Are Heat Pump Hot Water Systems Any Good?
Your hot water system could contribute as much as 25% of your overall household energy bill. While you could install water-efficient fixtures around your home to reduce your energy consumption from hot water use, you could also consider a more efficient hot water system such as a heat pump.
It’s worth noting that heat pump hot water systems aren’t a new technology. However, due to their energy efficiency and environmentally-friendly operation, they’ve become highly favoured and more prevalent in recent years. You might not know it, but you probably have one or two heat pumps in your home already – namely, your fridge and split system air conditioner!
There is a lot to consider about heat pump water heaters and whether or not they’re worth it for your home. We’re going to outline some of these points to help you decide if a heat pump water heater is right for you.
How Do Heat Pumps Work?
Before delving into the ins and outs of these highly energy-efficient systems, it helps to understand how hot water heat pumps work first.
The heat pump system absorbs heat from the surrounding air, even in cooler temperatures, and transfers it to the water. This process involves a heat pump compressor, which circulates a refrigerant that absorbs and releases heat. As the refrigerant passes through the system, it captures ambient heat energy and transfers it into the water storage tank, efficiently heating the water.
Unlike conventional electric water heaters that generate heat directly, heat pump water heaters are much more energy efficient. They use less electricity to transfer heat than to generate it, leading to significant reductions in energy consumption and costs. Additionally, since they rely on ambient air temperature rather than electricity or gas to heat water, they’re a more environmentally friendly option, reducing carbon emissions.
Types of Heat Pump Hot Water Systems
As if there weren’t enough hot water system types already, there are even different types of heat pump systems to choose between! You can break these down into their energy sources and the type of unit.
First and foremost, you can categorise heat pump water heaters by where they source their heat energy, whether that’s from the air, ground or water. Choose between a:
- air-source heat pump system
- geothermal heat pump system
- water-source heat pump system
Let’s explore them further.
Air-Source Heat Pumps
The most common hot water heat pump type you will find in Australia is an air-source heat pump.
Many people don’t consider heat pump hot water systems if they live in a cold climate, as they think their surrounding air is too cold to be effective. Air-source heat pumps might not work for colder climates that experience below-freezing temperatures frequently. Here in Australia, we’re lucky to rarely experience this kind of cold weather. Air-source heat pumps will work for most homes, and the refrigerants used are designed to work in cold temperatures, even at -10OC!
Geothermal Heat Pumps
Geothermal heat pump water heaters are a good alternative to air-source heat pumps. While the ambient air temperature might be below freezing, the temperature below the ground is much warmer and relatively constant.
Though geothermal heat pumps will initially set you back more than an air-source heat pump water heater, they are more efficient, and will save you money further down the line. As pipes are laid under the ground, they can be a great option for homes with minimal space as well.
Water-Source Heat Pumps
Water-source heat pumps can provide you with year-round hot water. Their main downside, however, is that it is uncommon for a home to have a large enough supply of ground-water available. If your home meets the requirement for a water-source heat pump, it can be an excellent option.
Air-Source vs. Geothermal vs. Water-Source
All three types of heat pumps can have the storage tank installed inside, while only the air-source heat pump can be outside. Air-source heat pumps have low output fluctuations with extreme outside temperatures, while water-source and geothermal have virtually no fluctuations.
Air-source heat pumps have the lowest upfront installation cost, but geothermal and water-source are more efficient. As most homes install air-source heat pumps, we will only be considering this source type from here on out.
Integrated or Split?
Air heat pumps can either come as one piece, called an integrated heat pump, or split. Integrated systems have the heat exchanger, fan and evaporator mounted on the storage tank as a single unit. Split systems have the heat pump mechanism installed at a different location to the storage tank.
Split systems offer the flexibility to install wherever it is more convenient, making them particularly useful for those with limited outdoor space. Integrated systems are easier to install, however, and require less plumbing work as the tank water heating system and pump mechanism already come connected.
Heat Pump Water Heater Performance
When it comes to comparing heat pump performance to other hot water systems, we can look at the coefficient of performance (COP). Most heat pumps have a COP of three or more. This means that for every unit of energy put into a heat pump, it will pump out 3 units in return.
When compared to a typical resistive electric hot water system that has a COP of one or less, a heat pump is more than three times as efficient. Some heat pumps even have a COP of up to five!
As the efficiency of a heat pump water heater varies with the ambient temperature, so too does its COP. When the outside temperature is warmer, the COP increases as it is easier to heat the water. This means that in winter it will be more difficult to heat your water, however.
Note that there is no consistent measurement of COP. Therefore, a better alternative for deciding if a heat pump will work for your home is the number of Small-scale Technology Certificates (STCs) that a particular heat pump earns in different climate zones.
Many refrigerants that heat pumps use have a quite high global warming potential (GWP). If the refrigerant leaks, it can pose quite a problem. Therefore a safe and appropriate disposal is always paramount.
The small quantities used for domestic heat pumps mean this is less of a problem. Thankfully, newer systems are moving to low-GWP refrigerants like carbon dioxide and propane. Australia is also phasing out the use of these high-GWP refrigerants which will accelerate this process.
With this in mind, heat pumps are proving to be more and more promising as technology improves.
Heat Pump System Boosting Options
Your heat pump works to heat water when it falls below a specified temperature. If it struggles to maintain this temperature over winter, you can install electric boosters to pick up the slack. These boosters will kick in only when your heat pump is struggling, so you have hot water all year round.
Are Heat Pump Water Heaters Noisy?
Yes, heat pump hot water systems can be noisy. Many heat pumps have a decibel rating that can help you pick one based on how noisy it can get.
Many modern heat pumps are only slightly louder than a whisper though! If noise is a concern, you can install your heat pump away from bedrooms and living rooms. You can also have a timer so it only works during your waking hours.
Rate of Recovery
If your home goes through a lot of hot water, the rate of recovery is an important metric for you to consider. This is the time it takes for your hot water heat pump to reheat the tank of water when you’ve used it all.
You can find the recovery rate of a heat pump hot water system from the manufacturer, but some systems are so energy efficient they can generate heat for a 50L tank in only 15 minutes!
Heat Pump Hot Water System Cost
Hot water heat pumps are one of the more costly hot water systems to install upfront. That being said, their energy efficiency makes up this cost within 5-10 years of use. Once installed, they have a very low running cost, second only to gas-boosted solar hot water systems.
Heat pumps also qualify for STCs that you can potentially exchange for government rebates on your system! The incentives vary depending on your state or territory, so it’s worth enquiring about them.
One of the major benefits of heat pump systems is the environmental impact of using one. They have a similar greenhouse gas emission to that of a gas hot water system. If you upgrade to a heat pump from a conventional water heater, you can reduce your carbon footprint by 70%! That’s equivalent to taking a passenger car off the road for 10 months.
For households that can’t accommodate a rooftop solar hot water system due to limited roof space but still want a full water heater that runs on renewable energy, heat pumps are the next best thing. In fact, they have a smaller carbon footprint than an electric-boosted solar water heater in a cold climate!
Trust The Experts in Heat Pump Water Heaters
When deciding if a heat pump is the right hot water system for your home, you’ll need to consider how the different types of heat pumps will work for your home, the upfront and ongoing costs, the environmental impact, how your family uses hot water and more. Want to read more? We have Hot Water Systems: The Complete Guide to help you out. Contact the Metropolitan Plumbing team to discuss heat pump options for your home.