I am in the planning stages of this project. I do not have any experience with HVAC systems, but am learning as I go. If you are going to undertake a project similar to this, please do your own research and consult an HVAC contractor. If you screw something up, you can end up damaging your HVAC system or burn your house down. I take no responsibility for any actions you take due to this guide. In the event you do encounter a problem, please share your experiences so that this guide can be updated.
Purpose of this guide
This guide is to provide you with a starting point for automating control of your HVAC system. I have an ELK-M1 Gold, so most of my research has been focused on systems that would integrate with my control panel. I'll have to rely on others for integration information for different control panels.
I have a home theater on the second floor of my two story house. When several people are watching a movie, the theater will get really hot while the rest of the bedrooms are much cooler. There can be temperature differences of 20ºF between the rooms. If I turned on the A/C, the nursery and other bedrooms become too cold. Sending cold air to a room that needs heat is a huge waste of energy.
Additionally, last December my natural gas bill was double that of the previous December for essentially the same amount of usage. I have a newly constructed 2 story house. The builder installed the cheapest split system HVAC (one per floor). The lack of efficiency for this system coupled with the rising cost of energy is making my energy bill to expensive.
My primary goal for this project is to improve comfort by better controlling the temperature. I want the system to be automated so that I can “set it and forget it”. My secondary goal is to improve HVAC efficiency and reduce my energy costs. With the cost savings, I hope to have a break even point within a few years.
I will need to split the single zone upstairs HVAC system into multiple zones. I would like to put each bedroom into a zone to optimize efficiency and comfort. The downstairs is more open so splitting it into multiple zones won't be as beneficial. I will probably keep that as a stand alone one zone system.
After my break even point, my system will be saving me money. It will make my house more comfortable to live in and increase its resale value.
HVAC System: This is one complete system that heats and cools your house. It includes a furnace (for heat), condenser (for cooling), blower (to move the air), duct work (to deliver the air to different locations).
A/C: Stands for air conditioning. This is usually made up of a condenser (usually located outside) and coils (located near your furnace and blower). An A/C system transfers heat from the coils to the condenser. The coils become cold and the blower moves the cold air to different parts of your house. The condenser takes the heat and dissipates it with its heat sinks and fan.
Furnace: This piece of equipment takes a fuel and converts it into heat. The fuel is usually natural gas, oil or electric. They have a capacity rating (BTUs) of how much energy they use. Natural gas furnaces also have an efficiency rating for how well they convert gas to heat. Most furnaces include a blower.
Blower: Most furnaces have a single speed blower. They are often included with the furnace and should be matched up with what the duct system can handle. The blower's output is measured in CFM. Variable speed blowers can throttle back the CFM. This can be useful for zoning or dehumidifying. For zoning, reducing the CFM helps to handle situations where only smaller zones are calling. For dehumidifying, the lower speed blower keeps the air circulating around the cooling coils so that they can extract more water than a single speed blower. Reduced speed uses less energy and a quicker reduction in humidity reduces perceived temperature faster.
Heat Pump: A heat pump is an A/C unit that can be reversed. When asked for cold air, it operates like an A/C condenser. When asked for hot air, it reverses the process by sending heat to the coils and cold to the condenser. Since the cooler condenser must warm up with ambient air, a heat pump's efficiency for heating is limited by the outdoor temperature. A heat pump operates best when the outside temperature is between 60F and 30F. After the temperature drops below 30F, the heat pump enters emergency mode and uses a lot of electrical energy to produce heat. The benefit of heat pump is that they use less energy when the outside temperature is within their optimal band. They can use as little as 1/3 less energy than a natural gas furnace (in terms of cost). An ideal solution would be to couple a heat pump with a natural gas furnace. When the temperature is with the heat pump's optimal band, you save money while maintaining a comfortable temperature in your house. If the outdoor temperature drops below 30F, the natural gas furnace takes over. This is a cost effective solution for most places (since natural gas typically costs more than electricity). This may not work well in California where electricity is expensive.
