Mercury bulb vs digital?

[Lorne]

Is the new digital thermostat more sensitive to temperature changes then the mercury bulb type. Does it react quicker without over cooling or heating?

[hvac1000]

Yes and no. It depends upon the manufacturer and how tight there tolerances are. I have had many mercury thermostats set up correctly (leveled) that work just as well as digital. Cheap digital thermostats are usually junk to start with. They do not have close tolerance parts (resistors and capacitors etc) so they do not hold the temp well.

A very good quality Honeywell or White Rodgers digital work just fine. Expect to pay 100.00 or more for a good one. The 29.99 specials are just not accurate and do not work well.

You might look at the next post for some professional information on thermostats. Over 1.5 million dollars was spent on testing to provide this info.

[hvac1000]

50-8935
Digital Thermostats–
Temperature
Control Study
Table of contents
Executive summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . a
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
What is comfort? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
What is a thermostat? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Thermostat performance: key elements of comfortable temperature control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
• Temperature swing: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
• Droop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Comfort vs. equipment performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
NEMA testing procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
• Temperature swing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4–7
• Droop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7–8
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Appendix A: Thermostat Data—Temperature control comparison testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Appendix B: Thermostat Cycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10–13
• Heat mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10–11
• Cool mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12–13
Executive summary
There is a common misperception that all electronic thermostats offer the same level of comfort. To dispel this misperception,
Honeywell1 conducted what is believed to be the industry’s most comprehensive comparison testing ever on the performance
of residential electronic thermostats. Twelve thermostat models (with three thermostats from each model) were tested from
Honeywell, Totaline2, White-Rodgers3, Lux4, Invensys5 and Braeburn6.
The testing, conducted in accordance with National Electrical Manufacturers Association (NEMA) standards, revealed
major differences in electronic thermostat performance and the ability to provide consistent, reliable comfort. The testing
looked at temperature swing and droop.
Testing showed that Honeywell electronic thermostats outperform the competition. Honeywell thermostats did the best
job—a superior job—of providing tight temperature control. Better than competing models, Honeywell thermostats minimized
temperature swing and droop, and maintained temperatures close to the setpoint.
Honeywell thermostats allowed the least amount of temperature swing and temperature droop of any manufacturer tested.*
Honeywell permitted, at the most, a 0.5 degree F temperature swing. The competition allowed, at the most, a temperature
swing of 1.9 degrees F (White-Rodgers), 3.2 degrees F (Totaline), 4.1 degrees F (Lux), 4.4 degrees F (Invensys), and 6.7
degrees F (Braeburn).
Honeywell permitted, at the most, a temperature droop of 0.2 degrees F. The competition allowed, at the most, a temperature
droop of 0.4 degrees F (White-Rodgers), 0.5 degrees F (Lux), 1.2 degrees F (Invensys), 1.4 degrees F (Braeburn), and
1.6 degrees F (Totaline).
Superior thermostat performance is important for contractors because it translates into superior comfort for residential
customers.
Read through the findings. Understanding the differences in electronic thermostat performance can help you better serve
your residential customers with thermostats that best balance temperature comfort and equipment performance.
*Test results are from the models listed in Table 1.
1 Honeywell is a trademark of Honeywell International Inc.
2 Totaline is a trademark of Carrier Corporation.
3 White-Rodgers is a trademark of Emerson Electric Co.
4 Lux is a trademark of Lux Products Corporation.
5 Invensys is a trademark of Invensys plc.
6 Braeburn is a trademark of Braeburn Systems, LLC.
50-8935 a
Introduction
Today’s electronic thermostats can offer many benefits for contractors and homeowners. A thermostat’s most important
function is to provide comfort. Electronic thermostats can also save energy (particularly when the electronic thermostat is a
programmable or “setback” model), maximize equipment performance and longevity, and offer far more features than their
electromechanical predecessors. As a result, the popularity of electronic thermostats is surging upward.
So choosing a thermostat should be simple, right? Just go for the electronic model, right?
Wrong.
Honeywell’s comparison testing revealed major differences in electronic thermostat performance. Conducted in accordance
with National Electrical Manufacturers Association standards (see section “NEMA Testing Procedure”), test results identified
striking performance differences among electronic thermostats from the various manufacturers. These differences are noticeable
when it comes to the thermostats’ ability to balance comfort and the need to optimize equipment performance.
The following sections will cover the definition of comfort, the functions of a thermostat, and the key elements of thermostat
performance. This paper will then lay out the findings of the comparison testing, which shows that Honeywell electronic
thermostats outperformed comparable competitive models in each phase of testing.
What is comfort?
Providing indoor comfort is the most important benefit that the heating and cooling equipment manufacturer and contractor
offer the homeowner.
But what is comfort? In respect to this paper, comfort is defined as a state of well being that’s enabled because the indoor
environment is “ just right.” Ironically, we are not typically aware of comfort. It often goes unnoticed. Not so with discomfort.
Discomfort distracts occupants, and that commands attention. People notice.
In simple terms, developing an indoor climate of comfort requires the elimination of any environmental distractions, such
as temperatures that are too high or too low, poor indoor air quality, or air that is simply too humid or too dry. These distractions
make occupants aware that something is “not right.”
Consider temperature comfort. People are very sensitive to temperature. Many can detect even slight fluctuations—as
little as 2 degrees F (±1 degree F). That’s enough to cause noticeable discomfort. It’s enough to make some people adjust
the thermostat setting.
Today’s high-performance electronic thermostats—those that control to within ±1 degree F of setpoint—maximize comfort.
