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HVAC & Refrigeration: What To Look For & Where

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Heating, ventilating, air-conditioning and refrigeration (HVAC&R) equipment is often included in building damage loss claims or forensic building assessments, especially those system components that are installed outdoors. If you write or review large estimates, this paper will explain the most common HVAC&R systems and how their components work. It will also cover how these systems can fail or allow water intrusion to a structure.

HVAC&R System Functions

In current times, we take heating, air conditioning, and refrigeration for granted. We walk into toasty homes in winter, cooler and less humid homes in summer, and grab a cold one from the refrigerator with little thought. Did you know that air conditioning was first used in 1902 at New York’s Sackett & Wilhelms Lithographing and Printing Company?¹ The printer published a four-color edition that required four separate runs. The air conditioning system was installed to keep the humidity level even between printing runs. It was not installed to comfort the workers in their sweltering environment. In 1906, Carrier first began installing air conditioning for comfort applications.

While many of the functions performed by HVAC&R systems are apparent from the acronym, some are not. Air-conditioning is most often associated with cooling air, but also includes dehumidification as a byproduct of cooling the air. Heating is required in colder climates to offset heat loss through the building envelope and maintain adequate indoor temperatures for occupancy. Ventilation is the process of introducing fresh outdoor air into a building to dilute indoor air pollutants generated by people and building materials (off-gassing). This often includes exhausting air from spaces like bathrooms and kitchens with heavy pollutant sources. HVAC systems almost always include a means of filtering or cleaning the air they circulate, and sometimes include a humidifier.

Refrigeration systems have a single function, to keep food and beverages at the right temperature. This extends their useful life and preserves quality and freshness. The refrigeration system cools the interior of a well-insulated compartment.

Common to most HVAC&R systems is the refrigeration cycle which uses chemical refrigerant in a closed system to cause heat to move from a “cold” area to a “warm” area. This is opposite to the way heat moves naturally, from warm to cold. The four basic components of a refrigeration system are:

  • In the compressor, the warm refrigerant gas is compressed to a high pressure and temperature.
  • In the condenser, the hot gas is cooled enough to cause it to condense to a warm liquid. The heat is rejected to the “warm” area, usually outdoors.
  • The expansion valve allows the warm liquid to pass to an area of much lower pressure. When the pressure reduces, some of the liquid flashes (evaporates) to a gas and cools the remaining liquid.
  • In the evaporator the rest of the liquid refrigerant evaporates to a gas, absorbing heat from the “cold” area.

Both the condenser and evaporator usually incorporate a blower to move air through the coils. The evaporator will be mounted above a drain pan positioned to collect any moisture (water vapor) that may condense out of the cooled air. Note that some systems may also incorporate a reversing valve so that the evaporator and condenser can switch roles. This is called a heat pump which can be used to either cool or heat an area.

¹BBC World Serve, (June 5, 2017) How Air Conditioning Changed the World. Tim Harford.
Figure 1 – Basic Refrigeration Cycle
Figure 1 – Basic Refrigeration Cycle

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HVAC System Components & Configurations

Within the realm of residential and light commercial buildings, there are many types of HVAC systems used, with many variations available within the types. Some of the most common system types include:


These are all-in-one units where all the system components are contained in one cabinet that is mounted on an exterior wall in a wall or window opening. They include packaged terminal air conditioners (PTAC) and window air conditioners. These are typically used in hotels and residential applications. The cooling capacities in packaged units are low.

Figure 2 – Packaged Window Air Conditioning Unit
Figure 2 – Packaged Window Air Conditioning Unit

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In this configuration, there are two main components mounted separately, an outdoor unit with the compressor and condenser (called a condensing unit) and an indoor unit with the metering device and the evaporator. The indoor and outdoor units are connected by insulated copper tubing that allows the refrigerant to flow between the units. The indoor unit can take several different forms (wall-mount, floor-mount, or ceiling cassette), but it is usually exposed in the space it serves. These systems can have multiple indoor units connected to a single condensing unit. Condensing units are typically mounted on grade but can be mounted on a wall bracket, a shelf, or on a roof.

Figure 3A
Figure 3A
Figure 3B
Figure 3B

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This configuration is similar to mini-split systems except that the indoor unit is concealed in a mechanical room, attic, or basement and the conditioned air is distributed from the indoor unit to the spaces served through ductwork. These systems are typically used in single-family homes and small commercial buildings and often include a gas furnace for heating.


These types of systems are also packaged units in that all components are contained in a single cabinet. However, unlike PTAC and window AC units, RTUs almost always include ductwork to distribute the conditioned air. These systems are rarely used in residential buildings and can vary from small to very large and include many options and accessories.

