HE 4 and HE 5: renewable energy in buildings

The requirement applies to buildings with domestic hot water demand, new construction and relevant interventions on existing ones, and its current formulation is technologically neutral, one of the fundamental changes of the 2019 revision. The previous version of the document required a minimum solar contribution; the current one requires a minimum renewable contribution, leaving the technology to reach it to the design.

The required levels are substantial: as a general reference, the renewable contribution must cover at least 60 percent of the annual domestic hot water demand, rising to 70 percent when the building's demand exceeds the five thousand litres per day threshold set by the section, with computation rules and defined exceptions in the document itself. The exact percentages are verified in section HE 4 of the text in force.

The technological range for compliance is now threefold. Solar thermal, the requirement's historical protagonist, remains valid and competitive in concentrated demands and favourable climates. The heat pump, air-to-water in ordinary practice, counts its renewable share under the performance conditions the document and its guides establish, and has become the market's dominant route through its double service of climate control and hot water and the simplicity of its implementation. Hybrid combinations, dedicated photovoltaics included in specific configurations, complete the repertoire in singular projects.

For the budget, the 2019 philosophy change had a major consequence: the requirement stopped dictating a specific item, the solar collectors of another era, and became integrated into the building's general generation decision. The cost of HE 4 compliance is no longer read in isolation: it is read within the global HVAC trade-off, where the heat pump that satisfies the section is often the same machine that heats and cools.

Section HE 5 obliges buildings exceeding the built-area thresholds set by the section, generally in uses other than private residential and from areas in the order of thousands of square metres, to incorporate renewable electricity generation systems, photovoltaic in practice. The minimum required power is determined as a function of the building's area, between the minimum and maximum values defined by the section, with computation rules and exceptions, shading and heritage protection among them, defined in the text itself.

The section's economic reading is twofold. As an obligation, it is an identifiable item, photovoltaic field, structure, inverters and connection, whose unit cost has fallen steadily and whose roof integration must be coordinated with the other roof easements, maintenance and fire protection included. As an opportunity, the obligation increasingly coincides with the economic optimum: in much of the commercial sector, the required photovoltaics pay for themselves through self-consumption, and the mature design question is not how to meet the minimum but what the optimal size above it is.

Both sections are at the centre of the CTE reform currently going through approval, which transposes the 2024 European directive. The announced lines point to the extension of the scope of required renewable electricity generation and to a new minimum solar energy generation requirement, within the general framework of the zero-emission building. For long-horizon projects, the operational recommendation repeats itself: size roofs, structures and electrical provisions with an eye on the final text, because generation-capable roof area is becoming a design resource as plannable as buildable area.

In the method of the article on the cost of CTE compliance, HE 4 increasingly belongs to the category of requirements that make more expensive or reorient an item that would exist anyway, thermal generation, while HE 5 keeps the profile of an item created by the requirement, with the particularity of its self-consumption return. The distinction changes the whole reading of the regulatory premium.

The first is designing HE 4 with the old regulation's reflexes, placing solar thermal by default without comparing the heat pump route, or the reverse, dismissing solar where it remains the most efficient. The comparison is made with the efficiencies of the specific case.

The second is counting renewable contributions without the performance conditions the document requires of heat pumps, an error verification detects late. The conditions are checked on the equipment's technical data sheet.

The third is treating HE 5 photovoltaics as an object resting on the roof: without early coordination of structure, self-shading, maintenance and easements, the required installation ends up curtailed or more expensive. The roof is designed with the installation from the outset.

The fourth is sizing to the legal minimum without a self-consumption analysis, leaving economic return on the table in the uses where additional generation pays for itself. The analysis uses the building's real consumption profile.