They provide tight, consistent control, by keeping the temperature within the 2-degree band of comfort.
Note: This paper addresses temperature comfort. This is one aspect of total comfort, which also includes proper humidity,
ventilation and air filtration.
What is a thermostat?
A thermostat is a switch that turns the heating or cooling equipment on and off when the sensed room temperature changes
from the setpoint (temperature setting). To maintain comfortable temperature control and limit deviations from the setpoint,
the thermostat must act as all of the following:
• A temperature-sensing device. This device senses deviations from the desired temperature.
• A setpoint controller. This device establishes the desired temperature that the system is required to maintain.
• A final control element. This element, a switch, turns the heating or cooling equipment on and off.
1 50-8935
Thermostat performance: key elements of comfortable temperature control
The two key elements of comfortable temperature control are minimizing temperature swing and limiting temperature droop.
Temperature swing
Residential thermostats, by design, do not maintain the exact setpoint temperature because such frequent cycling would sacrifice
the efficiency of the equipment. Instead, residential thermostats cycle the equipment on and off and control to a range
of temperatures above and below the setpoint temperature. The difference between the highest and lowest temperatures
in that range is known as temperature swing (Figure 1).
Temperature swing
Temperature swing directly reflects the equipment on and off time (cycle rate). As the equipment cycle lengthens, the amount of
temperature swing increases. As the cycle length decreases, the amount of temperature swing decreases.
A thermostat should allow the smallest amount of temperature swing while optimizing the performance and efficiency of the
heating and cooling equipment. To maintain occupant comfort in residential applications, the temperature swing should not
exceed 2 degrees F (±1 degree F).
Most people won’t tolerate uncomfortably cool or warm conditions, so when the room temperature isn’t right, they’ll simply
adjust the thermostat setting. This leads to temperatures that are higher or lower than necessary for comfort, and that wastes energy.
Droop
Minimizing temperature droop is another key facet of thermostat performance. Temperature droop is the decrease in the control
point temperature (average room temperature) as load conditions increase. (See Figure 2.) Temperature droop is calculated by
taking the difference between the control point temperature at a 20% load condition and the control point temperature at an 80%
load condition.
Droop
Outside temperatures place a particular load or demand on the heating and cooling equipment. In the heating season, low outside
temperatures place a high load or demand on the heating equipment. This is simply referred to as a high-load condition. In the
cooling season, a high-load condition is caused by high outside temperatures.
In high-load conditions the system is required to run longer, which causes more heat from the flow of electrical current to
build up in the thermostat. This additional heat causes the thermostat to respond to a temperature that is higher than the actual
room temperature. In the heating mode, the thermostat turns off the equipment before reaching the setpoint. In the cooling mode,
the thermostat runs the equipment longer, cooling the room below the setpoint. Homeowners typically raise the temperature setting
to compensate for the uncomfortably cool conditions that are associated with droop. This is how droop causes occupants
both discomfort and inconvenience.
The good news is that well-designed thermostats compensate for the internal heat buildup, thus thwarting droop. These thermostats
ensure consistent room temperatures and comfort under a variety of load conditions.
72.0°F (22.2°C)
71.0°F (21.7°C)
70.0°F (21.1°C)
69.0°F (20.6°C)
68.0°F (20.0°C)
Setpoint Temperature Swing (Room)
Figure 1. Temperature swing is the difference between the highest and
lowest temperatures permitted by a thermostat at a given setpoint.
0 20 50 80 100
Droop
Load - %
Figure 2. Droop is the decrease in the control point temperature
(average room temperature) as load conditions increase.
Homeowners typically raise the temperature setting to compensate
for the uncomfortably cool conditions that are associated with droop.
Control Point Room
Temperature
x
x
50-8935 2
Comfort vs. equipment performance
A high-performance thermostat is sensitive enough to respond to changes in temperature before the temperature goes so low
or so high (±1 degree F) that people in the room feel discomfort. A thermostat must balance several objectives: providing
consistent comfort, optimizing equipment efficiency, prolonging equipment life, maximizing energy savings and delivering
lasting, trouble-free service.
As mentioned earlier, thermostats are not designed to maintain the exact setpoint temperature because such frequent cycling
would sacrifice equipment efficiency; nor are thermostats designed solely to operate the equipment at maximum efficiency,
which would sacrifice comfort. Quality electronic thermostats are sensitive and “smart” enough to maintain comfort while
minimizing cycling.
NEMA testing procedure
The National Electrical Manufacturers Association (NEMA) publishes the industry standard for thermostat testing7. Using
a test chamber design based on NEMA standards, Honeywell engineers tested 12 comparable electronic thermostat models
from Honeywell, White-Rodgers, Totaline, Lux, Invensys and Braeburn. The thermostat models are listed in Table 1.
Electronic thermostats tested
To ensure fair representation, three different devices were tested from each model number. Each device (with its sealed
packaging intact) was obtained from a distributor or distribution center. Each thermostat was placed in a test chamber that
is designed to test the performance of a thermostat under extreme and nominal conditions. Each test chamber was checked
for accuracy and calibrated if not within specifications. The thermostats were tested at their factory settings with a setpoint
of 70 degrees F in heating and 78 degrees F in cooling and were subjected to an air flow velocity of 30 feet per minute (±2
FPM). Each thermostat was connected to a 27-volt control circuit with a 0.4 amp load (0.4 amps per load terminal) and tested
at 20%, 50% and 80% load conditions as specified by NEMA DC 3 standards. (NEMA specifies a 20% load condition as
a “ light” thermal load and an 80% load condition as a “ heavy” thermal load).
