Equipment Control Logic

[VVT-C Core Logic] 

Alright, so you understand how to calculate the loop output for VVT-C. Woopie.. All I wanted to do was control a YWG RTU... How did all that help me? 

Glad you were thinking that.. Now we get to talk about the method of using the loop output for controlling the actual equipment. From here it gets pretty easy. The loopOutput is by far the more complicated things to do. 

|1. Fully Modulating Equipment Control

When you think of fully modulating equipment control you should be thinking of an AHU with chilled water coil and hot water coil with a VFD fan. You can also think of advanced RTUs that have intelligent controls built in for DAT resets. 

You know how to calculate the loop output as 0-100%. What you do now is make sure that your loopOutput scales correctly to your make, model, and settings of your on site equipment. You will find some configuration options available for setting the analog output min and max for heating, cooling, and the fan. In this way you will create a simple linear relationship between 0% loop output and your min analog output value and between 100% loop output and your max analog output. 

That's it. Say you have a 2-10Vdc Valve for your cooling, or your AO1 from the CCU. 

0% loopOutput = 2Vdc 
50% loop output = 6Vdc
100% loop output = 10Vdc 

|2. Staged Equipment Control

Staged equipment control is a little trickier to understand how it relates to the loopOuput but just as simple to configure. Let's take a simple RTU to start. This unit has two stages cooling, two stages heating, and a single stage fan. It is going to use a standard configuration as shown below. You'll see we switched our system profile now to VVT-C Staged RTU to limit the available options and reduce confusion. 

Now let's expand on the example we were using before and decide when the relay stages would turn on and off based on the loopOutput. Let's look at the math of a cooling example and then the example. 

stagePercent = loopOutputMax/numberConfiguredCoolingStages

When systemCoolingLoopOuput > 0 Turn on Stage 1 Cooling, when systemCoolingLoopOutput = 0 Turn off Stage 1 Cooling

When systemCoolingLoopOuput > stagePercent*stage Turn on that cooling stage. When systemCoolingLoopOuput <= stagePercent*stage - relayDeactivationHysteresis Turn off that stage. 

Now lets use a 3 mechanical stage cooling + economizer example.. Economizer always acts as the first stage. The relayDeactivationHysteresis = 10

stagePercent = 100/4 = 25%

Economizer On when systemCoolingLoopOuput > 0% (we will get into economizer logic later)
Stage1 On when systemCoolingLoopOuput > 25% and off when systemCoolingLoopOuput <= 25-10
Stage2 On when systemCoolingLoopOuput > 50% and off when systemCoolingLoopOuput <= 50-10
Stage3 On when systemCoolingLoopOuput > 75% and off when systemCoolingLoopOuput <= 75-10

Let's take the same example with no Economizer. Just 3 mechanical stages of cooling. 

stagePercent = 100/3 = 33%

Stage1 On when systemCoolingLoopOuput > 0% and off when systemCoolingLoopOuput =0
Stage2 On when systemCoolingLoopOuput > 33% and off when systemCoolingLoopOuput <= 33-10 Stage3 On when systemCoolingLoopOuput > 66% and off when systemCoolingLoopOuput <= 66-10

Let's take the example as a 2 stage unit.

stagePercent = 100/2 = 50%

Stage1 On when systemCoolingLoopOuput > 0% and off when systemCoolingLoopOuput =0
Stage2 On when systemCoolingLoopOuput > 50% and off when systemCoolingLoopOuput <= 50-10

Now lets take that 2 stage example and look at it graphically. Current Temp is actually your weighted average current temp in a VVT-C system. 

|Fan Loop Output
The Fan output is directly proportional to the loop output of the mode you are in. 

Cooling Mode:
systemFanLoopOutput = systemCoolingLoopOutput*analogFanSpeedMultiplier

Heating Mode: 
systemFanLoopOutput = systemHeatingLoopOutput*analogFanSpeedMultiplier

Fan Stages
Fan stage 1 - Simple. Enables anytime the system is occupied or conditioning. 
Fan stage 2 - Runs when systemFanLoopOutput >0 and Off when systemFanLoopOuput = 0
Fan stage 3- Runs when systemFanLoopOutput > 50% and Off when systemFanLoopOutput <= 50-relayDeactivationHysteresis

|Humidity Control
Humidifier
Humidifier turns on when humidity < targetMinInsideHumidity
Humidifier turns off when humidity > targetMinInsideHumidity + humidityHysteresis

Dehumidifier
Dehumidifier turns on when humidity > targetMaxInsideHumidity
Dehumidifier turns off when humidity < targetMaxInsideHumidity - humidityHysteresis