When we talk about energy balance in buildings We are not dealing with a mere theoretical concept, but with the foundation of any serious energy efficiency projectComfort and long-term savings. Understanding where energy comes from, how it circulates through the building, and where it is lost allows for informed decisions, rather than blindly changing equipment without knowing if it's truly worthwhile.
In practice, a good energy balance is like a technical energy accountingAll energy inputs (electricity, fuels, renewables) are recorded, all energy uses (heating, cooling, domestic hot water, lighting, equipment, ventilation, etc.) are analyzed, and gains are compared with losses through the building envelope, ventilation, and air infiltration. From this, priorities for action are identified, systems are sized, and ambitious goals such as nearly zero-energy buildings or passive houses can be achieved.
What is energy balance in buildings and why does it need to be balanced?
The energy balance of a building describes all energy flows between the building and its surroundingsIt is an exercise in comparing the sum of energy gains (what comes in or is generated) and the sum of losses (what comes out), so that, in steady state, both quantities are equal: what comes in must exactly compensate for what is lost.
Many texts talk about energy balance This is synonymous with energy consumption, because if we consider the building as a nearly stationary thermodynamic system, the energy inputs must be identical to the outputs. This implies that energy consumption is not a mystery: it is determined by the magnitude of the losses that must be covered to maintain comfortable indoor conditions.
If we only look at the building's facade, it might seem that the balance is limited to the energy transmitted through the walls and windows. However, a rigorous analysis incorporates many more terms: controlled ventilation, parasitic air infiltration, incident solar radiation, internal heat gains from people and equipment, and even the heat removed with wastewater or combustion gases.
This assessment can be done at different levels of detail. It is possible to analyze only the heating demand and domestic hot water, or extend the scope to all energy uses in the home or office: lighting, office equipment, elevators, mechanical ventilation, internal data centers, etc. You can also work with final energy, primary energy, or with actual measured consumption data instead of theoretical calculations.
In its simplest form, the calculation is limited to the energy transmitted by the envelopewithout considering solar or internal heat gain, and without taking into account ventilation and infiltration. This basic approach can serve as a first estimate in a conventional house, but It falls far short. if you want to make investment decisions or certify the building's performance.
Gains and losses: how energy really moves in a building
To make the concept clear, it is helpful to separate the power inputs and outflows or lossesOnly in this way can we understand why consumption skyrockets or remains under control.
On the input side we find the classic energy vectors: fuels (natural gas, LPG, diesel), electricity from the grid and, increasingly, renewable energy generated on site such as photovoltaic or solar thermal energy. Passive solar gains through well-oriented windows and internal gains from people, appliances, and electronic equipment should also be considered.
On the losses side appear all the mechanisms by which the building releases energy to the outsideHeat transmission through walls, roofs, floors and windows; ventilation needed to ensure air quality; unwanted air infiltration (leaks through joints and poorly sealed connections); and heat carried by fluids at a different temperature than the environment, such as air expelled by ventilation systems or combustion gases from boilers.
If we analyze the balance from a thermodynamic perspective, all the energy that enters the building ends up, sooner or later, converted into heat. An oven, a light bulb, or an electric motor performs its function, but the electrical energy consumed does not disappearIt transforms into heat, which eventually raises (even if only slightly) the indoor temperature. That's why even energy consumption that we don't mentally associate with air conditioning ends up influencing the thermal balance.
The first law of thermodynamics guarantees that energy is conserved, but the second law introduces the concept of exergyExergy, that is, the capacity of a given form of energy to perform useful work. Wasting high-exergy electricity as uncontrolled heat (for example, in inefficient lighting) means foregoing its use where it would provide much greater value, such as in a bomba de calor which could generate several times more useful thermal energy with the same electrical input.
Thermal energy flows and representation using Sankey diagrams
A very practical way to visualize the energy balance of a building is through a thermal energy flow diagramsimilar to a Sankey diagram. It represents, on the input side, the total energy that reaches the system (heating, DHW, electricity, solar and internal contributions) and, on the output side, the different paths by which that energy is distributed or lost.
