Unlocking the power of heat pump water heaters: how they work and when to choose them

The use of a heat pump as a winter and summer air conditioning system is becoming increasingly popular because it is an efficient technology with economic and environmental benefits.

Depending on the user’s needs, there are different types of heat pumps available on the market, based on the heat source they use to heat the building and the way this heat is distributed inside. Among the most common ones are:

• air-to-air heat pumps;
• air-to-water heat pumps;
• water-to-water heat pumps;
• geothermal heat pumps;
• absorption heat pumps.

Among the various types of heat pumps, the novelty is the heat pump water heater, also known as a heat pump water heater, which is a particular air-to-water heat pump that uses external air to heat sanitary water.

What is a heat pump water heater?

A heat pump water heater, also known as a domestic hot water heat pump (DHW) or heat pump water heater, uses the thermal energy already available in the external air to produce sanitary hot water for sinks, washbasins, and showers inside a home.

They are configured as boilers, consisting of a storage tank and a heat pump system, specifically an air-to-water heat pump, and are made up of an air inlet system and an air outlet system.

The heat pump extracts thermal energy from the external air and uses it to heat the water, which is then stored in the storage tank.

While an electric water heater uses electric resistors to heat the water directly in the tank, and a gas water heater uses natural gas or propane for the same purpose, a heat pump water heater allows for significant energy savings, serving as a true green solution because it harnesses renewable solar external energy.

Typical diagram for heat pump water heater

How does a heat pump water heater work?

As we know, a heat pump works as a closed circuit and consists of a compressor, condenser, expansion valve, and evaporator.

Thanks to the evaporator, it absorbs heat from the outside air, which is then conveyed to the compressor. The superheated vapor, exiting the compressor, releases heat to the condenser, which transfers it to the domestic hot water, typically raising it to a maximum of 60°C. The hot water is then stored in the accumulator, ready to be used.

The electrical energy used is only that necessary for the operation of the compressor and the fan, thanks to the technology of the air-water heat pump, therefore consumption is reduced by about 60% compared to using an electric water heater, where electrical energy is used for the direct heating of water in the boiler.

Where to install a heat pump water heater?

It is generally preferable to install the boiler in indoor locations, in the bathroom or if available inside a technical room.

If it is placed directly in the bathroom, it will be directly connected to the sanitary fixtures, thus dispersing less heat.

Boilers usually come in various sizes, depending on the DHW (Domestic Hot Water) demand: therefore, if they need to serve an apartment, they can be wall-mounted or floor-standing and installed in small spaces, but if they need to serve larger structures, the size of the water heater will be larger, and it will be necessary to provide a technical room of adequate size.

It is also recommended to maintain sufficient free space around the boiler to allow for any maintenance activities.

Advantages of installing a heat pump water heater?

A heat pump water heater is an innovative and ecological solution, with high energy efficiency, as it allows saving about 60-70% of electrical consumption compared to a traditional boiler, resulting in reduced costs on the bill.

These devices are highly durable, designed to work very well for many years, requiring low maintenance.

Furthermore, a heat pump water heater has a low environmental impact: it is a sustainable solution capable of reducing polluting emissions, especially if integrated with other devices such as photovoltaic or solar thermal systems.

Lastly, modern technologies have led to silent devices, rich in features, optimized with home automation systems, and remotely controllable, providing the maximum living comfort.

When is it convenient to choose a heat pump water heater?

The operation and efficiency of a heat pump water heater are strongly influenced by external climatic conditions, so before choosing one, it is advisable to evaluate the minimum outdoor temperature value reached in the coldest periods and the performance of the heat pump itself.

If the building is already served by a photovoltaic or solar thermal system, the convenience will be even greater, given the economic and environmental advantage that results from it.

In any case, to proceed correctly, it will be necessary to carry out a survey of the property to be served and develop a thorough study based on the type of dwelling and the DHW demand it requires.

Calculating the DHW demand means defining a series of important parameters, such as:

1. number of people in the building;
2. number of devices and sanitary fixtures to serve;
3. power of the water heater;
4. size of the accumulator;
5. typical water flow rate;
6. average duration of a shower/wash;