Healthy Indoors Magazine
Issue link: https://hi.iaq.net/i/327414
ventilated, work with HVAC contractor to add mechanical ventilation or HRV/ERV." Most HVAC systems are oversized to account for excess air leakage, which directly affects the energy efficiency as well as effectiveness of dehumidification. The application of spray polyurethane foam insulation and resultant reduction in air leakage may therefore allow for the downsizing of the HVAC system for bet- ter performance. Appropriate adjustments or downsizing of HVAC systems help to achieve good IAQ, avoid short-cycling of the AC system, meet the minimum mechanical ventilation rate, and provide better control of relative humidity. Once the results of the Test-Out blower door evaluation are in, your home's mechanical system requirements must then be properly calculated using a Manual J for load calcula- tion, a Manual S for equipment selection, and a Manual D for proper duct design. Manual J is the name for a specific protocol (often called "Heat Load Calculation" or "Cool- ing Load Calculation") used to determine how much heating/cooling a home needs to stay cool and dry in the summer and warm in the winter. This load calculation process was devel- oped by engineers in the heating and air condi- tioning industry and has been used for decades to accurately size heating and air-conditioning equipment. A Manual-J load calculation report provides three main pieces of information regarding heat- ing and cooling load. The "heating load" is how much heat your house will require on the almost coldest day of the year, in the middle of the night (when there's no help from the sun). This is the number, or load, used to select a piece of heating equipment. The "sensible cooling load" is the amount of sensible heat (the type you measure with a thermometer) that your system should be able to remove on the almost-warm- est day of the year, during the daytime (when the sun is heating up the building). The "latent Guidance on Best Practices for the Installation of Spray Polyurethane Foam Important note about air handlers If a ventilation system that uses the HVAC air handler fan to provide the needed outdoor air (as is the case in many supply ventilation strategies) is used, it is imperative to ensure that the air handler fan operates often enough to provide sufficient fresh air. During periods of mild weather, or at night in the summer, the air handler fan may not be called on to run for several hours, so the house would get no outdoor air during these times. To address this, control units are now available that will ensure the house always gets the needed ventilation. If the air handler does not operate enough for sufficient ventilation, the monitors will call for the fan to operate and provide sufficient fresh air. Typically, most homes need for the fan to run for between 10 and 20 minutes each hour to meet the home's ventilation needs. An ex- ample of this type of fan control unit is the Aprilaire 8100. The introduction of outdoor air not only affects the temperature in the house, it also impacts the humidity in the house. Here in Florida, the humidity can be a critical factor that is often overlooked. Our hot humid southern Florida outdoor air supply will require mechanical de- humidification. It's critical to include ventilation air in the ACCA Manual J, Eighth Edition (J8) HVAC sizing calculations. Spray Poly Foam Continued from previous page Healthy Indoors 51