What is Whole Home Ventilation and why is it important for your home? Whole home ventilation is the most important factor when it comes to improved indoor air quality in any closed structure or home - Unless you're reading this article on the international space station, no amount of readily available consumer air purification products are going to affect your indoor air quality like properly ventilating your home, as inadequate ventilation is the number one cause of poor indoor air quality. Without proper ventilation and the exchange of fresh air and oxygen with the outdoors, contaminated and polluted air can soon build up to concentrations that are much more polluted than the outdoors. And without ventilation, this polluted air can then accumulate inside our homes only to get circulated over and over by our air conditioning systems for us to breathe and has been linked to many adverse health effects which is why Indoor Air Quality is one of the EPA's (Environmental Protection Agency) top 5 environmental concerns.
The EPA estimates that the air circulating in most modern homes is 2 to 5 times more polluted than the the outdoor air, and this is mostly due to lack of fresh air exchanges and the build up of indoor pollution. But how can this be? There's no way the air inside our homes is more polluted than the air outside, right? After all, there are more sources of pollution outdoors such as factories, trucks, buses and smog just to name a few. How can the air inside our homes possibly be more polluted than the outdoor air? The answer in a nutshell: Lack of Home Ventilation. Let's explore some of the in depth reasons why and how air pollution accumulates to such high concentrations in our homes often exceeding outdoor levels:
Why Indoor Air Pollution Occurs
During the 1970s when the energy crisis was felt at both the gas pump and with cooling and heating costs, home architecture changed in order to reduce energy consumption and maximize energy efficiency in order to help alleviate spiraling energy costs. As Heating and Cooling equipment are the primary source of home energy consumption, homes started being constructed in an 'air tight' manner in order to preserve the energy in the air and reduce the run time of HVAC equipment. When this occured two main design changes started being implemented during home construction phases: Superinsulation was incorporated into home construction and fresh air exchanges were reduced in order to prevent outdoor air infiltration and energy loss via the exchange of indoor air with the outdoor air due to the occurrence of air leaks via air gaps within a home's construction. In fact, even today, the federal government still gives tax breaks for reducing your homes HVAC energy consumption and encourages energy efficiency by doing so. Every year air conditioning systems and their regulated minimum SEER (Seasonal Energy Efficiency Rating) rating is raised - This year in 2017 the minimum SEER rating for any piece of air conditioning equipment that you can purchase within the United States is 14 SEER, next year it will be 15 SEER, and so on. HVAC manufacturers no longer produce 13 SEER and below. Home owners receive tax benefits when they upgrade their entire air conditioning system to higher SEER ratings and should take advantage of these programs when doing so, all in order to encourage energy efficiency. The same phenomena is also still occurring in the motor vehicle industry with the emissions and efficiency standards being raised to 50 miles per gallon by 2025 and the electric car industry is booming with every major motor vehicle manufacturer in the process of developing electric motor vehicles with Tesla's Model S Sedans selling faster than any other high-end used vehicle on the market today according to Autolist.
As energy prices raise, the demand for energy efficiency raises, homes are being sealed tighter and tigheter in order to prevent our cool and conditioned air from escaping through the air gaps in a homes envelope and although we may be conserving energy with modern home architecture, the quality of indoor air has consequently declined. This is because the majority of residential HVAC equipment does not mechanically ventilate and exchange air with the outdoors, allowing harmful pollutants to build up indoors and get circulated over and over allowing concentrations of indoor pollution to reach unhealthy levels. And as more time is being spent inside by people these days, with an estimated 65%-90% of our time being spent indoors, indoor air pollution has inevitably become one of the EPA's top 5 environmental and health concerns, and rightfully so.
Unlike the environment within our homes, the outdoor environment has a unique life sustaining function and ability to purify the air we breathe and create fresh oxygen due to plants and their amazing ability to remove toxins and convert many toxic gasses into fresh breathable oxygen. Toxic gasses found in almost every home such as Benzene, Trichloroethylene and Formaldehyde are all naturally reduced by plants as nature has evolved to produce an environment that is inhabitable and sustainable for itself, man and life of all kinds on Earth - It's no wonder why that without it in our homes that indoor air pollution levels seem to increase. Within our tightly sealed and insulated homes this sustainability and purification process simply doesn't occur and this is primarily why indoor air pollution reaches dangerous and unhealthy levels often exceeding concentrations beyond those found outdoors - This is why home ventilation is so important in modern home architecture practices. According to studies performed by the NIOSH (National Institute of Occupational Safety and Health) the lack of ventilation is the main issue when it comes to poor indoor air quality.
How Indoor Air Pollution Occurs
Indoor Air Pollution comes from numerous sources, but sources that release gasses or particles into the indoor air are the primary cause of indoor air pollution, and lack of ventilation is what allows this pollution to reach highly concentrated levels. The EPA has classified indoor air pollution into 3 different categories including Particulate Matter, Biological Pollutants, and Gaseous Pollutants - All of which have varying levels of adverse health effects with Gaseous Pollutants being the most harmful form of indoor air pollution. Health effects from exposure to indoor air pollution or repeated exposure to indoor air pollution may appear soon after exposure or even years later and the likelihood of adverse health effects depends on many factors including age, preexisting medical conditions, exposure level, and individual sensitivity.
The 3 Types of Indoor Air Pollution
Particulate Matter - Including small physical particles of various sizes known to cause allergic reactions and respiratory ailments and are composed of Dust, Dirt, Allergens, Smoke, Soot. The most dangerous particles are 10 micrometers and smaller, which are tiny enough to be inhaled directly into the bloodstream and can cause heart and lung damage. Sources include particles generated with Cooking Stoves, Candles, Fireplaces, Chimneys, Diesel Engines, Tobacco Smoke.
