Adding Multi Zone HVAC Control??

[Steve Sullivan]

Hey all,

 

I'm very new to this forum as well as ISY and insteon. In fact I'm in the research phase of automation for my house and have an ISY99 on order with a bunch of Insteon lighting products. I hate economy shipping!

 

This forum seems awesome and I'm impressed with the responsiveness and helpfulness of all participants.

 

I've been trying to figure out what it would take to eventually add different zones to my current heating system. I have forced hot air in a 2 story house plus a basement. There is a single thermostat in the 1st floor hall. The temperature variations between 1st and 2nd floor is pretty significant, worse off are temp variations on each of the 3 bedrooms. We also have a older inefficient fireplace and when it's cranking the upstairs gets freezing.

 

As far as I see it now I could add dampers to create control for different zones. I'd like to cost effectively add thermostats or just temp sensors to different rooms in order to monitor temperatures and adjust the different dampers based on programs running on the ISY99. I see there are a few Venstar thermostats but didn't really see slaves for them. I also saw some RCS zone controllers but wasn't sure if you could interface them with the ISY99.

 

I'm wondering if any of you have done a project like this and what type of hardware/programs you've used.

 

I appreciate the feedback in advance.

 

Thanks,

 

Steve

[IndyMike]

Steve,

 

Welcome to the forum.

 

You've picked a rather complicated task for automation. In my opinion, while your goals can be accomplished, I would not choose any automation technology to implement it.

 

You situation is complex because you have an existing system. Your ductwork, vents, and cold air intakes have all been sized to provide the proper airflow across the heat exchanger in your furnace. If you begin to shut off sections of the ducting via zone controls, you will reach a point where the airflow is insufficient across the heat exchanger and it will overtemp and shut down. At best this is inefficient. At worst you will continually overtemp the exchanger and cause premature failure.

 

This becomes more complex if you have A/C. A/C coils also require a minimum amount of airflow across them to prevent freezing the unit. The problem here is that the cool air is heavy and doesn't want to be pushed to your second floor. Normally a furnace will use a 2-speed blower to overcome the heaviness of the cold air. If you implement a zone system to for more air to the second floor, you risk reducing the airflow below the minimum level. If coil freeze up does occur you can feed liquid freon back to the compressor (outside) and destroy it.

 

Retrofit zoned systems typically include a "barometric bypass" (dump zone). This is essentially a vent that opens when the system is constricted (zones closed) in order to provide enough airflow across the heat exchanger/A frame.

 

Next come the "Zone Control Panel". This dedicated panel interfaces to the multiple thermostats, controls the zone dampers, and monitors the furnace temperatures to prevent over stress. This is the piece of the puzzle that I would not trust to automation.

 

The next step is the thermostats themselves. Here you have the latitude to use HA. For your problem with the fireplace you could use an Insteon compatible thermostat and simply monitor the room temp. When the room rises above a certain temperature (heat mode) turn on the circulating fan to warm the rest of the house. No much, but it will help.

 

Give us some more details on your heating distribution problems. Is the upstairs cold during winter and hot during summer? You may need more insulation in the attic or "tuning" of your existing vents.

 

Sorry for the "downer", but this isn't a simple job.

IM

[Steve Sullivan]

Steve,

 

Welcome to the forum.

 

You've picked a rather complicated task for automation. In my opinion, while your goals can be accomplished, I would not choose any automation technology to implement it.

 

You situation is complex because you have an existing system. Your ductwork, vents, and cold air intakes have all been sized to provide the proper airflow across the heat exchanger in your furnace. If you begin to shut off sections of the ducting via zone controls, you will reach a point where the airflow is insufficient across the heat exchanger and it will overtemp and shut down. At best this is inefficient. At worst you will continually overtemp the exchanger and cause premature failure.

 

This becomes more complex if you have A/C. A/C coils also require a minimum amount of airflow across them to prevent freezing the unit. The problem here is that the cool air is heavy and doesn't want to be pushed to your second floor. Normally a furnace will use a 2-speed blower to overcome the heaviness of the cold air. If you implement a zone system to for more air to the second floor, you risk reducing the airflow below the minimum level. If coil freeze up does occur you can feed liquid freon back to the compressor (outside) and destroy it.

 

Retrofit zoned systems typically include a "barometric bypass" (dump zone). This is essentially a vent that opens when the system is constricted (zones closed) in order to provide enough airflow across the heat exchanger/A frame.

 

Next come the "Zone Control Panel". This dedicated panel interfaces to the multiple thermostats, controls the zone dampers, and monitors the furnace temperatures to prevent over stress. This is the piece of the puzzle that I would not trust to automation.

