I would be more than happy to do the testing, if you are willing to be patient with my erratic work travel schedule. I am sometimes away for a week at a time, so turn around would be slow during those times. On the plus side, I am home for long periods of time as well and turn around would be very quick at those times.
It seems a similar methodology would work for the heat/emergency heat switch over. Select a lower temperature for the transfer from heat to emergency heat (say, 25Ā°F), and a higher temp (say 35Ā°F) for transfer back to heat. This would allow an acceptable window in between where either mode works well and prevent constant cycling back and forth when the temperature fluctuates are in this range.
Pacman45, I would also like to try to incorporate a system that would work for people who donāt have an external sensor outside (all optional of course). I was thinking something like, if the heat pump is on, but the temperature doesnāt hit the desired value within a certain amount of time, kick on the EMERG HEAT. Is this a good idea? Keep in mind that this means that EMERG HEAT may kick on while someone is not home. Would that be dangerous? If it is dangerous, I could put in a check that would limit EMERG HEAT to only run if someone is home ā¦ Also, I would imagine that EMERG HEAT coils should only be run for limited stretches of time. Do you know, about how long would be the longest stretch that someone should run, letās say an older, low end EMERG HEAT system (for safety), for? How much cool down time would it need before it could run again? Or does the unit take care of all of that like it does for heating/cooling? If youāre not sure, Iāll see if I can ask an A/C guy ā¦ But I think I remember reading warnings about EMERG HEAT systems somewhere ā¦
What you describe is more of a tactical decision and is how my system works. My thermostat uses two separate algorithms to decide whether or not to activate emergency heat (notice I said activate emergency heat, not switch modes to emergency heatāthereās a difference. Activating emergency heat while still in the normal heat mode applies to that heat cycle only. It is a tactical decision that applies to that particular situation such as when the thermostat set point changes by a significant mode switching from night time to day time programming. The algorithms are run each time the thermostat recognizes a call for heat).
The first algorithm is a comparison between the current indoor temp and the set point. If they differ by more than 2Ā°, emergency heat is called for.
The second algorithm is a measurement of the heat rise rate, as you proposed for your app. If emergency heat was not called for on the basis of the first algorithm, the heat pump kicks in and the system measures how long it takes to register a small heat rise (exact amount uncertain, but say 0.5Ā° in two minutes for example). If that minimum heat rise does not occur in the measurement period, the emergency heat is activated.
I would think having an external program making these types of tactical decisions would add complexity and possible conflicts to the decision making process and have unintended undesirable results, such as switching to emergency heat mode unnecessarily when all that was required was a one time emergency heat activation to bring temperature up from the night time program set point to the day time set point. Once that initial warm up occurred, remaining in normal heat mode would be fine, but if an external app switched the thermostat to emergency heat, now your system is locked into external heat for the day or foreseeable future until another set of conditions were met.
I guess what Iām saying is that because there is a lot of diversity in how heat systems make this emergency heat activation decision, it might not necessarily be dangerous, but it would at least be inefficient to have another process making similar decisions.
Thermostat systems that use an external temperature sensor are more efficient because they have factual evidence to make a mode switching decision versus a one-time mode activation decision. Thatās why I thought the ability to have Thermostat Manager access a smart sensor placed outdoors, or optionally collect a GPS adjusted outdoor temperature from the cloud somewhere (my weather channel app displays my local temperature with surprising accuracy), Thermostat Manager could then make this strategic decision to switch the modes. Your methodology employed with the heat/cool decision would work well if outside temperature could be sourced.
Matthew,
Iām in a new house with heat pump. How do you find out detailed info about how the system handles emergency heat?
(Sorry for tangent)
Jmarkwell,
I donāt want to force heating or cooling on. This time of year, we can have day temps of 80s and night temps of 50s. My thermostats donāt have any ability to change between heat and cool mode. So if we go to bed with heat off, it can get quite chilly in the house, and similarly can get very stuffy if cooling isnāt on during the day.
Iād like to be able to change modes based on outside temperature. The thermostatsā setpoints would control activating. Mine maintain separate heating and cooling setpoints and schedules.
Iām open to helping you test multi-thermostat code.
Also, FWIW, the thermostats are reporting outdoor temperature (āoutdoorTemperatureā) and humidity (āoutdoorHumidityā)
āHal
Pacman45,
Thanks for the details. I agree with you. If it is common that this kind of decision is made by the thermostat, it could be problematic to try to compete with it. This makes my task easier. Iāll let you know as soon as I have a working prototype.
