Balanced fresh air ventilation design, installation, & troubleshooting in buildings:
Tthis building ventilation design article explains the use of balanced fresh air ventilation systems, heat recovery ventilators, and energy recovery ventilators to improve indoor air quality in homes.
Lots of people consider dust, pollen, mold, animal allergens, pet hair as the main culprits in indoor air quality issues, allergies, and asthma aggravators. But many indoor contaminants are simply too small to see, or are not particles at all but rather gases or chemicals. Balanced ventilation systems combine fresh air input with stale or contaminated air exhaust to improve indoor air quality while saving on building energy cost.
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As reported in Best Practices Guide to Residential Construction:
Balanced ventilation uses both a supply and exhaust fan to provide fresh air while keeping house pressures neutral. Linking a multiport supply system (described above) with a bathroom exhaust fan on the same switch is a form of balanced ventilation.
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Well suited to extreme climates, balanced ventilation provides optimal distribution of incoming fresh air and tempers it for comfort.
HRFs reclaim heat from the exhaust air while ERFs, recommended for hot humid climates, dehumidify and cool incoming air. For good performance, systems must be properly installed, balanced, and maintained.
Illustration Source: Recommended Ventilation Strategies for Energy-Efficient Production Homes, 1998, by Judy A. Roberson, et al., Lawrence Berkeley National Laboratory, appearing in the text cited above.
Most balanced ventilation systems, however, use a heat-exchanger to transfer heat and, with energy recovery ventilators (ERVs), humidity between the two air streams. These systems, sometimes called air-to air heat exchangers, are the most expensive option for whole-house ventilation; but, if installed properly and well-maintained, provide optimal comfort and ventilation. Depending on the type of heat exchanger, balanced ventilators are referred to as either heat-recovery ventilators (HRVs) or ERVs.
One of our clients became so frustrated with problems balancing fresh air in her home that she simply cut out a window pane. This article discusses a better approach.
HRVs and ERVs are typically run continuously, but they also may be set to run 8 to 12 hours per day when people are at home.
In addition, most have a high-speed mode that can be manually activated for spot ventilation of kitchens and bathroom.
Some balanced ventilation systems also use dehumidistats to automatically turn on or increase ventilation when the air reaches a preset humidity level.
While a dedicated ductwork system is the best approach for HRVs and ERVs, to save money they are often piggybacked onto the home’s HVAC ductwork. In one approach, the HRV or ERV draws exhaust air from the return ductwork and feeds fresh air into the furnace’s return plenum. In a slightly better arrangement, the HVAC ductwork is used only for supply, while the exhaust side picks up stale air in bathrooms, laundry, and kitchen. Neither approach distributes fresh air as well as a dedicated duct system.
Also, since HRV/ERV fans operate at 100 to 200 cfm while air-handler fans are often sized at over 600 cfm, trying to integrate the controls, balance airflows, and provide the correct amount of ventilation air is challenging and rarely works well.
The most common approach is to run the ventilation system only when the thermostat calls for heating or air-conditioning, providing too little ventilation. Heat-recovery efficiencies are also compromised, typically due to unbalanced airflows.
One drawback of HRVs and ERVs is that they require more maintenance than other ventilation systems. Numerous studies have found that many of these systems significantly under perform in the field due to both installation errors and poor maintenance.
In addition to cleaning or changing intake, outtake, and internal filters, the homeowner or service person needs to clean the core once a year or more to prevent mold and bacteria growth. It is important to follow closely the manufacturer’s recommendations.
Unless the homeowner enjoys the responsibility of HVAC maintenance, the work is best handled by a professional service company.
For HRVs and ERVs to work properly and achieve the rated efficiencies, they must be installed correctly and balanced well, and the house must be very tight.
Even so, the added cost over a basic ventilation system will be recouped only in the most extreme United States climates with the highest energy costs. However, in very cold or hot climates where mechanical ventilation is needed during most of the year, the added cost may be justified by the comfort of tempered, filtered ventilation air, the effectiveness of the distribution, and the lack of pressure-related problems.
Used primarily in cold climates, HRVs have two air streams that pass over one another in a plastic or aluminum heat exchanger.At left we show a photograph of a heat recovery ventilator.
Used primarily in cold climates, heat-recovery ventilators (HRVs) pass two air streams by one another within a plastic or aluminum heat exchanger, recapturing 60 to 75% of the heat from the outgoing air stream. This unit, installed in an attic, is hung from chains to reduce noise and vibrations.
Recovery of heat from the exhaust air typically ranges from 60 to 75%, if properly installed and balanced.
During the summer, if air-conditioning is used, the heat transfer reverses, cooling the incoming hot air. Systems generally have exhaust ports in rooms that generate moisture or pollutants, including bathrooms, laundry, and kitchen and supply ports in bedrooms, living rooms, and other main living spaces.
Because they have both supply and return ducting, HRVs provide the best distribution, exhausting air from bathrooms and other wet areas and providing fresh air to primary living space. The kitchen typically has its own range hood, so grease does not get into the HRV system.
Original Best Construction Practices Guide photo source: courtesy of David Hanson, memphremagog Heat Exchangers, appearing in the text cited above.
In cold climate applications, a defrost cycle is required. It usually switches on at about 20°F to keep frost from building up in the core as condensation from the exhaust stream begins to freeze. Systems either recirculate indoor air or preheat incoming air to prevent freeze-ups.
Energy-recovery ventilators are primarily used in air-conditioned homes in hot, humid climates. They are generally recommended for climates where the cooling load exceeds the heating load and where sustained freezing temperatures are rare. Sustained temperatures below 10°F can damage the permeable core material used in many ERVs.
