Originally posted by jacob perkins
Yes the temperture of the cooling coil will vary based on indoor and outdoor tempertures.Same with heatpump.
Originally posted by knightofoldcode
I didn't realize that the temperature in the main duct can change. I thought the unit made it cool to 40F, (Or whatever is common, I dont' know!) and that it stayed there unless it was heating. Is the temp supposed to change, or does it only change when the zoning system is stressing the HVAC system? Also, how do I know when the temp is getting too cold (AC) or hot (Heat), and what actions should be taken when it gets too cold or hot, other than opening dampers to increase airflow?
Furnace(gas or electric) is more constant but will also vary based on indoor temps...
Your heating/cooling equipment will have safties built in to prevent dangers,and maybe to prevent breakdowns.You could try your local library to find a book to help understand the wirng diagram on your furnace and its sequence of operation.Post your make/model numbers.
You know more than me on the "zoning",but I will read along and share what I do know.
I'd like to ask a question though. If I make certain to have at least 2 zones open at any time, and two zones are determined to have enough CFM to allow the system to operate correctly, then so long as I maintain that 2 zones be open at any time, I should be safe and not need a LAT.
I do NOT know the correct values, however if for example the unit puts out 500 CFM, and each duct can handle 250 CFM, then so long as I make sure that two zones are open, then I'd be fine, and it would (from a pressure and duct temp view) be the same as if it was controlled by a central thermostat, correct? I know this CFM value is very low for real life, but just an example. My HVAC tech knew about the zoning and that I was going to be zoning it myself, and he ran all 12 or 14 inch ducting to every zone, then told me that so long as I had two zones open at any time, I'd be safe.
OK then, You should really put a thermister in your air stream to measure the air temperature and cycle the furnace/ and or condensing unit if needed. This is what most zoning boards do. They check the air temperature in the cooling and heating mode and if the temps go over or under a set point then they shut down the heat or cooling source while leaving the blower running. You then have to allow for the 5 minute short cycle delay. If the ductwork was sized right this should be a non-issue and this control is really just a safety. You could also set this control to open up extra dampers when your temperature gets within a range near the setpoint. IE: your high limit is set at 130 degrees for heating. So when you get to 120 you open up extra dampers. If the temp still continues to climb you shut off the burner. These temperatures are just an example.
Look at http://www.ewccontrols.com/ultrazone/bmplus_3000.htm. You will find some zoning boards there along with schematics for those boards. They also list manuals which have sequence of operations, temperatures and time-delays.
Still need a LAT, incase a damper fails in the closed position .
Example, your furnace needs 1000cfm, 2 zones open equal 1000cfm. One fails to open, now you have a 500cfm duct moving 650cfm, and an overheated heat exchanger.
You know, there are commercial systems that will do pertty much every thing you want.
You set the temp diff, can check the cfm, return air temp, and leaving air temp, all from the same console.
You don't have to reinvent the wheel.