It’s Not Always the Contractor’s Fault.

Although the time has come when warmer weather is upon us, the effects of this past winter are still being felt.  Recently, we were involved in an investigation that focused on the cause of damage to a water cooling coil located inside of a cooling tower (see photo below).  This might seem strange to some but, it is possible to require the cooling of a building during the winter.  In the investigation we were performing, the system was comprised of a water cooled water chiller.  This might not mean anything to most people but to those familiar with chiller operation, water was the fluid used to both cool the air and remove the heat absorbed by the refrigerant.  On the condenser side, water was circulated through a shell and tube heat exchanger and then pumped to another coil type heat exchanger located inside the cooling tower.  The problem arose when the local air temperature began to drop below freezing.  As the water temperature dropped below 40 F, water flow between the condenser and water coil was stopped (as part of the automatic control sequence).  As the air temperature continued to drop, the water temperature also dropped until the water froze inside the coil and caused it to burst in several places.  Since this was new construction, it was the engineer’s position that the mechanical contractor had erred and was negligent in their responsibility to protect the equipment.  However, it was later determined that the building had been turned over to the building owner under the substantial completion part of the contract.  As a result, the building owner was responsible for the protection of the building as well as the building’s mechanical systems.  Regardless of the positions taken by the various parties, the design of the HVAC system including the incorporation of freeze protection, was the responsibility of the mechanical engineer.  This responsibility is not an arbitrary assignment.  It has been long recognized by engineers and specifically, those engineers that are involved in HVAC design.  Although freeze protection had been designed into other parts of the system, no provision for freeze protection was made for the cooling coil located inside the cooling tower.  When all was said and done, the engineer failed to incorporate an adequate way to protect the coil and blamed the contractor in order to avoid the appearance of failure on their part.

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HVAC Equipment – Repair or Replace?

Following periods of extreme weather such as with hurricanes Harvey and Irma, the damage caused will invariably lead to questions posed by insurance adjusters of whether to repair or replace certain items.  Using HVAC equipment as an example, repair or replacement will depend on such things as the type of unit and the extent of damage compared with the cost for replacement.  Split systems have a condensing unit located outside while the air handler is located inside the building to be heated or cooled.  Condensing units will be exposed to wind and water and can experience damage while the air handling unit is less likely to see damage because it is protected to some extent by the structure in which it is located.  While flying debris and flooding can impact the condensing unit, the air handling unit may or may not become flooded depending on how close to floor level it is located.  The condensing unit part of a system contains the compressor, condenser coil, and some refrigerant piping.  All of these components are sealed and should not accept water.  However, condenser coils usually have fins that can become damaged if struck by debris carried through the air or water.  Similarly, refrigerant piping can become damaged and leak refrigerant if struck by debris.  If flooding is severe enough and the condensing unit is completely submerged, electrical components will be damaged.  Water can enter motors, relays and transformers.  All of which may or may not work on startup or work for a short time (a matter of months or less) and then fail.  As stated above, the damage to an air handler will depend on how close the unit is positioned to the floor.  Many times the air handler is a combination of a cooling coil and a gas or electric furnace.  If wall or attic mounted, the unit probably won’t sustain any damage.  However, if the unit is floor mounted it can be affected by water intrusion.  Here again, motors and controls will be the primary losses resulting in the need for replacement and not repair. If the air handler is a counterflow or downflow unit, then ductwork will also be damaged.  Sheet metal ductwork can be dried, cleaned and reinsulated but, flexible duct cannot.  This assumes that the ducts have not collapsed under the weight of the water.

