Operating Instructions

Applications
Application 2274: Multiple Heating and Cooling
Heat Pump with Mixed Air and Internal Reversing
Valve Control
ln Application 2274, (Figure 2-2) the controller controls one or two heating compressors for
heating and one or two cooling compressors for cooling. The reversing valve is controlled
internally by the heat pump. ln addition to compressors, this heat pump may also be
equipped with electric heat for auxiliary heat and mixed air control for free cooling. This
application also controls small air handling units with two position heating and cooling control.
The mixed air control can use either a spring return or a floating control damper motor.
Compressor/Electric Heat Staging
This application can support up to two cooling compressors and up to two heating
compressors. Each compressor heat has a time delay (at least 30 seconds) to lessen the
demand of having more than one compressor start at once.
Application Notes
1. lf the heat pump cycles excessively, temperature swings in the room are excessive, or
there is trouble maintaining the setpoint, the cooling loop, the heating loop or both need
to be tuned. Contact your local Siemens Building Technologies representative for more
information.
2. The Heat Pump Controller—Multi-Stage, as shipped from the factory, keeps all
associated equipment OFF. The controller and its equipment are released to application
control at start-up.
3. Running the mixed air loop during night mode can increase energy savings by taking
advantage of free cooling at night to pre-cool the building for day mode, and thereby,
reduce the need for mechanical cooling during day mode. This method for pre-cooling
the building can also improve indoor air quality because it is accomplished with fresh air.
A field panel program can be written to pre-cool the building with this application. Contact
your local Siemens Building Technologies representative for more information.
4. ln this application the maximum configurations are as follows:
•
•
•
The maximum of HTG CMP TOTL (Point 75) = 2.
The maximum of CLG CMP TOTL (Point 77) = 2.
The maximum of EHTG STG CNT (Point 76) = 1.
lf these limits are exceeded, HTG CMP TOTL, CLG CMP TOTL, and EHTG STG CNT
will all be set to 0. These points will remain at 0 until they are set correctly. This prevents
the application from trying to control equipment that it does not have.
Siemens Building Technologies, Inc. 13