Creative Solutions For ASHRAE 62.2 Makeup Air Requirements
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 Buildings is now a requirement for all new ENERGY STAR (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, AZ, developed a solution based on the air temperature and the time of day. Obviously, in Phoenix where the Manual J design temperature is 108˚F, 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. The system allows them to take advantage of the 62.2 option that lets them to bring in more air during off -peak temperature times, thus lowering the negative load implications of operating under 100˚F 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 temperatures are closer to the desired indoor temperature.
Jolene Methvin of Bay Area Air Conditioning & Heating, Inc. reports that due to the unrelenting high humidity levels in Crystal River, FL, 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 be minimized.
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 homeowners understand that reducing the potential for mold growth coupled with lowering the peak cooling load’s effect on their electric bill over the life of their system is the best option.
In Syracuse, NY, Ellis Guiles of TAG Mechanical Systems takes an approach based on individual engineering cost analysis calculations for each job. Guiles 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 operate in upstate New York was also relatively inexpensive to install. The key to the design’s success is three-fold.
The first part is to operate a low sone, low wattage, ES-compliant exhaust fan 24/7. The exhaust fan is balanced to exhaust the exact amount of makeup air needed to meet the ASHRAE 62.2 requirements.
The second part is to add the exact amount of makeup air needed to the return duct plenum. To make this approach work properly without complaints of cold draft s, TAG Mechanical has found that they needed to precisely control the amount of air coming from the outside. This is accomplished by utilizing a mechanically controlled damper designed to automatically maintain a constant CFM.
The third 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 damper amounts to 70 to 100 percent of the exhaust fan’s CFM value.
It is obvious that there are many approaches for meeting ASHRAE 62.2 requirements. However, a good 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.
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