Need Very Smart Thermostat

I want to create a 3 zone HVAC system out of my regular one zone HVAC system.
However I am not talking about just having 3 thermostats. I only want one thermostat in control of the HVAC system at a time. The controlling thermostat will be determined by the home owner when he presses a momentary switch next to the thermostat he wants to control the HVAC. This same momentary switch will control linear servos (with baffles) to direct the flow of air to that same zone he is in. Basically as I move about the house I just press that momentary switch where I’m at.
This is a big improvement over Nest and all the other smart thermostats. Those smart thermostats do not know which remote thermostat made the call for HVAC and do not have the ability to control the flow of air from the HVAC system.
I need someone to show me how to design this.

Is this an accurate description:
3 thermostats, one in each zone (A,B,C)
3 momentary push buttons, one next to each thermostat.

When a button is pressed, the other thermostats are disconnected from the HVAC system, the current thermostat is connected to the HVAC system and some sort of motorized baffle system will move into the correct position to deliver HVAC to this zone.

That sounds like a pretty ambitious project.

As a start, you will have to figure out how powerful your motor will be to move the baffles. This will determine how beefy your driver will need to be and how much current it will have to supply.

This controller will also need to have a connection to each momentary button so it can detect when one of the buttons has been pressed.

This controller will also have to electrically disconnect the current thermostat and connect the new thermostat to the HVAC system. That will really depend on what type of thermostat and how many wires each has, etc. I believe most thermostats run on 24V so you will need switches capable of handing that.

Do you have the baffle system built yet? I would take that as a starting point, because it is probably the most difficult part.

Duct dampers are the easiest part
Lots of automated dampers available.
Make a dampet sith a shaft spme sheetsheetmetal and an actuator.

But why .make it so manual?
Motion sensors.
Cell phone tracker.
Just set pdiority for where the action is.

Correct, the duct dampers are the easiest part. Lots of automated dampers available. I want it manual because one of the zones is my pool table room. I use that room every other day for 1-2 hours. It is initially very warm in the summer when I first enter it. So I would like to "push a button" to start the cooling without having to be in the room according to the "motion sensors".

ken52:
Correct, the duct dampers are the easiest part. Lots of automated dampers available. I want it manual because one of the zones is my pool table room. I use that room every other day for 1-2 hours. It is initially very warm in the summer when I first enter it. So I would like to "push a button" to start the cooling without having to be in the room according to the "motion sensors".

'smart' would be to know that you intend to go into that room if about an hour... then have it ready for you.

DS18B20 for accurate temperature in a room
BME280 for humidity and temperature.

Read each sensor

Any zone is too hot and any zone is too cool, open the dampers full on one and shut them to minimum on the other.

When you enter a zone, it would go full on to get that to your set-point

If you work it right each zone would be under control all the time.

I would offer that there are lots of tutorials on how to make an Arduino thermostat.
The zone options should also be abundant.

Your override is not hard to add, but it would be wise to get a functioning thermostat operating first.

Dave,

Let me provide a little more background. The whole idea behind this project is to cut down on utility bills. It is not to make every room exactly perfect. Why heat/cool an entire house when you are only in one part of the house at a time. The two HVAC duct dampers are already installed and wired back to a “control board”. Each damper also provides feed back to a “control board” as to how much it is open or closed. You can not close one damper entirely down without causing back pressure problems on the HVAC. The HVAC system only has one speed, FULL on. I just want to redistribute that air flow a little differently based upon were I am in the house. All 3 thermostats with their momentary switches are installed and wired back to a “control board” The only thing I am missing is the “control board”!
I like your idea about using a DS18B20 or BME280. I can think of two problems with that solution. First the wife is going to want to temporary change the set point in a zone from time to time. Example, she cooking on all 4 burners and wants more COOL. Second when I go to bed in the winter time I want the room warmed up before entering but after a couple of hours I want the room to drop way down in temperature (Electric blanket). Thermostats will take care of these situations.
I really have thought this out for some time (what I want) how to do it (not so much). I also have separately wired my HVAC system for a before and after the evaporator coil humidity and temperature probe. This will allow me the ability to check on the efficiency of the unit (maybe its time for more Freon or clean the fins)
So what I need in a “control board” is for it to disengage the current thermostat in control of the HVAC and then engage the one just selected by the momentary switch pressed. And then move the two damper baffles accordingly.

Ken

It sounds like your "control board" will need 3 inputs - one for each of the momentary buttons and then 3 x how ever many thermostat wires there are (4,5,6?). You can probably just use simple transistors to connect/disconnect each of the thermostats. One control wire on the "control board" would go to all the bases of the transistors for a given thermostat.

