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Rev 2.0
63-7048 1998 Honeywell Inc.
Page 11 of 22
Nobody has more knowledge about heating loads than Honeywell, the world leader in
temperature control. More furnaces are controlled by Honeywell thermostats than any
other, so nobody understands the science of temperature control better than we do.
In order for the prediction of outdoor temperature based on furnace cycling to work, we
needed to develop an algorithm to filter out changes in heating load that are not the result
of changes in outdoor temperature. We have developed a two-stage filter, which we've
shown to be very effective in preventing the humidity control from being thrown off by
heating load changes due to setpoint changes.
The first filter looks at the furnace cycle times that can be expected under normal, steady-
state conditions. We analyzed the limit of furnace cycle times for heating loads varying
from 5 to 95 percent, and cycle rates varying from 3 to 9 cycles per hour and determined
the minimum and maximum length of a heating cycle that can occur in steady state
conditions. Times measured that are shorter or longer than these limits are ignored,
known to be the result of some outside influence, not normal cycling.
The second filter is in place to compensate for the cycling pattern that exists as the
heating system works through a setpoint change. When a thermostat starts a recovery
period from a setback temperature, the first on cycle will typically exceed the “normal”
maximum, and thus will be ignored in our percent on calculation. The subsequent on
cycles will likely be within the “normal” limits, but longer than the steady-state cycling
pattern that will ultimately develop. In order to prevent the percent on calculation from
being severely affected, we limit the amount that the percent on value can change after
each cycle for the number of cycles that are typically required to reach steady-state
conditions.
Performance Curves
Extensive testing of this algorithm has been done over the past year including:
Software simulation, run entirely on a computer, using the house models
developed for the Perfect Climate Comfort Center
, with the H1008 software
algorithm.
Closed loop testing with the H1008 hardware and software actually controlling
the inputs to the simulation models. This approach was also used in the
development of the Perfect Climate Comfort Center
.
Field testing with devices and data logging equipment installed in sites in
Minnesota, West Virginia, and New Hampshire in the United States, and
Alberta, northern Manitoba, and Northwest Territories in Canada for portions
of the ‘97-’98 heating season.
Some very interesting observations were made during this test program. Shown below
are samples of how the H1008 Automatic Humidity Control performed under a wide
range of conditions.