Heating, Ventilation and Air Conditioning (HVAC) are the collection of systems that heat, cool, ventilate and de-humidify a home.
HVAC can be mechanical or passive. In mechanical systems, air passes over a hot or cold element that conditions the air before it is distributed to rooms in the house. The element can be cooled either through refrigerants, water or by using ground temperature (geothermal).
Mechanical HVAC is critical in most homes. Not only does it condition the air by heating or cooling it, but it also removes moisture (humidity) from the air – an important factor for Thermal ComfortThe state of mind in humans that expresses satisfaction with the surrounding environment. Maintaining thermal comfort for occupants of buildings or other enclosures is one of the important goals of HVAC design engineers. in hot, humid climates. Mechanical systems also play a large role in removing contaminates from inside the home. Mechanical systems change the air several times an hour, removing dust, pollen and stagnant air. Mechanical HVAC is also the largest electric load for most houses, meaning Insulation, R-Value and high efficiency windows must all contribute to reducing energy costs.
Common mechanical types are:
- Window Units – These type units are stand-alone HVAC systems that sit in a window and cool one room. Window units are widely available and easy to install. They are also relatively inefficient and take up a large portion of the window where they’re installed. Window units are often used in older homes because of the high cost of running ducts through existing structure.
- Central Units– A central system can be either low velocity or high velocity:
- Low velocity systems typically have low air speeds and larger Trunk Lines Main line that runs directly into the air handler. This is typically the largest duct in an HVAC system. (8”-18”) and Duct Line Hard or soft pipe that runs from the Trunk Line and distributes cool or hot air to a room. (6”-8”). Low velocity systems have large rectangular and square RegistersEndpoint of the branch off a trunkline where the air comes in and out of a room. in floors or ceilings and are the industry standard for conventional homes. Low velocity HVAC systems work by dumping air into a single location in the room, stopping and allowing Conductive Heat Transfer to occur.
Low velocity systems are relatively affordable and widely available. Low velocity systems require a large amount of space and can lead to drafts. They can also make a Retro-FittingTerm referring to the process of upgrading a pre-existing house or building with newer materials or systems. project more complicated and expensive.
- High velocity systems use a higher air speed and smaller Trunk Lines Main line that runs directly into the air handler. This is typically the largest duct in an HVAC system. (6”-8”) and Duct Line Hard or soft pipe that runs from the Trunk Line and distributes cool or hot air to a room. (2”-5”). High velocity HVAC systems are growing in popularity because they are easier to install and workable for retro-fit projects. The smaller infrastructure of a high velocity system minimizes the amount of space needed for installation. These systems also have a high moisture removal rate, sometimes 30% greater than low-velocity systems. High velocity systems push air from the smaller diameter ducts to keep a constant airflow circulating in a room. Instead of one, large rectangular RegistersEndpoint of the branch off a trunkline where the air comes in and out of a room. found in conventional low velocity systems, high velocity HVAC systems feature multiple, smaller registers that constantly circulate air.
Not all installers are familiar yet with high velocity systems which can raise cost. A high velocity system is not any noisier than a standard low velocity system.
After using low velocity systems on our first few homes, Make It Right switched to Unico high velocity systems to minimize the larger structural members and dropped ceilings that are often needed for larger Trunk Lines Main line that runs directly into the air handler. This is typically the largest duct in an HVAC system. and Duct Line Hard or soft pipe that runs from the Trunk Line and distributes cool or hot air to a room.. High velocity HVAC systems reduce materials needed and labor costs, making them a more sustainable and affordable option for our homes.
- Geothermal Units – This type of units use the Ground Temperature as a way to pre-condition air. The interior infrastructure of Trunk Lines Main line that runs directly into the air handler. This is typically the largest duct in an HVAC system. and Duct Line Hard or soft pipe that runs from the Trunk Line and distributes cool or hot air to a room. are similar to a low velocity system. Before the air is brought into the house, it runs through below-ground pipes in a series of vertical and horizontal loops. Because the Ground TemperatureThe temperature of the ground near the surface. Often called soil temperature. is constant year round, air temperature can be lowered or raised by running it through pipes in the ground. By pre-conditioning the air this way, less energy is needed to heat or cool the air before it is brought into the house. Geothermal units require less energy, low maintenance and have a smaller Carbon FootprintCarbon Footprint is the total set of greenhouse gas (GHG) emissions caused by an organization, event, product or person. Greenhouse gases can be emitted through transport, land clearance and the production and consumption of food, fuels, manufactured goods, materials, wood, roads, homes and buildings and services..
However, geothermal systems are costlier to install and few installers are familiar with these systems. Make It Right has geothermal HVAC systems, but due to cost and lack of experienced installers, we do not currently use this system.
Passive Heating and Cooling
Passive heating and cooling uses radiant heat from the sun to heat spaces and uses hot or cool air to condition spaces. Successfully passive heating and cooling greatly depends on local climate and experienced designers and engineers. 100 years ago, passive heating and cooling design strategies were widely used in hot and humid climates. However, modern standards of Thermal Comfort The state of mind in humans that expresses satisfaction with the surrounding environment. Maintaining thermal comfort for occupants of buildings or other enclosures is one of the important goals of HVAC design engineers. have changed and most people require mechanical air conditioning to be comfortable.
In the developed world, the way we live, products we use and food we eat often are dependent on some form of mechanical heating or cooling. In a sustainable home, Insulation and Air TightnessNot permitting the passage of air either in or out create a high level of energy efficiency and use less energy to heat and cool the home.
Make It Right constantly looks for ways to reduce costs while maintaining the high quality of our homes. We have worked closely with structural engineers, mechanical engineers and framing consultants to design the right size structural members, minimize dropped ceilings and use correctly sized Unico high velocity air conditioning systems. We now are able to run our Trunk Lines Main line that runs directly into the air handler. This is typically the largest duct in an HVAC system. and our Duct Line Hard or soft pipe that runs from the Trunk Line and distributes cool or hot air to a room. through our ceiling framing members and limit Dropped Ceiling A ceiling that is lower than the roof above it. Dropped ceilings are often installed to create attic spaces or spaces to run plumbing, electrical or HVAC. areas. This has allowed us to create higher ceilings in the majority of our houses and eliminate Dead SpotsAreas in a house that HVAC systems can't reach. In some home designs, dead spots can create zones that are too hot or cold. that often occur with standard low velocity systems.
Additionally, in the case of the Lower Ninth Ward, we use high standard filtering that rate MERVMinimum Efficiency Reporting Value is a measurement scale designed in 1987 by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to rate the effectiveness of air filters. 11 or greater. This high level of filtering removes very small particulates from the air which greatly improve interior air quality. At this level of filtering, particles as small as milled flour, pollen, or auto emissions are removed from conditioned air, which also can help in the mitigating of respiratory problems like asthma or allergies.