Where to start with HVAC?

[tritium6]

I'm starting electrical in my build and will tackle low voltage next. What should I consider for HVAC automation? I don't know much about the subject yet.  I think I've read about systems that have multiple temperature sensors that communicate back to a central location. What kind of wiring goes between the sensors and the thermostat, or is it wireless? What kind of wiring goes between the thermostat and the furnace?
 
I don't have much money to spend on this now, so my plan is to get the wiring in place now to support upgradeability. I plan to be in this house for a few decades. Any pointers on how to start thinking about this, what options are available or online learning resources are much appreciated. Thanks!

 

[drvnbysound]

What is it that you want to accomplish?
 
You mention temperature sensors. How large is the home? Are you having a multiple zone system installed?

 

[NeverDie]

If you want to build a multi-zone system, you could at least run the thermostat wires now so that they're there behind the walls and available for later use somewhere down the road.

 

[LarrylLix]

Run a few empty conduit pipes from the basement ceiling to the attic.
 
If it is a two story drill joist holes from top to bottom in a few places and run good pull strings in them tied at each end.
 
Run at least 12 conductors from furnace area to thermostat area and a CAT 6 to common network area.
 
Home automation is usually done wireless. HVAC is usually wired for reliability and cheapness.

 

[pete_c]

I think I've read about systems that have multiple temperature sensors that communicate back to a central location.

 
Here utilize a Leviton HAI OPII panel with a wired RS-232 Omnistat (Thermostat).  The Leviton HAI OPII panel is considered one "mothership" in the home which takes care of security, lighting, audio and HVAC.  The touch screen consoles to the "mothership" can adjust the thermostat from anywhere there is a console.
 
The panel has multiple temperature and temperature/humidity sensors connected to it.
 
The Omnistat models work in wired or wireless mode.  If you running wires then take advantage of the wired thermostat. 
 
You can also divide up your home into multiple heating and cooling zones as mentioned above.
 
Here I have only one thermostat.  One catXX cable goes to the controller and a multiple wire bundle goes to the furnace.
 
WIth the Leviton HAI thermostat; you can wire remote temperature sensors right to the thermostat and adjust it based on one or more external temperature sensors or averaging them.
 

 
The HVAC automation realms are changing every day. 
 
I mentioned only what I have; but the choices today are endless.
 
Honeywell's new system even handles the rest of your home automation and talks and uses voice recognition.
 
Take advantage of the wiring today.  Wiring before walls are up is relatively inexpensive. 
 
The automation pieces (hardware or software) can be looked at with granularity and time. 
 
The wiring pieces typically are short time frames and will always be beneficial and typically inexpensive.

 

[wkearney99]

This is perhaps better posed to an HVAC pro.  Because where things get placed has more to do with actual functionality and NOT appearance.  While it may be pretty to install a thermostat at one location, that might be a horrible choice based on duct and airflow patterns.
 
I've got Honeywell Vision Pro thermostats.  They're capable of using a remote thermometer wirelessly (and also an outside thermometer).  This we used to overcome an unanticipated problem with afternoon sun hitting the installed thermostat location.  That and there's a wireless bridge to wired ethernet that allows IOS & Android app control.  They're actually pretty smart in that they learn the necessary run-up time to bring a given zone TO the setpoint temperature.  As in, if you call for 75F at a location, and it takes 30 minutes to get there, the thermostat will kick in that half-hour beforehand.  That and their vacation mode can be set by date and time, both for departure and return. 
 
That said I also pulled a CAT5E line to each thermostat location, 'just in case'.
 
I passed on the voice recog stuff, mainly because it's really a rather pointless gimmick.  Once you learn your patterns you really don't see much benefit in screwing around with it manually (or by voice).  With the exception of temporary holds and vacation there's no need for much other control.

 

[Del91574]

If you want the cat's meow and can support the infrastructure, the best is to run VAV's and a bacnet controller with appropriate sensing and control functionality, but that's going to be overkill and expensive, not to mention difficult to interface with HA equipment....building automation has been around for years and all you need is the appropriate hardware for I/O and sensing and the server can take over the rest.
 
Basic anticipation type controls and monitoring the outside ambient, load and inside does exist but you need to determine if the control portion justifies the means and end result.

 

[tritium6]

What is it that you want to accomplish?
 
You mention temperature sensors. How large is the home? Are you having a multiple zone system installed?

 
I want to pre-wire in an intelligent way that allows for taking advantage of whatever features exist today and are likely to appear soon. I don't know what most of those features are, so I am looking for input. 2 features I want are 1) the ability to control the thermostat via software, like the Nest API and 2) remote temperature sensors.
 
The home is 3600 feet - 2400 downstairs and 1200 upstairs. There are 2 furnace units and 2 A/C condensers, one for upstairs, one for down. The upstairs has 2 zones, the downstairs has 3 zones.
 
Is the normal situation to have 1 thermostat per zone? That thermostat functions as both the control system as well as the temperature sensor, right? Which is why you'd put it in an appropriate place given sunlight and airflow consideration. However it seems more convenient to separate the control and temp sensor components so you can put the controls wherever you want. That's my understanding of the remote temperature system. Does this type of system require multiple thermostats (1 per zone or per furnace)? 
 
My light controls (radiora dimmers) are in my AV closet along with my other home-run systems. Does it make sense to run the thermostats to this central location if I have remote temperature sensors? Can someone point me to a remote temperature sensor for sale online?
 
Thanks a bunch.