Biological Pollutants - Biological Pollutants are technically a sub-category of Particulate Matter and includes living air borne organisms or particles generated by living organisms that cause Illnesses, Allergic Reactions, Respiratory Ailments and Infections such as: Viruses, Mold, Fungi, Bacteria, and other air borne biological contaminants created by such organisms including: Rodent Waste and Proteins found in Dried Mouse Urine, Insect Droppings and Debris and Body Parts, Proteins found in Cat and Dog Saliva, Pet Dander and Feathers, Mold Spores, Fungal Spores, Endotoxins from Bacteria, and Pollen.
Gaseous Pollutants - Including pollutants in a gaseous state such as Carbon Monoxide, Nitrogen Dioxide, Sulfur Dioxide which come from combustion processes - Sources include: Stoves, Space Heaters, Furnaces, Fireplaces, Tobacco Smoke, Improperly Vented Appliances. Other sources include VOCs (Volatile Organic Compounds) such as Formaldehyde, Benzene, Perchloroethylene that slowly evaporate, emit and 'gas off' at room temperature from sources such as: Building Materials, Textiles, Carpets, Furnishings, Drapery, Adhesives, Paints, Varnishes, Cleaning Products and Pesticides.
With Gaseous Pollutants being the most dangerous, it's important to explore where these contaminants come from and why they are considered to be the most dangerous to our health. Gaseous Pollutants of concern are known to, or suspected to cause cancer or other serious health effects. Some Gaseous Pollutants fall into the category of Volatile Organic Compounds, or VOC's, and in energy efficient homes filled with modern furnishings, electrical equipment, and building materials there are literally hundreds of volatile organic compounds that evaporate or 'gas off' at room temperature and interact or react with each other and contaminate indoor air, some of which, even at very small concentrations can adversely affect the health of people.
Volitile Organic Compounds
So where do VOCs come from and how do they enter our homes? VOCs are a part of many products we use every day, such as cleaning products. Many VOCs are used during various manufacturing processes to produce building materials which are then used to construct various everyday items that make up our homes or the furnishings within our homes such as vinyl flooring. Since VOC's have very low boiling points, these compounds slowly evaporate out of the materials we used to build our homes and the furnishings inside our homes and enter the air stream - Whenever we replace carpet, spray household cleaners or pesticides, repaint walls, refinish floors, use air fresheners, and buy new furniture, without taking careful consideration in purchasing 'Zero-VOC' products we are most likely introducing volatile organic compounds into our homes. Once brought into our homes, these compounds continue to slowly evaporate at room temperatures, some for several months, which is why they tend to accumulate and compromise our indoor air. Imagine a toxic stew of harmful fumes and chemicals circulating and reacting with each other in our homes only for us to breathe, this is the primary concern of Volatile Organic Compounds. Some common sources of VOCs include:
Common Sources of Household VOCs
Paints, Lacquers, Varnishes
Copiers and Printers
Upholstery and Fabrics
Glues and Adhesives
Plywood and Pressed Wood Furniture
The EPA has identified over 180 hazardous air pollutants, and what make's some of these compounds so hazardous is not only their persistent ability to evaporate from the products in our homes over long periods of time, but their ability to accumulate in our body tissues for long periods of time, which is why home ventilation and limiting our exposure to hazardous air pollutants is important to the health of everyone in our homes. Children, the elderly, pregnant women, and those with asthma or allergies and other respiratory ailments are of particular concern when it comes to exposure of hazardous air pollutants. Health effects can develop from immediate exposure and range from Headaches, Nausea, Eye Irritation, Nose and Throat Irritation, and worsening of Asthma Symptoms. Other health effects may develop years later in more severe forms such as Cancer, Liver and Kidney Damage, and Central Nervous System Damage. Some of the most common and notable indoor gaseous pollutants include:
Common Indoor Gaseous Pollutants
Benzene is a common solvent found in many household items including: Rubber, Ink, Paint, Plastic, and Oils and Lubricants. Benzene is also used in many manufacturing processes including: Detergents, Dyes and Pesticides. Benzene is a known carcinogen and embryotoxin. Acute Benzene inhalation is known to cause dizziness, weakness, headache, nausea, respiratory diseases, tremors, irregular heartbeat, liver and kidney damage, paralysis and unconsciousness.
Trichloroethylene is a commercial solvent with a wide variety of industrial uses with the majority it being used as a Degreaser or Aerosol Dry-Cleaning Spot Remover but it's also used in Printing Inks, Paints, Lacquers, Varnishes, and Adhesives. Trichloroethylene is a known carcinogen and an embryotoxin and poses many health risks. When inhaled, Trichloroethylene produces a central nervous system depression resulting in general anesthesia. Acute exposure has resulted in liver and kidney damage and cancer. In December 2016 the EPA moved to ban certain uses of Trichloroethylene due to such strong health risks.
Formaldehyde is an important building block and precurser to many other materials and chemical compounds and is in some shape or form found in virtually every home. Some popular products include Particle Board, Plywood, or Compressed Wood in furniture. Formaldehyde is also found in Paints, Paper Products, Grocerie Bags, Wax Papers, Facial/Tissue Wipes, Paper Towels, Carpet Backing, Permanent Press Clothing, and many Household Cleaning Products. Formaldehyde is a known carcinogen, it is highly toxic to all animals, it is known to cause asthma and allergic reactions, and it a very reactive compound that reacts with many other compounds including other air borne VOC's.
The USGBC (U.S. Green Building Council) suggests that levels greater than 500 ng/L (nanograms per liter) of VOCs could pose a health hazard in homes. However, data from thousands of homes tested show the average value is 1,200 ng/L - More than twice the recommended level. With Indoor Air Pollution present to some degree in every home and with harmful levels of volatile organic compounds present in most North American homes, what's the best procedure for controlling this form, or any form of indoor air pollution?