Well this is what Thermostat Manager is primarily designed for. To change the modes for you. If the temp falls below a threshold or rises above a threshold then it will change modes. Maybe Iām not understanding what youāre asking for ā¦
What would be the purpose of this? To attempt to predict what mode is necessary without having to wait for it to hit a threshold?
Roger that. Iāll set up a test program for you and let you know when it is ready.
A little setback on my end. The Radio Thermostat CT-101 I ordered to incorporate into my ST network would not work with my HVAC in stand alone mode. Iām returning it and considering other options. Although my setup is not too uncommon (single stage heat pump with gas fired water circulated baseboard as emergency/auxiliary heat), the installation and interface with the air handler seems to be non-standard and my old (non-radio) thermostat is an expensive custom programmed unit that works well, but unfortunately canāt be included in my ST.
I read the manual on my Pro T755 thermostat and it gave the basics of the system. I also read the manual on my Ducane 4HP14L to learn about some of the logic built into the controller board of that unit. I must admit the technical details are a bit obscure and perhaps Iām inferring more than I should from what little is revealed there, but it seems to make sense. A two-stage heat pump system might behave differently. Researching both the heat pump and thermostat details is essential to understanding your system.
Thanks. The ownerās manual for my thermostat is pretty uninformative. Perhaps the installerās manual will help. Then Iāve got to find where the builder hid the manuals for the heat pump.
āHal
Yes, I feel like outside temperatures are predictors of whatās going to be needed. For example, we just had a cold front blow thru. The outside temps dropped from 76 to 63 in an hour. Right now, the thermostats are set to cooling mode with setpoint at 74, Thermostat Manager heating threshold is set to 68.
Based on the outside being chilly weāre not going to need to run A/C so Iād like to have the system change over to heat mode where the daytime heating setpoint is 72. As it is, Therm Mgr wonāt flip the system over until I hit 68.
I canāt use a much higher limit for heating threshold in Therm Mgr because we like to cool the bedroom down to 70 at night. Since I have a single system with three thermostats I feel like I need to have all three instances of Therm Mgr use the same thresholds. I donāt want to end up with a mixture of heating and cooling modes.
Perhaps Iām missing somethingā¦ ?
āHal
I use a ZEN thermostat. It is a dumb (no AI) smart (zigbee connectivity) thermostat that looks nice. I donāt like the ones with AI because I like to have 100% control (we make our own software here in the ST community). Iām pretty happy with it. I think the CT-101 is similar just with buttons instead of a touchscreen.
The thing is, we can get the thermostat to switch modes based on your external sensor, we just canāt get the thermostat to kick the air on based on that. As mentioned before, the thermostat will use its own internal thermometer (or its internal thermometer + its remote thermostat thermometers) to decide when to kick on (start blowing hot or cold air). This is where the distinction between thermostat setpoints and Thermostat Manager thresholds is important. If the setpoint on your thermostat is 70, we can put the thermostat into heat mode, but the thermostat wonāt kick on until the temperature falls below 70 at the thermostat itself. Which in essence means that Thermostat Manager didnāt really do anything at all except to prepare for the coming eventuality that the temperature is dropping. This would have happened anyway when the temperature actually does drop. I can only think of a few ways to get what you wantā¦
- Use something that dynamically adjusts thermostat setpoints based on your external sensors (like āKeep Me Cozyā). An app like this will modify setpoints in order to match the demands of your external sensors. Mileage may vary with apps like this, FYI.
- Place one of your remote thermostats outside.
- Use a scheduling system to change the setpoints of your thermometer based on the calendar/time of day. (Keep in mind that Thermostat Managerās heating threshold should be set to a value less than or equal to the thermostatās heating setpoint and Thermostat Managerās cooling threshold should be set to a value greater than or equal to the thermostatās cooling setpoint.)
- Increase your heating threshold a bit.
The system you propose just wonāt work. When I first wrote Thermostat Manager I tried doing this and figured out why it doesnāt work. The remote sensor system in Thermostat Mode Director doesnāt work for this reason. Please correct me if I am misunderstanding your request. I would suggest trying a scheduler of some sort that sets different setpoints for different times of day. There are some good apps out there that can do this for you. And as long as they only change setpoints and donāt set modes, you can still continue to use Thermostat Manager as well.
It can work, but there are possibilities for conflict depending on the settings you choose. For now, let me work on unifying the thermostats and see how that goes.
HalD/Pacman45, just FYI, Iām pretty swamped at work right now so it might be a little while until I can get the test software out to you. But itāll get done.
