Is HVAC Control Possible With Logic (aka replacing 5070's with a SHAC)

Hi All,

Is it possible to emulate the functionality of the old 5070xxxx style thermostats using a mixture of PLC's (eg: SHAC), I/O, and Temperature sensors to manage a multizone (dampers) central A/C through the units standard 5 wire RWG control interface, or am I missing something fundamentally (happens more often than I would like) ?

It is not clear to me if there is a replacement for the 5070 series in the pipeline that is compatible with C-Bus but the OEM for my multizone heading and cooling system is stuck in 1992, and are still busy patting themselves on the back about their 7 day programmable thermostats and are unlikely to add any modern functionality in the near/mid future.

My initial thought was to use some IP logic to integrate with a NEST/EcoBee system but they lack the ability to integrate with dampening systems (at least without some Nest Pro voodoo). My goal then would be to use something like a SHAC to control some logic to create a HVAC interface to manage multiple NEST inputs to a compatible RWG setup with damper control or alternatively use the still available wall temperature sensors and eDLT's for inputs and again manage the RWG/Dampers via something like a low voltage free relay. It seems to me that it would be a relatively straight forward process to replace the 5070 with a SHAC if using their external relay/HVAC interface topology?

Not sure if anyone has done something like this already, it would be great to hear if anyone has. Alternatively, am I missing anything here in my thinking, that is to replace the 5070xxxxx's "brain with something like a SHAC and continue the use of external relays / and inputs to provide the HVAC interface and damper control.

Thanks in advance.

 

Yes, I have done this on several multi zone jobs, the fleability of the logic and the screen design on the Shac/nac make almost anything possible. I use the cbus temp sensors and relays etc

 

I'm hoping to use a NAC to control my AC units and dampers also.

@Laurence: I'd be interested to know what you think about using variable damper actuators? They are available with 0-10v signal input so I guess could be used with a L5504AMP?

With a little logic this should allow some degree of temperature variation between zones.

 

Thank you, Laurence. I appreciate you validating the concept. I appreciate you have put allot of work into developing your solution so I don't expect a free copy of the solution but are there any hidden catches someone undertaking this kind of project should be aware of, eg: Lockout/purge timers when switching modes?

PS: Great to see your wiser app on the app store and the Saturn style iPad housings look great!

 

you a quick one, I will try and reply in more detail later.
re catches
for me one of the biggest things, not really a SHAC thing , but was to use change over relays, so thing such a fan low med high etc could only have one operational at a time, I know it can be done in logic, but to have physical lockout , I feel a lot safer.

 

I hear what you are saying loud and clear about the physical lockout's. Logic is great until it is something important where I trust physics over my software (or anyone else's for that matter) any day of the week. Plus I figured if it was straight forward everyone would be doing it.

Will really look forward to any further details, but only when you have the time.