The EPA's first recommendation is to remove, eliminate or relocate the source of the pollution. However, this is not always a feasible solution especially with some gaseous pollutants such as Radon, which typically emits from the ground underneath a home. It's also very expensive and difficult to replace or remove gaseous pollutants emitting from building materials, furniture and carpeting, which all involve home remodeling.
The next best step recommended by the EPA is to then ventilate a home so the pollutants don't accumulate and concentrate into harmful levels. When a home is properly ventilated, contaminants are ejected out of the home and fresh air is brought in via mechanical whole home ventilators, essentially diluting polluted air with fresh air and lowering concentrations of pollutants below harmful levels.
Finally, the last recommendation is to purify or filter the air with the addition of a Whole Home Air Purification System to your existing HVAC system. There are many types of Whole Home Air Purifiers designed specifically to control one or several of the 3 different forms of indoor air pollution (Particulate Matter, Biological Pollutants, and Gaseous Pollutants). Making the addition of certain plants to a home's interior is also a great IAQ option. NASA has performed studies showing certain species of plants have been shown to be better at removing toxins from the air than others, such as the Gerbera Daisy and Janet Craig plants. Incorporating plants into our homes is a relatively inexpensive IAQ improvement to purchase and maintain and by doing so bringing nature's life support system indoors and a quick and easy way to improve indoor air quality.
Whole Home Ventilation for Better IAQ
So have you been holding you breath for cleaner and healthier air in your home? With the majority of residential HVAC systems not mechanically ventilating and making adequate fresh air exchanges with the outdoor environment it's important to determine if your home's air conditioning system falls into this category and if indoor air quality is an important concern in your home, Adams Air provides installation and repair services for many types of whole home ventilation systems, including: Exhaust Ventilation Systems, Supply Ventilation Systems, Balanced Ventilation Systems, Energy Recovery Ventilators, Heat Recovery Ventilators, and Energy Recovery Ventilators with Cooling and Heating all of which provide healthy IAQ benefits and comfort benefits as well.
Adams Air's Premier Home Ventilation Services in Houston and the surrounding areas
Fresh Air Ventilators
Energy and Heat Recovery Ventilators
Conditioning Energy Recovery Ventilators
For more information on the types of Whole Home Ventilation Systems we offer at Adams Air, select the tab labled "Whole Home Ventilators" at the top of this page.
Official Studies and Resources Concerning Hazardous Air Pollutants
When it comes to modern homes, efficiency, and indoor air quality, at Adams Air our motto is: “Seal Tight and Ventilate Right”. Every home needs adequate ventilation in order to maintain healthy levels of indoor air quality and with modern homes being built superinsulated and air tight in order to conserve energy and reduce heating and cooling costs, there is even a greater need for home ventilation - Houses are so well sealed and insulated that not only do they trap and maintain temperatures in our homes in turn reducing energy consumption by reducing central air conditioning run time, but they also trap indoor air pollutants in our homes as well, and without adequate ventilation hazardous air pollutants such as formaldehyde and other volatile organic compounds can build up and accumulate into highly concentrated levels that may cause health problems. Curious about what's in your home's air and if IAQ is a problem in your home? A company called Home Air Check provides a relatively simple solution for testing your home's indoor air and if your home isn't being ventilated the results may surprise you. Home Air Check provides several types of test kits that you can purchase, they'll send you the kit and a little electrical pump that you set up in your home and after running the test you just send the equipment and test sample back and within a few business days they'll send you the results outlining the air pollutants found in the air. Test kits include kits for testing for Mold, VOCs, Formaldehyde, and Tobacco Smoke. So if testing the levels of contaminants in your own home's air is something you interested in, search around for Home Air Check IAQ Test Kits. In the meantime though, lets get back to whole home ventilators and adequate air ventilation:
What is adequate home ventilation? The ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) recommends that in order to maintain a healthy indoor air environment that homes should be ventilated at a rate of 7.5 cubic feet per minute (CFM) per person, plus 3 more CFM per every 100 square feet of the home. Proper air exchange ensures that fresh and oxygen rich air enters our homes while expelling stale and polluted air out of our homes and whole home ventilation systems automatically and continuously provide this process, in turn creating a healthy indoor air environment, well most of the time anyway - Sometimes the outdoor air quality being brought into a home is worse than the indoor air, essentially adding pollutants and making indoor air quality worse. Other times the outdoor air is too hot or humid and ventilation systems can add too much moisture and heat to a home, making air conditioners run constantly or allowing mold to grow indoors. Thankfully there are several forms of home ventilation systems. Some lean towards indoor air quality benefits, while others lean toward energy efficiency benefits. So which is right for your home?
Exploring the different types of Ventilation Systems
Ventilation Systems vary according to climate and scenario with the main differences being the air pressure differentials they create within an an internal occupied space - Either negative, positive, or neutral. Therefore, there are 3 types of ventilation systems - Exhaust Ventilation Systems, Supply Ventilation Systems, and Balanced Ventilation Systems. Each type of system comes in a variety of configurations and depending on application and climate determines which type of ventilation system is most beneficial. These negative, positive, and neutral internal air pressures within the occupied space consequently affect how external pressures outside the occupied space react to these differences in pressure. Negatively pressurized spaces utilizing exhaust ventilation systems tend to suck outdoor air into the indoor environment through dedicated vents and (unfortunately) unsealed air gaps within the space's outer envelope such as soffits and air gaps on exterior walls of a home. While positively pressurized spaces utilizing supply ventilation systems will force the indoor air out through such vents and air gaps. Finally, spaces with balanced ventilation systems are neither pressurized nor depressurized. Instead, balanced ventilation systems intake and exhaust equal quantities of fresh outdoor air and polluted indoor air in and out of the occupied space, keeping air pressure neutralized. Depending on the situation and climate each type of system is both useful and applicable.
