Key points of this article:

What Is Efficiency?

Efficiency in the simplest terms, means the amount of energy an equipment produces out of the amount of energy it consumes. This produced energy is often called “useful energy”; Therefore, in a mathematical term, equipment efficiency is the division of useful energy, by consumed energy. For example, to keep your house warm via a gas heater, you get useful heat by burning natural gas. The more heat you get out of burning a unit mass of natural gas, the more efficient your gas heater is.

Benefits of Efficient Equipment Use

The use of equipment with high efficiency compared to low-efficient equipment has the following benefits:

• Energy costs: when you use efficient equipment, by consuming a unit of energy, you can extract more useful energy compared to less-efficient equipment. Thus, to get the same amount of energy, you use less energy in the form of electricity or natural gas. This saves on your energy bills. Although efficient equipment helps you financially on the matter of energy use, they are more expensive to buy and due to their complexity and smart features, they may also impose a higher maintenance cost.
• Impact on infrastructure: low-efficient equipment does the same job but with higher energy consumption compared to efficient equipment. They often need to stay “on” for more hours to deliver what they have been manufactured for. Higher energy use during more hours in a big city means the electricity grid must be maintained regularly to deliver the energy on peak usage hours. This increases the maintenance costs and public spending and in some cases, increases the possibility of system overload and blackouts. Therefore, a new term is often used to compare two homes in terms of energy use, called “societal cost of energy”; meaning that a household that possesses low-efficient equipment, imposes higher costs to the society. Read more about it here.
• Climate change: low-efficient equipment uses more energy to deliver the same performance as efficient equipment. When energy is used (e.g. electricity is used or gas is burnt), greenhouse gases, specifically CO2 are emitted as a by-product of this energy use. The more energy a non-efficient equipment uses; the more CO2 it emits to the atmosphere. Needless to say, these greenhouse gases contribute the most to climate change.

How do you measure efficiency?

As we discussed before, the efficiency formula is very simple and inclusive: It is useful energy or output energy, divided by consumed energy or input energy. However, considering the type of equipment, the metric that represents the efficiency differs between different types of equipment. Here, we focus on three types of equipment and all you need to know about their terms of efficiency:

Gas heaters

Gas heaters or boilers use natural gas to produce heat; Therefore, their efficiency equals the ratio of heat produced by the gas heater, divided by the energy they extracted from the burnt natural gas. For example, a gas heater with an efficiency of 90% means that the gas heater converts 90% of the burnt natural gas to useful heat.

LHV efficiency, HHV efficiency

Although manufacturers report efficiency as a percentage of this energy conversion, we must be aware that most of it is based on Low Heating Value (LHV) or Net Calorific Value (NCV). Note that these values do not represent the actual efficiency of the equipment, also, you cannot derive fuel consumption or greenhouse emission based on these values. If you read that a condensing gas heater efficiency is above 100%, note that this efficiency has been derived by using LHV or NCV. In the simplest terms, LHV does not take the heat of vaporization of water (as a by-product of burning fuels) into account. It assumes that water remains vapour and escapes with the exhaust gases. When calculating the efficiency based on High Heating Value (HPV) or Gross Calorific Value (GCV), the heat that is released during the condensation of water is taken into account. To calculate efficiency based on HHV or GCV, simply multiply LHV efficiency by 0.9; especially when following alternative compliance pathways for energy compliance like Green Star and JV3 modelling.

Refrigerant cooling systems and heat pumps

Refrigerant cooling systems use electricity to transfer heat from a habitable space to the outdoors. Heat pumps do just the opposite of that. The efficiency of a refrigerant cooling system (e.g. Ducted split, packaged unit or VRF system) could be explained as the amount of heat removed from a space, divided by the electricity consumed by the system (i.e. compressor’s electricity consumption).

