Aerothermal energy
The next step towards nearly zero-energy buildings
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. On the market we can find a greater number of thermal comfort solutions that are increasingly efficient and, more significantly, are powered by renewable energy.
First things first
We architects are facing changing and, at times, ambiguous regulatory scenarios until the imminent publication of the update of the Technical Building Code which is the Spanish Building Regulation known as the CTE for short. It is now the guide for the design of new buildings that are geared towards lower energy consumption and the importance of renewable energies.
In the very near future (they are saying 2020) the CTE will require new buildings designed in 2020 to comply with nearly Zero Energy Building (nZEB) legislation. Compliance will force us to increasingly design better and more efficient buildings, which will have a dramatic reduction in the demand for heating and cooling.
In this scenario of nZEB buildings, with increasingly reduced air conditioning demands, the demand for hot water will be increasingly important in terms of consumption and required performance (since, in addition, our standard of comfort with regard to clean hot water is increasing and demanding in terms of water flow, with the use of showers and hydro massage columns, etc...), and must be very efficient since it will have a greater bearing on the building’s energy bill.
Heating comfort is essential, but in the case of hot water it is possibly more important. The displeasure on the part of the user when they cannot shower at the desired temperature is notable, since it is a much more sensitive type of demand and is also carried out throughout the year (unlike heating which is only used for a few months of the 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 enough 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 situation when we undertake the design of an installation for hot water. At this point it is also important to comment on the existing regulations regarding the renewable contribution to meet the demand for hot water in new buildings. So far, the energy that is best suited is solar thermal (allowing for the use of other renewable sources as long as it can be proven that the proposed system has a primary energy consumption and CO2 emissions equal to or lower than that of a boiler and solar thermal reference system).
The renewable percentage to meet the demand for hot water
In this case it is variable depending on the size of the installation and the climatic zone considered (the references for northern Spain are very different to those of the south-east).
The draft of the future CTE requires 70% of the annual energy demand for hot water and pool heating (the exact value will be confirmed when the document is published), to be covered with renewable energy (as was suggested in the EU Directive 31/2010), being a fixed renewable percentage regardless of consumption and climate. This will facilitate the use of other renewable energies to meet the demand for hot water - in addition to solar thermal.
New market solutions and trends for hot water production
There are currently many technical solutions for producing domestic hot water (gas condensing boilers, diesel boilers, electric boilers, biomass boilers, electric water heaters, gas heaters, storage tanks, coils, aerothermal systems, geothermal systems, solar thermal systems, photovoltaic, etc . ... ), and probably more systems and technologies will appear in the near future. The fact that there are an increased number of solutions on the market is positive, since it allows us to choose the best and optimal system 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 on the market. Optimal and more efficient solutions will reduce both installation and operating costs.
In relation to hot water production, the fundamental variable when considering the design of such an installation is that of meeting the needs of the users during peak periods (understanding that the calculation has 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 so, but we use the number of bedrooms as a guide). This service, which is essential for any type and size of installation, is especially sensitive for meeting the needs of buildings in the service sector (hotels, gyms, etc . ... ), since if the client does not have hot water when requested, it can mean the loss of business (especially today, where hot water systems are designed to be used to provide high comfort - such as showers with a rain effect, hot tubs, whirlpools, etc . ... ).