Examples of Exhaust Ventilation Systems
In applications such as the isolation rooms of hospitals where highly contagious infections must be isolated and contained in order to prevent the possibility of spreading contagions, Exhaust Ventilation Systems are utilized to constantly remove biological pollutants from the contaminated isolation area. In designated smoking areas of restaurants and nightclubs where contaminants are constantly being added to the indoor air via tobacco smoke it's also important to maintain a depressurized state via exhaust ventilation systems in order to constantly remove contaminated air from the indoor environment. Both of these types of Exhaust Ventilation Systems are designed to provide indoor air quality benefits. Homes in moderate outdoor climates with low humidity also incorporate exhaust ventilation systems due to their ability to 'pull in' cool and crisp air from the outdoors, in turn reducing energy costs by reducing the run time of cooling systems and sometimes eliminating their need entirely.
Examples of Supply Ventilation Systems
Supply Ventilation Systems are the exact opposite of exhaust ventilation systems and essentially pressurize buildings, homes and areas. For example, in operating rooms found inside hospitals where surgical operations take place it's important to maintain a positive air pressure via supply ventilation. Positively pressurized operating rooms constantly keep air blowing out of, and underneath the doors of the operating room. This positive pressure essentially creates an 'infection barrier' as a means to prevent harmful air pollutants from entering and infiltrating through such air gaps underneath or between doorways leading into the operating room which would cause dangerous infections in exposed patients during surgical operations. Homes in climates with high temperatures and humidity also utilize supply ventilation systems due to their ability to prevent hot and humid outdoor air from infiltrating into the home which reduces energy costs by reducing the run time of air conditioning systems.
Examples of Balanced Ventilation Systems
Commercial kitchens inside restaurants utilize Balanced Ventilation Systems for indoor air quality purposes. By code the amount of air being exhausted from a commercial kitchen has to equal the amount of air being supplied into the kitchen due to the high air exchange requirements for commercial cooking kitchens. In commercial kitchens, exhaust systems in the form of exhaust range hoods remove all the toxic gasses such as carbon monoxide generated by the cooking equipment and supply systems introduce equal amounts of fresh air back into the kitchen replacing the air that has been exhausted. Without these adequate air exchanges within the kitchen the indoor air would quickly be overwhelmed by hazardous fumes and gasses which would quickly spill into the dining area of the restaurant. In tightly sealed modern Houston homes where our outdoor climate is typically hot and humid, the most energy efficient and beneficial indoor air quality solution is also a Balanced Ventilation System. Balanced Ventilation Systems utilize both supply and exhaust ventilation techniques to maintain an equal or neutral air pressure within a home - We don't want the hot and humid outdoor air entering our homes which occurs with Exhaust Only Ventilation Systems. And, at the same time we don't want our cool and conditioned air leaving our homes like we see in Supply Only Ventilation Systems. Whole Home Balanced Ventilation Systems equipped with Energy Recovery Devices accomplish energy saving benefits through the conversion of energy by utilizing a heat exchanger which allows these systems to recover a large portion of the energy lost through the exhaust process or gained from the supply process by transferring the energy from the exhausted air back into the fresh air that's being supplied into the home. In turn providing both air quality and energy saving benefits, which makes these systems perfect for a hot and humid climate like Houston, TX.
Let's explore how all 3 ventilation systems work and discuss the differences, prose, and cons between the 3:
Exhaust Ventilation Systems
Have you ever noticed the extra light switch in your bathroom that operates the small exhaust fan located in the ceiling? This is an example of an exhaust ventilation system in its simplest form which serves to remove moisture, odors, and indoor air pollutants generated by the bathroom in order to provide indoor air quality benefits - The fan pulls air, odors and contaminants out of the bathroom, pushes it outside through the roof of your home, and fresher and cleaner air then rushes into the bathroom through air gaps around the bathroom door. However, exhaust ventilation systems can grow to be much more complex than a simple bathroom exhaust fan, applying the same depressurizing concept to entire homes and buildings depending on the outdoor climate and scenario.
Exhaust Ventilation Systems work by depressurizing a home, building or specific area - An indoor fan creates a negative pressure within the occupied space causing higher pressured air outside the occupied space to migrate into the occupied space through dedicated vents, open windows, and unfortunately in many cases through air gaps and air leaks in a building's exterior envelope. Exhaust Ventilation Systems utilize a rotating fan or impeller to create an air pressure difference and directional flow of air out of the areas they serve and essentially depressurize the areas they operate within. On the back end of the rotating fan blades the air pressure is low, causing higher pressured indoor air to rush toward the rotating fan blades of the exhaust system where it collides with the fan blades and gains velocity and directional flow. This air flow is then propelled and directed outside of the home, building or designated area(s) the exhaust system serves to depressurize, carrying along with it contaminants that are suspended within the air stream. As the exhaust system directs air and contaminants out of the area it serves, this area loses air pressure, which causes high pressured make up air from the surrounding areas to rush in and replace or 'make up' the air in area the exhaust system is operating within. Therefore, the main concern with exhaust systems is the make up air and what the make up air is composed of, and this is the primary factor that dictates if an exhaust system is applicable or not.
Whole Home Exhaust Systems are popular in moderate outdoor climates and cooler parts of the country with low humidity and where central air conditioning is in many times not even installed or needed. If you've ever been in one of these northern homes without central air you may have noticed a rather large fan device installed in the ceiling called a 'Whole House Fan', also known as an 'Attic Fan'. These Whole Home Exhaust Systems consist of a fan that pulls outdoor air into the home through the home's windows, throughout the home, and finally into the home's attic, either from a central location or from several locations at once. Once air enters the attic it naturally drifts away by temperature differences and draft by the wind penetrating air gaps in the home's eve and breathing soffits. These whole home exhaust systems are designed to be activated with the home's windows open and in cooler climates so they can draw in cool, crisp and fresh air into the home. In essence providing comfort benefits to homes without the need to run a central air conditioning system. Air sources from Whole Home Exhaust Systems such as these are also unfiltered and can also bring in outdoor air pollutants such as plant allergens like pollen and other air borne contaminants, so their fresh air intake properties can also provide IAQ problems, especially for those with asthma or allergy issues.
