4
Heat-Timer Corp.
Understanding Operation Concept
The Heat-Timer MPCQ Platinum is a microprocessor based control for multi-stage/multi-boiler steam heating systems. The control
operates a bank of modular steam boilers, automatically activating and deactivating stages so as to provide the desired heat pattern for
the application whether heating a building or a process application.
Cycle Operation Concept
Cycle-On
21 Minutes
Cycle-Off
39 Minutes
Heat On
Heat Off
Cycle-On
8 Minutes
Cycle-Off
52 Minutes
Sample Mild Weather Cycle
Sample Cold Weather Cycle
Cycle Length 60 minutes
Establish
Heat
Establish
Heat
The control operates on the CYCLE principle which was created specifically for steam heating systems. The CYCLE concept was
developed by Heat-Timer to overcome the inabilities of standard thermostatic controls to cope with the erratic properties of steam.
Steam heat can not be switched on and off instantaneously. Instead, it takes time to build up a “head of steam”. And, once the system
starts heating up, it has momentum which can not quickly be stopped.
By monitoring the outside temperature, the MPCQ Platinum is able to anticipate the heating needs of the building. Each fixed time
CYCLE period (usually 60 minutes long but adjustable from 10 to 240 minutes) is divided into a heat-ON segment and a heat-OFF
segment. The length of the ON segment will vary with the outside temperature. The colder it is outside, the longer the ON part of the
cycle will be.
The MPCQ Platinum constantly checks the outside temperature by means of a solid state sensor located on the exterior of the building.
At the same time it also monitors pressure by means of a heating system pressure sensor located in the common header. On the basis
of this combined data, the MPCQ Platinum sends instructions to the heating plant to control the heat level in the building.
In addition to adjusting the length of the ON part of a cycle, the outdoor temperature acts as a system cutoff. When the outdoor
temperature rises above an adjustable set point, the MPCQ Platinum will not call for any heat. When the outdoor temperature drops
below the set point, the MPCQ Platinum will automatically begin controlling the heating cycles. Meanwhile, the heating system
pressure sensor controls the number of boiler stages which are turned on, and the amount of steam pressure in the system. The effect
of these two sensors combined is to provide an even comfortable level of heat throughout the building.
1. The MPCQ Platinum starts activating steam stages when the outside temperature falls below the Outdoor Cutoff (factory set to 55°F
for the day and 40°F for the night, but fully adjustable). The MPCQ Platinum will continue to bring on more stages, and/or hold all
the stages on, until the system pressure reaches the set point. This indicates that steam has gotten entirely through the system, or
that pressure is established.
2. Once pressure is established, the heat-ON segment of the cycle will begin. During the ON part of the cycle, the MPCQ Platinum
will activate as many stages as necessary to achieve and hold the pressure set point. Stages which may no longer be needed once set
point pressure has been achieved will be turned off.
3. Once the ON part of the cycle has ended, the heat-OFF part of the cycle will begin. All the steam boilers will be turned off.
4. When the OFF part of the cycle is over, the MPCQ Platinum will once again start to establish pressure unless either the outside
temperature has risen above the outdoor cutoff, or the header pressure is more than Heat Establish Pressure setting. See page 29.
5. The boilers will start firing once the steam pressure in the system falls below the Heat Establish Pressure setting. See page
Cycle-On
21 Minutes
Cycle-Off
39 Minutes
Establish
Heat
Cycle-On
21 Minutes
Establish
Heat
Cycle Delayed until
pressure drops below
Heat Establish Pressure
1
2
3
4
5
60 Minute Cycle
(Cycle-On=21 + Cycle-Off=39)
