How to Extend the Life of Your HVAC Equipment – This Summer and Beyond (Part 1-3)

For most of us, seasonal maintenance on our home’s HVAC system is not a priority. The majority of homeowners use their HVAC system until a component fails. Understanding the basics of how our home’s HVAC system functions can help us to prioritize our HVAC maintenance.

Some results of diligent seasonal maintenance yield:

• Reduced equipment run times which increase mechanical equipment lifespan.

• Reduced energy usage which can mean decreased energy bills.

• Regular checks aid in preventing equipment downtime and can avoid uncomfortable scenarios.

In general, the HVAC system in our home circulates air that has passed the conditioned space. Most HVAC systems in residential applications are either split-type units, or self-contained packaged units. Both types of units contain similar components, such as the supply air fan, evaporator coil, and condenser coil. Split-type units consist of an indoor piece of equipment as well as an outdoor piece of equipment, whereas the self-contained packaged units are an all-in-one unit located outside. Regardless of whether the HVAC system is a split-unit, or a self-contained packaged unit, a supply air fan is the device used to move the air to be conditioned. In the cooling season, the supply air fan moves the air across the evaporator coil where moisture from the interior, conditioned spaces is removed in liquid form, known as condensate. The result is cool, dry air which is passed back to the conditioned spaces. The thermostat, located within the conditioned space, tells the system when the conditioned space is satisfied, which de-energizes the unit. With the goal of extending equipment life, reducing energy costs, and preventing unwanted downtime, it is important to understand the following.

Return Air: Fight Premature Wear on Your HVAC Unit

The term return air often refers to the air that has absorbed moisture from the interior, conditioned spaces and is upstream, or before the cooling coil. The cooling coil is a series of intricate tubes and fins which, when in contact with the return air, results in water condensing on the cooling coil. Gravity then carries the water to an internal drain pan where it is disposed of. Dirt and airborne particles are removed from the return air to prevent a build-up on the cooling coil. A build-up on the cooling coil would increase equipment run times and, in some cases, can cause premature wear. Therefore, the best defense against a build-up of dirt and particles on the cooling coil is to ensure the particles are filtered. The method of filtering the dirt and particles from the return air, in most cases, is with the use of a return air filter which resides within the return air grille. The filter captures any dirt and particles. The first line of defense against premature wear is to ensure the return air filter is changed-out at proper intervals. The interval of change-out will depend on the household. For example, a household with multiple occupants and pets may require a filter change-out each month; whereas, a household with a single occupant might require a return air filter change-out every three months. With the ever-increasing popularity of smartphones in our lives, setting alarms/reminders aids in maintaining the required filter change-out period.

Cooling & Condenser Coils: Optimize Your HVAC Unit Run Times

Some integral components of an HVAC system include the cooling coil (evaporator) and the condenser coil. For purposes of this section, we will focus on equipment operating in cooling mode (summer). The cooling coil is the component which transfers heat from the conditioned space to refrigerant. On occasion, even with regular return air filter change-outs, the cooling coil (evaporator) will accumulate dirt and debris. As a result, the equipment must operate longer to satisfy the conditioned space temperature (sometimes referred to as setpoint). The increased equipment run times take place due to a reduction in airflow passing over the evaporator. A good maintenance practice for homeowners is to have the evaporator coil cleaned prior to the start of each cooling season. The cleaning process, performed by a qualified technician, consists of evaporator cleaning by means of approved chemicals. Due to the fragile nature of the evaporator, care must be taken to use the manufacturer-approved chemicals. In addition, the evaporator fins may be cleaned by using fin combs. It should be noted, the appropriate fin comb for the evaporator must be used to prevent damage to the fins. In most cases, the chemical cleaners will remove built-up dirt and debris, allowing the dirt and debris to drain out the condensate drain piping.

Note: Dirt and debris must be removed on the upstream side of the evaporator coil; dirt and debris must never be forced through the evaporator.

The outdoor portion of the HVAC system, known as the condenser, rejects the heat to the outside. The condenser contains a condenser coil. The condenser coil may also accumulate dirt and debris, and must be cleaned by a trained, qualified technician. A common mistake is to clean the condenser coil with high-pressure water; this will damage the condenser coil. Like the evaporator, the condenser coil is fragile, and care must be taken not to bend or damage the coil fins. A qualified HVAC technician will use approved chemicals on the condenser coil, then if needed, use low-pressure water to remove dirt and debris from the inside out. Dirt and debris must never be forced through the condenser coil as this will damage the coil.

In general, the recommended intervals for evaporator and condenser coil maintenance are on an annual basis. Diligent maintenance ensures the equipment functions by design and does not operate longer than required. Reducing run times leads to reduced energy costs and improved overall equipment life.

