HVAC Fail/Protect Programming Question

[ldrinc]

I have three Venstar thermostats in my home.  All three have the Insteon Venstar Adapters attached to them.  In the past I have had a situation where my hvac units where failing causing the temperature on the thermostat to rise higher which made the AC unit run non stop.  

 

I would like to put a protect program in the isy to have the TStats turn off if the AC if temperature in the home reaches a certain point in the summer.  Below is my attempt at this programming.

 

Am I on the right track with programming?  Is there anything that you could add/subtract?

If

        Status  'First Floor Thermostat' > Mode Cool

    And Status  'First Floor Thermostat' > 77° (Temperature)


Then

        Set 'First Floor Thermostat' Mode Off

        Send Notification to 'Default' content 'First Floor Thermostat'


Else

   - No Actions - (To add one, press 'Action')

[ISYhbsh01]

 

I have three Venstar thermostats in my home.  All three have the Insteon Venstar Adapters attached to them.  In the past I have had a situation where my hvac units where failing causing the temperature on the thermostat to rise higher which made the AC unit run non stop.  

 

I would like to put a protect program in the isy to have the TStats turn off if the AC if temperature in the home reaches a certain point in the summer.  Below is my attempt at this programming.

 

Am I on the right track with programming?  Is there anything that you could add/subtract?

If
        Status  'First Floor Thermostat' > Mode Cool
    And Status  'First Floor Thermostat' > 77° (Temperature)
 
Then
        Set 'First Floor Thermostat' Mode Off
        Send Notification to 'Default' content 'First Floor Thermostat'
 
Else
   - No Actions - (To add one, press 'Action')
 

 

I would add the following in the if section:

 

        And Status  'First Floor Thermostat' < 77° (Cool Setpoint)

 

This will ensure that the A/C will not be turned off in a case where the reason the temperature is 77 degrees is just because the setpoint was intentionally set to be higher than 77 because you are leaving the house etc. 

[ISYhbsh01]

As I am thinking now about this again, I see that this is not going to work without additional modifications. Imagine the following scenario: You are just walking in to the house now after being away for a few hours. Let’s assume that when you were out the setpoint was set to 80 degrees, or it was off all together, so now the temperature is 80 degrees. You go ahead & set the thermostat to 74. This program is immediately going to run & turn off the A/C.

 

If I will come up with another idea I will post it here.

[paulbates]

I would add a wait statement as the first line. How long does it take HVAC to cool the house within normal operating parameters? 15 minutes, half an hour worst case?

 

If it's sitting in the wait statement, and the temperature drops in the time expected, the program will stop executing.  However, if it goes past the wait, then it will take action

 

Paul

[larryllix]

.... In the past I have had a situation where my hvac units where failing causing the temperature on the thermostat to rise higher which made the AC unit run non stop.  

 

.....

This sounds a little nonsensical. Aren't you basing a protection mechanism on the thermostats system that is failing? It also sounds like the A/C is stuck on and yet you are sensing a high temperature to turn it off.

 

Wouldn't an independant thermostat be in order to protect this from overheating and over cooling? Maybe just a mechanical thermostat in series with the cooling wire for reliable protection against runaway. I would be sure it may be more complicated than first glances.

[ISYhbsh01]

I would add a wait statement as the first line. How long does it take HVAC to cool the house within normal operating parameters? 15 minutes, half an hour worst case?

 

If it's sitting in the wait statement, and the temperature drops in the time expected, the program will stop executing.  However, if it goes past the wait, then it will take action

 

Paul

I was thinking about adding a wait statement. The problem I saw with that approach was that it depends on to many variables making it impossible to come up with an always acceptable wait time. What was the setpoint before that & for how long? How hot is it outside? If the A/C was off long enough on a 95 degree day it might take hours to cool the house down.