Test results
This section summarizes the findings of the comparison testing as they relate to temperature swing and droop. (See Appendix A
and B for a complete compilation of the comparison testing and each thermostat model’s performance.)
Honeywell
Honeywell
Honeywell
White-Rodgers
White-Rodgers
Totaline
Totaline
Totaline
Lux
Lux
Invensys
Braeburn
T8600
T8001
T8112
1F78-144
1F78-151
P374-1500
P474-1050
P474-0100
PSP511
TX1500
9701i
5000
Powerstealing
Hardwired
Battery
Battery
Battery
Hardwired/Powerstealing
Hardwired/Powerstealing
Hardwired/Powerstealing
Hardwired/Battery
Battery
Hardwired
Battery
7 Day
5-2 Day
5-2 Day
Non-programmable
5-2 Day
7 Day
5-2 Day
Non-programmable
5-2 Day
5-1-1 Day
7, 5-1-1, 5-2 Day or 24 Hour
5-2 Day
Table 1. The comparison testing included 12 electronic thermostat models from six
manufacturers. Three different devices were tested from each model number.
Thermostat
Manufacturer
Model
Number Power Method Programming
3 50-8935
7 NEMA Standards Publication No. DC3-1989. Residential Controls—Electrical Wall-mounted Room Thermostats.
Temperature swing
Temperature swing, as discussed earlier, is the difference between the highest and lowest temperatures permitted by a thermostat
at a given setpoint. Temperature swing in excess of 2 degrees F (±1 degree F) is considered noticeable and therefore unacceptable
from a comfort perspective.
Figures 3 through 6 show the maximum temperature swing by manufacturer and by model number in both heating and
cooling modes.
Temperature swing*
8.0 (4.4)
7.0 (3.9)
6.0 (3.3)
5.0 (2.
4.0 (2.2)
3.0 (1.7)
2.0 (1.1)
1.0 (0.6)
0.0 (0.0)
Maximum Temperature Swing by Manufacturer (Heating)**
0.5 (0.3)
1.0 (0.6)
2.5 (1.4) 2.5 (1.4)
3.4 (1.9)
4.1 (2.3)
8.0 (4.4)
7.0 (3.9)
6.0 (3.3)
5.0 (2.
4.0 (2.2)
3.0 (1.7)
2.0 (1.1)
1.0 (0.6)
0.0 (0.0)
Maximum Temperature Swing by Manufacturer (Cooling)**
0.5 (0.3)
1.9 (1.1)
3.2 (1.
3.9 (2.2)
4.4 (2.4)
6.7 (3.7)
Temperature Swing F (C)
Thermostat Manufacturer
Temperature Swing F (C)
Thermostat Manufacturer
Figure 3. Maximum temperature swing allowed by manufacturer in
the heating mode.
Figure 4. Maximum temperature swing allowed by manufacturer in
the cooling mode.
8.0 (4.4)
7.0 (3.9)
6.0 (3.3)
5.0 (2.
4.0 (2.2)
3.0 (1.7)
2.0 (1.1)
1.0 (0.6)
0.0 (0.0)
Maximum Temperature Swing by Model Number (Heating)
Temperature Swing F (C)
Thermostat Model Number
Figure 5. Maximum temperature swing by thermostat model number in the heating mode.
0.5 (0.3) 0.4 (0.2) 0.5 (0.3)
T8600 T8001 T8112
2.5 (1.4) 2.4 (1.3)
1.9 (1.1)
P374-1500 P474-1050 P474-0100
1.0 (0.6) 1.0 (0.6)
1F78-151 1F78-144
2.5 (1.4)
9701i
3.4 (1.9)
5000
3.7 (2.1)
4.1 (2.3)
PSP511 TX1500
8.0 (4.4)
7.0 (3.9)
6.0 (3.3)
5.0 (2.
4.0 (2.2)
3.0 (1.7)
2.0 (1.1)
1.0 (0.6)
0.0 (0.0)
Maximum Temperature Swing by Model Number (Cooling)
Temperature Swing F (C)
Thermostat Model Number
Figure 6. Maximum temperature swing by thermostat model number in the cooling mode.
0.5 (0.3) 0.5 (0.3) 0.5 (0.3)
T8600 T8001 T8112
3.1 (1.7)
1.5 (0.
3.2 (1.
P374-1500 P474-1050 P474-0100
1.9 (1.1) 1.9 (1.1)
1F78-151 1F78-144
4.4 (2.4)
9701i
6.7 (3.7)
5000
3.3 (1.
3.9 (2.2)
PSP511 TX1500
Honeywell White-
Rodgers
Totaline Invensys Braeburn Lux Honeywell White-
Rodgers
Totaline Lux Invensys Braeburn
Honeywell Totaline White-Rodgers
Invensys Braeburn
Lux
Honeywell Totaline White-Rodgers
Braeburn
Lux
Invensys
50-8935 4
*Total amount of temperature swing (example 1° F = +/-0.5° F)
**Test results are from models listed in Table 1.
Based on testing data, Honeywell thermostats permitted the least amount of temperature swing of any manufacturer tested
by yielding, at the most, a 0.5 degree F (±0.25 degree F) temperature swing.
Manufacturers whose thermostats allowed a temperature swing of more than ±1 degree F include Totaline (3.2 degrees F), Lux
(4.1 degrees F), Invensys (4.4 degrees F), and Braeburn (6.7 degrees F).
Invensys (9701i)8 and Braeburn (5000)9 claim to provide an accuracy of ±1 degree F. The performance data on temperature
swing do not support these claims. Invensys allowed a temperature swing of 4.4 degrees F (±2.2 degrees F) and Braeburn
allowed a temperature swing of 6.7 degrees F (±3.3 degrees F).