How to Extend the Life of Your HVAC Equipment – This Summer and Beyond (Part 2)

There are admittedly times when HVAC service calls are unavoidable. However, in today’s discussion, we hope to reveal some practical ways to try and avoid unnecessary service calls, whenever possible.

Condensate: Avoid Unnecessary HVAC Service Calls

The term condensate refers to the water removed from the conditioned space. Once the condensate is removed via the cooling coil, it needs to be disposed of. A common disposal method is to discharge the condensate to the outside. While very effective, the condensate drain piping is another area that should be checked on a regular basis to help prevent unnecessary service calls and unit interruptions. Varmints and/or insects could find condensate piping to be a handy entry point for trying to enter your home. It’s also a good idea to ensure the discharge piping is free of debris. Located within the discharge piping is what is known as a ‘p-trap’. The p-trap’s job is to allow liquid condensate to drain while making a seal to prevent unwanted air, debris, or varmints from entering through the piping. The condensate p-trap can have issues of its own, such as microbial growth/scale build-up inside, or the liquid seal can dry. For example, if excessive odors are observed or insects discovered originating from ductwork, there may be an issue with the condensate p-trap. A qualified technician should be consulted if issues with the condensate drain piping are suspected.

An HVAC contractor will pour a chemical solution in the interior drain pan of the unit which will ensure any blockage is removed. To help ensure the condensate p-trap maintains its liquid seal, the piping must maintain the correct slope. If the slope is not maintained, the liquid seal may be allowed to dry. In addition, if the liquid seal becomes dry, conditioned air from the cooling coil will be able to pass through the condensate piping and as a result, the exterior of the piping will sweat. Sweat, or condensation in this case, forms when a surface reaches the dew point. In most scenarios, condensate piping is routed in unconditioned, humid areas such as attics or crawlspaces. It is not uncommon to see water stains on ceiling surfaces where condensate piping (routed above the ceiling) has a dry p-trap seal. As a result of the dry p-trap seal, moisture condenses on the piping surface and drips onto the ceiling below.

Insulation: Boost Your HVAC Efficiency

Generally speaking, our homes contain many types of insulation. HVAC systems use ductwork to move the conditioned air where needed. The ducts passing conditioned or return air, often referred to as supply and return, must maintain an insulative barrier. Note – exhaust ductwork, such as clothes dryer exhaust, does not contain insulation. In addition, exposed ductwork (sometimes referred to as spiral-wound) will contain an internal insulation liner rather than the external insulation.

The ductwork insulation serves multiple purposes, such as slowing energy transfer to/from the interior of the duct (little to no insulation increases energy costs) and preventing condensate from forming on the exterior surface of the ductwork (or sweating). Ductwork is constructed of fiberglass and metal materials. Regarding metal ductwork, the metal surfaces can reach the dewpoint; the insulation prevents this. Good maintenance consists of periodic visual checks of the ductwork, checking for tearing or inconsistencies with the insulation. In addition, if there is a break in the ductwork insulation and the metal surface sweats, signs of moisture will be visible. The repair of ductwork and insulation requires the use of correct methods, such as approved foil-backed adhesive tape and mastic to ensure a continuous seal.

For split-type units, refrigerant piping is used to transfer refrigerant from the outdoor equipment to the indoor equipment. The refrigerant piping consists of two (sometimes more) refrigerant lines referred to as the liquid and suction lines. Refrigerant piping is copper, which can sweat if exposed to elevated humidity levels. To prevent sweating, as well as maintain efficiency, the refrigerant piping must be insulated. Periodic visual checks should be conducted on any refrigerant piping, looking for any breaks in the insulation or even the piping, itself. Consult a qualified, licensed HVAC technician should any issues with refrigerant piping and its insulation be suspected.

Consider a Programmable or Smart Thermostat

A small but effective way to aid in reducing HVAC related energy costs is to use a programmable or smart thermostat. This type of thermostat offers an advantage in that it has the ability to be programmed to accommodate different settings during the times the space will be occupied. The thermostat is then able to adjust heating/cooling around your schedule. For example, a programmable thermostat may be programmed to set the temperature desired (or setpoint) five to ten degrees above what would otherwise be required, during times the space is unoccupied. This provides a degree of automation to your home; multiple temperature adjustments would no longer be needed.

Most programmable thermostats can be installed with basic tools and resources by a typical do-it-yourself homeowner. However, since the wiring on some HVAC systems can vary, the best practice would be to consult a qualified, licensed technician, to determine what is required to install a programmable thermostat on your particular HVAC system.

Checking Refrigerant Charge:

Leave it to the Professional

In this article, we have discussed several preventative steps you can take to extend the life of your HVAC system. But, there is one last and very important area to be checked on your HVAC system: the refrigerant charge. Proper refrigerant charge can ensure your system will perform at its listed/design capacity. Until now, the maintenance checks we discussed were tasks most homeowners could tackle on their own. However, checking refrigerant charge is a complex process which should be conducted by a trained, licensed professional. Even a small misstep in checking the refrigerant charge could result in damage to the HVAC system.

