Energy: High electricity bills, ENEA’s advice for “smart” summer consumption

Save on utility bills, protect the environment and help to reduce dependence on methane gas through a “smart” use of air conditioners. In order to make optimal use of air conditioning systems without sacrificing comfort during the summer, ENEA offers some practical and behavioural advice that, combined with the use of high-efficiency models and solar panels to produce domestic hot water, could allow savings of up to 1.8 billion cubic metres (m³) of methane gas per year nationwide, about 2.5% of Italian consumption in 2021 (76 billion m³).

"For summer air conditioning, the best way to lower electricity bills is to increase the indoor temperature setting by two degrees, raising the thermostat from 26 to 28°C, and to close the shutters when you’re not at home. In fact, in the summertime it’s essential to screen windows facing south and east”, explains Nicolandrea Calabrese, head of the ENEA Laboratory for Energy Efficiency in Buildings and Urban Development.

With these two measures, electricity consumption for summer air conditioning can be reduced by up to 50%, savings that vary depending on the home's exposure to solar radiation. “Assuming that 30% of the approximately 25.7 million Italian households have two indoor air conditioning units running for 350 hours a year, these two simple actions could save up to more than 1.3 billion kWh of electricity, corresponding to approximately 100 million m³ of methane in one year”, Calabrese stressed.

Replacing an old class D air conditioner (consumption of 243 kWh) with a new class A++ model (consumption of 103 kWh) can save 140 kWh of electricity, or about 60%. “If even just 5% of households replaced their energy-hungry air conditioner with a top-efficiency model, savings of 180 million kWh could be achieved, corresponding to 14 million m³ of gas in one year”, Calabrese added.

These annual reductions related to summer air conditioning alone (approximately 115 million m³ of methane) could be complemented by the far more significant gas savings of 1.7 billion m³ per year thanks to the installation of solar thermal panels for hot water production. “We calculated this figure by assuming adoption by 80% of households living in single-family houses, given the simplicity of the installation, and by 20% of those living in apartment buildings, for a total of about 9.75 million households. In fact, the use of solar thermal panels can fully cover a family's needs for domestic hot water from April until October, with savings of around 175 m³ of gas, considering an average consumption of 25 m³ per month”, Calabrese concluded.

Possible actions in the residential area are detailed below:

1. Pay attention to the energy class of the air conditioner

The choice of model is a key to reducing consumption and avoiding unpleasant surprises on the bill. Regardless of the technology, air conditioners with an energy class higher than A are always the best choice: not only do they consume much less, but they also reduce CO₂ emissions into the atmosphere. The annual energy consumption specified on the label of a 2.5 kW air conditioner is based on 350 hours of cooling, to which is added the energy consumption of other modes, like standby.[1]

Table 1: Savings from replacing air conditioners

2. Don’t cool the room too much, and pay attention to the humidity

The law states that during the summer the indoor temperature should not fall below 24-26°C, but most of the time two or three degrees lower than the outside temperature is sufficient. Moreover, the dehumidification function is often all you need to reduce the oppressive sensation of the heat, since the humidity in the air makes the temperature feel much hotter than it actually is.

Based on simulations made using dynamic time calculation software, it was found that raising the thermostat from 26 to 28°C can save approximately 25% in electricity consumption, taking into account different climate zones, different house characteristics and 350 hours of average use. Assuming that a household owns two intermediate energy class air conditioners with a total consumption of 346 kWh per year, savings of approximately 87 kWh of electricity could be achieved. If it is also assumed that 30% of Italian households have a cooling system (7,714,800 out of a total of 25,716,000), approximately 669 million kWh of electricity could be saved nationwide, corresponding to 52 million m³ of methane.

Table 2: Savings due to an increased set point temperature

3. Close the shutters during the hottest hours

It’s common for people to leave the shutters open even when they’re not at home, allowing heat to enter through the windows. Then when they come home and switch on the air conditioner, it has to work hard and consume more energy to cool the rooms. Closing shutters, lowering blinds or otherwise shielding windows during the middle hours of summer days reduces the amount of sunlight entering the home, and consequently the energy required by air conditioners.

The savings due to this simple measure vary considerably depending on the exposure of the house and the number of windows, but it’s estimated that it can reduce average consumption by up to 25% (approximately 85 kWh of electricity per household). Multiplying this figure by 30% of households results in a total savings of 658 million kWh of electricity, corresponding to 51 million me³ of methane.

Table 3: Savings from shading windows during the hottest hours

The above hypothesis assumes that all households with air conditioning can shield their windows during the central hours of the day. Conversely, if only half the households take these steps, the total savings are reduced to 26 million m³ of methane (see table below).

Table 4: Savings from shading windows during the hottest hours, second scenario

4. Choose inverter technology

In an air conditioner with an inverter control system, the rotational speed of the compressor is constantly regulated, which allows optimal performance in all conditions of use, adapting the cooling and heating power delivered to the actual need. These models, which are particularly well-suited when you plan to keep the air conditioning on for many hours at a time, cost more than those with on-off technology, but the energy consumption and noise level are lower, resulting in greater overall comfort in the rooms they’re used in.