Tables 2 and 3 show the excessively long on and off times of specific thermostats that allowed temperature swings of 2
degrees F or more at a 50% load condition. The tables consist of thermostats from Totaline, Lux, Invensys and Braeburn.
Temperature swing directly correlates to cycle rate: As the cycle lengthens, the amount of temperature swing increases; as the
cycle length decreases, the amount of temperature swing decreases. From a comfort perspective, the thermostats listed in Tables
2 and 3 failed to cycle the equipment correctly. As a result, these thermostats demonstrated poor temperature control that would
cause discomfort.
Excessive cycle rate length
The Lux PSP511 and TX1500 installation and operating instructions10 state that a system should cycle on about three to six
times per hour. However, the test results show that the Lux thermostats cycled the equipment less than once per hour in both
heating and cooling modes at a 50% load condition.
Figures 7-8 compare the cycling of the Honeywell T8001 versus the Totaline P374-1500 in both heating and cooling modes.
Note the sharp differences between the two models. The longer on and off times of the Totaline thermostat permit erratic,
unacceptably wide temperature swings and would cause noticeable discomfort. In addition to the large temperature swings,
the Totaline thermostat failed to keep the temperature close to the setpoint.
Totaline
Invensys
Totaline
Braeburn
Lux
Lux
P474-1050
9701i
P374-1500
5000
PSP511
TX1500
Table 2. This shows the excessively long on and off times of specific thermostats that allowed temperature
swings of 2 degrees F or more at a 50% load condition in the heating mode. Temperature swing directly
correlates to cycle rate: Longer on-off cycles can produce larger temperature swings and corresponding
discomfort. (Note: Table 2 only includes thermostats that allowed temperature swings of 2 degrees F or more at a
50% load condition.)
Manufacturer Model Number
Cycle Rate (CPH) On (min.) Off (min.)
Cycle Rate Temperature Swing
F C
1.20
1.10
1.02
0.79
0.77
0.70
25.0
27.3
29.4
38.0
39.0
42.9
25.0
27.3
29.4
38.0
39.0
42.9
2.4
2.5
2.5
3.4
3.7
4.1
1.3
1.4
1.4
1.9
2.1
2.3
Heating Mode
Totaline
Totaline
Lux
Lux
Invensys
Braeburn
P374-1500
P474-0100
PSP511
TX1500
9701i
5000
Table 3. This shows the excessively long on and off times of specific thermostats that allowed temperature
swings of 2 degrees F or more at a 50% load condition in the cooling mode. Temperature swing directly
correlates to cycle rate: Longer on-off cycles can produce larger temperature swings and corresponding
discomfort. (Note: Table 3 only includes thermostats that allowed temperature swings of 2 degrees F or more at a
50% load condition.)
Manufacturer Model Number
Cycle Rate (CPH) On (min.) Off (min.)
Cycle Rate Temperature Swing
F C
0.46
0.44
0.44
0.38
0.34
0.25
65.2
68.2
68.2
78.9
88.2
120.0
65.2
68.2
68.2
78.9
88.2
120.0
3.1
3.2
3.3
3.9
4.4
6.7
1.7
1.8
1.8
2.2
2.4
3.7
Cooling Mode
8 Invensys information from www.about-i-series.com. © 2001 Invensys, 8/01 - #150-1654.
9 Braeburn literature no. 5000-300-001© 2001.
10 Lux literature nos. 43221 Rev. C and 43340 Rev. A.
5 50-8935
Cycling comparison (heating): Honeywell T8001 vs. Totaline P374-1500
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
74.0 (23.3)
73.0 (22.
72.0 (22.2)
71.0 (21.7)
70.0 (21.1)
69.0 (20.6)
68.0 (20.0)
67.0 (19.4)
66.0 (18.9)
65.0 (18.3)
64.0 (17.
63.0 (17.2)
62.0 (16.7)
61.0 (16.1)
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
Honeywell T8001 - Heat Mode Totaline P374-1500 - Heat Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
74.0 (23.3)
73.0 (22.
72.0 (22.2)
71.0 (21.7)
70.0 (21.1)
69.0 (20.6)
68.0 (20.0)
67.0 (19.4)
66.0 (18.9)
65.0 (18.3)
64.0 (17.
63.0 (17.2)
62.0 (16.7)
61.0 (16.1)
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
Figure 7. Note the contrast between the cycling of Honeywell’s T8001 thermostat and the Totaline P374-1500 thermostat in the heating mode.
Excessively long on and off times directly correlate with excessive temperature swings.
50-8935 6
Cycling comparison (cooling): Honeywell T8001 vs. Totaline P374-1500
Figure 8. Note the contrast between the cycling of Honeywell’s T8001 thermostat and the Totaline P374-1500 thermostat in the cooling mode.
Excessively long on and off times directly correlate with excessive temperature swings.
Totaline P374-1500 - Cool Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
86.0 (30.0)
85.0 (29.4)
84.0 (28.9)
83.0 (28.3)
82.0 (27.
81.0 (27.2)
80.0 (26.7)
79.0 (26.1)
78.0 (25.6)
77.0 (25.0)
76.0 (24.4)
75.0 (23.9)
74.0 (23.3)
73.0 (22.
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
86.0 (30.0)
85.0 (29.4)
84.0 (28.9)
83.0 (28.3)
82.0 (27.
81.0 (27.2)
80.0 (26.7)
79.0 (26.1)
78.0 (25.6)
77.0 (25.0)
76.0 (24.4)
75.0 (23.9)
74.0 (23.3)
73.0 (22.