 

Let’s take an extreme example: You are away for a week on vacation with the A/C turned off. On the day you fly back its 100 degrees outside at home. Before you get on the plane for the 10 hour trip you turn on the A/C remotely & set the setpoint to 74 expecting your house to be nice & cool when you arrive. However this program will kick in after a wait of an hour or whatever you put in there, and will totally shut off the A/C. 

[ISYhbsh01]

This sounds a little nonsensical. Aren't you basing a protection mechanism on the thermostats system that is failing? It also sounds like the A/C is stuck on and yet you are sensing a high temperature to turn it off.

 

Wouldn't an independant thermostat be in order to protect this from overheating and over cooling? Maybe just a mechanical thermostat in series with the cooling wire for reliable protection against runaway. I would be sure it may be more complicated than first glances.

 

I think what the OP is talking about is a failure with the A/C system not with the thermostat. For example I had last year a Freon gas leak, which caused the A/C system not to cool adequately and I had to do a re-fill of freon. For such a case a program like that, if we can figure one out, would be helpful.

[Teken]

This sounds a little nonsensical. Aren't you basing a protection mechanism on the thermostats system that is failing? It also sounds like the A/C is stuck on and yet you are sensing a high temperature to turn it off.

 

Wouldn't an independant thermostat be in order to protect this from overheating and over cooling? Maybe just a mechanical thermostat in series with the cooling wire for reliable protection against runaway. I would be sure it may be more complicated than first glances.

 

I would second this line of thought unless the OP made a mistake in his presentation of the facts. To me if there is a fault in the TSTAT that issue needs to be identified and resolved.

 

Using a program to compensate for an existing problem is a band aid and will ultimately cause more problems down the road. To the OP what exactly is the problem with the TSTAT and is this problem still an ongoing issue?

 

If its not an issue and you simply want a fail safe program you can carry on . . .

[ldrinc]

I would second this line of thought unless the OP made a mistake in his presentation of the facts. To me if there is a fault in the TSTAT that issue needs to be identified and resolved.

 

Using a program to compensate for an existing problem is a band aid and will ultimately cause more problems down the road. To the OP what exactly is the problem with the TSTAT and is this problem still an ongoing issue?

 

If its not an issue and you simply want a fail safe program you can carry on . . .

 

The TSTAT is located in my vacation home three hundred miles away.  The program that I was suggesting is to prevent further damage (if any) until I can have the unit checked out.  

[ldrinc]

I think what the OP is talking about is a failure with the A/C system not with the thermostat. For example I had last year a Freon gas leak, which caused the A/C system not to cool adequately and I had to do a re-fill of freon. For such a case a program like that, if we can figure one out, would be helpful

 

That is correct.  I am talking about a potential failure of the A/C system not the thermostat in this case.

[stusviews]

Teken is correct. If something is amiss, then that specific item needs to be corrected or replaced. A workaround for a defect is a route for disaster.

[larryllix]

I guess we would need specifics to evaluate the value of using the stat to protect from further damage.

 

How did the A/C unit malfunction? If The A/C unit was running continuously the temperature should have dropped. Maybe a window is in order.

[shannong]

Doesn't seem totally nonsensical.

 

I would suggest you program an "occupancy" function. Create some way to establish "home" vs "away". A variable that tracks when  you're there vs when you're not. Then you could write a simple program that only runs when "away". The assumption being that when you're there you'll notice it's warm even though the system is running and you'd check on it.

 

You could use the status of a light, a KPL button you press, status of an outlet, etc to establish "home". For me, that's that status of my security system.

[larryllix]

The TSTAT is located in my vacation home three hundred miles away.  The program that I was suggesting is to prevent further damage (if any) until I can have the unit checked out.  

Would this be too much of a hardship to just shut the system down when you are away? Sounds like wasted energy and how often do you visit this second home?

 

I would be thinking about a Nest or other remote controlled thermostat that you could activate a few hours before you arrive. I know humidity takes a few days to reduce sometimes. I have gotten caught with my system set back on heating and from 10 C to 22 C takes about 18 hours. We have an electric blanket always standing by for the first night home.