Forced Air Zoning: Friend Or Foe?
Probably the biggest advantage for the contractor is that if you install a forced air zoning system correctly, one thing you're guaranteed to have is a happy customer. Not just a customer who is satisfied with the job or installation which the contractor performed, but a customer that is actually excited about the new comfort system they have in their home. This customer is excited because he is now able to control different areas of the home at different temperatures to satisfy different comfort levels for different family members. This is something that - until introduced to force air zoning - the customer never even thought was possible.
The Basic ConceptBefore I get into the specifics of the individual zoning products, let's talk about the basic concept of why forced air zoning should be an integral part of each contractor's presentation - whether new construction or retrofit (job permitting) - for each and every customer that they see. Throughout my travels in the Southeast, I've done many training seminars with contractors talking about forced air zoning. In each of these seminars I ask them a simple question: Who in this class has a zoning system in their home? The majority of the time, no hands are raised. At this point, I like to remind them that each and every one of them has a zoning system in their home.
I don't care if you live in a 10,000-square-foot house, a townhouse, or an apartment - everybody has a zoning system in their home. Point in case, when you go to cut the light switch on at the front door, does every light in the house come on? Of course not; we zone our lights. Why do we zone our lights? The number one answer: To save money. Look at the energy consumption of a 100-watt light bulb burning continually 365 days a year. At year's end, it would average $30; the cost is minimal. So are we really saving money by cutting off our lights? Or is it something that we've become accustomed to? Have you ever thought of a customer requesting only one light switch for their entire home?
Let's also take a look at when we go to the kitchen and turn on the water faucet. Does every faucet in the house turn on? Of course not; we zone the water in our homes, too. Why? To save on our water bill.
Two out of three mechanical systems in our homes are zoned. But the most expensive one to operate is the HVAC system. Yet as professional heating and air conditioning companies, we will go into a home and place one thermostat in the middle of the house, usually in a hallway with no supply registers and one return. It will not sense east sun or west sun, it will not sense north wind or south wind. But we expect that system to keep all the rooms on the perimeter of the house the same temperature. This is virtually impossible!
Why do we install this type of system? Because of competition. We have to be competitive. If our fellow contractors are only offering one thermostat and one return, it would be very difficult for us to go into that same job and be competitive offering multiple returns and multiple system alternatives. So we are forced to sacrifice quality and comfort for profitability.
Some of the problems that our customer, the consumer, faces each and every day are quite common in our industry. Let's look at a two-story house with one system and one thermostat located downstairs. The temperature difference between upstairs and downstairs can be anywhere from 4 to 10 degrees. Why? Because heat rises.
If the sleeping area is located upstairs, what will the customer do to the downstairs thermostat to maintain a 72 to 75 degree temperature upstairs? Crank it down anywhere from 65 to 68 degrees. That means that the downstairs living area, which isn't even being used, is extremely cold just to maintain a comfortable level of temperature upstairs while we are sleeping. That's not a very efficient way of cutting back on energy costs.
As a professional contractor in a retrofit application, what are our options to solve this problem? The number one answer I get in my classes is: Add another system. But think about what we just said. If we add another system, we have one system downstairs for the entire house. Are we going to put another system upstairs and then have a grossly oversized unit downstairs? Not a very economical solution.
We can use a ductless split system, which is expensive and not really suitable for area application; it's more suited for room application.
We could knock a hole in the wall and put in an incremental unit. Again, this is more suited for room application rather than area application.
We could always suggest a window unit. Unfortunately, it's hard for a contractor to be competitive with your local hardware store.
How about a manual damper to divert more airflow upstairs in the summer and allow for more airflow downstairs in the winter? This could help patch the problem, but not solve the problem.
The only real way to solve this problem (if the ductwork is accessible) is to zone this two-story home. With a thermostat upstairs and a thermostat downstairs, the concept is simple. As the thermostat downstairs is satisfied, we have the capability of diverting the capacity of the equipment upstairs and controlling the airflow upstairs.
In this scenario, is the customer concerned about the temperature downstairs in an area of the home that isn't being used all night? Or would he be more concerned about the comfort in the bedrooms which are being occupied each and every night? Think about the potential savings. Before zoning, in order to be comfortable upstairs, we had to set our thermostat downstairs anywhere from four to 10 degrees lower (in the cooling mode). Now that we have a thermostat upstairs, we're allowed to simply set our thermostat to our own comfort level upstairs and set our downstairs back significantly.