 

The next step is the thermostats themselves. Here you have the latitude to use HA. For your problem with the fireplace you could use an Insteon compatible thermostat and simply monitor the room temp. When the room rises above a certain temperature (heat mode) turn on the circulating fan to warm the rest of the house. No much, but it will help.

 

Give us some more details on your heating distribution problems. Is the upstairs cold during winter and hot during summer? You may need more insulation in the attic or "tuning" of your existing vents.

 

Sorry for the "downer", but this isn't a simple job.

IM

 

Well I certainly appreciate your detailed response, thank you!

 

These are all good points and I'm glad I asked because I had not considered the flow issues.

 

As far as the system being designed... I really think it was poorly designed and not implemented well at all. For example I have two returns in my living room, these are connected together so there is a vent at the top and one at the bottom and share a single duct in the wall. I've noticed for quite a while they really don't pull any air at all. After investigating this last night I found something interesting. The duct in the wall is supposed to continue to the basement where through a channel using the joists the return continues to the main return trunk. At the section where the wall duct joins the joist duct the wall duct was not cut. This blocked any chance of flow. I made the modification and at least have a return in the living room now.

 

Two of the three bedrooms are typically pretty cold in the winter no matter what I do to tweak the vents. Part of the reason is the path these ducts take going along the exterior sill and routed up exterior walls. The path is just very long.

 

There isn't really any central trunk in the design. Most runs go to exterior walls. As an example there is a return for two of the bedrooms that are next to each other. The path is from the central return in the middle of the basment to a 6 or 7 inch 10 ft long duct that goes up the exterior wall to the second floor, through the floor joists, then up a central wall. Seems really inefficent to me.

 

 

All the walls and the attic are well insulated. There aren't any ducts in the attic at all.

 

My goals wouldn't be to zone all of the areas that are heated, just some of the more difficult ones, so I would think there shouldn't be a lot of restriction.

 

Typically two of the three bedrooms on the 2nd floor are too hot in the summer and too cold in the winter.

 

Bathrooms are fine by adjusting the registers.

 

It's something I'll have to really think about. I appreciate the input though. Overall If I made changes to the system, I guess a independent zone controller is ideal, further than that the HA part could be to just adjust set points.

 

I looked into a GeoThermal heatpump solution to replace the furnace I had to get something more efficent. Using the existing ducts and well the quote was almost 30K. Since I'm not taking that route! I'd like to cost effectively level out the temp variations, in a cool geeky way.

[IndyMike]

 

Two of the three bedrooms are typically pretty cold in the winter no matter what I do to tweak the vents. Part of the reason is the path these ducts take going along the exterior sill and routed up exterior walls. The path is just very long.

 

There isn't really any central trunk in the design. Most runs go to exterior walls. As an example there is a return for two of the bedrooms that are next to each other. The path is from the central return in the middle of the basment to a 6 or 7 inch 10 ft long duct that goes up the exterior wall to the second floor, through the floor joists, then up a central wall. Seems really inefficent to me.

 

Steve,

 

The exterior wall routing isn't that good, but it's not all that uncommon either. You most likely have an "open" design on your first floor. The plumber got first dibs for drains and supply lines. The HVAC guys got what was left (the exterior walls).

 

I've been fortunate in that I had a hand in designing both of our houses. We included 6" interior walls at certain locations on the first floor to accommodate ductwork.

 

Even after detailed planning, a last minute "shift" in the design of my current house forced ductwork into a garage wall to feed my sons room (similar situation to what you've described). We tried to compensate for the bad routing by running two vents to the room (above the garage) but cooling the the summer was horrible (heating wasn't all that bad).

 

My workaround was to add a 6" inline boost fan that was triggered off the zone control. These are typically 110V fans so you would need a relay (24V input) off your furnace to switch the 110V to the fan. The fans are available at most hardware stores (I think I got mine at Menards ~$30). Downside is that these can be noisy. You can insulate around the fan to minimize noise in the basement, but it can echo through the ductwork (into the bedroom). The message here is don't overdo things. If you have space, a section of flex duct can help dampen the noise.

 

Past that, most newer thermostats have a programmable "circulate" mode. This turns on the blower at low speed (if available) to redistribute the heat/cold in the house. If your boost fan is triggered off the main blower, it would also activate.

 

If you wanted to get fancy, you could install temp sensors to monitor the differential between the bedrooms and the main thermostat location. If the temperature exceed XX degrees issue a call for fan only, XX+YY call for heat/cold. I'm not all that well versed on the capabilities of the Insteon thermostat adapters. Maybe another forum member can help here.

 

Bottom line is you will be tuning your system to work with the existing ductwork. Take things in small steps and take time to evaluate the results.

 

IM