Temperature F (C)
Setpoint
2 degree
comfort band
20% load 50% load 80% load
Honeywell T8001 - Cool Mode
7 50-8935
To review cycling data (heat and cool modes) for each thermostat tested, turn to Appendix B. Unlike Honeywell’s models, thermostats
from Totaline, Invensys, Lux and Braeburn had large temperature swings and/or a large deviation between the room
temperature and the setpoint temperature. As a result, these thermostats operated well outside the 2 degree comfort band.
As discussed earlier, it is essential to strike a balance between comfort and optimizing equipment performance. Honeywell thermostats
provide this balance between comfort and equipment performance. In contrast, thermostats from Totaline, Lux, Invensys
and Braeburn fail to meet this performance by allowing temperature swings of 3.2 degrees F and greater. To maintain occupant
comfort, the temperature swing should stay within 2 degrees F.
Droop
Droop, as discussed earlier, is the decrease in the control point temperature (average room temperature) as load conditions
increase. In high-load conditions the system is required to run longer, which causes more heat from the flow of electrical current
to build up in the thermostat. This additional heat causes the thermostat to respond to a temperature that is higher than the actual
room temperature. In the heating mode, the thermostat turns off the equipment before reaching the setpoint. In the cooling mode,
the thermostat runs the equipment longer, cooling the room below the setpoint. Homeowners typically raise the temperature setting
to compensate for the uncomfortably cool conditions that are associated with droop.
Figures 9 through 12 show the amount of temperature droop as load conditions changed from 20%-80% in heating and
cooling modes.
Temperature droop
Maximum Temperature Droop by Manufacturer (Heating)*
0.1 (0.1)
0.4 (0.2)
0.5 (0.3)
1.1 (0.6)
1.2 (0.7)
1.6 (0.9)
Maximum Temperature Droop by Manufacturer (Cooling)*
0.2 (0.1)
0.3 (0.2) 0.3 (0.2)
0.5 (0.3)
1.0 (0.6)
1.4 (0.
Thermostat Manufacturer Thermostat Manufacturer
Figure 9. Maximum temperature droop allowed by manufacturer in
the heating mode.
Figure 10. Maximum temperature droop allowed by manufacturer in
the cooling mode.
1.8 (1.0)
1.6 (0.9)
1.4 (0.
1.2 (0.7)
1.0 (0.6)
0.8 (0.4)
0.6 (0.3)
0.4 (0.2)
0.2 (0.1)
0.0 (0.0)
Temperature Droop F (C)
1.8 (1.0)
1.6 (0.9)
1.4 (0.
1.2 (0.7)
1.0 (0.6)
0.8 (0.4)
0.6 (0.3)
0.4 (0.2)
0.2 (0.1)
0.0 (0.0)
Temperature Droop F (C)
Honeywell White-
Rodgers
Lux Braeburn Invensys Totaline Honeywell White-
Rodgers
Lux Totaline Invensys Braeburn
* Test results are from models listed in Table 1.
50-8935 8
Temperature droop continued
1.8 (1.0)
1.6 (0.9)
1.4 (0.
1.2 (0.7)
1.0 (0.6)
0.8 (0.4)
0.6 (0.3)
0.4 (0.2)
0.2 (0.1)
0.0 (0.0)
Temperature Droop by Model Number (Heating)
0.1 (0.1) 0.1 (0.1)
0.0 (0.0)
Temperature Droop F (C)
Thermostat Model Number
Figure 11. Temperature droop by thermostat model number in the heating mode. The Honeywell T8112 thermostat tested showed no droop.
1.1 (0.6)
T8600 T8001 T8112
0.9 (0.5)
1.6 (0.9)
1.3 (0.7)
P374-1500 P474-1050 P474-0100
0.4 (0.2) 0.4 (0.2)
1F78-151 1F78-144
1.2 (0.7)
9701i 5000
0.3 (0.2)
0.5 (0.3)
PSP511 TX1500
1.8 (1.0)
1.6 (0.9)
1.4 (0.
1.2 (0.7)
1.0 (0.6)
0.8 (0.4)
0.6 (0.3)
0.4 (0.2)
0.2 (0.1)
0.0 (0.0)
Temperature Droop by Model Number (Cooling)
Temperature Droop F (C)
Thermostat Model Number
Figure 12. Temperature droop by thermostat model number in the cooling mode.
0.1 (0.1)
0.2 (0.1) 0.2 (0.1)
T8600 T8001 T8112
0.5 (0.3)
0.1 (0.1)
0.2 (0.1)
P374-1500 P474-1050 P474-0100
0.3 (0.2)
0.1 (0.1)
1F78-151 1F78-144
1.0 (0.6)
9701i
1.4 (0.
5000
0.2 (0.1)
0.3 (0.2)
PSP511 TX1500
Honeywell Totaline White-Rodgers
Invensys Braeburn
Lux
Honeywell Totaline White-Rodgers
Braeburn
Lux
Invensys
11 Totaline literature no. 570-564 01/99, 570-528 Rev. A 01/99 and 570-525 Rev. A 09/98.
Based on testing data, Honeywell best restricted droop, permitting a maximum of 0.2 degrees F. This tight, consistent temperature
control translates to greater occupant comfort and convenience (no need to adjust the temperature setting).