Since Whole Home Exhaust Systems are typically found in moderate to cool climates with low humidity, Exhaust Ventilation Systems in Houston residential applications are generally reserved to servicing 'spots' or areas such as bathrooms and kitchens for indoor air quality purposes. Because Houston's climate is so hot and humid, whole home exhaust ventilation systems are impractical ventilation strategies. Installing a whole home exhaust ventilation system in a Houston home would allow the heat and humidity from the outdoors to enter the home through windows, soffits, and other air gaps in the home's outer envelope. This would inevitably cause the central air conditioning system to constantly run in order to remove this heat and humidity pulled into the home by the exhaust system, in turn providing no comfort or energy efficiency benefits. Other than bringing in fresh air, whole home exhaust ventilation systems in Houston also provide little to no indoor air quality benefits because high pressured outdoor air saturated with heat and moisture is drawn into the home by the negative air pressure created by the exhaust system. Moisture problems would then occur throughout the home, windows may sweat with condensation when the HVAC system allows indoor temperatures to reach the dew point, and moisture would ultimately collect in crawlspaces and in between walls where it would provide a perfect breeding ground for fungi, mold, mildew, and bacteria. This basically limits home exhaust systems to servicing specific rooms or spots within Houston homes for specific indoor air quality benefits, such as in kitchens and bathrooms. Let's sum up the pros and cons of Home Exhaust Ventilation Systems:
Home Exhaust Ventilation System Pros vs Cons
Relatively inexpensive to install.
Applicable in environments with moderate climates and low humidity.
Can draw air pollutants into living spaces.
Not appropriate for hot and humid climates.
Can increase heating and cooling costs.
Can cause backdrafting of combustion appliances*.
* What is Backdrafting? Combustion appliances like water heaters, fireplaces and wood burning stoves have their own natural exhaust systems that carry small particles and toxic fumes such as carbon monoxide generated by the appliance out of the home via natural draft due to heat rising. Careful consideration has to be taken when installing Home Exhaust Ventilation Systems so they don't over-power an appliance's own natural exhaust system. When home exhaust ventilation systems are too powerful they cause Backdrafting, which means they essentially 'fight' an appliance's natural exhaust ventilation system, 'pulling', and backdrafting the dangerous particles and toxic fumes back into the home where they can cause health issues.
Supply Ventilation Systems
Supply Ventilation Systems are the exact opposite of exhaust ventilation systems - Unlike exhaust ventilation systems which negatively depressurize an occupied space, Supply Ventilation Systems positively pressurize occupied spaces. In homes, Whole Home Supply Ventilation Systems in their simplest form utilize the home's central air conditioning system's indoor blower motor as a fan to supply fresh outdoor air directly into the house. These systems work by drawing fresh outside air into the interior living space through a supply vent that penetrates an exterior wall with a duct that feeds into the return ducting of the home's central air conditioning system, essentially giving the return side of the HVAC system access to the outside air. This ventilation strategy allows the occupied space's air pressure to reach higher pressures than the surrounding unoccupied space's air pressure. Which, unlike exhaust ventilation systems that negatively depressurize a home in turn 'drawing' air into the home through windows, dedicated vents, and unsealed air gaps of a homes exterior. The positive pressure created by a supply ventilation system forces air out of such areas and gaps, essentially creating a pressurized vapor barrier that prevents outdoor heat, moisture, and contaminants from entering into the home. Since whole home supply ventilation systems connect directly to the home's central air conditioning system's return air ducting, the fresh air that is supplied to the occupied space by the HVAC system's indoor fan usually goes through the same process that air would normally go through when the HVAC system is running in cooling mode and is filtered and conditioned before being distributed into the home via the HVAC system itself (Although some supply ventilation systems do incorporate controls that will periodically run the HVAC systems blower motor independently while the air conditioning system is not running, or incorporate dedicated supply fan accessories, more about that below).
Although the general concept described above remains the same, supply ventilation systems can incorporate different features including mechanical dampers, barometric dampers, dedicated supply fans, dedicated filtering systems, sensors and controls. These accessories give the system improved control over the air being supplied into the occupied space. A whole home supply ventilation system's installation process is relatively simple and inexpensive - A hole is typically punctured through an exterior wall somewhere in the attic of the home close to the home's HVAC system. The exterior end of the new puncture is then covered with a weather-proof hood to prevent any water infiltration from rain and also to prevent any critters from crawling into the system itself. A duct is then ran from the hole in the exterior wall to the home's HVAC system and connected to the HVAC system's return air ducting, giving the HVAC system fresh air accessibility. It is here in this ducting between the HVAC system and the exterior wall that various features, other than barometric dampers, may accompany the system. Generally and at bare minimum a manually operated air damper or motorized actuator controlling an air damper should then be inserted inline with the new fresh air intake duct in order to control the rate of outdoor air being pulled into the home by the HVAC system's indoor blower motor. If the fresh air damper is controlled by motorized actuator or accessories such as a dedicated supply fan are being added to the system, they are then fed power and hard wired into the HVAC systems controls, which allow the air damper and accessories to operate accordingly based on certain factors such as temperature, humidity and whether the home's recommended ASHRAE air exchange rate has been satisfied. And finally with all supply ventilation systems it is a good practice to install an adjustable barometric air damper on the HVAC systems return air ducting somewhere before the fresh air intake ducting from the supply ventilation system, which will serve as an air pressure relief valve. This is especially true for tightly sealed homes without adequate exhaust systems or fireplaces to relieve pressure generated by the supply ventilation system, which would allow the indoor air pressure to reach unwelcome levels. A barometric air damper opens when air pressure within the home gets too high and becomes strong enough to force the damper open which essentially vents air directly into the attic, in turn relieving and dropping air pressure within the living space. Once the air pressure is relieved the barometric damper closes and stops venting air into the attic. Too much air pressure within a home's living space can cause doors and cabinets to fly open or close on their own, make opening and closing doors a very difficult and superhuman hulk-like task, create strange explainable noises, cause windows and cabinet doors to shake and rattle, and in general cause other annoying and spooky phenomena that may lead someone to believe their home is being haunted by ghosts.
