Posted on Aug 6 2014 by It's easy to see that this duct system is zoned because parts of the zone dampers are visible on the outside of the ducts. The green lights indicate that the zone dampers are open. Last week I wrote about what happens when you try to save energy by closing air conditioning registers in unused rooms. In the end, I recommended not doing it because you won’t save money and you may create some big problems for yourself, like freezing up the coil and killing your compressor. At the end of the article, I mentioned that zoned duct systems do close off registers, and that doing so can be OK with the right kind of equipment and design. But there’s one thing often done in zoned duct systems that’s rarely done well. Before we find out what that thing is, though, let's be precise in our language and clear up exactly what we're talking about. The word “zoning” is used in more than one way in the context of heating and air conditioning systems in a house.

First, larger houses are almost always zoned. That is, they have more than one thermostat so you can control the conditions separately in different parts of the house. In a two-story house, for example, there will probably be at least two thermostats — one upstairs and one downstairs. Keeping Cool in a Two-Story House How Duct Leakage Steals Twice Thou Shalt Commission Thy Ducts! The other way that the term “zoning” is used is to describe a single duct system attached to a single HVAC(Heating, ventilation, and air conditioning). system that serves multiple zones. In most homes with forced-air HVAC systems, each thermostat is connected to its own heating and cooling system. The home is zoned, but the HVAC system is not. In a “zoned system,” a single heating and air conditioning system is controlled by multiple thermostats in multiple zones. In the photo above, the three green lights are part of three zone dampers that control the flow of air to three separate zones.

Depending on the needs of the house, any combination of one, two, or three zone dampers may be open and sending conditioned air to their respective zones. If only one or two of the zones are calling for air, most air handlers will create extra static pressure because one or two of the pathways are closed off. Enter the bypass duct (shown in Image #2, below). When the system is running but not all of the zone dampers are open, the bypass duct — in theory — is supposed to relieve the extra pressure and maintain good air flow throughout the duct system. The problems with the bypass duct A few years ago at the ACI conference, I heard John Proctor and Rick Chitwood discuss the issue of bypass ducts. Proctor isn’t a fan of zoning at all, and Chitwood is. On one point, though, they both agreed: Bypass ducts should never be used. Here are three reasons why: Throwing cold air directly into the return plenum reduces the temperature of the air coming in to be cooled.

That makes the evaporator coil get colder, and the colder it gets, the less efficient it becomes. The bypass duct steals air. Even with all three zone dampers open, the bypass duct has a big pressure difference across it, and air is lazy. It'll cheat and take the path of least resistance whenever possible, in this case the bypass duct.air handling unit size calculation Not only is a colder evaporator coil less efficient, it's also more likely to freeze up, as the condensation it collects eventually drops below the freezing point. air handling unit materials(And if you think a bypass duct is bad for air flow, a frozen coil is way worse. outside ac unit not coolingIt's really hard to push air through a solid block of ice.) Savings from eliminating the bypass

Just this week, Proctor posted an article on zoning and bypass ducts on his website. With the article, he included a video demonstration of a zoned system, showing the changes in airflow and temperatures with and without the bypass duct open. Then he performed the calculations to show the efficiency for each configuration. In his little experiment, the three configurations with the bypass duct closed (with no air through bypass) were 22%, 27%, and 32% more efficient than the configuration with the bypass duct open. Of course, if you’re sending air to only one zone, you still have the issues of reduced air flow in a PSC blower and increased energy with an ECM blower, as I described last week for the register-closing scenario. To do zoning right, you’ve got to account for the extra air when one or more zones are closed during operation. Probably the best way to do that is with a multi-stage air conditioner that can also ramp down the fan speed to send less total air through the system.

My friend David Butler, one of the most accomplished HVAC designers I know, believes that bypass ducts can be done right... but it’s still best to avoid them. "It's a tool that should only be used when [other] options aren't feasible or possible." The bottom line with zoning is that it’s a tricky business no matter which way you go. ACCA has a zoning protocol called Manual Zr, and that’s a good place to start if you’re going to design a zoned system.Last updated: April 25, 2016. Shut that door and keep the heat in—it's a familiar cry inin summertime, you're more likely to see people closing doors and windows to keep the heat out and save on the air-conditioning. How can you have an airtight, energy efficient home that's also healthy andHeat recovery ventilation (HRV) and energy recovery ventilation (ERV) offer a solution, bringing fresh air into your home without letting the heatLet's take a closer look at how they work! Photo: The inside of a typical heat recovery ventilation (HRV) system.