Other manufacturers’ thermostats struggled with droop. Invensys allowed the temperature to drop by as much as 1.2
degrees F. Braeburn overcompensated for droop, raising the temperature 1.4 degrees F as load conditions changed from
20%-80%. Totaline allowed 1.6 degrees F of temperature droop, the most of any manufacturer tested. This stands as an
apparent contradiction to Totaline’s promotional claims of “no droop.” 11
Why is it so important for a thermostat to combat droop? The simple answer is comfort and convenience. Honeywell thermostats
compensate for the demands that extreme outdoor temperatures place on the heating and cooling equipment. Thus, occupants do
not have to experience the cool conditions associated with droop, nor do they have to walk over to the thermostat to turn up the
temperature setting. Honeywell thermostats deliver the type of performance that keep occupants comfortable in both extreme and
nominal weather conditions.
Conclusion
Honeywell tested 12 electronic thermostat models from six manufacturers. The findings revealed major differences in electronic
thermostat performance and the ability to provide consistent, reliable comfort while optimizing equipment efficiency.
Testing showed that Honeywell electronic thermostats outperform the competition. Honeywell thermostats did a superior job
of providing tight and consistent temperature control under a variety of load conditions in both heating and cooling.
Knowing the differences in electronic thermostat performance can help you better serve your residential customers with
thermostats that deliver the best comfort, while optimizing equipment efficiency.
9 50-8935
Temperature Control Performance
*Temperature Temperature Droop
Swing 20%-80%
F C F C F C
0.5 0.3 70 21 20%
0.5 0.3 0.1 0.1 70 21 50%
0.4 0.2 70 21 80%
0.5 0.3 78 26 20%
0.5 0.3 0.1 0.1 78 26 50%
0.5 0.3 78 26 80%
0.4 0.2 70 21 20%
0.4 0.2 0.1 0.1 70 21 50%
0.4 0.2 70 21 80%
0.5 0.3 78 26 20%
0.5 0.3 0.2 0.1 78 26 50%
0.5 0.3 78 26 80%
0.5 0.3 70 21 20%
0.4 0.2 0.0 0.0 70 21 50%
0.5 0.3 70 21 80%
0.5 0.3 78 26 20%
0.5 0.3 0.2 0.1 78 26 50%
0.5 0.3 78 26 80%
1.0 0.6 70 21 20%
0.7 0.4 0.4 0.2 70 21 50%
1.0 0.6 70 21 80%
1.2 0.7 78 26 20%
1.9 1.1 0.3 0.2 78 26 50%
1.3 0.7 78 26 80%
0.9 0.5 70 21 20%
0.7 0.4 0.4 0.2 70 21 50%
1.0 0.6 70 21 80%
1.3 0.7 78 26 20%
1.9 1.1 0.1 0.1 78 26 50%
1.4 0.8 78 26 80%
2.3 1.3 70 21 20%
2.5 1.4 0.9 0.5 70 21 50%
2.1 1.2 70 21 80%
3.1 1.7 78 26 20%
3.1 1.7 0.5 0.3 78 26 50%
3.0 1.7 78 26 80%
Temperature Control Performance
*Temperature Temperature Droop
Swing 20%-80%
F C F C F C
2.1 1.2 70 21 20%
2.4 1.3 1.6 0.9 70 21 50%
2.4 1.3 70 21 80%
1.3 0.7 78 26 20%
1.5 0.8 0.1 0.1 78 26 50%
1.5 0.8 78 26 80%
1.9 1.1 70 21 20%
1.9 1.1 1.3 0.7 70 21 50%
1.8 1.0 70 21 80%
3.1 1.7 78 26 20%
3.2 1.8 0.2 0.1 78 26 50%
3.1 1.7 78 26 80%
2.3 1.3 70 21 20%
2.5 1.4 1.2 0.7 70 21 50%
2.4 1.3 70 21 80%
4.2 2.3 78 26 20%
4.4 2.4 1.0 0.6 78 26 50%
4.3 2.4 78 26 80%
3.0 1.7 70 21 20%
3.7 2.1 0.3 0.2 70 21 50%
3.0 1.7 70 21 80%
3.1 1.7 78 26 20%
3.3 1.8 0.2 0.1 78 26 50%
2.9 1.6 78 26 80%
3.4 1.9 70 21 20%
4.1 2.3 0.5 0.3 70 21 50%
3.9 2.2 70 21 80%
3.3 1.8 78 26 20%
3.9 2.2 0.3 0.2 78 26 50%
3.6 2.0 78 26 80%
3.1 1.7 70 21 20%
3.4 1.9 1.1 0.6 70 21 50%
3.3 1.8 70 21 80%
6.5 3.6 78 26 20%
6.7 3.7 1.4 0.8 78 26 50%
6.3 3.5 78 26 80%
Honeywell T8600 Chronotherm® IV Plus-Cool Mode
Honeywell T8001-Heat Mode
Honeywell T8001-Cool Mode
Honeywell T8112-Heat Mode
Honeywell T8112-Cool Mode
White-Rodgers 1F78-151-Heat Mode
White-Rodgers 1F78-151-Cool Mode
White-Rodgers 1F78-144-Heat Mode
White-Rodgers 1F78-144-Cool Mode
Totaline P374-1500-Heat Mode
Totaline P374-1500-Cool Mode
Totaline P474-1050-Heat Mode
Totaline P474-1050-Cool Mode
Totaline P474-0100-Heat Mode
Totaline P474-0100-Cool Mode
Invensys 9701i-Heat Mode
Invensys 9701i-Cool Mode
Lux PSP511-Heat Mode
Lux PSP511-Cool Mode
Lux TX1500-Heat Mode
Lux TX1500-Cool Mode
Braeburn 5000-Heat Mode
Braeburn 5000-Cool Mode
Load
Conditions
Load
Conditions
Setpoint Setpoint
Honeywell T8600 Chronotherm® IV Plus-Heat Mode
Appendix A: Thermostat Data–Temperature Control Comparison Testing
*Total amount of temperature swing (example 1° F = +/-0.5° F)
50-8935 10
Appendix B: Thermostat Cycling–Heat Mode
Totaline P374-1500 - Heat Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
74.0 (23.3)
73.0 (22.
