10/30/2012

Packaged Terminal Air Conditioner Guide

Avoid mistakes with packaged terminal air conditioners that undermine wall systems

By Thomas A. Schwartz, Mark A. Brown, and Octavian Vlagea

 
  • /Portals/1/images/Magazines/2012/1112/B_1112_PTAC1.jpg

    FIGURE 1 is an example of a manufacturer’s schematic figure that guides installation of the PTAC. Manufacturer instructions fail to show fundamental waterproofing components. The manufacturer’s recommendation consists solely of sealant at the perimeter of the PTAC sleeve penetration.

    FIGURE 2 is an example of a solution for this problem. Although some design drawings include flashing, they commonly lack necessary aspects. Make sure your metal sill flashing includes a panned-up interior leg and end dams to collect water that penetrates the back-up wall construction, as illustrated below.

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  • /Portals/1/images/Magazines/2012/1112/B_1112_PTAC7.jpg

    The PTAC louver is typically set flush with the adjacent wall surfaces. The vulnerable joint between the louver and the wall sleeve is inside the wall. The copper apparatus in the photo is a water spray rack that investigators use to diagnose leakage problems.

  • /Portals/1/images/Magazines/2012/1112/B_1112_PTAC4.jpg

    The bird screen between the wall sleeve and grille is vulnerable to infiltration, allowing water to flow through the joint and onto the floor.

  • /Portals/1/images/Magazines/2012/1112/B_1112_PTAC5.jpg

    The bird screen between the wall sleeve and grille is vulnerable to infiltration, allowing water to flow through the joint and onto the floor.

Building wall systems would work great, if it weren’t for all the holes we put in them.

One of the leading examples of these holes is caused by the packaged terminal air conditioner (PTAC), most common in hotels and multifamily buildings. PTACs are permanently installed, through-the-wall units designed to cool or heat individual rooms. Design and construction methods involving PTACs vary, but all too often, they allow water leakage into the building.

No matter what the causes of water may be, fundamental principles of wall waterproofing can be applied to PTAC installations to produce reliable and durable solutions.

Internal Water Management of PTACs
The condensate pan of the PTAC chassis can drain to the sill of the surrounding sleeve by either overtopping if condensate is excessive, or through a valve in the sill of the chassis that is activated by low temperature to prevent frost forming on coils. Water also enters the sleeve sill directly from water penetration through the louver.

Water in the sill of the sleeve is intended to drain by one of two methods: either through drain lines in the bottom of the sleeve that connect to conduits within the building that conduct the water out of the building at lower elevations, or through weep slots in the upturned front edge of the sleeve and out through the louver or louver framing system, depending on the methods of louver installation.

Inadequate Manufacturer Guidelines
Manufacturer’s instructions generally include written guidelines and schematic figures to guide installation of the wall sleeve and other PTAC components. In many cases , these instructions fail to show fundamental waterproofing components of the exterior walls and therefore fail to provide proper guidance for integrating the wall sleeve with the exterior wall waterproofing. Make sure there is proper detailing from the designer and coordination among the trades to ensure the system is effective.

Typical Components in PTACs

  • Wall sleeve, usually sheet metal or molded plastic that is mounted in the wall opening.

  • Louver at the exterior face of the wall sleeve for air intake and exhaust.

  • Chassis, which includes the evaporator coil, blower (indoor fan), compressor, condenser coil, condenser fan, controls, and other equipment that perform the cooling and heating functions. The chassis includes a condensate pan to collect water that condenses on the evaporator coil and drain it to the exterior. Many PTAC designs incorporate a device called a slinger ring to throw condensate from the pan onto the warm condenser coil to evaporate some of the condensate and increase efficiencies.

  • Room cabinet that mounts on the interior side of the PTAC and contains end-user controls.
A typical schematic figure (Figure 1) depicts a section through a brick veneer wall and shows, from exterior to interior: brick veneer, drainage cavity, wall sheathing, wall framing, and interior wallboard. The brick veneer above the PTAC sleeve penetration is supported by a steel lintel.

The sketch omits the water resistive barrier on the exterior sheathing, flashing on the steel lintel above the PTAC, as well as flashing beneath the PTAC – all elements that are required for reliable and durable water penetration resistance. The manufacturer’s recommended waterproofing consists solely of sealant at the perimeter of the PTAC sleeve penetration on the exterior and interior. Manufacturers generally require the wall sleeve to project beyond the outboard face of the wall from one-quarter to five-eighths of an inch. PTAC installations rely on the watertight construction of the wall sleeve to collect wind-driven rain that penetrates the exterior louver as well as condensate that drains from the condensate pan.

Some PTAC manufacturers require the wall sleeve to be pitched to the exterior; some require the wall sleeve to be installed level. Manufacturers call for flashing beneath the PTAC sleeve only where a sleeve extension is required for deep wall sections, which protects against leakage through the joint between the PTAC sleeve and sleeve extension. The flashing details typically show end dams but no upturned leg at the interior, and no slope toward the exterior.


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Visit our website today to learn about the design flexibility of a Morton building and the endless possibilities of partnering with our designBUILD team.


Wood construction is both cost and energy efficient. Check out Morton Buildings and our designBUILD team online today to discover all the benefits of post-frame construction.


When choosing a metal-clad building for your next construction project, consider Morton Buildings, Inc., and their designBUILD team, we’ll make your dream a reality.

We Can Help You Reduce Energy by 30%

Our mission is to help our customers manage their buildings' energy costs, improve reliability, and enhance performance while having a positive impact on the environment.
CLICK HERE to find out how.

Add highly responsive multi-zone comfort to any building project, in any climate. Our CITY MULTI H2i R2- and Y-Series VRF systems give you flexibility to fit the needs of any building. Enjoy 100% heating capacity at 0°F outdoor ambient, and 85% heating capacity at -13°F outdoor ambient.  For more information, log on to www.mitsubishipro.com

 
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