Heating, ventilation and air conditioning (HVAC) systems utilize smart technology that conditions the temperature and air quality of a closed-door environment. The goal of an HVAC system is to achieve a certain level of comfort for dwellers.
As a system, HVAC is based on several principles of mechanical engineering. These principles include heat transfer, fluid mechanics and thermodynamics. Informally, people refer to HVAC simply as “refrigeration.” Refrigeration systems are used not only for refrigerators but also for air conditioners.
An air conditioning system controls the humidity and temperature of an enclosed environment. To control these two factors efficiently, the system requires sealed windows.
Open windows mean the room or vehicle is no longer an enclosed environment. The refrigeration will have to work harder to control both humidity and temperature. This strains the system, leading to the poor performance of the HVAC system.
Outside the enclosed environment, the system draws in fresh air into the vent. The air undergoes a heat exchange phase to create positive air pressure. The average intake of fresh air is 10%. By simply adjusting the vent, the system can manipulate fresh air intake.
The system works by removing heat from the air. The process of removing heat from the system includes a series of radiation, conduction or convection. They can also use refrigerants to pump out heat. Refrigerants can be chemicals, water, ice, and air. The system integrates the refrigerants through a heat pump system. This triggers the thermodynamic refrigeration cycle.
In a free cooling process, the refrigerants are pumped through a separate medium (usually glycol or water) into the system.
The efficiency of the system is rated based on a standard called the Seasonal Energy Efficiency Ratio (SEER).
Seasonal Energy Efficiency Ratio
Owners of refrigeration and air conditioning systems must have a good understanding of SEER standards. In its 2008 standard, the Air Conditioning, Heating and Refrigeration System Institute (AHRI) gives an extensive definition of the SEER rating system. The rating guide is published in a document called “Performance Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment.”
There is a parallel rating system employed in European countries. This system is called the European seasonal energy efficiency ratio (ESEER).
An air conditioning unit has a specific SEER rating upon manufacturing. This rating can be computed by dividing the cooling output by the electric energy input within a cooling season. Units with a higher SEER rating are more energy efficient.
In the United States, the SEER is computed by determining the cooling output in terms of British thermal unit (BTU) and energy consumption in terms of watt-hours. The ratio between the output and the input is the SEER ratio.
Computing for Cost Per Operating Hour
For instance, an air-conditioning unit is determined to have the following specifications: a cooling output of 5000 BTU, a SEER Rating of 5 BTU/(W · h). For this example, the total operation hours in a single annual cooling season is 1000 hours. Let’s say that’s an average of 10 hours a day in a span of 100 days.
On a yearly basis (single cooling season), the total cooling output is:
|5000 BTU||x||10 h||x||100 days||=||5000000 BTU|
Considering that the SEER rating is at 5 BTU/(W · h), the energy usage in a single cooling year is:
|5000000 BTU||/||5 BTU||=||1000000 (W · h)|
|year||(W · h)||year|
To calculate for the average power usage, the cooling output will be divided by the SEER rating as in the computation below:
|Average power||=||(BTU / h)||x||5000||=||1000W (or 1 kW)|
To compute the cost per operating hour, let’s assume that the electricity cost is at $0.10 per kW · h, the computation should look like this:
|1 kW||x||$0.10 per kW||=||$0.10|
Given the above conditions, the hourly cost of the air conditioning unit is at $0.10 per hour.
Coefficient of Performance (COP)
The Coefficient-of-Performance (COP) measures performance, but this dimensionless measure has not been adopted. Instead, the Energy Efficiency Ratio (EER) has traditionally been used to characterize the performance of many HVAC systems. EER is the Energy Efficiency Ratio based on a 35 °C (95 °F) outdoor temperature.
To more accurately describe the performance of air conditioning equipment over a typical cooling season, a modified version of the EER, the Seasonal Energy Efficiency Ratio (SEER), or in Europe the ESEER, is used. SEER ratings are based on seasonal temperature averages instead of a constant 35 °C (95 °F) outdoor temperature. The current industry minimum SEER rating is 14 SEER.”
SEER standards by the US government
In 1987, the US government set the minimum SEER rating to 10. In the ’90s, having a unit that is SEER 9 or lower was a rare sight. This is due to government legislation requiring private and public organizations to replace aging air conditioning units with more efficient units.
In 2006, the government raised the minimum SEER rating to 13. Units that were given ENERGY STAR rating had a minimum SEER rating of 14.5.
The government elevated the standards further due to the efforts of the US Department of Energy in 2011.