EDIT: Most systems are 24V AC so transistors would not be an option. Probably better to go with some sort of solid state relay or switch

ken52:
I want to create a 3 zone HVAC system out of my regular one zone HVAC system.
However I am not talking about just having 3 thermostats. I only want one thermostat in control of the HVAC system at a time. The controlling thermostat will be determined by the home owner when he presses a momentary switch next to the thermostat he wants to control the HVAC.

This description seems rather confused to me. It seems to me it is mixing up three separate issues

  • Having a thermostat in different spaces so that the temperature is set locally
  • Having the ability to direct heat to one space rather than another
  • Having a convenient means to tell the system which space is in use

The programming aspects seem straightforward if you have the means to connect the 3 thermostats and the selector switches to a central "computer". You have not told us the distances involved or whether the spaces are on different floors so I have no ide whether it would be practical to connect everything with wires or whether a wireless solution - perhaps with some ESP8266 boards - would be more practical.

The complex question will be the interfacing of the "computer" to the heating system. You have given us no idea what sort of control system already exists, or whether you plan a completely new control system. Nor do we know how the baffles work or where they are controlled from.

You will need to be very careful to ensure that whatever you do meets the requirements of building regulations and your home insurer.

...R

Blh64,

Correct most systems and mine as well is 24V AC. The “control board” will need 3 inputs for the momentary buttons and 3x for the thermostat wires (4). It will also need 2 inputs from the damping baffles to find out the degree of closed/opened. 2 outputs for power to the damping baffles (24V AC) and finally the output to the HVAC (4 wires)

Robin2,

I said everything was WIRED already. There is currently no control system in place. Its just a single zone system like everybody has. The baffle positioning will be controlled by the same “control board” that selects which thermostat to use

ken52:
I said everything was WIRED already.

Sorry, I missed the fact that it is already wired. However I presume there are no existing control wires in the three rooms where you want to put the extended controls.

There is currently no control system in place. Its just a single zone system like everybody has.

Do you mean that there is a single thermostat for the whole building? If it more complex, please explain.

The baffle positioning will be controlled by the same “control board” that selects which thermostat to use

Do you mean that the baffle system will be something new which does not now exist?

I presume you are talking about a warm-air heating system from a central duct at the core of the building? A simple diagram of the proposed layout would be a big help.

How is the existing heater controlled by the existing thermostat? Is the existing thermostat a simple ON/OFF system?

...R

ken52:
So what I need in a “control board” is for it to disengage the current thermostat in control of the HVAC and then engage the one just selected by the momentary switch pressed. And then move the two damper baffles accordingly.

Do you literally want the controller to connect the selected thermostat to the HVAC or do you want the controller to know which one you selected and just read what it's asking and pass it on?

In the latter scenario, the controller runs the HVAC itself, it just gets data from the thermostats to tell it what to do.

I can't quite envisage how it works though. If you go to the pool room and say "I'm here", it now has duct priority, which in the summer apparently means that its thermostat will be screaming for cooling. So HVAC can provide that and you can walk away and get a beer while it works. Or watch your old Ray Reardon videos.

What happens when you're done with pool for the night? You must remember to press the bedroom button? Or the Ray Reardon button? Is there a timeout? What if you want to play pool and your wife needs cooling in the kitchen? Do the two of you have to negotiate or do you slip off to the pool room when she isn't looking and confiscate her cold air?

It seems like it will be annoying to manage. I like the PIR sensors and DS18B20s etc. Your system has the potential for some clever controls, but I fear it will also start a fight among the different thermostats (and you and your wife :o )

Robin2,

The "whole building" is a house. EVERYTHING is already pre wired. The baffle system is in place, uncontrolled, wide open. The thermostats are simple ON/OFF types you buy at Home Depot.

Wildbill,

The latter scenario. No timeouts. No matter what zone has priority all the zones get HVAC. It just that the zone in control get more than usual amount of air flow and the other two zones get less than the usual amount of air flow. In this way the controlling zone reaches set point quicker and the HVAC shuts off sooner and I save on utilities. If two of us want priority and I want a happy life then I loose. Remember I still get HVAC, just not at the max rate. PIR sensors don’t see you under the bed sheets.

Most of what you want seems clear enough. It would help to know more specifically what the thermostats are. I don't know how the dampers tell you what their position is. Potentiometer I expect.

So I would treat it as several distinct learning projects: read and control the dampers, then read the thermostats, maybe choose one and let it pretend to drive the HVAC, then add the buttons to tell you which thermostat is in charge. Then combine it all.

