Improving the Quality, Performance and Operation of HVAC Systems through Plant Installation
The manufactured housing industry has a consistent construction method, design, and approach to sales with about 100,000 homes produced annually nationwide. However, many building and design practices have not changed in decades, sometimes resulting in system inefficiencies. One example is the practice of installing HVAC components in two stages, with some parts installed in the factory and others in the field, which also can increase costs. This project aimed to improve the design and fabrication of the HVAC system by installing all components in the plant.
Three full-scale prototype homes with alternate HVAC solutions were constructed and tested. The systems were selected considering design flexibility, ease of installation, efficiency, transportability, the HUD standards, among other factors. The goal was to make homes more affordable—both on a first cost and sustained basis—and improve quality and resilience. Using these new systems, key parts of the HVAC selection, design, and installation process would change, with the manufacturer taking on more responsibility that is currently under the purview of the HVAC distributor and site technician.
Case Studies
Packaged Unitary System
Process
A high-efficiency packaged unitary heat pump (Friedrich VRP36K10) was installed in a double-section home with a louvre on an exterior wall. The floor plan was modified because the Friedrich VRP had to be installed against an exterior wall to exchange air and heat with the outdoors. The door to the HVAC closet was widened to 36” to ensure that the heat pump could move in and out of the closet for installation, repair or future replacement. A plenum sleeve was installed on the exterior wall to which the louver was attached. A short, insulated plenum box was fabricated to connect to the supply air opening on top of the heat pump. Flex duct was attached to the top of this plenum box, then extended into the attic air mixing plenum.
Summary and Findings
Because the system had no separate outdoor unit labor was minimized and no special skills required. It did not require an alternative construction letter. Because the system had to be installed against an exterior wall, the number of floor plan designs it could be used for is limited. Although its simple installation reduced labor, this system was significantly more expensive than a standard split system. Other drawbacks were limited air flow options and a narrow capacity range of available products.
Non-Ducted Packaged Heat Pump
Process
Four Epocha HPAC 2.0 units were installed, in the bedrooms and living room of a double section home. The Ephoca unit is slim, self-contained with no outdoor unit. Two vents through the wall draw in and exhaust air for the heat pump. The units were mounted high on the wall to provide more flexibility for furniture placement. This made the touchscreen controller inaccessible to use but the unit also works with a remote control and a smartphone application.
Summary and Findings
Because the units were self-contained, labor was minimal and required no special skills. The Ephocas do not provide fresh air ventilation, therefore a separate ventilation system was required. An Alternative Construction letter was required because of abridged Air Conditioning, Heating, and Refrigeration Institute (AHRI) certifications held by the product. Because one unit is required in each room, the overall heating and cooling capacity greatly exceeded the thermal loads in the bedrooms.
Attic-Ducted Mini-Split Heat Pump
Process
A high-efficiency split heat pump (LG LV241HV4) was installed in a single-section home with the outdoor portion mounted on a chassis extension and the air handler located in an interior closet. To minimize refrigerant line length and risk of damage during transport, the line set was installed directly from the indoor air handler to the outdoor unit under the home through a 4” diameter PVC pipe fastened to the chassis cross-members with steel straps. Some refrigerant had to be added at the plant because the line length of 28 feet exceeded the maximum allowable with pre-charged refrigerant *24.6 feet).
Summary and Findings
The efficiency of the ducted mini-split system is superior to the standard split system heat pump that the plant typically uses. The indoor AHU was quiet and can be used for both up flow and downflow configurations. This system did not require an alternative construction letter and offers flexibility on floorplan designs. Adding the frame extension to accommodate the outdoor unit increased the total home length by 32 inches. A split system, such as this ducted mini-split, requires that the installer hold an EPA refrigerant handling license, which the plant does not typically hold. Additional work includes connecting the lines, evacuation and vacuum testing, charging, and protecting the refrigerant lines.