Staging: Most installed furnaces, heat pumps and A/C condensers are single stage equipment. This mean they only have on or off. Multi-stage equipment will have off and varying levels of on (like a dimmer). For example, a 100,000 BTU 2 stage furnace might have 50,000 BTUs for the first stage and 100,000 BTUs for the second stage. Staging equipment costs more money, but it saves money over time. Heating and cooling will start out with the first stage (thereby using less energy). If the runtime is too long, or the temperature difference is too much the thermostat or HVAC controller will upstage to the second level (full energy usage).
Call: This is a request from a thermostat to send cold or hot air to its zone.
Damper: These are like valves added to existing ductwork. Each zone should have at least one damper. If the zone calls for heat and the HVAC is currently sending heat to other zones, the associated damper will open to satisfy the request. If the zone doesn't need any additional heat or cold air, the damper will remain closed.
Zone: This is an area of space where temperature is regulated by a thermostat and an HVAC system. A zone can be the entire house (typical for a ranch), an entire floor (typical for a multi-story home), sections of a floor (east and west wings), or individual rooms.
How it works
You will need a zone controller if you want to turn a single zone HVAC system into a multiple zone system. The zone controller will connect to the HVAC system and control it. The HVAC system sees the zone controller as just one thermostat so it just does what it is told. The Zone controller's job is to take the request from all the connected thermostats and serialize and package the requests to the HVAC system.
If one or more thermostats request heat, the zone controller closes all the dampers to the zones not requesting heat. It tells the HVAC system to turn on the fan and supply heat. Heat is sent to all of the zones with open dampers (since they requested heat). If a zone requests cold air during this time, the zone controller must decide on how to share the HVAC's time. When it switches calls, the zone controller will request a purge, and then close the dampers for all zones requesting heat. It then opens the dampers for zones requesting cold air and turn on the HVAC system for cooling.
There are two main types of system. You can use a communicating zone controller or communicating thermostats. With a communicating zone controller, your home automation panel will talk only to the controller. The thermostats can be simple displays with a couple of buttons. All the logic is in the controller.
You can also use communicating thermostats (this is how Elk currently does it). The home automation control panel will talk to all the thermostats. Each thermostat will talk to a non-communicating zone controller. The zone controller will take the requests, package and serialize them and send it off to the HVAC system.
Using a communicating zone controller is cheaper since you don't have to buy expensive communicating thermostats. Also, the wiring is simpler.
I recommend reading this starter guide and the provided links before working with your HVAC contractor on your implementation. It would be best to tell the contractor what your goals are, what technologies (gas, electric, heat pump) you'd like to use. Let the contractor review your current system and plans and install any new equipment. Once the system is up and working, you (or the contractor) can add the zoning system.
There are two major considerations when adding a zone controller to an existing installation.
1) Your system must be able to handle air flow when the minimum and maximum numbers of zones call. You will need to calculate the minimum and maximum duct size and CFM capabilities of your system. You can use a variable speed blower to help adjust for varying calling conditions, but you will most likely need to add a bypass damper or dump zone to your system. A dump zone is just an area that will receive all the excess air. Dump zones are inefficient because you could be sending uncalled for heating/cooling to an area of your house. Bypass dampers connect the supply and return ducts of your HVAC system with a barometric damper. Depending on the pressure in your supply duct, the barometric damper will open or close to relieve the pressure on the output system.
2) If you use a bypass damper, the already heated or cooled air is in a feedback loop. If it continues for a long enough period of time, the air will become so cold or hot that it will damage the equipment. The zone controller must monitor the temperature leaving the unit and shutdown everything except for the blower if the temperature exceeds a threshold.
Here is a brief description of the zone controllers that I looked at (only the manuals). You should be able to use the zone controllers with communicating thermostats for integration with your home automation system (unless otherwise stated in the description). Attached is an Excel spreadsheet saved as an htm file showing a comparison matrix of the different zone controllers.