So with the setpoint of 80 degrees downstairs every night for six to eight hours while we are sleeping, we could virtually save ourselves 13 to 15 degrees per night during the cooling season, in the largest part of the home. What a huge potential for energy savings!
Now let's look at a ranch house with a centrally located thermostat. We have one system, with the garage on one end of the house where the air handler is mounted. And what's on the other end of the house? The master bedroom. This scenario could potentially create an airflow problem, as well as a temperature problem. With the thermostat located in the center of the house, it usually satisfies before the farthest run from the equipment has reached the desired comfort level. How do we, as professional contractors, go in and offer our customers a solution to this problem? I've heard a multitude of things: booster fans, extra units, rip out the ductwork and install all new ductwork, relocate the air handler to the middle of the house to equal out the airflow. Most of these solutions are labor intensive and expensive, and still doesn't guarantee us a solution to our problem. The solution: forced air zoning.
Separate the living area from the sleeping area. Again, as we satisfy the areas that satisfy first with the normal system, those areas will shut down and we have the ability to divert the capacity and control the airflow to the areas that weren't performing satisfactorily to begin with. We are solving the problem, rather than patching the problem.
A Viable AlternativeThere are a multitude of applications to which zoning lends itself to be a viable alternative to the common, everyday installation we're accustomed to. The room above the garage is virtually an impossible area to keep comfortable with a centrally located thermostat. Florida rooms or enclosed porches, entertaining areas, kitchens, bedrooms, areas with heat-generating equipment, in-law suites, babies' rooms - all of these, without zoning, are almost impossible to control separately with only one temperature-sensing device in the home or commercial dwelling.
The majority of zoning is sold in the northern part of the country. Why is zoning more prominent up north? Because it's a standard; they're accustomed to zoning their houses. Whether it be hydronics or baseboard heat, close to 80 percent of the homes are zoned in one way or another. Just as we expect our lights and our water to be zoned, we also need to expect our air conditioning and our heating to be zoned.
So from a comfort standpoint, we've established the fact that zoning is something that customers need for true comfort. But are customers willing to pay the extra money for that comfort? If a customer utilizes a zoning system properly, like they utilize multiple light switches in the house by cutting lights off that aren't being used, a zoning system can literally pay itself off in two to five years in the majority of cases.
As a matter of fact, you can tell your customer: It doesn't matter if you install a zoning system now, you're paying for it whether you have it in your home or not.
So the question should not be: Can the customer afford to put zoning in their home? The question should be: Can the customer afford not to put zoning in their home?
What other items do we promote as contractors that will actually pay for themselves in two to five years? I've asked a lot of contractors that question and the only two items that we've come up with are a setback thermostat (a fairly low-ticket item) and a heat reclaim unit.
Some have mentioned high efficiency. But if you use the audit program on the heat-load calculation software, you'll find that the majority of high-efficiency upgrades take around nine years to pay for themselves. Unless you're going into a retrofit job with a 6 SEER and improving it to a much greater SEER, then the payback would be quicker.
A zoning system, such as the EWC Ultrazone, can pay for itself and even provide the customer with return income. How? Because after the payback period, the money saved on their bills each and every month actually gives them a return on their investment.
The Bypass MethodEWC strongly supports the bypass method of relieving excess air pressure when all zones are not calling. If you install a zoning system without a bypass, you'll never truly realize the maximum potential of the equipment that's installed in the home.
What is a bypass? A bypass is simply a branch of ductwork connecting the supply to the return, usually mounted in the supply plenum. So as dampers close, creating a back-pressure to the unit, the bypass damper is forced to open to relieve this back-pressure and recirculate the air through the return and back to the unit.
EWC offers two types of bypass dampers. One is a barometric bypass, which is simply a weighted arm that you set to the static pressure to relieve the amount of back-pressure needed to keep the system balanced and quiet. The other type of bypass damper is a static pressure-sensing bypass damper with a fully modulating blade. This damper will automatically adjust to static pressure increases and decreases. The bypass damper will modulate to keep the ductwork at a constant static pressure.
If you install a zoning system with a bypass, it is highly recommended to install external high and low limits other than the equipment's emergency limits. This will make sure your equipment is always protected from undesirable temperatures or pressures.
As we relieve this precooled or preheated air back through our return and back across our coil or heat exchanger, realize the advantageous discharge temperatures we can achieve.