You can see the blue and red air ducts on the left, the diamond-shaped heat exchanger in the middle, and the air blowers on the right. HRV systems are made by many different companies, including Broan, Fantech, Honeywell, Vaillant recovAIR, Renewaire, and Venmar. and US DOE/NREL (Department of Energy/National Renewable Energy Laboratory). Modern homes are usually built to far higher technical standards than buildings constructed a few decades ago and are much more energy efficient, largely thanks to better heat insulation. One key area of improvement has been to make buildings more airtight so they hold onto the heat we put into them for longer. But there's a drawback: our homes need regular changes of air to keep them healthy. Baths and showers, doing the dishes, and even simple breathing produce astonishing amounts of water inside our homes: according to leading ventilation manufacturer Vaillant, a typical family will produce 10–15 liters (3–4 gallons) of moisture

Let that problem go unchecked and you'll get problems like mold and mildew, dust mites and a greater risk of asthma. doors and windows is the obvious way to get rid of moisture and bring in fresh air, but if you do that in winter you might just as well flush your money down the toilet: all the heat you've expensively introduced into your home will blow away in the breeze. house solves this problem by being automatically well ventilated, but it's probably also freezing cold because it's useless at holdinga modern energy-efficient home solves the draft problem but may be stuffy and underventilated. So what to do? Let's look to nature, which solved this problem some time ago. bodies are a bit like our homes inasmuch as they need regular supplies of fresh air and have constant clouds of damp, "stuffy" air to get rid of. How do they do it? With an ingenious inventionAs a child, you might have learned that it's better to breathe through your nose than through your mouth because your nose

warms and filters incoming air. What your nose actually does is called heat exchange: it lets cool incoming air flow very close to warm outgoing air so heat energy is transferred between the two instead ofAs a result, the air you breathe in is warmer and the air you breathe out is cooler—and (among other things) that helps your body to retain heat energy. Photo: The basic principle of a heat exchanger: a hot, outgoing fluid (red) flows past a colder, incoming fluid (blue). Without them actually mixing together, the hot fluid gives up most of its heat to the cold fluid. HRVs are essentially noses on houses: they consist of two ventilation ducts running next to one another passing between the inside and the outside of a house. One carries cool, fresh air in; moist, stale air out. The clever bit is that the airstreams run through a device called a heat exchanger that allows the outgoing air to pass most of its heat to the incoming air without the two

airstreams actually mixing together (read how this works in our article on heat exchangers). Usually there's a fan (blower) in each duct that can be turned up or down either manually or automatically depending on the temperature and humidity levels. supply may also have a bypass fitted to it so that on summer days when it's cooler outside than in, cold outside air can be channeled straight into the home without meeting outgoing air (much like opening a Artworks: Left: How an HRV works (simplified): The hot, moist waste air from the home (passing down the yellow duct) gives up virtually all its heat as it passes through the heat exchanger on its way out of the building. The cold, dry incoming air (flowing through the brown duct) picks this heat up as it flows in. Ideally, no heat is lost. Since the incoming and outgoing air flow past in opposite directions, this approach is known as a counterflow. Artworks: Right: How an HRV works (in more detail): This is the layout of an actual HRV unit showing the two airflow paths and six isolated compartments in a bit more detail.

Fresh air enters the building from outside at point 1 and is pumped into the room at point 2, inside the building, passing through the three compartments colored gray, and following the blue arrowed path. On the way, it picks up heat from the diamond-shaped heat exchanger (red), pulled by the pink blower. Stale exhaust air exits from the room at point 3 and leaves the building at point 4, passing through the three blue compartments along the red arrowed path. It also passes through the heat exchanger, giving up heat, and is helped on its way by the second blower, colored cyan. From US Patent 5,632,334: Heat recovery ventilator with room air defrosting feature by Peter K. Grinbergs and Grant W. Miles. Nutech Energy Systems Inc., May 27, 1997, courtesy of US Patent and Trademark Office, with colors added for clarity. In small homes, an HRV might consist of a single unit on one wall that effectively ventilates the entire building over time as doors open and close between rooms.

In larger homes and offices, there may be ventilation grids in each room feeding into ducts that run between the floors or ceilings of the the building to a single ventilator on the outside wall. Not all HRVs work in exactly the same way. called energy recovery ventilation (ERV) works in a similar way but transfers some of the moisture from the outgoing airstream into the incoming air, so it keeps the humidity in your home at a constant level. That's important if you don't want your home too dry. As a general rule, ERV is a better option if you have air conditioning and live in a humid climate, because it will help to keep moisture outside, reducing the load on your air conditioner and saving on the air-con bills. HRV is often better if you don't have air conditioning, or live in a less humid climate, since it will help keep the humidity down by transferring excess indoor moisture outside. HRVs and ERVs have an obvious appeal: they give you a warm well ventilated

home and stop you "emptying your wallet" into the atmosphere every time you open your windows. In winter, they can help save on yourin summer, they reduce the need for air conditioning. By keeping excess moisture out of your home, they're better for your building, your furnishings, and your health and they help to keep the "climate" inside your home at a more constant level. they retain about two thirds to three quarters of the heat that would normally be lost from your home through ventilation (some manufacturers claim 85–95 percent), so they really do save energy. Photo: Large HRV systems use ducts like these running between floors and ceilings. Photo by Warren Gretz courtesy of US DOE/NREL (Department of Energy/National Renewable Energy Laboratory). On the downside, HRVs are expensive to install initially (several thousand dollars is typical) and they're not guaranteed to pay for themselves (typical annual savings might be a few hundred dollars).