Heat Pump Water Loop Controller


The SZ2161 is a microprocessor-based controller designed for water source heat pump plant control applications.


  • Stand-alone or network operation
  • 365-day time clock with two holiday schedules, automatic leap year and daylight savings correction
  • No backup battery required for control parameters, schedule or clock
  • Supply and return condenser water temperature input
  •  Supply and return loop water temperature inputs
  • Outdoor air temperature input
  • Boiler supply water temperature input
  • Four digital inputs for status
  • External time clock input
  • Local override and remote override capability
12 digital outputs for control of:
  • Damper
  • Spray pump
  • 2 loop pumps
  • 2 boiler pumps
  • 2 fan speed selections
  • 4 boiler stages
  • Adjustable offsets and differentials on relay outputs
  • Two modulating analog output for speed drive or boiler
  • Mixing valve control
  • LEDs for monitoring status
  • Automatic rotation of pumps
  • Automatic rotation of boiler stages

Call to order:


Specs & Docs



Accuracy: +/- 0.5%
Programming: EIA RS485 interface
Communications: RS485, half duplex
Memory backup: Non-volatile EEPROM, no battery required


Operating temperature: 32 to 131°F (0 to 55°C)
Operating humidity: 0 to 100% RH, non-condensing
Storage temperature: 14 to 140°F (-10 to 60°C)


Supply voltage: 24 VAC +/-20%
Inputs: Six 1000Ω PtRTD, momentary override and five digital (dry contact)
Range: Loop water supply and return: 20 to 120°F Condenser water supply and return: 20 to 120°F
Boiler water: 40 to 240°F
Outdoor air temp: -40 to 160°F
Outputs: 12 digital (SPST dry contact, 24 VAC @2A) analog and Two 4 to 20 mA DC
Max load resistance (analog output): 600 Ω
Common mode rejection: 100 db @ 60 Hz
Power consumption: 15 VA max.

Specifications subject to change without notice.