Figure 4 – Rooftop Packaged Unit
Figure 4 – Rooftop Packaged Unit

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Refrigeration System Configurations

Refrigeration equipment has two basic configurations, stand-alone units and split systems with remote condensing units. Stand-alone units are like a household refrigerator, where all of the components are contained in a single package that can be located anywhere inside a building. This also includes larger commercial units found in retail spaces and commercial kitchens. Split systems with remote condensing units are more often seen in commercial settings such as supermarkets and commercial kitchens. They can also be found in high-end residences with wine cellars.

The most common applications are refrigerated display cases in retail buildings and walk-in coolers and freezers found in restaurants. Like HVAC split systems, the indoor and outdoor components are connected by insulated copper tubing that allows the refrigerant to flow between the units.

Figure 5A
Figure 5A
Figure 5B
Figure 5B

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With a basic understanding of these systems and components, where they might be located, and how they might be part of a problem, you can be more skilled at addressing building envelope failures involving HVAC and refrigeration systems.

Outside units such as the compressor/condenser units for homes or commercial rooftop units mounted on stands and curbs are often damaged by wind or hail. Improperly secured units can be toppled over by wind and the softer metals, such as the exposed evaporator coil cooling fins, can be damaged by hailstones. Larger more dense hail may also cause impact damage to unit chassis. Rooftop HVAC equipment on low-slope roof systems is often the source of roof leaks, particularly at the sheet metal mounting curbs. Proper flashing of the roof membrane at the curbs or at thru-deck flashings such as pitch pockets which allow for the passage of refrigerant, water, and natural gas piping, and electrical cables and conduit through the roof to the HVAC equipment. Building codes require proper mounting and securing of rooftop units. Units that are simply mounted on timbers or resting directly on the roof membrane system are not building code compliant and will likely result in damage leading to water infiltration.

Package units mounted outside exterior walls that include thru-wall ducting are often the source of water intrusion if the thru-wall components are not properly protected from rain, or if the thru-wall passages allow for the exchange of air (inside/outside) which affects the balance and efficiency of the HVAC system.

Refrigeration equipment can generally be repaired if it is a recent vintage and exact replacement parts are available. However, for older units and systems, especially those using ozone-depleting refrigerants such as R-22, replacement parts are likely not available. In this case, the entire unit will need to be replaced. If a split system condensing unit is replaced, then the indoor unit will need to be replaced as well. This is required because most building Energy Efficiency Codes require that all system components be designed to work together and certified for efficiency by an approved testing agency such as the Air-Conditioning, Heating, & Refrigeration Institute (AHRI).² Although other avenues are available to certify the operation and efficiency, they are seldom used due to the high cost.

Interior refrigeration systems such as walk-in freezers or wine rooms can foster mold in wall/ceiling cavities if the enclosures are not properly insulated and exchange of air promotes condensation.

Attic and closet mounted air handlers can be a source of moisture inside the building from condensation on cold surfaces (ducts and refrigerant pipes) and overflowing condensate pans. As an example, condensation dripping from an uninsulated copper line could cause stains to ceilings or finishes. This moisture can also lead to structural deterioration and possible mold contamination.

²2015 International Energy Efficiency Code (Country Club Hills, IL: International Code Council Inc., 2014): C-40


In summary, HVAC and refrigeration (HVAC&R) system components add well-being and safety to our lives. HVAC systems keep us comfortable at home and make it safer for us at work. Refrigeration systems cool our beverages and food which extends their useful life while preserving quality and freshness. These systems can also cause damage to structures if not properly installed or maintained or get damaged during a loss event. It’s important to know how they function and where they are generally located to perform an accurate assessment of their components.

Prompt evaluation by an expert is often necessary for proper repair or replacement of HVAC and refrigeration components, since even minor damage to a component could cause or extend business interruption or substantial loss of refrigerated materials. Depending on the type and complexity of the loss, HVAC&R claims can require mechanical, electrical, and plumbing experts; environmental health, and safety experts; origin and cause experts; and forensic engineers to assist in the evaluation of the equipment. Additional experts, including building consultants and forensic accountants, may be needed to assist with the valuation of the damages and any business interruption from the loss.


We wish to thank our colleagues Stephen Towne, RRC, CBC and Walter Janus, PE who provided insight and expertise that greatly assisted this research.


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This publication is for educational and general information purposes only. It may contain errors and is provided as is. It is not intended as specific advice, legal, or otherwise. Opinions and views are not necessarily those of J.S. Held or its affiliates and it should not be presumed that J.S. Held subscribes to any particular method, interpretation, or analysis merely because it appears in this publication. We disclaim any representation and/or warranty regarding the accuracy, timeliness, quality, or applicability of any of the contents. You should not act, or fail to act, in reliance on this publication and we disclaim all liability in respect to such actions or failure to act. We assume no responsibility for information contained in this publication and disclaim all liability and damages in respect to such information. This publication is not a substitute for competent legal advice. The content herein may be updated or otherwise modified without notice.

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