Aerothermal energy. Next step ahead to nearly zero-energy buildings | Part 1 |

It is a fact that we are in a period of energy transition in Spain with a progressive change of trends in the design of thermal installations for heating and domestic hot water. we can find in the market a greater number of thermal comfort solutions, increasingly efficient and with a more significant importance of the origin of the sources of renewable energy.


First thing first

We architect find a changing regulatory scenario and with some ambiguity until the imminent publication of the update of the Technical Building Code which is the Spanish Building Regulation known as the “CTE” for short, which is now the guide to the design of new buildings towards a lower consumption of energy and with a more relevant importance for renewable energies.


In a very near future (there are talking for 2020) that the CTE will require new buildings designed in 2020 must comply with Almost Null Energy Consumption Buildings or nZEB. Compliance with these indicators will force us to increasingly design better and more efficient buildings, which will have a dramatic reduction in heating and cooling demands.


In this scenario of nZEB buildings with increasingly reduced air conditioning demands, the demand for hot water. it will be increasingly important in the building in terms of consumption and required performance (since, in addition, our standard of comfort in sanitary hot water is increasingly high and demanding in terms of flow, with the use of shower and hydro massage columns, etc ... ), must be very efficient in this provision since it will have greater weight in the energy bill of the building.


Heating comfort is essential, but in the case of hot water is more important if possible. The displeasure on the part of the user when he cannot shower at the desired temperature is notable, since it is a much more sensitive type of demand and that is also carried out throughout the year (unlike the heating that is only used for a few months at year).


Sufficient power but with little energy.

Therefore, the installation as a whole and the heat generating equipment that is selected must be sufficient and adequate to deliver the power demanded at all times depending on the needs of the users.


The aforementioned, puts us in a much more complex and diverse context when we undertake the design of an installation for hot water. At this point it is also important to comment on the existing regulation on new build regarding the renewable contribution to meet the demand for hot water. So far, the energy contemplated is solar thermal (allowing the use of other renewable sources as long as it is justified that the proposed system has a primary energy consumption and CO2 emissions equal to or lower than the reference system formed by boiler and solar thermal). The renewable percentage to meet the demand of hot water. In this case it is variable depending on the size of the installation and the climatic zone considered (the references for north Spain is very different compared with south-east).


In the draft of the future CTE, will require that 70% of the annual energy demand of hot water and pool heating (value to be confirmed until the final publication of the document), be covered with renewable energy (as it is contemplated in the EU Directive 31/2010), being a fixed renewable percentage regardless of consumption and area Climate considered. This will facilitate the use of other renewable energies to meet the demand for hot water. In addition to the solar thermal.


New market solutions and trends for hot water production.

There are currently many technical solutions to produce domestic hot water (gas condensing boilers, diesel boilers, electric boilers, biomass boilers, electric water heaters, gas heaters, storage tanks, coil coils, aerothermal systems, systems geothermal, solar thermal systems, photovoltaic, etc. ...), and probably more systems and technologies will appear in the near future. The fact of having a greater number of solutions in the market is positive, since it allows us to choose the best and optimal solution depending on the characteristics, type and size of the installation considered.


Of course, rational criteria should also be applied in terms of proposing the most efficient and economically viable solutions within the various technologies existing in the market. Optimal and more efficient solutions will reduce both installation and operating costs.


In relation to the hot water production, the fundamental variable when considering the design of such an installation is to meet the hot water needs of the users during the peak periods of the installation (understanding that the calculation poses the difficulty of not knowing with total precision the number of users who are going to use the installation, or when they are going to do it but we use the bedrooms as a guide). This service, essential for any type and size of installation, is especially sensitive for the facilities of type services (hotels, gyms, etc ...), since if the client does not have hot water when requested, it can mean the loss of it (specially today in which hot water systems are raised with high comfort of use such as showers with rain effect, hot tubs, whirlpools, etc ...).


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