I want to replace the standard zone controller and thermostats in my house with zwave devices to be controlled by my Vera. It seems feasible to do by adding temperature sensors to each room and putting relays in line with the zone dampers and compressor controls. I should then be able to program my Vera to only heat/cool rooms that need it. It seems like it would be easier and more flexible than replacing my last two standard thermostats without too much additional cost.
I’m wondering if anyone has done this and/or has a good reason NOT to do this. I’m concerned there might be reliability issues though I haven’t experienced any myself.
It sounds like a good solution to me, but I’m not really an HVAC guy. All I would say is on the subject of reliability: if you make your HVAC functioning dependent on the Vera, just treat your Vera like a “production system” – meaning, if software changes (or power outages) on the Vera could impede its current functions, then you are putting your HVAC system at risk. Systems can be “testing” or “production,” but usually not both at the same time. Just a thought.
I was just thinking of that. A better route might be to hook up the Vera Controller in parallel with the standard controllers. Then let the Vera inhibit the standard controls if it’s operating properly. If it’s not operating properly then the standard controls would allow for normal operation. This way, worst case scenario I’m right where I started.
I did find a document outlining the principles of zoning. I will have to be careful to make sure that any combination of open ducts will maintain a given airflow (~2/3rds the CFM of the HVAC unit’s capacity). Apparently allowing too much or too little airflow will increase wear and tear on the system.
That’s a very important point about making sure you always allow the proper air volume through your dampers. My house has a retrofitted high-velocity A/C system that I dare not add dampers to, because restricting the flow even a little could burn out the blower or worse.
If you were going to make a Vera-based damper control system, one approach would be to add a device variable to every damper switch that indicates the CFM when fully open, and never close the next damper if the total would go below the rated minimum for the system (total the (status on/off * cfm) for all damper switches.)
You can put an energy monitor on the fan motor (Wraps around the power wire for the fan)
The air handlers have a minimum and maximum operating current … which changes as you change the fan speed and load (by opening and closing dampers).
This will protect the fan motor.
In cooling mode there is also a minimum airflow across the coil to make sure you do not send liquid from the evaporator to the compressor. This happens if the coil gets to cold for lack of airflow. Very bad things happen when the Refrigerant compressor tries to compress a liquid … when it’s designed to compress a gas!
There is also another minimum airflow if you have AUX heat panels … You need a minimum amount of air so that you do not over heat the panels and cause a fire!
In general it’s not a good idea to dynamically control a system that was not designed for this.
They now have multi-drop heat pumps … where you put a fan-coil unit in each room, all run as parallel drops from the outside unit. This is designed to allow scaling from 1 to N (Approx 10) drops, and you can run just 1 zone or all N of them.
I like that. Address the problem of burning out the motor by directly measuring the current being passed through it.
My current system has an air capacity of 3300 CFM and is currently split into two zones connected by a staircase (they are not isolated). The fan is either on or off and does not have variable speed settings. From what I have read, the ducts should be designed to pass at least 2/3rds of the air capacity (2200 CFM) into the smallest zone. That means there always needs to be enough enough ducts open to pass 2200 CFM of air to ensure the fan isn’t working too hard and the airflow across the heating/cooling elements will be the same as it is now.
By figuring out how much air each vent will pass and assigning that as a device variable, I should be able to track the amount of expected air flow. This audit with additional protection in the form of current monitoring on the fan motor will be provide two indicators that the system is operating safely within original parameters.
What do you think of adding temperature sensors to the Aux panels and cooling coils? Would that be overkill?
If you put a temperature sensor just down stream of the heat element you can sense both
too cold air (potenial liquid return to outside unit and coil freeze up restricting air-flow even more)
Not less that 25 degF of House Temp would be a good limit.
or too high a temparature (not enough airflow going across the heat source … safety problem!)
No more than 40 defF of House Temp would be a good limit.
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