Understanding How HVAC Systems Works

As a homeowner, it’s always good to know how various systems in your home work – from the washing machine to the plumbing. Most homes today are, however, equipped with Heating, Ventilation and Air-conditioning systems – also known as HVAC systems. If you want to know how your HVAC works, read on for the basics to find the answers to the question “How do HVAC systems work?”

The basics

The heating, ventilation and air conditioning components that work together to manage the climate of your home, work and other living spaces, are called HVAC systems. To learn how HVAC works, you need to understand the key parts that make up HVAC systems and how they all work together.

Key components of HVAC systems:

  • The furnace: This is the heart of all HVAC systems, and it has the largest physical footprint.

    The furnace requires the most storage space out of all the HVAC systems components. The furnace heats the indoor air, then sends that heated hair throughout the living space via ducts or pipes. Furnaces run on different types of heat sources, including combustion, electric resistance, solar, heat pumps, etc.

  • The condensing unit: This unit is another component of HVAC systems and is located on the outside of the home, office or other living space.   Condensing units are filled with refrigerant gas, which is a compressed chemical with high heat-absorbing properties.  Condensing units convert the refrigerant from gas to liquid form.
  • The evaporator coil: The evaporator coil extracts indoor heat from the air in the home, office or other living space by sucking in this air via “return” ducts and forcing this air over the refrigerant liquid in copper tubes. The refrigerant absorbs the heat from the indoor air, which is then circulated back into the living space via “supply” ducts as cooled or “conditioned” air.

    When the hot air moves over the cold copper tubes, condensation is triggered, which lowers the humidity in the cooled air. The refrigerant flows to the condensing unit where the heat component of the refrigerant is expelled outdoors as vapour.

  • The refrigerant lines: These lines carry the refrigerant back to the condensing unit in the form of gas.  This gas is transformed to liquid, then sent back to the evaporator coil.
  • The vents: These are the outlets that distribute hot and cold air from the duct system into each room in the living space.  They are usually located near the ceiling with angled slats designed to send the air downwards. Alternately, you may also find vents in the floors, which shoots heated or cooled air upwards.
  • The thermostat: The most visible component of HVAC systems, the thermostat is what you interact with the most and enables you to select the cooling or heating option and set the temperature.  Thermostats also allow you to pre-program your heating and cooling needs by day, time of day and temperature, so that these processes run automatically based on your programmed specifications.

How does HVAC work, you ask?  Well, learning about the basic components above gives you some idea about how HVAC works.

What to look for

When shopping around for HVAC systems, you’ll find some variations on the basic components described above.

Various types of HVAC systems:

  • Duct-free split system: This type of system is constructed to function without any ducts or ductwork.  These HVAC systems consist of a heat pump or air conditioner, a fan coil and wires and tubing that connects the outdoor unit to the fan coil. They may come with optional accessories, including air purifiers and cleaners.
  • Zoned systems: How HVAC works in these systems is that they let you cool or heat different areas in your living space by controlling valves or dampers with the ductwork.   The dampers are used to selectively block airflow.  Zoned systems can be highly cost effective, since they allow area and time-based cooling and heating.
  • Humidity control systems: These HVAC systemsoffer humidity management features such as humidifiers and dehumidifiers, depending on your needs.  Humidity control HVAC systems let you automatically control the humidity levels throughout your living or working spaces when the HVAC systems are running.

    It is also important to understand that adding or removing humidity from indoor air can have a significant impact to your comfort levels in the indoor space.

  • Heating and air conditioning split systems:  These are the standard, basic type of HVAC systems.  They have components inside and outside the living space or building and provide for both cooling and heating of indoor air.These HVAC systems consist of an air conditioner designed to cool refrigerant outside the building and a furnace with a fan or coil inside the building. These systems feature ductwork, which carries the hot or cold air throughout the various rooms of the living space.

When learning how HVAC works, remember to choose the right-sized system for your needs.  Bigger does not always mean better and this is very true of HVAC systems.    If the system is too big for the living space, it will run through its heating or cooling cycle too quickly, leading to excess condensation, mould and decreased comfort.