Advantages of whole home supply ventilation includes the ability to control where incoming air is coming from, treat and filter the incoming air, and minimize the humid air that is pulled into the living space from the outdoors. Supply ventilation systems, unlike exhaust ventilation systems, prevent backdrafting of combustion appliances due to the positive air pressure they create within a home. And since supply ventilation systems pressurize the house, this generates a pressurized vapor barrier that keeps outdoor air pollution, moisture and heat out in hot and humid climates although it may cause moisture to condense in walls in cold climates if warm air escapes through unsealed air gaps to the outdoors.
Whole home supply ventilation systems are typically found in hot and humid climates as a means to introduce fresh air into homes and improve indoor air quality by positively pressurizing the house, which prevents outdoor air pollutants, heat and humidity from entering the home through air gaps. Installing a supply ventilation system can add latent and sensible heat and moisture from the outdoor environment directly into the home's HVAC system, where it will have to be removed by the air conditioning system and this translates to increased run time of the HVAC system which increases energy consumption. This is exactly why manufacturers of these systems have started incorporating humidity and temperature sensors and other accessories into their designs. These sensors monitor outdoor humidity and temperature and affect how far open or closed the fresh air damper is, and controls the rate of fresh air intake in a more energy efficient manner while still providing IAQ benefits. Supply Ventilation Systems may not be the perfect answer when it comes to energy consumption, but they are applicable in Houston's hot and humid climate and are relatively inexpensive indoor air quality solution to fresh air. Let's sum up the pros and cons of using this ventilation strategy:
Home Supply Ventilation System Pros vs Cons
Relatively inexpensive to install.
Applicable in environments with hot climates with high humidity.
Does not draw outdoor air pollutants into living spaces.
Keeps heat and moisture out of homes.
Allows control and filtration of fresh air entering a home.
Can increase energy consumption and HVAC system run time.
Not appropriate for cold climates.
Balanced Ventilation Systems
Unlike whole home exhaust-only and supply-only ventilation systems, which rely solely on natural ventilation created by internal and external pressure differentials delivered by a single fan to move air and pollutants. Whole Home Balanced Ventilation Systems utilize 2 fans in order to execute both exhaust ventilation strategies and supply ventilation strategies at the same time and introduce fresh outdoor air into a home at the same rate that stale and polluted indoor air is exhausted from the home. This equal exchange of opposing supply and exhaust air streams neither pressurizes nor depressurizes living spaces which allows balanced ventilation systems to provide superior indoor air quality benefits and, as we'll soon learn, take advantage of energy efficiency benefits as well when compared to conventional supply-only and exhaust-only systems.
Balanced Systems with Energy Recovery Features
It's easy to assume that with balanced ventilation systems, since they incorporate both supply and exhaust ventilation processes, that these systems would also incorporate the same flaws that accompany supply-only and exhaust-only systems such as the fact that supply-only and exhaust-only systems can raise heating and cooling costs because they force conditioned air out of a home and introduce unconditioned air into a home, in turn making air conditioning systems have to make up for this excessive heat loss or heat gain (which increases energy consumption). Although this is true to a certain extent, whole home balanced ventilation systems also incorporate energy transferring mechanisms called Energy Recovery Devices which help alleviate the handicaps of excessive heat loss or heat gain from ventilation. Balanced systems with energy recovery devices, unlike supply-only and exhaust-only systems, actually 'recover' a portion of the thermal energy that is normally gained and lost by exhaust-only and supply-only ventilation processes by exchanging the temperature and humidity between the opposing air streams (see below).
Energy Recovery Theory (100% Air to Air Energy Exhange)
Hypothetically speaking - There are two opposing air-streams traveling in and out of a home. One at the temperature of 0ºF, and the other at 70°F. What happens to the temperature after it passes through an Energy Recovery Device? Many would assume each air stream would equalize and balance to the average temperature of 35ºF each. However, with recovery devices the thermal energy in the air-streams actually switches and the 70°F stream of air from the inside of the home now becomes 0ºF, and the 0ºF stream from the outside of the home becomes 70°F. This is the fundamental theory behind balanced systems with recovery devices. The case described above transfers 100% of all total energy, which has yet to be accomplished with traditional heat recovery ventilators (HRVs) or enthalpy or energy recovery ventilators (ERVs) - An energy recovery rating of 75%-85% much more realistic with HRVs and ERVs.
In order to achieve this energy recovery technique, balanced systems with recovery devices implement unique features within the system such as heat exchangers, enthalpy exchangers and other methods of transferring sensible (temperature) and latent (humidity) thermal energy which allow the balanced system to recover the heat and moisture being lost or gained through the exhaust and supply ventilation processes. For example, in Heat Recovery Ventilators (HRVs) a sensible heat exchanger is incorporated into system's design that allows these HRV systems to recover a large portion of the sensible heat energy (temperature) that is being lost or gained through the system's exhaust and supply processes. And, in Enthalpy or Energy Recovery Ventilators a sensible and latent heat enthalpy exchanger is used to recover portions of both heat and moisture from the supply and exhaust ventilation processes. There are also specialized energy recovery ventilators with cooling and heating functions which are balanced ventilation systems that utilize air source heat pumps to transfer air to air energy, which provide the greatest energy exchange benefits (100% and more) when compared to other forms of balanced home ventilation. Let's take a moment to look inside a typical Balanced Ventilation System that utilizes an Enthalpy or Energy Recovery Ventilator to transfer both heat and moisture between the supply and exhaust air streams and explore how it works.
