Creative Solutions for Ventilation in New Homes
ACCA members are taking the lead in developing methods that economically meet the ASHRAE 62.2 ventilation requirements for residential applications. The creative solutions reflect the design requirements for specific regions of the country.ANSI/ASHRAE Standard 62.2 -2010 Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildingsis now a requirement for all new ENERGRSTAR (ES) homes. Solutions for new construction provide an excellent baseline for existing homes retrofits and upgrades as well.
Greg Cobb of Sonoran Air, Inc. in Phoenix Arizona developed a solution based on the air temperature and the time of day. Obviously, in Phoenix where the Manual J design temperature is 108oF,bringing in outside air via a constant volume method would increase the cooling load considerably. So Sonoran Air developed a time-of-day control system. That way they could take advantage of the 62.2 option that allowed them to bring in more air during off-peak temperature times, thus lowering the negative load implications of operating under 100oF plus conditions. Programmable controls were designed by Sonoran Air that measured outside air temperatures, inside air temperature, and a makeup air fan’s speed and run times per 24 hour cycle. That data was utilized by the control programming to operate within the ASHRAE 62.2 design guidelines. The installed system automatically adapts to take advantage of the daily outside temperature swings.Thus,it brings in most of the required outside air at night when the temperaturesare closer to the desired indoor temperature.
Jolene Methvin of Bay Area Air Conditioning & Heating, Inc. reports thatdue to the unrelenting high humidity levelsin Crystal River Florida,makeup methods without mechanical humidity control can do more harm than good. In areas that have extended periods of time when the weather is hot and humid, the potential for mold problems related to elevated home humidity levels needs to beminimized. Additionally, the latent heat load in the air being brought in becomes a larger factor in the total peak load for cooling. Energy recovery ventilators (ERV) or whole house dehumidifiers for fresh air makeup systems are the preferred methods. When properly informed of the pluses and minuses in their options, most Florida homeowners understand that reducing the potential for mold growth coupled with lowering the peak cooling load’s effect on theirelectric bill over the life of their system is the bestoption.
In Syracuse New York Ellis Guiles of Tag Mechanical Systems takes an approach based on individual engineering cost analysis calculations for each job. Ellis reports that they were initially surprised with the results of their cost benefit analysis for typical homes in their region. The operating system most economical to operatein upstate New York was also relatively inexpensive to install. The key to the design’s success is three-fold. The first partis to operate a low sone, low wattage,ES-compliant exhaust fan 24/7. The exhaust fan isbalanced to exhaust the exact amount of makeup air needed to meet the ASHRAE 62.2 requirements. Thesecond part is to add the exact amount of makeup air needed to the return duct plenum. To makethis approach work properly without complaints of cold drafts,Tag Mechanical has found that they needed to preciselycontrol the amount of air coming from the outside. This is accomplished by utilizing use a mechanicallycontrolled damper designed to automatically maintain a constant CFM. Thethird part is calculating the exact makeup airflow needed.This is accomplished by subtracting the measured infiltration rate (utilizing a blower door) from the exhaust fan’s total CFM setting (from the first part). Thus, when the controlled damper CFM is set,the home is provided with a neutral pressure difference between entering and leaving air. Generally, in tightly sealed homes the total CFM of airflow brought in through the controlled damperamounts to 70% to 100% of the exhaust fan’s CFM value in tightly sealed ES homes.
It is obvious that there are many approaches for meeting ASHRAE 62.2 requirements. However, agood approach for one climate zone, latitude, or altitude may not work as well in another. So, it is up to the professional HVAC contractor to ascertain appropriate solutions that resolve ASHRAE 62.2 requirements for their residential applications. At this time, ASHRAE 62.2 is still in the early code adoption stage by many states. ACCA members who are willing to share their unique compliance methods should contact Donald Prather at: firstname.lastname@example.org ACCA will continue providing updates to members on the evolution of ASHRAE 62.2. For additional information, ACCA members can download the Technical Bulletin entitled Ensuring Compliance with ASHRAE 62.2-2010 at: https://www.acca.org/members/downloads/technical-bulletins.
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