Quality matters

How does HVAC work from a quality perspective?  There are industry-standard HVAC systems ratings you can rely on to determine how HVAC works for you:

To ensure you select HVAC systems that best suit your needs, look for these ratings:

  • AHRI: the Air Conditioning, Heating and Refrigeration Institute is an independent laboratory that provides objective, accurate SEER ratings for HVAC systems.   The institute is tasked with certifying that a manufacturer’s efficiency claims are verifiable and accurate.
  • AFUE: this rating stands for Annual Fuel Utilization Efficiency, which measures the efficiency of a gas furnace’s ability to convert fuel to energy.
  • EER: this rating stands for Energy Efficiency Ratio, which measures how efficiently the cooling system operates when the outdoor temperature reaches a specific measurement. The higher the rating, the more efficient the system.
  • SEER: this rating stands for Seasonal Energy Efficiency Ratio, which measures the efficiency of air conditioning and heat pump cooling in HVAC systems. The higher the rating, the more efficient the system.  The federally-regulated minimum SEER rating is 13 or 14, but the ranking can go as high as 25.
  • HSPF:  this rating stands for the Heat Seasonal Performance Factor, which measures the heating efficiency of heat pumps. The higher the HSPF rating, the more efficient the heat pump.
  • MERV Rating: this rating stands for the Minimum Efficiency Reporting value, which is a standard measurement used to rate the overall efficiency of air filters. The higher the MERV rating, the finer the air filtration system.  Higher quality filtration is important since it cleans the air of contaminants.
  • NATE Certification: this certification is important if you are researching HVAC technicians.  This rating stands for North American Technician Excellence, which is a non-profit certification program for HVAC technicians.

Now that you know how HVAC works, you may be asking yourself if it is time to replace or repair your HVAC system. If your cooling and / or heating is not performing as well as you would expect, you may want to consider some key factors.

Before deciding on repair over replace, think about whether you can get a better return on your investment dollars by replacing your HVAC system instead of repairing it.

Replacing HVAC Systems

If your HVAC system falls into one or more of the scenarios below, you would likely be better off replacing versus repairing.

  • Your HVAC system is over 10 years old.   HVAC systemstypically last 15 years or so, but once you hit the 10-year mark, you should seriously consider the savings of replacement over repairs.

    With older HVAC systems, you will be spending more on utility costs than if you were using a newer model.   This means that over the long-run, your current system is costing you more than if you upgrade to a more efficient, modern system.

  • You are frequently repairing your HVAC system.   If you have undertaken repairs more than a couple of times each year in the recent past, you are probably spending too much money on repairs.    A basic rule of thumb is that if your labour and parts are costing you more than $1000 per repair, you should seriously consider replacement.
  • You are concerned about the safety of your HVAC system.  If you think your current HVAC system may pose a safety concern for your home and family, you should seriously consider replacement.   HVAC systems that are malfunctioning can have serious safety impacts such as carbon monoxide poisoning and fire risks.

If you are still not sure whether to repair or replace, call in the HVAC systems professionals.   Get an HVAC technician’s advice for any of the following scenarios:

  • No ductwork inspection for the last few years.  Ductwork can leak up to 30% of its air, which means you are paying for cooling or heating that you are not receiving.  An HVAC technician can do a duct-leakage test to find out how much leakage you may have in your ductwork.   Leakages can be fixed with sealants, avoiding the need for a full system replacement.
  • You see a degradation in system performance, with the HVAC system taking a longer time than expected to heat or cool your living space.

    An easy way to measure performance of HVAC systems is to turn on your air conditioner and set the thermostat to a temperature well below room temperature on a hot day.   After 15 minutes of run time, use a thermometer to check just outside the return duct, from where hot air is pulled in for cooling.   Then, check the temperatures just outside the strongest, most accessible vent, where you should have cold air flowing out.   Subtract the second reading from the first and if the difference is fewer than 14 degrees, that indicates your cooling system is not performing as well as should be expected.

Hopefully now you understand how HVAC works. If you are still thinking a repair of your HVAC system is what you need, do the maths to determine the return on your investment.   While replacement costs are initially quite high, the new system should deliver considerable operational savings as opposed to the repaired system, so factor in both the investment cost and the operating cost over time to decide which option gives you the most bang for your buck.

Your return on investment will be highest if you invest in one of the latest energy-efficient HVAC systems, where you will both save on annual operating costs and have lower repair costs down the line.

Now that you know how HVAC works, you are well on your way to making educated decisions about the installation, maintenance and running of your HVAC system.

Comments are closed.