You should be able to build/simulate all this on the bench to test the concept, your code and your wiring. You'll need an Arduino (or other micro controller), an eight count relay board plus power, a breadboard, interconnect wires, buttons, leds and resistors and some pots if my guess about the dampers is right.

I count at least 21 I/O pins and you'll need to leave serial free for debugging, so that rules out the Arduinos like the Nano and the Uno for the finished product. You might want to start with a Nano though while you do your discovery. Be aware that you can destroy components with simple electrical mistakes. I'd buy more than one of whatever micro controller you're going to use for this reason.

WildBill,

Regular 4 wire thermostat.

  1. 24 VAC
  2. Call for heat to come on
  3. Call for Cooling to come on
  4. Call for Fan to come on

Potentiometer is used to determine damper position.

There is a 4th zone. The dead zone. Leaving the house for the day. HVAC off.

I have soldered stereo kits together but never messed with Arduino's or whatever micro controllers. Just what am I up against in a learning curve? Or can I get someone to design it and I'll soldered it together? I have been/am a computer programmer for 40 years so I can learn and write code easy enough.

Ken

A Ds18B20 in each space.
A button in each space.
Push a button and the authority goes to that zone.
New zone damper opens fully other zones go closed

ken52:
The "whole building" is a house. EVERYTHING is already pre wired. The baffle system is in place, uncontrolled, wide open. The thermostats are simple ON/OFF types you buy at Home Depot.

I'm still not clear if there is already a thermostat in each of the three places where you want to control the temperature. If there are then how do they currently interact with each other?

When you say "simple ON/OFF types" I presume that means that the heater is either full on or full off - is that correct. If so it may be possible to control it with a relay. But that might be against building regulations.

I presume you will need to build the machinery to move the baffles - how do you propose to do that? Will the "machinery" need to be in separate rooms or can it all be in one place.

As I said earlier, if you make a simple diagram of the proposed system it would be a big help so we can visualise what you want to do.

...R

a thermosat is nothing more than a temperature sensors and relay contacts.
as you get extra parts, they become more accurate with the bimetal spring
and a heater that will allow for the control logarithm called 'anticipation'. The heater in the thermostat is just a wire that takes time to get hot. it is designed to add the hysteresys that is not possible in a bi-metal spring design.
of course there is a local display.

but at the heart is the temperature sensor and a relay.
the Arduno can make three 'smart' thermostats look dumb in a zone application.

a simple DS18B20 in each space and then either a library or some programming you can balance the load easily.

in this case, the system it not using zone thermostats to ballance the entire space.

so, the existing thermostats have to be ignored and overridden. in orther words, not needed all the time.

The button is really only saying 'this zone' is the master and everything else gets a minimum flow.

so, that means that if the existing thermostats are single home stats, then they are worthless in this application. they only output "need air" or "do not need air". there is no temperature signal.

If they are zone stats then they will open a damper and the when the damper opens, it opens a switch that turns on the fan.
again, digital, not analog. or there is a smart board that looks at the zone temperature and does the logic in a central location. Since this is a retrofit to an existing system, this is probably not the case.

The Arduino with a simple temperature sensor will allow intelegent control of the zones by estimating heat loads in each individual space and also in all spaces.
The operator can decide what is the primary zone, and currently other zones will get spill over to maintain fan volume output at a proper volume for the heating/cooling coils.

as a note the heating/cooling coils are the primary device that is the master. too little air over the coil and it can freeze up, or overheat. both can be dangerous. too much air over and they will be outside of there efficeny zones and cost more to operate.

To balance that the zone damper will have a full open for one zone that gets the majority of the air, the other zone dampers open to provide a way to maintain the total unit CFM to make sure the coils are in their proper range.
if two are open at the same time, then they should be modulated to a lower postion to balance the CFM.
but really, they are balancing the duct pressure. pressure after-all is the basis of flow.

a BME280 in the duct and outside of the duct should be able to determine duct pressure. some fluctuations are normal as things move, coils or filters get dirty, etc. also one BME will be in the cold while the other is in the hot, so each will be in a different environment. lets hope the internal temperature offset is good enough to allow the pressure signals to be accurate.
Once the OP starts with his 'smart control' design, he will see the need to try to control pressure by regulating dampers and may come to find that a variable speed blower will make his overall system truly smart and offer more control.

ken52:
I have soldered stereo kits together but never messed with Arduino's or whatever micro controllers. Just what am I up against in a learning curve? Or can I get someone to design it and I'll soldered it together? I have been/am a computer programmer for 40 years so I can learn and write code easy enough.

If you can code and solder, this shouldn't be hard. Just do the usual software thing and build it a small bite at a time.