Ventilation air heat exchanger - what is it?
Ventilation air heat exchangers are among such devices. But if central recuperators, albeit in limited quantities, have been used since Soviet times and are more or less known today, then decentralized recuperators have not been produced by industry until quite recently, because. for objective reasons, they were not in demand, and therefore they were not known not only to consumers, but also to specialists working in the relevant fields of technology.
COK N 12 | 2006 Heading: AIR CONDITIONING AND VENTILATION
V.G. BARON, Ph.D., director of Teploobmen LLC, Sevastopol
The problem of energy saving and energy efficiency from the category of speculative, lying in the area of interests of a narrow circle of professionals, has recently resolutely and unconditionally moved into the area of interest not only of broad the masses of the public, but also reached the highest interstate, moreover, planetary level. This is confirmed by the inclusion of energy supply issues on the agenda of the G-8 summit in the summer of 2006.
The heads of the leading world powers discussed issues related to the obvious dilemma - the observed rapid growth of mankind's needs for energy resources, on the one hand, and the counter the process of no less rapid depletion of the reserves of these same resources (at least their traditional component, which is most widely demanded in the world today). on the territory of the CIS machines and devices capable of reducing the required level of energy consumption while maintaining modern requirements for thermal comfort.
Ventilation air heat exchanger - what is it?
Such devices include < strong>ventilation air heat recovery. But if central recuperators, albeit in limited quantities, have been used since Soviet times and are more or less known today, then decentralized recuperators have not been produced by industry until quite recently, because. for objective reasons, they were not in demand, and therefore they were not known not only to consumers, but also to specialists working in the relevant fields of technology. The situation has changed radically with the advent of modern, high-quality windows with high-density porches and double-glazed windows, and recently, in our opinion, it has sharply escalated and the issue of using decentralized heat exchangers may require a priority solution.
Indeed, the use of modern, energy-saving windows, no matter how sad to admit, still continues to be hushed up by their manufacturers, and brings with it significant problems. Moreover, these are multifaceted problems that lie both in the field of protecting the health of people who are in rooms equipped with such windows, and in the field of safety of the buildings themselves, the rooms in which have such windows. Briefly, it can be recalled that the use of such windows without associated special measures to ensure controlled forced ventilation leads to a change in the qualitative composition of the air in the premises (the level of oxygen decreases, the content of carbon dioxide, radon, etc. increases), which negatively affects the current state of health, and on the general health of people. In addition, the use of such windows leads, as a rule, to an increase in humidity in the premises, which causes the appearance and development of (later very difficult to remove) mold, i.e. colonies of fungi, which has a double manifested, delayed negative consequences - firstly, some types of mold fungi are deadly to humans and, secondly, all types of mold fungi have a devastating effect on the building structures of buildings and structures. In Europe, in connection with the accelerated process of destruction of buildings that stood before this century, which began after the replacement of previously installed windows with modern energy-saving ones, the term “sick building syndrome” was even formed, and at present it is prohibited to install such windows without taking special measures to ensure the necessary ventilation.
The aggravation of the situation in terms of the need to use recuperators in the CIS is facilitated by both rapidly rising energy prices (which objectively pushes people to look for ways to reduce energy consumption to maintain a comfortable temperature in the premises), and calls from managers of various levels, from the highest to the lowest , massively replace previously installed windows with modern ones.
Our enterprise, which has developed and produces decentralized heat exchangers for ventilation air of the TeFo type (according to our information, we are the only enterprise in the CIS that produces this kind of equipment, and European counterparts, which appeared on the market almost simultaneously with our products, are inferior to us in most consumer indicators), I felt from my own experience that people who seek to save heat and install modern windows are increasingly faced with the indicated problem, i.e. with the need to somehow solve ventilation issues. In particular, if during 2005, which has elapsed since we completed the work on putting these products into production and entering the market with them, only a few showed interest in these products, then only for the 1st quarter of 2006, those who applied for additional information was more than in the entire previous year.
So, what is a heat recuperator, how and when to use it and what does it provide?
Ventilation air heat recuperator - this is a device that necessarily incorporates a heat exchange element, which, as a rule, has fans (usually two) for pumping through this heat exchanger flows of exhaust air removed from the room and fresh air supplied to the room and often equipped with various additional devices, designed to automate the operation of the device, improve the quality of the supplied air (or at least prevent its deterioration), etc. In such a device, heat from the air that must be removed from the room is given off to the air entering the room (and in summer, on the contrary, the incoming air is cooled by cooler exhaust air, if, of course, the room is equipped with air conditioning), i.e. practically for nothing, thermal preparation of air is carried out before it is supplied to the room. The diagram of the recuperator operation is shown in fig. 1.
Thus, the heat exchanger, in fact, performs the role of an ordinary window, which for centuries has successfully coped with the task of air exchange in the premises, but only the heat exchanger is, figuratively speaking, a warm window (in relation to the winter, basic mode of operation), t .to. air passing through the heat exchanger into the room is simultaneously subjected to heat treatment. (The first letters of the words "warm window" gave the name to the heat exchanger - "TeFo".)
In principle, as noted above, heat recuperators of ventilation air have been used before, but in very limited quantities and exclusively for heat treatment of the total air flow, incoming-removing from the building as a whole (the so-called central recuperators). The need to use decentralized heat exchangers arose relatively recently and is completely due to the use of modern energy-saving windows in buildings. The fact is that the use of such windows, especially in previously built buildings (however, the same problems often arise in buildings currently under construction), leads to a complete disruption of the ventilation of the premises, and the central ventilation, which makes it possible to use central recuperators, such buildings either they don’t have it, or for a number of reasons it is inappropriate to use it.
