit.

Cooling — The purpose is to provide an economizer cooling function by using the water loop when the entering water loop temperature is suitable (at least 5° F below space temperature). If the water loop conditions are suitable, then the valve will modulate open as required to maintain a supply-air temperature that meets the load conditions. Should the economizer coil ca- pacity alone be insufficient for a period greater than 5 minutes, or should a high humidity condition occur, then the compressor will also be started to satisfy the load. Should the SAT ap- proach the minimum cooling SAT limit, the economizer valve will modulate closed during compressor operation.

Heating — Additionally, the control will modulate the water valve should the entering water loop temperature be suitable for heating (at least 5° F above space temperature) and heat is required. The valve will be controlled in a similar manner ex- cept to satisfy the heating requirement. Should the economizer coil capacity alone be insufficient to satisfy the space load con- ditions for more than 5 minutes, then the compressor will be started to satisfy the load. Should the SAT approach the maxi- mum heating SAT limit, the economizer valve will modulate closed during compressor operation.

Two-Position Water Economizer Control — The control has the capability to control a NO or NC, two-position water valve to control condenser water flow through a coil on the entering air side of the unit.

Cooling — The purpose is to provide a cooling economizer function directly from the condenser water loop when the en- tering water loop temperature is suitable (at least 5° F below space temperature). If the optional coil is provided and the wa- ter loop conditions are suitable, then the valve will open to pro-