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Deposition Designation Station
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There are many types, manufacturers, and sizes of commercial HVAC systems which can make it difficult to create general guidelines for repair procedures and estimates for hail-damaged units. This guide uses the most common "light commercial" rooftop units (RTUs), which are 5-tons, 7.5-tons, and 10-tons in capacity, for estimating time to repair or replace.

Defining Hail Damage to an RTU

Hail damages a condenser coil when it impacts and bends the fins which prevents the appropriate airflow across the coil and inhibits cooling of the refrigerant. If the refrigerant is not cooled the system can overheat reducing the life of the unit. Coils are designed with extra capacity to allow for some reduction in airflow due to debris in the coils or minor bending of the fins, but proper practices to maintain unobstructed coils is important for extending the life of the unit.

Repair versus Replacing Damaged Coils

It is uncommon for the coil of the system to be so badly dented that the only way to return the unit to preloss condition is to replace the coil or entire unit. Hail typically does not have the mass or fall at the required trajectory to impact the coil with enough force to cause it to leak refrigerant, which would require more invasive repairs. Most of the hail impact's energy is lost when it bends the fins on the condenser coil and the refrigerant tubing behind the fins is left unaffected. If the coil is leaking refrigerant there is typically a noticeable oil spot at the impact or on the roof below the impact. Occasionally a coil may not be able to be combed because the fins are too closely spaced together to place a comb between them, the fins are too brittle and break when they are combed, or the cost to comb the coil exceeds the cost of replacing it. In these instances a replacement coil needs to be installed or the unit replaced if the coil is no longer manufactured.

Combing is the most efficient way to repair coils and by far the most common repair method recommended by Donan's forensic technicians. About 85% of Donan hail studies recommend repairing the unit by combing the coil. To comb a coil, a plastic or light gauge metal comb or a precision blade is inserted between the fins and pulled down to straighten them and allow the appropriate airflow to cross the coil. This is a tedious process and can take a contractor from two to four hours to perform at an hourly rate of $150 per hour, but $300 to $600 is much more reasonable than the cost to replace a coil ($3,000 to $5,000) or replace the RTU ($10,000 to $20,000).

Site Studies

Donan forensic technicians follows the scientific method when determining if the RTU can be repaired and if the damaged coil has caused a reduction in a unit's efficiency and capacity. The steps to the site study are:

  1. Identify any leaks or other deficiencies.
  2. Determine the percentage of the coil with dents.
  3. Test comb an area to document the ability and the time to comb.
  4. Determine the cost to comb and compare with repair/replacement options.
  5. Provide additional services if efficiency and capacity are claimed to be compromised, including hooking up meters and gauges to determine the running pressures and operational vitals.
  6. Write a report which includes the data gathered in steps one through five, a cost estimate to repair/replace, and photographs documenting the unit's condition and the ability to comb the coil.

Assessing hail damage to RTUs can be complex, especially when common myths about the effects of hail damage abound. A process grounded in years of experience and technical expertise, and vetted through sound scientific principles, can help ensure accurate, confident claims decisions are made.

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DONAN, a family owned company founded in 1947, provides full-service Forensic Engineering and Fire Investigation Services. For over 60 years, Donan Engineering has been providing unbiased answers to their client's complicated questions. Their team of licensed and experienced forensic experts provides investigative services in the fields of engineering investigations, fire and explosion origin & cause, roofing investigations, and component testing. The diversity of their multidisciplinary staff allows them to provide not only a complete service, but a complete service whose conclusions can be successfully and completely supported.

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