HVAC

Designing an HVAC System for a Passive Home

The traditional process of designing an HVAC system is to determine size and cost based on square footage and then wait until after framing to begin installation. This approach offers limited flexibility for customization based on architecture.

To better achieve the goals of this historic-modern passive house in Austin, Texas, I teamed up with the fine team at Positive energy, a local engineering company. The entire system was designed in Revit to dial in the assemblies and account for hot and cold spots within the layout. This ensures and enables an even distribution of the conditioned air correct dimensioning of the drains to fit into the structural system and meet the specifications of the home. The 3D modeling made the installation smoother because the installers knew exactly what was needed and could plan accordingly.

FRESH AIR FOR COOKINGFRESH AIR FOR COOKING The fresh air system in the kitchen replaces the exhaust air from the cooker hood with filtered fresh air from outside. The induction cooker is also part of the air quality strategy, avoiding the many toxic by-products of a gas combustion cooker.

Mitsubishi VRF heat pump: A VRF (Variable Refrigerant Flow) heat pump modulates the amount of refrigerant passed through the system, saving energy by circulating the minimum amount of refrigerant needed for each individual zone to meet heating or cooling loads.

IQAir Perfect 16 air purifier: Given the home’s proximity to a freeway and train line, indoor air quality was a priority. The IQAir filter box provides MERV 16 filtration of the air on the return side of the VRF heat pump.

Panasonic Intelli-Balance 100-CFM ERV: This balanced ventilation system supplies fresh air to the main living areas and removes stale air from the bathrooms and kitchen. It positively pressurizes the home and helps prevent airborne pollutants from entering.

Santa Fe Ultra70 Dehumidifiers: In a passive house, the air conditioning does not run often because the house does not heat enough to require it. We added dedicated dehumidification to counteract the potential for microbes due to Austin’s high humidity.

Custom Makeup Kitchen Air System: This system brings in outside air to replace contaminated indoor air that is exhausted through the range hood. The incoming air is filtered by a Honeywell Media Air Cleaner.

See the entire article: Passive house renovation in a historic neighborhood

Photo by Leonid Furmansky. Drawing by Christopher Mills.

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