Let's take a look at the advantages of using a bypass in both the cooling season and the heating season. In the cooling season, one of our main concerns is dehumidification. The bypass will naturally increase dehumidification when all of the zones in the house are not calling. When certain zones are not calling, we will bypass that extra air and Btu (which would normally be wasted in zones not calling) back across our return, across our coil, therefore naturally dropping the temperature of our coil to help increase dehumidification. By taking the Btu that normally would have been wasted in a zone that didn't need conditioned air, and reducing the temperature of our coil, we will also reduce our discharge temperature, and thus reduce the run time on our condenser outside.
Now, let's take that one step further. If we reduce our coil temperature, what are we doing to the amp draw of the compressor in our condenser? We're unloading it because we're reducing the load on the condenser outside. If we reduce the load on the condenser, then we will also reduce amp draw. Amp draw can greatly be reduced during the bypass cycle, thus increasing efficiency. Think about what we just said. We just increased the efficiency of the equipment naturally by not using unneeded air in areas of the house that didn't need conditioning. And we are allowing our unit to perform at its peak efficiency just by putting in a zoning system and giving us the airflow and temperature where we want it when we want it.
The equipment manufacturers over the past few years have even designed a unit - a variable-speed air handler - to help accomplish better dehumidification. But how does a variable-speed air handler dehumidify? By dropping the fan speed on the air handler 20 percent, we slow the air across the coil. By having less air going across the coil, we allow our coil to get colder. As the coil gets colder, we increase dehumidification by pulling more moisture out. But we do this at a price. At the same time we reduce static pressure and reduce airflow in our ductwork by 20 percent; we reduce the throw from our registers by 20 percent, not giving us the coverage in the areas where the registers were designed to throw the air. Also, by reducing the airflow and the coverage, our run time on our equipment should be extended while we're in this 20 percent reduction mode.
Please don't misunderstand me. Variable-speed air handlers have many advantages other than dehumidification. The ultimate zoning system is a variable-speed air handler coupled with zoning. But if dehumidification is your main objective, a zoning system will dehumidify much more effectively and much more efficiently than a variable-speed air handler.
The pitfalls of bypass are bypassing too much cold air or too much hot air, resulting in undesirable scenarios for the equipment. But with the EWC system, we take care of this with our Supply Air Sensor (SAS) integrated with our zone control panels. We can internally control, through our board, the high and low limits you, the contractor, wish to keep the equipment.
The SAS low limit is adjustable from 35 degrees to 50 degrees (in one degree increments). The SAS high limit is adjustable from 100 to 170 (in one degree increments). This makes sure that no matter what type of equipment you're using, the control is taking care of your needs and protecting your equipment's performance.
The position and sequence of operation for the Supply Air Sensor is very simple. For non-heat pump systems, the sensor will be mounted in the supply air plenum. For heat pump systems, the sensor will be mounted in the air handler between the coil and the heat strips, to make sure we do not pick up any residual heat from our auxiliary strips when they are used. Here, our main concern is going to be on the first stage of the heat pump, what our coil is actually producing in the first stage of heating.
Recommended Supply Air Sensor setpoints depend on the part of the country in which you're located. On the cooling side for the Northern states, it will be somewhere between 38 degrees and 45 degrees. In the Southern states, it will be somewhere between 45 degrees and 50 degrees. This greatly depends on the moisture content of the air. As for heating setpoints for heat pump mounted sensors inside the air handler, we want that to be between 110 and 120 degrees. This will make sure we don't run high head pressure on the first stage of a heat pump system. For fossil fuel furnaces, it should be somewhere between 5 and 10 degrees below the emergency cutoff on the furnace itself.
We want to make sure the board controls the limit rather than the equipment because of a possible lock-out scenario. EWC provides you with integrated adjustable high and low limits, allowing you to tweak the system to overcome any obstacles specific to your application.
Many of the manufacturers of zoning systems don't recommend the bypass method, predominantly because they don't have the integrated high and low limits which are an integral part of a bypass installation. With bleed-through dampers, modulating dampers, and dump zones to relieve the excess pressure, none of these avenues allow you to take total advantage of the capacity and the efficiency that this equipment can achieve like the bypass method can.
Regarding sizing, installation, and adjustments of the bypass damper, it is extremely important to understand the right way to do this. This is covered in detail in EWC's literature titled "Duct Sizing with Ultrazone." It is available from your local distributor, or call 800-446-3110 for a copy.
Trey Miller is Southeast regional manager for EWC Controls Inc., headquartered in Englishtown, N.J. For more information, visit www.ewccontrols.com.
Publication date: 02/07/2005