HVAC systems, both split-type and self-contained packaged units, contain refrigerant circuits which are considered closed-systems. This means the refrigeration circuits should not be opened by anyone other than a trained technician who is using the proper equipment and following proper procedures. However, despite being a closed-system, issues such as leaks may take place within the refrigeration circuit. In today’s post, we will discuss checking refrigerant charge on a split unit in cooling mode (summer) which operates on R-22 (commonly known as Freon) refrigerant.

HVAC systems contain a metering device which modulates the quantity of refrigerant entering the cooling coil (or evaporator). The metering device of the system, as well as the refrigerant used, will determine the method of charging required. Typical metering devices are a fixed-orifice type, or a thermal expansion valve (TXV). It is common to see the fixed-orifice metering device used with R-22 systems, whereas modern refrigerant systems use the TXV metering device. R-22 systems are being phased out due to EPA regulations; most modern systems use less ozone-depleting refrigerants, such as R-410a (sometimes called Puron). However, R-22 systems are still quite common in residential use because most R-22 systems are just now reaching the end of their service life. This means it is not uncommon to encounter refrigerant leaks with this type of system, and it is relevant for technicians to repair leaks as necessary.

A trained technician will use refrigerant manifold gauges as well as multiple types of thermometers to check refrigerant charge. Ideal conditions for checking refrigerant charge are hot and humid weather. The first step in the technician’s process is to set the system to provide cooling throughout the process. The technician will then measure the indoor/outdoor temperatures, the humidity conditions, and the refrigerant piping line temperature. The technician will also measure the refrigerant line pressures using special gauges suited for the particular type of refrigerant that is being checked.

These temperatures and pressures are required for the technician to determine what is known as superheat – the temperature rise of the refrigerant without a rise in pressure. The refrigerant, by design, changes states from a liquid to a vapor (boiling) then from a vapor back to a liquid (condensing) during the refrigeration process. The superheat is the amount of energy in the refrigerant above the temperature at which the refrigerant changed state from a liquid to a vapor. While it’s important for the professionals to understand all the factors and variables related to superheat, what the average homeowner really needs to understand is that the superheat of the system being checked determines the quantity of refrigerant charge required.

Properties of refrigerant, such as temperatures and pressures, are known and tabulated for ease of access and are required to determine the system’s superheat. Once the system’s superheat is determined, the technician will compare that data with the known data for the refrigerant, (i.e., what the superheat would be under perfect, lab conditions).

We know that HVAC service calls can be expensive, and it is not uncommon for a system to be misdiagnosed. Below are some “rules-of-thumb” to keep in mind when talking with your HVAC technician. Hopefully, this information will provide some insight into your HVAC problems and avoid unnecessary costs. (Note: the conditions of each HVAC system will vary and the topics below are included for reference purposes only).

• If the system being checked is found to contain too little superheat, the system may be over-charged (too much refrigerant); alternatively, if it is found to have too much superheat, the system may be under-charged (too little refrigerant).

  
  

• One of the two refrigerant piping lines is referred to as the suction line (sometimes called low or liquid side). If the temperature of the suction line is too low for its conditions, the evaporator may not be absorbing as much heat as it should. This may indicate the evaporator requires cleaning, the return air filter is dirty, or there is poor airflow, in general, across the evaporator.

  
  

• The second refrigerant piping line is referred to as the vapor line (sometimes called hot gas, or high side). Elevated vapor pressure, coupled with low suction pressure, may indicate a blockage or restriction within the metering device.

In summary, checking refrigerant charge is a complex process and should be conducted by licensed, trained professionals. It is, however, valuable for homeowners to understand the common terms we’ve discussed here, and to have a high-level understanding of what the professionals will be looking for in your unit. If the HVAC system is suspected of not performing as intended, homeowners should not attempt to check the refrigerant charge themselves. A variety of other factors may need to be considered prior to checking refrigerant charge.

There is no doubt that performing routine maintenance on your HVAC system can save you time and money. As we have discussed in this three-part series, the HVAC system is quite complex with many components working together to provide heating/cooling to your home or place of business.

We hope, this series of articles has served to make you more comfortable with performing routine checks that can not only extend the life of your HVAC system but, just as importantly, better help you know when to call a professional and what steps they will take to repair and restore your system.

About the Author

Michael W. Dickenson, P.E., CFEI, CVFI is a Consulting Engineer in our Nashville, Tennessee Office. Mr. Dickenson provides technical consultation and analysis on commercial, industrial, and residential incidents involving mechanical and heavy equipment. His services include origin and cause, failure analysis, damage assessment, interpretation of codes and standards, and evaluation of fire and explosion origin and cause.