 

[pvrfan]

I don't want to highjack your thread, but what is the advantage of having two HVAC systems?  Seems to me that 3,600 sf isn't that big and two systems are going to cost more than one.  They are forced-air, central heating/cooling systems (natural gas,  heating oil, propane?) with ducting, right?  With appropriate size ducting, a few dampers and adjustable registers, it is easy enough to get balanced airflow throughout my house.  What climate zone are you in?
 
Craig

 

[wkearney99]

There's little point in having more than one thermostat per zone.  Because a zone is only going to act as an individual element.  More than one thermostat won't 'do anything'.  More often than not adding a thermostat to a zone overrides whatever other one might have already been present.  We did that for our setup.  There's now a remote thermostat in a better location to allow for more balanced temperature overall.  The thermostat specifically recognizes the added one as an override and ignores the in-built one.
 
If you want more fine-grained temperature control then you usually need additional zones.  These need not be additional climate units but typically just in-line dampers branching off the main duct trunk.  We have a unit in the basement that has two such trunks; one for the home theater and the other for the rest of the basement.  Either unit can 'call for' conditioning and the air handler will come on and open only the damper leading toward that zone.  There's typically a zone control unit in-between the thermostats and the climate unit.  But the ductwork needs to be engineered to work properly.  As in, there needs to be a return from within each zone; not just one main return.  
 
Again, climate management within the house DOES NOT BENEFIT from people laying hands on the controls for it.  Being able to "control it" manually is NOT a smart way to look at it.  Sometimes it's helpful to NOT have controls readily accessible, if just for behavior modification...

 

[wkearney99]

There's little point in having more than one thermostat per zone.  Because a zone is only going to act as an individual element.  More than one thermostat won't 'do anything'.  More often than not adding a thermostat to a zone overrides whatever other one might have already been present.  We did that for our setup.  There's now a remote thermostat in a better location to allow for more balanced temperature overall.  The thermostat specifically recognizes the added one as an override and ignores the in-built one.
 
If you want more fine-grained temperature control then you usually need additional zones.  These need not be additional climate units but typically just in-line dampers branching off the main duct trunk.  We have a unit in the basement that has two such trunks; one for the home theater and the other for the rest of the basement.  Either unit can 'call for' conditioning and the air handler will come on and open only the damper leading toward that zone.  There's typically a zone control unit in-between the thermostats and the climate unit.  But the ductwork needs to be engineered to work properly.  As in, there needs to be a return from within each zone; not just one main return.  
 
Again, climate management within the house DOES NOT BENEFIT from people laying hands on the controls for it.  Being able to "control it" manually is NOT a smart way to look at it.  Sometimes it's helpful to NOT have controls readily accessible, if just for behavior modification...

 

[wkearney99]

I don't want to highjack your thread, but what is the advantage of having two HVAC systems?  Seems to me that 3,600 sf isn't that big and two systems are going to cost more than one.  They are forced-air, central heating/cooling systems (natural gas,  heating oil, propane?) with ducting, right?  With appropriate size ducting, a few dampers and adjustable registers, it is easy enough to get balanced airflow throughout my house.  What climate zone are you in?

 
One downside to a larger single unit is greater duct sizes, longer lengths and the possibility of more noise from them.  That and reduced efficiency.  I'm sure there's more to it, but HVAC isn't my area. 

 

[NeverDie]

I don't want to highjack your thread, but what is the advantage of having two HVAC systems?  Seems to me that 3,600 sf isn't that big and two systems are going to cost more than one.  They are forced-air, central heating/cooling systems (natural gas,  heating oil, propane?) with ducting, right?  With appropriate size ducting, a few dampers and adjustable registers, it is easy enough to get balanced airflow throughout my house.  What climate zone are you in?
 
Craig

At least in Texas, I'd say it's completely normal for a 3,600sf house to have two HVAC systems.  I think part of the reason is that 5-tons is the natural breakpoint for high-end tonnage, and you need more than 5 tons to quickly cool 3,600sf.  It probably doesn't get as hot in Canada, so maybe the load calculations give a different answer for there.

 

[tritium6]

I don't want to highjack your thread, but what is the advantage of having two HVAC systems?  Seems to me that 3,600 sf isn't that big and two systems are going to cost more than one.  They are forced-air, central heating/cooling systems (natural gas,  heating oil, propane?) with ducting, right?  With appropriate size ducting, a few dampers and adjustable registers, it is easy enough to get balanced airflow throughout my house.  What climate zone are you in?
 
Craig

The home is a remodel that went down to the studs. The plan was to keep the ductwork and furnace for the ground floor in place. I'm not prepared to change that much of the HVAC system at this late stage, but there is still time to tweak the control system.

 

[wkearney99]

Ok, so you're *very* confident in how the HVAC contractor engineered the setup to take into account the renovation?  
 
Too late and wrong just means more money and hassles later, instead of at the present.
 
We've got an AC line running up from the basement geothermal unit up to the attic air handler.  It's inside spray-foamed insulation in an exterior wall.  I was unsure about the routing of the line but let them set it up that way.  Last winter that line would tick-tick-tick inside the wall, but only when the heat was running.  But not always and not during the hotter months when used for AC.  So now I'm waiting until winter returns to repeat the symptoms.  If it does that again I'll have to pull apart of ton of drywall and abandon a lot of copper tubing to re-run it down along a basement ceiling bulkhead and up in through an interior closet.  So trust me, it's FAR better to cause delays DURING construction than after...