72.0 (22.2)
71.0 (21.7)
70.0 (21.1)
69.0 (20.6)
68.0 (20.0)
67.0 (19.4)
66.0 (18.9)
65.0 (18.3)
64.0 (17.
63.0 (17.2)
62.0 (16.7)
61.0 (16.1)
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
74.0 (23.3)
73.0 (22.
72.0 (22.2)
71.0 (21.7)
70.0 (21.1)
69.0 (20.6)
68.0 (20.0)
67.0 (19.4)
66.0 (18.9)
65.0 (18.3)
64.0 (17.
63.0 (17.2)
62.0 (16.7)
61.0 (16.1)
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
Honeywell T8001 - Heat Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
74.0 (23.3)
73.0 (22.
72.0 (22.2)
71.0 (21.7)
70.0 (21.1)
69.0 (20.6)
68.0 (20.0)
67.0 (19.4)
66.0 (18.9)
65.0 (18.3)
64.0 (17.
63.0 (17.2)
62.0 (16.7)
61.0 (16.1)
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
Honeywell T8112 - Heat Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
74.0 (23.3)
73.0 (22.
72.0 (22.2)
71.0 (21.7)
70.0 (21.1)
69.0 (20.6)
68.0 (20.0)
67.0 (19.4)
66.0 (18.9)
65.0 (18.3)
64.0 (17.
63.0 (17.2)
62.0 (16.7)
61.0 (16.1)
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
Honeywell T8600 - Heat Mode
White-Rodgers 1F78-144 - Heat Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
74.0 (23.3)
73.0 (22.
72.0 (22.2)
71.0 (21.7)
70.0 (21.1)
69.0 (20.6)
68.0 (20.0)
67.0 (19.4)
66.0 (18.9)
65.0 (18.3)
64.0 (17.
63.0 (17.2)
62.0 (16.7)
61.0 (16.1)
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
White-Rodgers 1F78-151 - Heat Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
74.0 (23.3)
73.0 (22.
72.0 (22.2)
71.0 (21.7)
70.0 (21.1)
69.0 (20.6)
68.0 (20.0)
67.0 (19.4)
66.0 (18.9)
65.0 (18.3)
64.0 (17.
63.0 (17.2)
62.0 (16.7)
61.0 (16.1)
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
11 50-8935
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
74.0 (23.3)
73.0 (22.
72.0 (22.2)
71.0 (21.7)
70.0 (21.1)
69.0 (20.6)
68.0 (20.0)
67.0 (19.4)
66.0 (18.9)
65.0 (18.3)
64.0 (17.
63.0 (17.2)
62.0 (16.7)
61.0 (16.1)
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
Invensys 9701i - Heat Mode
Totaline P474-0100 - Heat Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
74.0 (23.3)
73.0 (22.
72.0 (22.2)
71.0 (21.7)
70.0 (21.1)
69.0 (20.6)
68.0 (20.0)
67.0 (19.4)
66.0 (18.9)
65.0 (18.3)
64.0 (17.
63.0 (17.2)
62.0 (16.7)
61.0 (16.1)
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
Totaline P474-1050 - Heat Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
74.0 (23.3)
73.0 (22.
72.0 (22.2)
71.0 (21.7)
70.0 (21.1)
69.0 (20.6)
68.0 (20.0)
67.0 (19.4)
66.0 (18.9)
65.0 (18.3)
64.0 (17.
63.0 (17.2)
62.0 (16.7)
61.0 (16.1)
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
74.0 (23.3)
73.0 (22.
72.0 (22.2)
71.0 (21.7)
70.0 (21.1)
69.0 (20.6)
68.0 (20.0)
67.0 (19.4)
66.0 (18.9)
65.0 (18.3)
64.0 (17.
63.0 (17.2)
62.0 (16.7)
61.0 (16.1)
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
Braeburn 5000 - Heat Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
74.0 (23.3)
73.0 (22.
72.0 (22.2)
71.0 (21.7)
70.0 (21.1)
69.0 (20.6)
68.0 (20.0)
67.0 (19.4)
66.0 (18.9)
65.0 (18.3)
64.0 (17.
63.0 (17.2)
62.0 (16.7)
61.0 (16.1) Temperature F
(
C)
2 degree
comfort band
20% load 50% load 80% load
Lux PSP511 - Heat Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
74.0 (23.3)
73.0 (22.
72.0 (22.2)
71.0 (21.7)
70.0 (21.1)
69.0 (20.6)
68.0 (20.0)
67.0 (19.4)
66.0 (18.9)
65.0 (18.3)
64.0 (17.
63.0 (17.2)
62.0 (16.7)
61.0 (16.1)
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
Lux TX 1500 - Heat Mode
Appendix B: Thermostat Cycling–Heat Mode continued
50-8935 12
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
86.0 (30.0)
85.0 (29.4)
84.0 (28.9)
83.0 (28.3)
82.0 (27.
81.0 (27.2)
80.0 (26.7)
79.0 (26.1)
78.0 (25.6)
77.0 (25.0)
76.0 (24.4)
75.0 (23.9)
74.0 (23.3)
73.0 (22.
Temperature F (C)
Setpoint
2 degree
comfort band
20% load 50% load 80% load
Honeywell T8001 - Cool Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
86.0 (30.0)
85.0 (29.4)
84.0 (28.9)
83.0 (28.3)
82.0 (27.