For example, in heating systems we find flows that are considered internal losses: heat that remains in the boiler room, losses through the flue, or residual heat that doesn't reach the living space. A heating system with a portable stove won't have these leaks in the boiler room, but it can still generate heat. indirect losses due to increased ventilation because it is necessary to renew the air to ensure indoor quality.
On the output side, in addition to the useful energy that actually provides comfort, losses due to transmission through the building envelope (walls, roofs, floors, windows) and those due to ventilation and infiltration are recorded. Heat lost with the sewage water after heating the domestic hot water, a flow that is often ignored but can be very significant in buildings with high DHW consumption, such as hotels or gyms.
This graphical representation helps to accurately size the installations. By adding up all the losses, we can precisely calculate the power and energy required for heating, cooling and domestic hot water, instead of relying on general rules or "templates" that do not reflect the reality of each building.
The main benefit of energy flow analysis is that it allows you to see at a glance the relative importance of each energy path. Depending on the objective (cost savings, emissions reduction, energy certification, passive design), you can decide how deeply it is worthwhile to analyze each flow and how much detail is needed.
Strategies for achieving an efficient energy balance
Once the energy flow map has been described, it's time to act. Strategies to reduce heating, cooling, and domestic hot water energy consumption are based on two fundamental pillars: increase useful profits y reduce unnecessary losses.
On the one hand, the increase in the passive solar gains This translates directly into energy savings. This involves designing the building with good orientation, adequate glazed surfaces, mobile sunshades and bioclimatic architectural solutions. It's not about filling the facade with glass, but about intelligently harnessing the winter sun and protecting oneself from the summer sun.
On the other hand, the reduction of the transmission losses through the envelope (walls, roofs, floors, openings) is the main construction strategy. It's not just the insulation thicknessAlso critical are thermal bridges (junctions of slabs with facade, roller shutter boxes, embedded pillars), humidity control in materials and correct execution on site to avoid pathologies and loss of performance.
Air infiltration losses, that is, unwanted leaks through cracks and joints, are energy wasted out the windowIdeally, they should be practically nonexistent, and their presence is usually a sign of a poorly designed building envelope. Hygienic ventilation, on the other hand, cannot be eliminated because it is essential to guarantee indoor air quality; what can be done is to optimize it.
For this necessary ventilation, one can work with well-managed natural ventilation (window opening habits, cross ventilation, schedule control) or with mechanical ventilation with heat recoveryThis is very typical in high-efficiency buildings such as passive houses. These systems recover a good portion of the heat from the outgoing air and transfer it to the incoming fresh air, significantly reducing the energy needed for heating and cooling.
Internal heat gains, from people and equipment (appliances, computers, lighting, machinery), are a double-edged sword. On the one hand, they provide heat that can help in winter; on the other, To generate them, energy needs to be consumed.Increasing these profits intentionally as a "savings" strategy is a bad idea, because it involves increasing the overall consumption of the building, and usually in forms of high exergy energy such as electricity.
Energy balance, efficiency and certification in the building sector
The energy balance has become established as a fundamental pillar for understanding the dynamics of energy efficiency This applies to both residential and commercial/industrial buildings. A rigorous analysis of the relationship between energy consumed and energy supplied reveals real opportunities for improvement, reducing costs and emissions.
In this context, the following becomes relevant: Energy efficiency certificateThis certificate is mandatory in Spain for selling or renting properties since the entry into force of Royal Decree 235/2013. It provides a quantitative measure of a building's energy performance, assessing the annual consumption needed to maintain standard usage and occupancy conditions, including heating, cooling, lighting and domestic hot water production.
The rating is expressed using a letter scale from A to G and a color range from green to red. A building with A class It typically has near-zero or very low energy consumption, with a well-insulated building envelope and intensive use of renewables, and can consume up to 90% less than a G-rated building. In between, categories B and C indicate very high or above-average efficiency levels, while classes D and E are associated with typical buildings constructed under older regulations, with clear room for improvement. Classes F and G reflect buildings with high energy waste and high COâ‚‚ emissions.
