Aerothermal energy. Next step ahead to nearly zero-energy buildings. Final Part

In the previous article we discussed how the update of the Technical Building Code known as the “CTE” for short which is the Spanish Building Regulation, is pushing us the architects to design new buildings which must comply with Almost Null Energy Consumption Buildings or nZEB. This means buildings that will use nearly 0 none renewable energy.


Architect gravitate towards aerothermal systems.

Having to look for very efficient installation systems the aerothermal system seems to be the one that we architect are betting for.

These systems allow to meet both the demands for air conditioning (cold-heat), and the demand for domestic hot water using the same equipment.


The pros of this type of solution are clear: high energy efficiency, relative ease for compliance with the indicators of non-renewable primary energy consumption of the future Spanish Building regulation for most climatic zones within Spain, consideration as renewable energy, simplification of the installation because it does not require a gas connection in the building and the possibility of hybridizing with other renewable systems such as thermal or photovoltaic solar energy.


And against…

The main point against these systems is their direct dependence on the ambient temperature from which they take advantage of the energy, a fact that can substantially influence the temperature of hot water reached, as well as the overall efficiency of the machine. In cold areas with low cooling loads, the traditional system with condensing gas boiler combined with thermal solar can be a solution to take into account to meet the demand for heating and domestic hot water.


Another issue, at least today and with the CTE in force today, is its consideration as renewable for domestic hot water, which can be complex to justify in certain areas of Spain and in some climatic zones with a lot of solar radiation (basically zones IV and V). Sometimes, for domestic hot water of the machine, it may be necessary and mandatory to install these systems together with solar thermal energy to be able to comply with the aforementioned CTE.


Continuing with the area of housing, but with e optics of the reform, aerothermal systems may have their place, but in direct competition with the condensing gas boiler. The replacement of obsolete boilers with current condensation technologies is the most appropriate solution in terms of comfort and performance, energy efficiency (think that a condensing boiler can provide fuel savings of the order of 30% compared to one that is not), and return on investment in a reasonable time. Another issue is when it will be profitable and appropriate to install a natural gas boiler as we approach 2050 and want to achieve decarbonization objectives. In a new building the rules are clear, but in reform it is not very clear today as we will have to undertake in the future in terms of technical and economic feasibility on the building stock of a certain age that exists in Spain.


What about the service sector?

Speaking of centralized facilities oriented to the service sector, the scenario is somewhat more complex compared to the housing market. It is true that the aerothermal system spreads rapidly in the building of collective type (being prescribed on a recurring basis for gyms and hotel sector, for example), but in this type of facilities there are more variables to consider when selecting the optimal product.


A first point to consider would be the type of consumption curves that can be found in centralized facilities. In this type of installations, the consumption points can be very high (up to 60-70% of the total daily consumption). If we want to satisfy and maintain the comfort of use, a fundamental premise in any installation, to solve the installation with aerothermal systems we will have to go to very specific and efficient technologies that allow working at high temperature with a minimum variation of its performance depending on the area Climate considered (systems with CO2 cycle, for example), relying on large accumulation systems to store the energy needed to meet the consumption tip.


Regardless of the issue of comfort, in centralized facilities (except in residential buildings), there is a regulatory requirement to comply with in relation to RD 865/2003 regulation and UNE 100030: 2017, regarding the prevention and control of legionella on site. In installations within the scope of this sanitary regulation, it is necessary to carry out mandatory thermal shocks at 70 ºC, which require a high temperature primary circuit water production.


Reaching higher temperatures.

Other solutions that naturally cannot reach these temperatures, need support systems with low energy efficiency (usually by means of electrical resistors) to be able to reach these working values. In the case of aerothermal technology with R744 (CO2) refrigerant, this temperature need can be met without problem.


It is very likely that, as the various technologies try to find a place in both type and size of installation and depending on the climatic zone where the installation has to be undertaken, the trend in new building will be hybridizing production systems both to the part of air conditioning as production of domestic hot water. Everything seems to indicate that the alliance between the aerothermal systems and the photovoltaic production systems will be a recurring solution and aligned with the carbon free objectives that are intended to be achieved in 2050. In that sense, The Spanish Royal Decree 244/2019 regulating self-consumption simplifies the installation of photovoltaic solutions.


In any case, there are still 30 years still to go by and on that road, the combination of condensing gas boiler and solar thermal energy to produce A.C.S. should not be forgotten. (especially for installations of centralized type with high demands of hot water). Regardless of the market's perception of this technology, solar thermal energy is the most efficient way to produce A.C.S. in a country with a level of solar radiation as high as Spain. In relation to carbon free, it is interesting to note that the carbon footprint for each kWh generated is 14.9 times higher in the case of photovoltaic panels in relation to thermal collectors. We should not, therefore, forget this technology for the production of A.C.S.


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