81.0 (27.2)
80.0 (26.7)
79.0 (26.1)
78.0 (25.6)
77.0 (25.0)
76.0 (24.4)
75.0 (23.9)
74.0 (23.3)
73.0 (22.
Temperature F (C)
Setpoint
2 degree
comfort band
20% load 50% load 80% load
Honeywell T8112 - Cool Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
86.0 (30.0)
85.0 (29.4)
84.0 (28.9)
83.0 (28.3)
82.0 (27.
81.0 (27.2)
80.0 (26.7)
79.0 (26.1)
78.0 (25.6)
77.0 (25.0)
76.0 (24.4)
75.0 (23.9)
74.0 (23.3)
73.0 (22.
Temperature F (C)
Setpoint
2 degree
comfort band
20% load 50% load 80% load
Honeywell T8600 - Cool Mode
White-Rodgers 1F78-144 - Cool Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
86.0 (30.0)
85.0 (29.4)
84.0 (28.9)
83.0 (28.3)
82.0 (27.
81.0 (27.2)
80.0 (26.7)
79.0 (26.1)
78.0 (25.6)
77.0 (25.0)
76.0 (24.4)
75.0 (23.9)
74.0 (23.3)
73.0 (22.
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
White-Rodgers 1F78-151 - Cool Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
86.0 (30.0)
85.0 (29.4)
84.0 (28.9)
83.0 (28.3)
82.0 (27.
81.0 (27.2)
80.0 (26.7)
79.0 (26.1)
78.0 (25.6)
77.0 (25.0)
76.0 (24.4)
75.0 (23.9)
74.0 (23.3)
73.0 (22.
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
Totaline P374-1500 - Cool Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
86.0 (30.0)
85.0 (29.4)
84.0 (28.9)
83.0 (28.3)
82.0 (27.
81.0 (27.2)
80.0 (26.7)
79.0 (26.1)
78.0 (25.6)
77.0 (25.0)
76.0 (24.4)
75.0 (23.9)
74.0 (23.3)
73.0 (22.
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
Appendix B: Thermostat Cycling–Cool Mode
13 50-8935
Totaline P474-0100 - Cool Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
86.0 (30.0)
85.0 (29.4)
84.0 (28.9)
83.0 (28.3)
82.0 (27.
81.0 (27.2)
80.0 (26.7)
79.0 (26.1)
78.0 (25.6)
77.0 (25.0)
76.0 (24.4)
75.0 (23.9)
74.0 (23.3)
73.0 (22.
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
Totaline P474-1050 - Cool Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
Setpoint
86.0 (30.0)
85.0 (29.4)
84.0 (28.9)
83.0 (28.3)
82.0 (27.
81.0 (27.2)
80.0 (26.7)
79.0 (26.1)
78.0 (25.6)
77.0 (25.0)
76.0 (24.4)
75.0 (23.9)
74.0 (23.3)
73.0 (22.
Temperature F (C)
2 degree
comfort band
20% load 50% load 80% load
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
86.0 (30.0)
85.0 (29.4)
84.0 (28.9)
83.0 (28.3)
82.0 (27.
81.0 (27.2)
80.0 (26.7)
79.0 (26.1)
78.0 (25.6)
77.0 (25.0)
76.0 (24.4)
75.0 (23.9)
74.0 (23.3)
73.0 (22.
Temperature F (C)
Setpoint
2 degree
comfort band
20% load 50% load 80% load
Braeburn 5000 - Cool Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
86.0 (30.0)
85.0 (29.4)
84.0 (28.9)
83.0 (28.3)
82.0 (27.
81.0 (27.2)
80.0 (26.7)
79.0 (26.1)
78.0 (25.6)
77.0 (25.0)
76.0 (24.4)
75.0 (23.9)
74.0 (23.3)
73.0 (22.
Temperature F (C)
Setpoint
2 degree
comfort band
20% load 50% load 80% load
Lux TX1500 - Cool Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
86.0 (30.0)
85.0 (29.4)
84.0 (28.9)
83.0 (28.3)
82.0 (27.
81.0 (27.2)
80.0 (26.7)
79.0 (26.1)
78.0 (25.6)
77.0 (25.0)
76.0 (24.4)
75.0 (23.9)
74.0 (23.3)
73.0 (22.
Temperature F (C)
Setpoint
2 degree
comfort band
20% load 50% load 80% load
Lux PSP511 - Cool Mode
Time (hours)
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0
86.0 (30.0)
85.0 (29.4)
84.0 (28.9)
83.0 (28.3)
82.0 (27.
81.0 (27.2)
80.0 (26.7)
79.0 (26.1)
78.0 (25.6)
77.0 (25.0)
76.0 (24.4)
75.0 (23.9)
74.0 (23.3)
73.0 (22.
Temperature F (C)
Setpoint
2 degree
comfort band
20% load 50% load 80% load
Invensys 9701i - Cool Mode
Appendix B: Thermostat Cycling–Cool Mode continued
50-8935 12/02 RC/PC Printed in the USA
© Honeywell 2002 All rights reserved
Printed on recycled paper containing 40%
preconsumer waste and 10% postconsumer waste. www.honeywell.com/yourhome
Automation and Control Solutions
In the US: Honeywell, 1985 Douglas Drive North, Golden Valley, MN 55422-3992
In Canada: Honeywell Limited, 35 Dynamic Drive, Toronto, Ontario M1V 4Z9

[Lorne]

Thanks for the detailed heads up.
It might well be worth the money to keep from getting up to change the thermostat when it gets too cold, only to find it was a hairs breath away from turning it's self down.