Inside an Energy Recovery Ventilator
Inside Whole Home Balanced Ventilation Systems such as Heat Recovery Ventilators, Energy Recovery Ventilators, and Energy Recovery Ventilators with Cooling and Heating functions, there are opposing 2 fans which are responsible for the supply and exhaust processes of the system - One fan supplies fresh air into the home while the other exhausts polluted air out of the home. These fans direct the opposing incoming and outgoing air streams through various forms of energy exchanging components depending on the desired energy to be transferred and savings outcome, and this is where balanced systems with recovery ventilators begin to differ internally.
Heat Recovery Ventilators
Heat Recovery Ventilators transfer only portions of Sensible Heat Energy, or Air Temperature between supply and exhausted air streams. In colder and less humid climates where heating a home dominates the HVAC process the majority of the year (and the utility bill) making it important to focus on preserving heat within the house, such as northern parts of the country, Heat Recovery Ventilators are primarily used in order to exchange only the heat energy that is gained or lost during the balanced air exchange process. During the winter time with HRVs, a large portion of the heat in the indoor air being exhausted from the home is removed and transferred into the cold outdoor air being supplied into the home, in turn preheating the fresh supplied air as it enters the home and in turn saving energy by reducing heating system run time and providing comfort and IAQ benefits. No moisture is transfered during this process with HRVs and only energy in the form of temperature is exchanged within the air which is why these systems are particularly useful in colder climates with low humidity. During the summer months with HRVs the exact opposite is true and a large portion of the hot outdoor air being supplied into the home gets cooled down by the conditioned indoor air exiting the home.
Heat Recovery Ventilator Pros vs Cons
Recovers a large portion of the heat gained or lost through ventilation.
Preferable in climates with low humidity.
Neither pressurizes nor depressurizes a home.
Prevents air infiltration through air leaks in a homes envelope.
Allows percise control and filtration of fresh air entering a home.
Does not recover humidity.
Supply and exhaust fans require electricity to operate.
Not appropriate for humid climates.
More expensive to install than supply and exhaust systems.
Contains filters that have to be replaced.
Energy Recovery Ventilators
Enthalpy or Energy Recovery Ventilators take the energy transfer process a step further than HRVs by exchanging both sensible heat (air temperature) and latent heat (humidity). In hot and humid climates where cooling a home dominates the majority of HVAC usage during the year, such as here in Houston Texas, Enthalpy or Energy Recovery Ventilators are utilized in order to minimize both heat and humidity gained or lost during the fresh air exchange process. ERVs are essentially HRVs with the bonus feature of transferring latent heat energy or moisture. During the summer with ERVs a large portion of the heat and moisture from the outdoor air being supplied into the home is removed and transfered to the cold and dry indoor air being exhausted out of the home, essentially precooling and dehumidifying the supplied outdoor air as it enters the home and by doing so taking the load off of the air conditioning system. This transfer of energy provides energy efficiency benefits by reducing the run time of the cooling system when compared to the other conventional ventilation methods. During the wintertime with ERVs, like HRVs, the process reverses and the heat and moisture in the warm and humid indoor air being exhausted out of the home is removed and transfered into the cold and dry outdoor air as it is supplied into the home, essentially preheating and humidifying the incoming air taking the load off the home's heating system, which again saves energy and provides IAQ and comfort benefits.
Energy Recovery Ventilator Pros vs Cons
Recovers a large portion of the heat and moisture gained or lost through ventilation.
Preferable in climates where humidity is a concern.
Neither pressurizes nor depressurizes a home.
Prevents air infiltration through air leaks in a homes envelope.
Allows percise control and filtration of fresh air entering a home.
Supply and exhaust fans require electricity to operate.
More expensive to install than supply and exhaust systems.
Contains filters that have to be replaced.
The Difference Between HRVs and ERVs
The main difference between enthalpy or energy recovery ventilators and heat recovery ventilators is the type of heat exchanger located inside of the system located at it's core which dictates how much of what type of energy is actually transferred between supply and exhaust air streams. HRVs simply exchange thermal temperatures via a sensible heat energy exchanger whereas ERVs utilize a sensible and latent heat energy enthalpy exchanger which transfers both heat and moisture between the two opposing supply and exhaust air streams. Both HRVs and ERVs typically (but not always) make use of counter-current heat exchangers in one form or another due to their ability to efficiently transfer heat energy without the air streams every actually mixing. These types of heat exchangers are essentially metallic tubes, plates, or cells placed close in proximity to each other that the opposing exhaust and supply air streams are channeled through, allowing sensible heat (temperature) to transfer across air streams by means of convection. The difference between then between ERVs and HRVs that utilize counter-current heat exchangers is that the ERV's version of the counter-current heat exchanger also incorporates a permeable membrane of silica, or some specialized synthetic micropourous material which also allows latent heat (moisture) to be transfered beween the air streams through evaporation and condensation processes. Some ERVs utilize a rotating heat-wheel instead of the counter-current method described above. These types of heat exchangers are found in higher-end models of ERVs because they have a higher energy exchange ratio when compared to counter-current heat exchangers. However, heat-wheels also mix a percentage of the air streams, which means a certain portion of the air leaving the living space re-enters the living space. Typically this ratio of air portions mixed is very low (around 10%). Heat wheels simply recover more energy at the cost of indoor air quality, so using them to ventilate areas such as close to kitchens or bathrooms should be re-considered.