5. Pay attention to the position

When installing the units it’s important to place the air conditioner at the top of the wall: cold air tends to move downwards and will mix more easily with warm air, which tends to rise. Avoid placing the air conditioner behind sofas or curtains as they act as barriers and block the diffusion of cool air.

6. One air conditioner per room

Installing a powerful air conditioner in the hallway hoping that it will cool the whole house is pointless: the only result will be to catch a chill every time you walk through the hall going from one room to another, since it will be the only space in the house that is cooled.

7. Don’t leave doors and windows open

The air conditioner cools and dehumidifies the room it’s installed in by transferring heat and humidity to the outside. The entry of “new” warm air into the room forces the equipment to perform additional work to bring the temperature and humidity back down to the desired levels, with a consequent expenditure of energy.

8. Insulate the refrigerant pipes outside the house

In order to avoid unnecessary dispersion, it’s necessary to thermally insulate the pipes of the refrigeration circuit outside the house. You should also make sure that the external component of the air conditioner is not exposed to the sun or bad weather.

9. Use the timer and “night” function

Thanks to these functions, it’s possible to minimise the conditioner’s running time and increase comfort. Furthermore, they allow the air conditioning system to be switched on and off even remotely and to keep it running only for the time when it is really needed. The “night” or “sleep” function regulates the room temperature at night in response to changes in body temperature.

10. Pay attention to cleaning and proper maintenance

Air filters and fans must be cleaned when turned on at the beginning of the season and at least every two weeks, because this is the place where mould and bacteria harmful to health, including the legionella bacterium that can be deadly, most frequently lurk. It’s also important to make sure that the gas circuit is sealed. Note also that regulations require a system booklet and periodic inspections for systems with an output of more than 10 kW for winter and 12 kW for summer.

11. Replace incandescent bulbs

Additional heat produced by lights are a non-negligible part of the heat load inside dwellings. Indeed, incandescent lights transform 90% of the electrical energy absorbed into heat, part of which is dissipated into the surroundings by radiation (80%), and part by convection and conduction (10%).

The internal thermal load can be reduced by replacing existing lights with LED-type bulbs. LED lights consume much less energy than incandescent lighting and produce minimal heat, reducing the need for cooling.

12. Use of solar panels

The installation of solar thermal and photovoltaic panels can allow homes to be completely independent of external supplies of electricity and/or other fuels.

As noted above, the use of solar thermal panels can fully cover a family's needs for domestic hot water from April until October, with savings of around 175 m³ of gas.

Table 3: Savings from installing solar thermal panels

13. Give your home a check-up

Asking a technician to perform an energy check-up of the building is the first useful step to assess the thermal insulation of walls and windows and the efficiency of air conditioning systems. The diagnosis will suggest solutions to be implemented, assessing their value for money. In addition to lowering the costs for summer air conditioning, these solutions can become even more cost-effective if government incentives are used.

14. Keep an eye on incentives

To facilitate the replacement of existing systems and the installation of energy-efficient technological solutions, there are various forms of incentives. In fact, the installation of solar thermal systems is eligible for the Conto Termico 2.0 programme, 50% tax deductions (home bonus) and 65% tax deductions (ecobonus). This also applies to the installation of heat pumps if they are intended to replace an old heating system. For photovoltaic systems the incentive to be considered is the home bonus, which offers a 50% tax deduction (https://www.efficienzaenergetica.enea.it/detrazioni-fiscali.html).

As far as offices are concerned, a study[2] conducted by ENEA in cooperation with Assoimmobiliare found that summer air conditioning accounts for 57% of total electricity consumption. The measures listed for homes can also be considered valid for offices.

For example:

• Installation of high-efficiency air conditioners
• Increased indoor cooling temperature setting
• Installation of LED lighting
• Installation of photovoltaic systems
• Introduction of intelligent control systems

Changes in the working world due to the pandemic, with the consequent increase in teleworking, make it necessary to identify flexible solutions for managing the energy demand of office buildings, maximising efficiency even when they’re only partially occupied. It’s estimated that the introduction of intelligent controls based on the detection of the actual presence of people in offices can lead to energy savings for cooling of between 2 and 4%.[3]

[1]  See ENEA (2021). I quaderni dell’efficienza energetica. L’Etichetta Energetica 2021, (Available here: https://www.efficienzaenergetica.enea.it/pubblicazioni/l-etichetta-energetica-2021.html)

[2] Study based on the actual consumption of 123 office buildings nationwide (with a total annual consumption of approximately 40,000 toe)
https://www.enea.it/it/Stampa/File/Rapporto_BenchmarkConsumiUffici_EneaAssoimmobiliare_2019.pdf

[3] Source: “Flessibilità energetica e controlli intelligenti negli uffici e negli edifici commerciali”, Giovanni Pernigotto, Environmental Physics Research Group, Faculty of Science and Technology, Free University of Bolzano