Pacman45,
Question regarding EMERG HEAT modification: If you were to manually turn on EMERG HEAT, does it stay on indefinitely? Or will your thermostat or AC unit eventually turn it off automatically? Are there any EMERG HEAT systems that can be controlled by thermostat that would just stay on indefinitely like this that you are aware of? I think some of them do, if I remember correctly, the thermostat that came with my house had a EMERG HEAT switch (hardware) and it was an old electronic system. I donāt know how that would have worked because my unit doesnāt have EMERG HEAT but I would assume that the coils would just stay on until I flipped the switch to another position? I donāt want to burn out anybodyās unit ā¦
Just to help my reasoning here, letās say that I built in a toggle to Thermostat Manager that said, āUse EMERG HEAT instead of HEAT modeā. What would happen? Is this a good idea? Why/why not.
Another question ā¦ I did a bit of research on how EMERG HEAT works and all of the articles I read say NOT to use EMERG HEAT unless the heat pump is broken or frozen up ā¦ Are they wrong? Being overly safe? It sounds like the EMERG HEAT coils are fired up automatically by the AC unit once the temperature becomes cold enough ā¦
Yes. Understood. I donāt want/need to force it to on, just change the mode. Some thermostats will automatically change from heat to cool, mine will not.
Let me try a one thermostat example from today:
- System in cool mode
- Cooling setpoint at 74, Therm Mgr cooling threshold at 76
- Heating setpoint at 72, Therm Mgr heating threshold at 68
- Outside temperature 76. Inside temperature at the cooling setpoint of 74.
Cold front blasts thru and outside temperature drops to 63.
With Therm Mgr as-is, Iād have to wait until the house cool to 68 degrees before it would go to heating mode. That puts the house 4 degrees below the setpoint and will trigger the (more expensive) emerg/aux heat.
If I could have Therm Mgr set to heat mode based on the outside temp going below maybe 66, then the house wouldnāt drop below 72 (more or less).
āHal
- Dynamic adjustment of setpoints: hmā¦ maybe. But sounds complicated and prone to race conditions.
- I donāt have remote thermostats. I have a three-zone heat pump system. Zones are master bedroom, living areas, and guest bedrooms. Each zone thermostat cause the airflow to be adjusted for its zone. So if only one zone needs cooling, airflow will be cut off to zones that donāt need it.
- The thermostats have scheduling capability, up to four time segments. I use two, daytime and nighttime. But they only allow setpoints, not mode changes. So warm days needing cooling with cold nights needing heating canāt be automated in the thermostats, I need something that will change the heat/cool mode.
- Maybe. But on warm nights we like the bedroom cooled to 70. So the heating threshold canāt be much higher that 68
For what itās worth, I may be getting totally OCD about this. LOL
Our previous house had non-connected thermostats which could automatically change between heating and cooling. As long as the heating setpoint was a couple degrees below the cooling setpoint they just handled it with minimal intervention.
Ah, work. I remember work. 
Iām retired so totally not in a hurry.
My current thermostat is a Pro 755. It is not compatible with ST. In fact, it is not even a smart thermostat (no radio). Itās modes are: OFF, COOL, HEAT, and EMERG HEAT. The thermostat remains indefinitely on whatever mode is selected. The thermostat is configured for a heat pump and a separate emergency heat system (some heat pumps use an electric resistance coil in the air handler as their auxiliary heat and the heat pump and auxiliary heat together constitute emergency heatāthis powers different terminals on the thermostat than a heat pump and a separate heat system). So in normal HEAT mode, the heat pump is primary and switches to emergency heat temporarily when the gap between actual temperature and setpoint temperature exceeds a certain threshold OR when the heat rise is too shallow. I found out also that there is a parameter in the configuration called MORNING that can be switched ON or OFF. When selected ON, the thermostat will use emergency heat in the morning when transitioning from an overnight low setpoint to a higher day setpoint. There may be other logic nuances that Iām not aware of. However, when I select EMERG HEAT, the heat pump is locked out and only my gas boiler/baseboard heat works.
My attempt to replace this thermostat with a Z-wave thermostat was disappointing. The unit I selected (Radio Thermostat CT-101) did not activate the heat pump or the emergency heat, no matter what combination of terminals I used. Iām looking at trying a Centralite Pearl thermostat, but it does not seem to have a separate EMERG HEAT setting. Iām beginning to think my idea might be limited to a very small subset of thermostats. Iām trying to research other units, but the needed technical detail is difficult to collect.
I think having a toggle to allow the user to decide whether or not they want to run indefinitely in EMERG HEAT mode is a great idea.