Energy Recovery Ventilators with Cooling and Heating
Energy Recovery Ventilators with Cooling and Heating functions take the energy recovery process even further than the previously discussed balanced ventilation systems by incorporating an air sourced heat pump into their design which precools and preheats opposing supply and exhaust air streams beyond the energy recovery ratio. Since the heat exchanger inside both ERVs and HRV's fails to completely transfer 100% of the thermal energy contained within the exhaust and supply air streams, there is always some amount of energy being lost or gained through the balanced ventilation processes. Typical HRV's or ERV's can achieve a 75% energy recovery rating, with the most advanced models effectively recovering upwards to 95%-96%. But, even at this impressively high level of energy recovery, a small percentage of heat or humidity is still not being recovered, and in some climates where humidity is often high and a contributing factor to comfort (such as here in Houston) an HRV or ERV can actually cause humidity levels to rise indoors. Let's take a look at how this might happen: For example, in a tightly sealed Houston home where the air conditioner rarely runs because the house is so well insulated, running an ERV will slowly add humidity to the home on a very humid day. The air conditioner may only occasionally turn on to cool the home's temperature down which occurs rather quickly due to the home's superb insulation factor. However, this short run-time doesn't give the air conditioning system enough time to effectively remove moisture from the air within home and with the ERV slowly adding small amounts of humidity to the home despite all its recovery efforts, the temperature may remain cool from the air conditioner occasionally running but humidity can continue to rise indoors - This is why manufacturers have developed energy recovery devices with heating and cooling functions. Inside these systems, the manufacturer inserts a sensible and latent heat exchanger along with a heat pump in between the exhaust and supply air streams, essentially achieving 100% of energy transfer and more so that even on a hot and humid day, the air supplied into a home will never raise indoor temperatures or humidity.
Inside an ERV with Heating and Cooling
How does it work? On a summer day, A supply fan channels the incoming hot and humid outdoor air over the supply side of a sensible and latent heat enthalpy exchanger, which removes some heat and moisture from the supply air as with an ordinary ERV. The now-energy-recovered supply air is then directed over the internal heat pump's evaporator coil, which cools and dehumidifies the supply air even further and beyond the 100% recovery ratio before distributing the air into the home. At the same time on the exhaust side of the ventilator, the cool and dehumidified exhaust air from the home is channeled over the exhaust side of the sensible and latent heat enthalpy exchanger, where it picks up the heat and moisture removed from the supply air as with an ERV system. This exhaust air is then directed through the heat pump's condenser coil, which adds the heat to the exhaust air that it removed from the supply air when it was directed over the heat pump's evaporator coil, and expels it outdoors. During winter months, the same process takes place in reverse and provides the home with warm air. This precooling and preheating technique takes the heat and moisture load off the HVAC system no matter what the outdoor climate is and provides all the benefits of the other balanced ventilation systems without all the flaws or the possibility of increasing indoor humidity in very humid climates.
With 2 exhaust fans and a small heat pump, you would be correct in assuming these systems consume the most electricity when compared to the other ventilation systems we've discussed. So why would anyone have one installed? Other than their dehumdification properties, these systems are designed to ventilate homes that are very well insulated, so well infact that an air conditioning system rarely has to run in order to maintain the temperature in these types of superinsulated homes. Air leaks and air infiltrations are rare in homes that are insulated very well, and like a well insulated Yeti cooler, these superinsulated homes maintain their temperature for long periods of time. In these applications running 2 variable speed exhaust fans and a small heat pump often consumes less electricity than running the entire air conditioning system, which in turn reduces energy consumption. Lets go over the pros and cons of a system like this:
ERV + Cooling and Heating Pros vs Cons
Recovers over 100% of heat and moisture gained or lost through ventilation.
Preferable in any climate.
Neither pressurizes nor depressurizes a home.
Prevents air infiltration through air leaks in a homes envelope.
Allows percise control and filtration of fresh air entering a home.
The heat pump feature, and exhaust and supply fan features, mean this unit costs the most to operate.
Most expensive ventilation system to have installed.
Contains filters and mechanical components that must be maintained.
Choosing the right whole home ventilation system
With so many types of whole home ventilation systems, which is the right system for your home? Choosing the right whole home ventilation system requires a little detective work and depends on many factors including the outdoor climate, your comfort level, your current HVAC system, energy savings expectations, how many people live in your home, and how well your home is insulated. Here in Houston our choices are limited to supply-only and balanced systems due to our hot and humid, cooling dominated climate. If you're building a new home and plan on having it superinsulated or have a modern superinsulated home where air infiltration and air leaks are uncommon, the best choice is a balanced ventilation system. Although these systems initially cost more to install, these systems were designed to ventilate a well insulated living space and their benefits really shine in this type of application. If you have an older home that's not superinsulated then supply-only ventilation systems are also applicable. And finally, if you're unable to decide which type of whole home ventilation system you should incorporate into your home, turn to the indoor air quality experts at Adams Air. Our well qualified staff can help you design the perfect whole home ventilation solution whether you're building a new home or ventilating an existing one. A simple home inspection is all it takes to determine which type of ventilation system would best suit your needs and with over 30 years of experience keeping Houston homes cool and comfortable you can rest assured you're in good hands.
Turn to the Houston Home Ventilation Experts
So are you ready to ventilate your entire home and say hello to better air quality? Adams Air representatives are available 7 days a week to answer any of your Whole Home Ventilation questions and offer competitive family operated rates any Houstonian would be proud of. Our whole home ventilation systems will ensure everyone in your home is breathing fresh and healthy air for years to come. For more information or to schedule your whole home ventilation consultation, call (281)-375-2011 or contact Adams Air via the form below and we'll call you back in no time.
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