In air conditioning, there are many ways to save on expenses energy, among them, are the recovery systems of energy, the most famous, the recoverer of heat. A device that, in addition to minimizing the energy losses and air conditioning, controls the ventilation of the building, what more do you want!
The recuperators are not a whim of chance, it is a solution to the demands required by the different regulations; the obligation to recover the heat of the extract air, the savings energy and healthy air that we breathe.
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A heat recovery unit is equipment that allows to recover part of the energy of the air conditioning of the interior of a room or premises, through the system of mechanical ventilation of said air.
In most air conditioning installations, it is use Air/Air heat recovery units. The main functions are:
The recuperators provide us with tangible advantages in the quality of the indoor environment and in the air conditioning, and the keys, are in the exchanger, fan and filters air we use But… Why are they important?
In addition, since we are channeling both indoor air and from the outside Why don't we clean it up! so a retriever of heat is formed mainly by an exchanger, a fan and some filters:
This equipment allows to recover up to 60% of the heat that would be lost in a ventilation system mechanics, allowing energy savings that can be reach over 40% of the consumption in the equipment of air conditioning.
The operation of the recuperators of heat part of the fact that there is a temperature difference between two elements, room air indoor and outdoor environment, the first, gives off heat to the second (in winter), according to the law of thermodynamics (the Energy cannot be created or destroyed, but yes, it can be transformed).
The exchanger is the device that puts contact the indoor air that is extracted, with that of the outside that is introduced, without mixing the air of the two circuits.
Although we have already explained the basis of operation, It is always better to understand it through a video in a home installation:
As we have seen, there are also heat recoverers for domestic use – residential – like a house simple, commercial sector (offices and premises), tertiary sector (hospitals, universities, etc) or for large air conditioning installations in buildings and industrial sector.
Basically, in the field of air conditioning, marketed in Europe two types of recuperators depending on the exchanger used, those of plates (either parallel or crossed) and the rotors with their different models. So what we have:
The thermal recuperator consists of a static mechanism inside a galvanized steel casing and a matrix with aluminum plates. The extracted air passes through its channel giving up its heat to the metallic wall and this, by thermal conductivity, transfers it to air introduced.
Only sensible heat is recovered, that is, the temperature. And the air flows have different channels entrance and exit.
They are equipment where there is NO moisture recovery, whose performance and thermal efficiency is less than 80%. highlighting, that we can opt for two models of exchangers:
The rotary recuperator consists of a mechanism containing an aluminum rotor that will transfer the heat when cycling inside a steel casing galvanized. It recovers both sensible heat and the latent heat, that is, the temperature and humidity.
Unlike plates, they have the same channel for the extraction current that stops the impulsion... And what advantage does it bring? Through evaporation, the air introduced into winter will be less dry.
It is important to note that, in these devices there are moisture recovery and different models with thermal efficiency:
As we can see, the exchanger is the key to the recuperators. As a summary we would have:
| Types of reclaimer heat | Thermal efficiency (Sensible Heat) | Moisture recovery (Heat latent) |
| Recuperator with static flow exchanger parallels | > 80% | No |
| Recuperator with static flow exchanger crusaders | > 50% | No |
| Recuperator with rotary exchanger with NO rotor hygroscopic by condensation | > 50% | Only in winter. For hot and dry climates |
| Recuperator with rotary rotor exchanger enthalpic hygroscopic | > 60% | In winter and summer. For intermediate climates |
| Recuperator with rotary rotor exchanger absorption hygroscopic | > 60% | In winter and summer. For humid climates |
More from a technical perspective you can consult the article published in the Atecyr magazine from page 10, Although it is old, it is very good!
In winter, the heat recovery units work by heating the cold air that enters from the outside, while, in summer, using a by-pass, allows to cool the air outside (
To understand it better, we leave the following schemes with Examples that simplify use in winter and summer, both day as night:
The recycler facilities can become very complex: from the industrial sector to the residential in buildings, premises and offices, or the requirements required in Passive House houses it is definitely relegated to professionals! what yes we have to take into account is that we have two slopes:
We must consider that these devices have evolved much, with shapes and characteristics to be able to adapt to different spaces and needs. installation types common would be:
It has fans that allow the flow and circulation of air both to take it from the outside, and to expel the one inside (both in the impulsion flow and in the in the return), which implies energy consumption and its efficiency should be assessed based on the flow of air and the temperature difference between the outside air and the interior.
For construction in Spain, excluding European standards / UNE, there are two regulations that regulate ventilation, both of buildings as well as premises and other uses... When is it Is it mandatory to install a heat recovery unit?
According to the Technical Building Code – Document Basic Sanitation HS
Watch out! Although the CTE does not oblige the residential sector, the Basic Document of limitation of the energy demand of the building – HE 1 of the CTE, makes it almost mandatory to incorporate it into new construction to meet energy demand limits.
In addition, although the technical code does not require the installation of this equipment in a mechanical ventilation system in home, yes we can reduce energy consumption inserting a recuperator between the intake system and the extraction, being able to achieve energy savings up to 40%
According to RITE – Regulation of Thermal Installations in the Buildings
According to the Technical Building Code – Document Basic Sanitation HS
According to RITE – Regulation of Thermal Installations in the Buildings
With the publication of the corresponding Royal Decree 178/2021 The new RITE modifies some aspects. According to the instruction technique IT 1.2.4.5.2 – Heat recovery from air extraction:
«In the air conditioning systems of buildings in which the flow of air expelled to the outside, by means mechanical, is greater than 0.28 m³/s, (Before it was 0.5 m³/s) of in accordance with the provisions of the ecological design regulation for ventilation units, energy will be recovered from the expelled air.”
That is, for an extraction flow of 1,008 m3/h the recovery of energy from the extraction. In addition, the European design regulation ecological, depending on the type of building and the quality of the air, as a minimum, the following filters will be selected:
As we have seen throughout the article, using a recuperator can bring great benefits. It's true that they are more machines for large air conditioning installations, but, In isolated houses, it also has its use.
An example is the Passive House – Casa pasiva where it already forms an essential element…
The vventilation with Canadian well and recovery of heat is also a very good option. In this case, the air that enters the house is already preheated in winter or pre-cooled in summer, from the duct circuit buried from the Canadian well.
Another case of application would be in systems de high energy efficiency air conditioning with heat pumps and air pretreatment through ducts in Canadian wells with heat recuperators. This teams heat exchangers allow to improve and achieve a higher energy use of energy renewable.
In this way, the air that enters in winter is less cold and the one who enters in summer is less hot, being achieved more easily to reach conditions of comfort.
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