Single stage heat, single stage cooling example

Here’s an email I received today along with some explanation on how to do a config file for a single stage heat, single stage cooling example.


Thanks, it’s controlling a single stage gas furnace with single stage dx cooling.
Basically a residential style split system, but they want to monitor discharge air temp. I currently have it wired as:
K com 24 volt positive
K1 fan
K2 cooling
K3 heating
AI 3 discharge air temp I’ll be using a 10k@77 thermistor

So the first step as always is to fill in the names and ragens for the inputs & outputs for the system. Here’s the outputs, give each item a name and set the range up, in this case the default of ON-OFF is fine.

Next configure the inputs, in this case we just have one external temp sensor wired to AI1 which leaves the other seven inputs as spares. We have set it up as a Type2 , 10k thermistor in DegC but you can adjust it to suit.

And next up is the big PID table where all the staging acion takes place.

At Tab1 I have selected the number of modes to be 2, the default name of the modes is Off and Auto which are already filled in and can be adjusted at Tab2. First we select the Auto table at Tab3 and the associated yellow/green spreadsheet pops up below. Each mode gets one of these tables.

At Tab4 we set the number of stages of heat and cool to one each.
At Tab5 this row represents the FAN output and the column Heat1 at Tab6 represents the mode of operation. We have the fan output 1 set to on for both heating and cooling modes. When the system is coasting the fan will be off. The cooling output is in row2 and shows on for the Cool1 column and off for Heat1 column. The heating output is in row3 and shows the opposite, on for Heat1 and off for Cool1.

For the OFF mode, this is the unoccupied mode table, the system can be set to maintain the night (unoccupied) setpoint by enabling the fan and heat like below. Notice that cooling is disabled.
image

Or you could go like this and turn everything off at night. This would be for a milder climate where you dont need to worrry about the building freezing up at night:
image

And finally, set the PID to operate off the return temperature sensor ( I assume) which is wired to input1. I have the P term set to 5 (DegC) which means there will be a full response from 100% heat to 100% cool over a 5DegC band. You could adjust that to around 10 if you’re working in DegF, its not too critical. I always suggest setting the I term to zero till you have finished commissioning becuase the I term and the resulting ‘reset windup’ can give unexpected results. Later you can fill in a small value of 5 or so once the system is ready for handover.

There are a lot of other settings but they are not used for most applications. These quick & basic steps will get you the functionality of a basic single stage heat/ single stage cool thermostat.

Here’s the config file as saved by the T3000 software. You can load this into your own thermostat as a starting point and once you have finished tweaking it, save and load to the other stats on the project.

ConfigFile: 1Heat1Cool.txt (14.3 KB)