ERVs either use a dessicant-coated plastic wheel or a special “enthalpic” core material to move moisture (latent heat), as well as sensible heat, between the two air streams. In summer, incoming air is cooled and dehumidified. Since dehumidification is the biggest component of air-conditioning costs in humid climates, it is important to find a unit with a high TRE (total recovery efficiency) rating, indicating that it can transfer large amounts of moisture. To achieve the rated efficiencies, the units must be run at the recommended airflows.
In cold weather, an ERV will tend to humidify the incoming air, since the moisture transfer is always toward the less humid air stream. This is rarely a problem, however, since the cold incoming air holds so little moisture to begin with that the net effect of the air exchange is to remove humidity from the house.
We recently exchanged a few replies in the page bottom Comments section of this InspectApedia article: ASBESTOS in DRYWALL
Regarding glass fibers around a ventilation unit in a spare room we plan to store cooking supplies in etc., in a home we just started renting. The room is directly off our living room/kitchen. The building was built roughly 10 years ago.
Here is a picture. [Click to enlarge any image]
The taped areas used to have white/grey insulation sticking out but we had the landlord tape it up before we started moving in. However, I notice on the unit and black wrapping/sleeving on the duct (pipes?) that there are dozens, if not 100+, shiny fibers all over it. Most of them are short, ~1-2 mm long. The pictures are unable to pick it up, so I didn't try getting a close-up.
There doesn't seem to be any in the other rooms or anywhere else, so I'm assuming none of it ever got into the actual air flow of the unit, or at least not a noticeable amount.
I've damp wiped some of the unit, but there are areas hard to get into and I'm unsure how to try cleaning off the black pipe sleeving. I'm also unsure how much of an issue this actually is and whether I should be even concerned. I just want to make sure if it is an issue, I don't spread it and clean it properly. Some google searches of fiberglass hazards don't seem too helpful and have me worried, bringing up anything from it being just a nuisance dust all the way to cancer/mesothelioma links and blindness.
I look forward to your thoughts, thank you very much for your time.
Sincerely, - Anonymous by private email 2017/04/29
Got it - so the ventilator is a Venmar system and we're seeing dust on the duct exterior.
At FIBERGLASS FRAGMENT HAZARDS in AIR or DUST we explain that expert research indicates that while large fiberglass fragments found in buildings are not likely to be a carcinogen nor serious health concern, very small fiberglass fragments might indeed be a serious health risk. I add that without expert forensic microscopy very small fiberglass fragments are hard to spot and I suspect they have been missed in various studies.
Still small fiberglass fragments are not the normal product of fiberglass insulation or ductwork installation. Rather these tiny particles are made when fiberglass insulation or ductwork is damaged by foot traffic, grinding, chopping of existing insulation, or by running a mechanical duct cleaner inside of un-lined fiberglass ducts - or by similar events.
If you want to be most-meticulous, the easiest cleanup of dust that will also avoid aerating (and breathing) it is to use a HEPA-rated vacuum cleaner.
While in my OPINION the amount of fiberglass fragments of any size that will be released into the air from the edges of the flex-duct where it is banded to the connection ports on your Venmar heat recovery ventilator will be close to or below the limits of detection in the air in your h ome, even anxiety itself can be unhealthy, so you can certainly, if you wish, use foil adhesive tape to cover-over the edges of the flexduct at its connections.
This will make any future service or repair that requires removal of the flexible ductwork more difficult but certainly not impossible.
I can't see which Venmar model you have but as you may know Venmar produces air-to-air heat-exchanging ventilation systems to provide fresh air to a building without increasing heating or cooling costs. I have the company's product specifications and installation manuals if you need more information.
Venmar heat recovery ventilators (HRVs) or more currently called Venmar energy recovery ventilators (ERVs) are installed using standard third-party flex-duct that's standard, in a diameter that matches the HRVs connection ports. Beginning at DUCT ROUTING & SUPPORT
you will find a series of articles on flex duct that includes naming some problem brands, deterioration, contamination.
Generally the flexible ducts are made of a plastic or mylar liner, a coiled wire spring, fiberglass insulation, and a plastic exterior.
(A few problem brands had exposed interior fiberglass and others suffered from plastic that disintegrated when exposed to heat and time). As long as the flex-duct is lined and undamaged, fiberglass shedding into the air path into the building is not likely to be a concern.
Dust and debris on the duct exterior won't affect the ventilator's nor ducts' peformance. If there's a significant amount of fiberglass or other house dust in an area, perhaps left over from construction or accumulated over time, you can remove that by damp wiping and HEPA-vacuuming.
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(Sept 10, 2011) Brion Black said:
We have been asked by a person who is acutely effected by multipul toxics illness to create a very low VOC and allergens interior air environment within a studio apartment that is located in an 80 year old NYC apartment building. We plan to start by sealing all existing finishes with a special VOC containment paint and varnish.
However, it seems likely a fare amount of contaminated air will be entering from the rest of the building. Yes, we are sealing the envelope as much as possible. QUESTION: how can we bring in fresh air from outside (window opening) to exchange 30% of air by volume an hour, WHILE maintaining a small interior pressure (say 5 pa) to avoid building infiltration?
Any ideas would be very welcome. This may have to be a custom made (home made) unit.
I imagine you will want to do a blower door test to measure the actual building area air leakage rate. That measurement, combined with a careful survey of all of the vents and fans in the apartment to be sure you're not going to upset the balance, will let you specify the net air inflow rate to maintain a positive pressure with respect to the rest of the building.
I'd consider adding a manometer or similar air pressure gauge such as those used on radon mitigation systems to compare apartment air pressure to air pressure outside the apartment but inside the building. That lets the occupant as well as designer keep an eye on the proper air pressure balance.
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