The certification process is carried out by a qualified technician (architect, engineer or specialized technician) who analyzes the thermal envelopeThe systems for air conditioning, domestic hot water, ventilation and lighting are analyzed. Reference climatic conditions and standardized usage assumptions are used to obtain annual indicators related to the building's usable area, both in CO₂ emissions (kg/m²·year) and in non-renewable primary energy consumption (kWh/m²·year).
In addition to these overall indicators, supplementary indicators are calculated that break down the energy demanded and consumed by each main service: heating, cooling, ventilation, domestic hot water, and lighting. This information is key to proposing concrete improvement measures, as it allows you to identify whether the main problem is in the building envelope, the installations, or a combination of both.
How is a building assessed and what improvements are usually recommended?
The energy assessment of a building goes beyond theoretical calculations. The responsible technician gathers real consumption information This is done through invoices, on-site visits, facility analysis, and, where appropriate, measurements with specialized equipment. All of this is integrated into a model that simulates the building's performance and generates the rating.
The end result is a certificate that includes the energy label and a report with recommendations for improving the ratingThese proposals usually focus on several fronts: reinforcing insulation in facades and roofs, improving carpentry and glazing, eliminating obvious thermal bridges and properly treating watertightness to reduce infiltration.
It is also advisable to update heating and hot water installations, replacing obsolete systems with more efficient ones: condensing boilers, heat pumps air-water or geothermal systems, micro-cogeneration systems, or solutions that integrate renewable energy such as solar thermal or biomass. In many cases, it is proposed to incorporate mechanical ventilation with heat recovery, which both improves air quality and reduces heating demand.
Another set of measures is aimed at energy management and controlInstallation of monitoring systems, automation of operating schedules, occupancy sensors for lighting, regulation of airflow in ventilation and air conditioning, and review of occupant usage habits. Seemingly small changes in control can lead to significant reductions in the bill.
To facilitate the implementation of these improvements, the European Union promotes aid programs such as the funds Next Generation USThese grants subsidize interventions related to energy efficiency improvements, including controlled mechanical ventilation and other sustainable technologies. Taking advantage of these grants allows for significant improvements in a building's energy performance while reducing the initial financial investment.
Energy balance, monitoring and advanced energy management
Alongside the regulatory framework and certification, the most advanced organizations work with systems of real-time energy monitoringThese systems, supported by sectorized meters, network analyzers and monitoring platforms, collect continuous data on energy flow by circuit, use and area of ​​the building.
With that information, the energy balance ceases to be a static snapshot and becomes a dynamic management toolAutomation and control allow for adjusting setpoints, schedules, and operating strategies based on actual demand, hourly electricity rates, and even the availability of renewable generation, whether on-site or from the grid.
The development of solutions for energy storage Electric batteries, thermal storage in buffer tanks or phase-change materials are playing an increasingly important role. They allow for shifting consumption to cheaper hours, smoothing peak demand, supporting the integration of variable renewables such as photovoltaic solar power, and improving building resilience to power outages.
In the context of decarbonization, integrating renewable sources such as solar and wind energy The energy system requires careful management of the balance. Variations in production demand adaptability and flexibility in both generation and demand, and buildings are evolving from passive consumers to active elements that generate, store, and manage their own energy.
This entire approach aligns with international standards such as ISO 50001 energy managementThis standard establishes the requirements for implementing continuous improvement systems for energy performance, and it aligns with technical reference standards such as those of ASHRAE for the design and operation of thermal installations. Furthermore, it connects with ISO 14001 for environmental management, which incorporates energy efficiency and emissions reduction as part of the organization's overall environmental performance.
In day-to-day operations, the combination of a good initial energy balance, continuous monitoring, and periodic review allows a shift from reactive management—where action is only taken when the bill skyrockets—to a proactive approach. proactive and data-driven managementwhere investment decisions are prioritized by economic return, environmental impact and improvement of occupant comfort.
Understanding the energy balance of a building as a thermodynamic system, relying on certification, taking advantage of passive design strategies and quality building envelopes, incorporating efficient and renewable technologies, and supporting it all with rigorous monitoring and management makes any property, from a house to a large commercial complex, a key piece of a much more rational, economical and environmentally friendly energy model.