ZoneX System 2000 - The zone thermostat connects to the zone's damper. The control board is connected to each damper via daisy chaining. There are several different configurations based on which controllers you need. I didn't get an on-line price for this setup, so it is difficult to compare. Feature-wise it looks decent. The majority voting system could be abused if a bunch of smaller zones out vote one large zone. I'm not sure what the economizer is, or does. ZoneX recommends using their thermostats for maximum compatibility, but you are free to use other thermostats at your own risk. Because of its unique design, it looks like you have to use their dampers. Using their thermostats limits you to their communicating thermostat. It only works with their windows based software, so integrating this system with your home automation system will be difficult to impossible at this point.
Honeywell TZ-4 - This zone controller has a standard feature set and is made by a well known company. The price is on the higher end for the base unit.
RobertShaw SlimZone Deluxe: This is a reasonably priced zone controller. The add-on zones are cheaper than other manufacture's. It has a standard feature set with a smoke detector trigger.
Zone-A-Trol MZS4:It has a standard feature set. I could not find a price for this controller. It may be difficult to buy this controller through retailers.
Jackson Systems Z-300-HC-MS: The base unit is the cheapest, but add-ons are more expensive. This zone controller seems to have a standard feature set, but only minimum details were available. I wouldn't recommend it because of the lack of information from the manufacture.
Aprilaire 6404: This is a reasonably priced zone controller with reasonably priced add-ons. It's in the same price range as the RobertShaw controller. This unit can control and humidifier or electronic air purifier. I would recommend this over the RobertShaw controller.
EWC UCZ4: This controller has the highest base price. The price correctly reflects its more comprehensive feature set. In addition to the standard features offered by other manufactures, this controller can connect to an optional return air temperature sensor (to tune upstaging), optional CO2 monitor (to open the outdoor vent damper when CO2 levels are too high), smoke detector trigger to shutdown system, dehumidifier interface, and optional electron bypass damper to reduce noise on system startup. I recommend this unit, if you can afford this controller and its options.
EWC BMPlus-5000: This controller is a cheaper version of the UCZ4, but it is still more expensive than other controllers. In addition to the standard feature set, it includes an optional return air temperature sensor (to tune upstaging). Although the Aprilaire doesn't have the return air temperature sensor, it seems to be a better buy since it costs less.
RCS ZCV4: The ZCV series of controllers only works with RCS wall unit thermostats. The wall units are cheaper than communicating thermostats, so using the ZCV series controller is enticing. The controller has an RS-485 port for integration with your Home Automation system. Currently the Elk system only supports RCS thermostats and not the controller, but they are investigating adding this feature. This controller includes a Thermal Equalizer, which is useful if one HVAC supplies heat to more than one story. The ZC6R does not support dual set points, but could be an alternative to the ZCV series. I could only find limited documentation on this controller.
Where I'm at
Since my house if newly constructed, if I were to replace too much of the existing system, my break even point would be over a decade away. Currently I'm considering replacing my A/C condenser unit with an energy efficient heat pump. This way, I'll reduce my cooling cost and have a 2 stage heating system. If possible, I'd like to replace the single speed blower with a variable speed one. This; however may require replacing the furnace, which I don't really want to do at this time. I'll have an HVAC contractor install the heat pump. I'll install the zone controller and dampers after the system is up and running.
I'm currently leaning toward the EWC UCZ4 with an add-on controller. It is $800 more expensive than the RCS solution, but has many more features. With the EWC system, I'll be able to add on outdoor venting when CO2 levels get high, tune upstaging on return air temperature (energy savings), and connect up a dehumidifier in the future. The bypass damper will also be electronic, so the system will be quieter during start up.
Since I'm still in the planning stages of this project, I'm going to evaluate not using a zone controller. Instead, I'll look into using relay boards and my Elk M1G as a zone controller. If this is a viable solution, I could save up to $800 on the controller. The controlling algorithms would be configurable, and if the Elk were not operational, the system would fall back to normal operations (each floor is one zone). If you have already done this, or investigated doing this, please submit some feedback on this thread.
If you have any comment, or more information to add to this guide, please submit feedback on this thread.