Heat Pump Efficiency Vs Temperature

 In Energy Management News, General News, Questions & Answers

Heat Pump Efficiency Vs Temperature

Heat Pumps Efficiency Vs Temperature

You may be considering having a heat pump installed in your home, for your business, greenhouse, for your pool, or even just for your hot water system. After all, heat pumps are known as a much greener way of providing your house with hot water and heating.

However, before you commit, it is incredibly important to research the topic. On this page, we go through heat pump efficiency and temperature, and what to look out for.

Hopefully, it will help you to make the right choice.

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Toyesi Heat Pumps

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Are Heat Pumps Efficient?

Heat pumps are considered energy efficient. Their efficiency comes from the fact that they use the power of a refrigerant cycle to turn small amounts of electricity energy into much larger amounts of heat energy.  The term used to describe this efficiency is Coefficient of Performance or COP for short. Therefore at first glance the higher the COP the more efficient the heat pump will appear to be.  COPs of 5 is considered good.

A COP of 5 means for every 1kW of electricity it provides 5 kW of heat energy.

In chillers or coolers like air-conditioners, they often use the term Energy Efficiency Ratio (EER) or Seasonal Energy Efficiency Ratio (SEER) instead of COP as the performance ratio.  The formula for EER is a little trickier to work out, but if you multiply the COP by 3.41214 you will get an approximate EER. Chillers are less efficient than heaters and an EER of 8.5 or better is considered good.

A COP of 2.5  would give you an EER of  8.5 which means for every 1kW of electricity it provides 2.5 kW of cooling energy.

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Some heat pumps come with inverter systems. Inverters are a smart way to slow or speed up how the heat pump works to help maintain a steady temperature or capacity output. These heat pumps will use a variable COP. For example 3 to 16 COP. In many situations inverter systems are a great choice, however, care must be taken when selecting them.

The heat pump efficiency (COP) of 16 can be deceptive or misunderstood.  When heating in summer, much less energy is required to heat. During this period there is very little work to be done and requires only a small amount of energy to do it. The unit will trickle feed the heat giving the appearance of a COP of 16. However will have to run for much longer than the “on-off” standard heat pump. In the end, it gives very similar power usage over 24 hours, think about it, if a pool requires 10 kW of energy over 24 hours, it does not matter if it is 5 x 2 kW allotments or trickle-fed all day, the pool till needs 10 kW of energy use.

During winter when there is a lot of work to be done and very little energy available to get it done, you will find that the COP of an inverter system will be the same or less than the “on-off’ based system and again will run longer to get the same work done.

So if you are considering an inverter system, do not fall for the marketing COP pitch, instead, find out the COP in mid-winter where it has to work the hardest. Compare this with your on-off system for comparison. This will give you more apples for apples comparison.

Heat Pumps and Energy Consumption

Heat pumps turn electricity into heat energy. Thus they are considered an electric heater. But to put things into perspective. An electric element bar heater, a kettle, or electric hot water system, or even an aquarium electric element drop heater, all use a resistance form of heating. By passing electricity through a metal bar the resistance of that bar makes it heat up. Typically an efficient element heater is a 1 to 1 ratio. This means their COP would be 1.  1 kW of electricity gives 1 kW of heat.

A heat pump with a COP of 5 would be 5 times or 500% more efficient than the bar heater. You can straight away see the consumption and money saved by swapping an element heater to a heat pump heater.

However, when comparing this to gas-based systems, which run at only 80% efficiency, that is a COP equivalent to 0.8, the consumptions and savings are not as obvious. It comes to consumption and value. We must look at the power tariffs of electricity and gas. In the current market, a heat pump can save you 45 to 75% of the running costs over a gas-based system.

However, the operating temperature of the system will change the final savings and efficiencies. Heat pump efficiency can be a very seasonal thing.

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Revers Cycle Heat Pumps

We know heat pumps can be used to heat your home, and we also know that chillers can be used to cool your home. However, some heat pumps are reverse-cycle systems. This means they are both heaters and chillers in one.

Meaning they can be used to heat your home in winter and cool your house in summer. Saving you money in equipment costs as well as enjoying savings in energy usage throughout the year.

Many of Toyesi’s heat pumps can be set as heaters only, chillers only, and reverse cycle heater chillers. However, some systems add more smarts and allow you to heat, chill, and provide hot water. These are known as multi-function heat pumps.

Toyesi’s Platypus Home Heat Pump (Click Link Here) is considered a Multi-Function heat pump ideal fo domestic use.

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Efficiency Vers Temeprature

As we previously mentioned temperature output of a heat pump directly affects the perceived efficiency of a heat pump. The ambient conditions also directly affect the perceived efficiency of a heat pump.

In heating mode, the heat pump draws energy from the air and converts this to heat energy to heat water. The warmer the air temperature the more energy is available to capture for use. During summer the energy (kW) output will go up, yet still use a similar energy input. Thus COPs of 8 are not uncommon during summer.

However in winter when ambient temperatures drop below 15 degrees, the amount of free energy to capture and use goes down. Often during very cold winters COPs can go as low as 2 to 3.  This means a 20kW heat pump in winter may only provide 10 kW of heating.  This must be considered when selecting the right heat pump for your project.

Chillers are opposite to heat pumps in that they are more efficient during winter ambient conditions and less efficient in hot summers.

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In some locations, winters are below zero and summers are above 40 degrees, swapping to a geothermal heat pump may be the solution. With ground temperatures sitting at 13 to 18 degrees all year round, they will flatten the curve and give consistent energy outputs all year long. However, across most of Australia geothermal may not be recommended or suitable as it is not for everyone and can be quite expensive, (Click Here for GEO – Considerations).

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Not only do ambient conditions affect the output capacity of a heat pump, but the required water temperature affects the heat pump efficiency and output capacity. Most heat pumps love working in ambient conditions 15 degrees to 35 degrees. They also like working at water temperatures of 15 to 35 degrees.

When heating water higher than 35 degrees the heating capacity of the refrigerant begins to drop off. So at 27 degrees, for a pool let’s say, the COP may be 5, but at 55 degrees, for a hot water system, the COP may only be 3.

Heat pump refrigerants also have a max temperature threshold. R407C has a 55-degree max temp, whereas R134a can go up to 75 degrees in hot water. But there is a trade-off, R134a is not as efficient and you trade higher temperatures for kW output capacity.

The same can be said for chillers. Cooling water below 15 degrees begins to reduce the chillers’ capacity output. For example, a 20 kW chiller at 15 degrees may only be a 6 kW chiller at 5 degrees.

So care must be taken to not just buy heat pumps based on their nominal ratings, but work out their capacity output for both operating conditions and ambient conditions, and by selecting the unit that can give you the desired output your project requires.

Want to Know More

Toyesi has over 30 years of tacit knowledge in sizing heat pumps and chillers. We have a range of Toyesi Australian-made equipment, as well as a range of imported more domestic-oriented systems.

We can take your project, and your working conditions and choose the correct equipment for you. We know that a 50kW heat pump in Tasmania is very different from a 50kW heat pump in Darwin. Not all off-the-shelf heat pump solutions fit all projects.  So why not drop us a line (Click Here)

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