For those applications where a packaged unit has been installed, whether on the ground or on a roof, the package itself is not sufficient to keep wind or water damage from occurring.  Packaged units are cooling units or cooling and heating units that have been combined into one “package”.  If installed on the ground, both wind and water can cause damage.  As with split systems, air or water borne debris can collide with the unit and damage the condenser coil necessitating repair and recharge. However, if the condenser has been damaged to the extent that it cannot be repaired, then the condenser will have to be replaced and the unit recharged.  It is also possible that a new condenser coil is no longer available from the manufacturer and as a result, the entire unit will have to be replaced.  Similarly, if the gas controls on the furnace side have been submerged, it is likely that they will malfunction, possibly leading to a dangerous and explosive scenario.  Needless to say it would be better to replace the gas controls (or the entire unit if necessary) in order to avoid further property damage and personal injury.  If the unit is mounted on a roof, it is more likely that the unit will sustain damage due to wind or is wind related.  Impact with flying debris is obvious and depending on the amount of damage, the cost to repair might be much less than the cost to replace the unit.  However, if the roof is blown away or collapses and takes a unit or several units, then those units will have to be replaced.  There is no point in reinstalling units that have been shaken, dropped, and otherwise “jostled”.  The cost to replace the unit(s) will certainly outweigh the cost to remove, repair obvious damage, reinstall and then troubleshoot the damaged unit(s).  The same reasoning applies to roof-mounted condensing units.

There is another type of HVAC unit that can also sustain wind or water damage: chillers.  A chiller is a large tonnage refrigeration unit typically found installed in multi-storey office buildings, university campuses, and factories.  Chillers can be installed at ground level or on roof-tops.  As a result, chillers are subject to the same wind and water perils.  However, chillers are made a little differently than conventional air cooled equipment.  Chillers are made so that all of the refrigeration components are inside one package but, instead of cooling air directly, the unit cools water that is circulated to a central station air handler or individual fan coil boxes.  Since chillers are physically large pieces of equipment, the physical size of the compressors, condenser coils and piping are larger than residential or commercial units and may or may not come in contact with flood water.  Debris could still cause damage to chiller frame supports and piping.  Once again, if water comes in contact with electric or electronic components, they will most likely have to be replaced.  Another characteristic of chillers is that not all chillers are air cooled, some are water cooled.  The implication being that a cooling tower is in use with the chiller unit.  A ground mounted cooling tower can be subject to damage by flood water.  Flood water carries all sorts of debris and if some of that debris makes its way into the supply line that carries cooling water to the condenser, the pump(s) impeller(s) and possibly the pumps themselves could sustain damage.  In order to use a cooling tower, the chiller has to have a special type of condenser. Instead of the fin and tube configuration used in air cooled units, water cooled units use a shell and tube configuration.  That is, a type of heat exchanger where the refrigerant flows through tubes encased in a steel shell and cooling water flows through the inside of the shell but on the exterior side of the tubes.  It is also possible for small solid objects like rocks to be carried into the condenser where they can create obstructions and possibly puncture tubes.  In order to determine the proper course of action, the condensers will have to be dismantled and inspected.  If the shell and the tubes are found undamaged, then the condensers can be cleaned and placed back in service.  If however, the tubes are damaged, the condenser will have to be replaced.  It should be noted that the condenser can be re-tubed but, this will involve weighing the cost of repair against replacement for this component.

As stated above, chillers can be connected to a central station air handler or fan coil boxes.  Central station air handlers are air moving devices that contain a motor driven blower and a combination of cooling only or cooling and heating coils.  Once again, these components are contained in a single package.  If flood water is going to cause damage, the air handler has be located in a part of the building that is low enough to allow flood water to enter the building and access the air moving equipment.  If the air handler is located in an upper floor that is above the level of flood water, then flood water will most likely not damage the unit.  The unit has to sustain damage in another way such as building collapse.  If flood water does enter the air handler, it will have to rise to the level where it can actually do damage.  Air handlers are physically large pieces of equipment and depending on the size, ladders may be necessary in order to reach motors, pulleys, belts, damper mechanisms, and controls.  Needing a ladder to service the unit shows that the water level might have to be quite high, say above 6 feet, to cause real damage. While water contact with the lower parts of the air handler, including the cooling and heating coils, can be cleaned; there is little damage that flood water can do unless the unit is practically submerged or there is a building damage that results in damage to the air handler.  If there is damage to a cooling or heating coil, the coils can be replaced and the system refilled with water if the remainder of the air handler is in good condition.

Finally, equipment varies from manufacturer to manufacturer and the component layout will vary.  The component position will determine what comes in contact with wind or water or both.  Those components that are deemed to have been damaged will drive the cost of repair and has to be evaluated on an individual basis.  The cost of repair then has to be weighed against the cost to replace the entire unit.

 

 

 

 

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