Faced with this, people, sometimes not even realizing the reasons for increased fatigue, decreased performance and other symptoms of malaise, formulate their vision of the problem very simply - “it’s stuffy in the room”, and open (slightly open) windows, thereby reducing their energy-saving function to almost nothing. The only way out is to use decentralized ventilation air heat exchangers. Such recuperators, being installed in each room, allow, firstly, to ventilate only those rooms that objectively need it, for example, those in which there are people (which is already an energy-saving measure), and secondly, to ventilate in a controlled manner, i.e. to. we are still talking about forced ventilation, and, most importantly, with such ventilation, it is possible to maintain almost the entire energy saving of modern windows. True, nevertheless, “almost completely”, because. part of the thermal energy will inevitably leave with the exhaust air due to the fact that there is no (and cannot be created in principle) device that provides 100% recovery.
The use of a decentralized heat exchanger, unlike a central one, is available to each individual owner of the premises . Moreover, its use is not associated with any more or less significant construction or repair work. It is enough to make a fundamental decision, purchase a suitable heat exchanger and install it indoors. Moreover, even on-site installation, in principle, can be done independently by any owner of the premises (another thing is that not everyone will independently perform these works). Installing the heat exchanger in place comes down to the formation of two holes in the outer walls (we note right away that they are small in size), fixing the heat exchanger in the chosen place and connecting it to a power supply (very, very low-power). The use of a decentralized heat exchanger is advisable if the room is equipped with modern energy-saving windows and does not have central forced ventilation. Otherwise, a dilemma arises: what is more important - the health and safety of the building or energy saving. And only the use of a decentralized heat exchanger satisfactorily solves this dilemma. breathing of the people there and excluding the formation of mold colonies, but also has some other, less significant positive aspects. In particular, such as supplying air to a room with a temperature close to that which a person in the room considers comfortable for himself. Indeed, if we chose health as a priority in the above dilemma (consciously sacrificing energy saving), then this would involve partially opening the windows to ensure air exchange in the room. But such an opening, almost imperceptible at a positive outside temperature, will be perceived as extremely undesirable and creating thermal discomfort at a deeply negative outside temperature, for example, at -20 ° C, which will still force a person to close the window. In addition, the use of a heat exchanger makes it possible to distribute it more evenly immediately when air enters the room than is the case when the window is partially opened, when a sharp stream of outside air is created (by the way, there are cases when such a jet led to defrosting risers). Thus, the use of recuperators is at the same time an investment in health, energy saving and provision of thermal comfort.
However, the author has already encountered a negative attitude towards the very idea of using recuperators, especially decentralized ones. In all these cases, in the absence of any arguments supporting such an opinion, an unsubstantiated assertion was made that it was economically unprofitable, because. and the product itself is not cheap, in addition, it requires electricity to operate. Such claims cannot simply be ignored. On the contrary, since such doubts exist, they must either be recognized or reasonably refuted. The figures and considerations given in this article should serve as such an evidence base.
What are heat recuperators and by what criteria to compare them
According to the principle of operation, heat recuperators are of regenerative and recuperative type (mixing type are not considered here as meeting sanitary and hygienic requirements to the least extent). Regenerative type devices, as a rule, have a higher degree of energy saving, reaching up to 85% for the most advanced models (i.e. up to 85% of the heat that could be lost with the exhaust air is returned back to the room). However, these devices are characterized by increased specific energy consumption, are structurally unable to ensure the exclusion of the admixture of the removed air into the incoming air (or, at least, the influence of the properties of the removed air on the incoming air), have a large specific volume and specific cost, and, most importantly, the author is not aware of decentralized regenerative devices, i.e. e. devices designed for relatively small air flows, for example, in the range of 20–100 m3/h.
As for recuperative type devices, there are already a number of decentralized devices of this type. On the territory of the CIS, apart from recuperators manufactured by our company, we do not know of similar products. However, in Western Europe, decentralized heat exchangers are produced by several companies, and it should be noted that the vast majority of them have mastered the production of such products literally over the past year and a half. consumer?
Obviously, it is impossible to give an unambiguous and formalized answer, that is, a “concrete consumer”, his preferences and priorities are always specific and often subjective. But still, it is possible to identify the main objective criteria and we will try to do it.
Firstly, the degree of recovery, i.e. actually the degree of energy saving. This indicator fluctuates depending on the manufacturer and even on a specific model within a very wide range - from 40% to more than 70%, it is one of the main ones.
Secondly, energy efficiency, which characterizes its own specific energy consumption. This value shows how much energy the heat exchanger consumes to capture and return a unit of energy from the removed air.
Thirdly, acceptable price characteristics. This indicator, although it turned out to be pushed into third place, is one of the main ones in market conditions and, unfortunately, can sometimes be decisive.
Fourthly, (or maybe “firstly”) - sanitary and hygienic indicators. The fact is that the heat exchanger is a device through which the air entering the room passes and which people subsequently breathe. Thus, the recuperator should create as few preconditions as possible for the pollution of the air passing through it, and also be maximally adapted for carrying out operations to monitor its condition and clean it.
Fifth, resource characteristics. The device must have a long service life under normal operating conditions, incl. taking into account the necessary periodic cleaning (flushing), require minimal maintenance and have good maintainability.
Finally (if we talk about the list of key indicators), these are weight and size indicators. The heat exchanger should take up as little space as possible and be conveniently assembled on site. There are a number of secondary indicators, such as the degree of automation (providing, for example, switching on and off according to some predetermined indicator), equipment with additional functions (for example, air ozonation), case design, etc. An objective analysis of these indicators is very difficult, yes and is a thankless task, because the significance of each of them is deeply subjective (for someone, for example, appearance can be decisive).
Ventilation and air conditioning
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