COP, EER

Since refrigerant heating and cooling systems do not produce but transfer heat from one place to another, the term efficiency is not a good word to represent the device’s performance. Instead, another metric called the Coefficient of Performance (COP) is used here. Since the heat is not created or absorbed, but rather transferred, COP can exceed 100% to a value even as high as 500% or a COP value of 5. A COP value of 5 means that by consuming a unit of energy (say 1kWh), the heat pump can transfer 5 units of heating energy (or 5kWh in this case) from outdoors to a habitable space. COP is mainly used for heat pumps in heating mode, whereas, to calculate the efficiency of a refrigerant system in cooling mode, another term is used called Energy Efficiency Ratio (EER) which is the same as COP. EER therefore equals the amount of heat transferred from a habitable space to outdoors divided by the energy the equipment consumes.

ACOP, SEER

Manufacturers report COP and EER based on standard indoor and outdoor temperature and humidity levels. For example, manufacturers report their device’s cooling EER based on an outdoor temperature of 35C and indoor temperature of 26.7C with a relative humidity of 50%. Although these standard conditions provide an acceptable way to compare different models with one another, they ignore the overall efficiency of the device in non-standard conditions. In perspective, a specific device may perform poorly in the standard condition (outdoor temperature of 35) but perform exceptionally well in milder temperatures. To capture the big picture here, other metrics were developed to account for the performance of refrigerant systems during the whole heating or cooling seasons, not just the standard condition. For heating, the Annual Coefficient of Performance (ACOP) is the average efficiency of a heat pump during the whole heating season. For cooling, the Seasonal Energy Efficiency Ratio (SEER) is the average efficiency of a refrigerant cooling system during the whole cooling season. Using ACOP and SEER, we can compare the efficiency of different devices better.

HSPF, TCSPF

ACOP and SEER are good metrics and average out the performance of a device during a season. What we mean by season is a variety set of outdoor test conditions. Although these metrics are fine, they lack one thing: These metrics are not climate-based; they are put to the same test conditions as any other device, any other place. But consider a region with very hot summer days most of the time and a large daily temperature fluctuation, compared to an area with very mild summers. The climatic specifications of each region should be taken into account separately. To account for these climatic specifications, two new metrics are developed:

The heating Seasonal Performance Factor (HSPF) is the division of the heating output of a device, by the total electricity energy input, using specific climate data. Similar to HSPF, the total Cooling Seasonal Performance Factor (TCSPF) is the total cooling energy transferred from a habitable room to the outdoors, divided by the total electricity energy consumed by the device, using specific climate data. The term “Total” in total cooling includes the energy wasted due to condensation of water vapour on the coil surface.

In Australia, the new Greenhouse and Energy Minimum Standards (GEMS) 2019 Standard has been developed as a region-based efficiency rating. The old star rating of equipment is now changed due to this newly developed standard and a 4-star device with the old rating system, could be a 3-star device in the new standard. This new rating system separates the efficiency into three climate zones:

• Hot climate (cities like Brisbane or Darwin)
• Mixed climate (cities like Adelaide or Perth)
• Cold climate (cities like Launceston or Melbourne)

The new rating system rates devices from 1 to 10 stars and from April 2020, all new devices are required to have a Zoned Energy Rating (ZER). This new rating system is included in the BASIX and Whole of Home assessments.

Domestic water heaters

Conventional domestic water heaters come in three types: gas water heaters, electrical resistance/element water heaters and heat pump water heaters. The new technology integrates solar collectors with conventional heaters to reduce the need for heat on a sunny day. Since these systems are made of conventional heaters, all the above efficiency metrics apply here. This means that a gas water heater has a specific LHV or HHV efficiency (%) and a heat pump water heater has a specific COP value reported in the manufacturer’s catalogue.

Number of STCs

Although manufacturers report their system’s efficiency and COP under standard conditions, there is no official energy rating scheme for heat pump water heaters, solar electric and solar gas water heaters. Therefore, these types of domestic water heaters are considered to generate Small-scale Technology Certificates (STCs) under the Clean Energy Regulator’s website.