Before deciding to choose a mechanical ventilation system and a recuperator
At the beginning, it is necessary to analyze the benefits of using mechanical ventilation systems with heat recovery in residential houses. We can consider this problem in two aspects: comfort and economy. Most studies say, that these systems provide:
– air filtration
– effective removal of unpleasant odors
– no drafts and more and more bothersome street noise
– elimination of excessive amounts of water vapor from the rooms
– constant supply of fresh air
– significant savings in heating costs
As far as the first three points seem clear, the next ones are not so obvious. They should be understood through the prism of the so-called. climatic comfort. We must also remember that the air, that surrounds us had such physical properties, so that a person feels comfortable in the room in various states of work and rest. So the right amount of fresh air, its temperature, motion, cleanliness, humidity and ionization are factors that determine the perceived comfort, which should be especially considered when deciding whether to use mechanical ventilation.
The use of mechanical ventilation with heat recovery is the most cost-effective in residential buildings with very good thermal insulation. In such buildings, the heat consumption for heating the ventilation air accounts for a significant part of the total heat consumed, and therefore also the energy used. The second important condition is the use of mechanical ventilation in the building.
The above statements lead to the conclusion that in order to take full advantage of the advantages of a ventilation system with heat recovery in residential buildings, this solution should be taken into account already at the building design stage.. This system can also be used in modernized buildings, where the thermo-renovation was carried out. It is important to properly select devices and to properly distribute air in the ventilation system. The efficiency of the recuperation unit can be selected based on the sanitary and hygienic criterion, i.e.. minimum fresh air per person. You should not save on the efficiency of the heat recovery unit, because we may not obtain the above-mentioned minimum amount of fresh air in rooms in certain periods. The distribution of air in a properly ventilated house should be such that fresh air from outside flows into the rooms that are usually the least polluted: living rooms or bedrooms. From there it flows into the hall, and then to the rooms, which gives off a lot of impurities and moisture, that is, to the kitchen, bathrooms or toilets, from where it is removed through a recuperator to the outside. This way of flow causes, that no dirt and moisture from the kitchen flow into the rooms, bathrooms and toilets. Taking into account the documentation provided by the manufacturers, the use of recuperators for heat recovery allows even savings in optimal conditions 75%, and sometimes over 80%, thermal energy needed to heat the ventilation air. These data do not differ significantly from the results obtained during normal operation.
The main factor determining the selection of an appropriate ventilation heat recovery device is the energy criterion – operating costs and energy efficiency. Therefore, when choosing a recuperator, special attention should be paid to the efficiency of the exchanger and the efficiency of heat recovery. The costs of purchasing devices with a rotary and cross-flow exchanger are similar. The use of a heat pipe will be associated with a greater initial cost as it is more expensive, but the operating costs are lower because it does not require external energy supply and has small dimensions. Glycol exchangers are relatively expensive, mainly due to the cost of the circulation pump, pipes and fittings. The greatest cost is incurred when purchasing the heat pump, This is due to the fact that this device provides both heat recovery in winter, and in summer it cools the air. When using heat pumps, we also incur higher operating costs due to the increased consumption of electricity. However, the heat generated by the operation of the pump is dissipated into the supply air. The lowest operating costs are incurred when AHUs with rotary exchangers are used (high efficiency). Operating costs of AHUs with plate-cross exchangers, cross-flow and heat pipes are comparable.
When choosing a recuperative device, you should also pay attention to the types of insulation and anti-corrosion protection. In a properly constructed recuperation unit, the transmission of fan vibrations to the device housing should also be eliminated. The fans should not be forgotten at the same time, which must be of the right size. It will guarantee it , that they will have adequate capacity at relatively low revolutions, which will result in a low noise level. In addition to the quality of the filters, their location is also important, so in the case of supply and exhaust air, they should be placed in front of the fan (on the suction) thanks to which they are able to catch various dusts, which has a positive effect on the service life of the fan and the engine. When the control panel is equipped with a filter contamination sensor, then she herself will "remind” us about the need to replace them. Protections against frost on the exchanger are also important.
Due to the necessity to operate the described devices by a human, automation and control are also important. It may be a mechanical-electrical control, electronic or digital. In units intended for use in single-family houses, it is usually simplified. However, the possibilities resulting from digital or electronic control significantly affect the ease and convenience of the system operation, allowing e.g.. for temporary switching off and on of the air handling unit in daily or weekly cycles, dependence of the operating parameters of the device on the conditions inside and outside the premises, or to include it in the building control system. However, all these facilities increase the investment costs significantly.
The purpose of using ventilation with heat recovery is to provide fresh air in a way that ensures thermal comfort, while saving energy, thanks to the use of a recuperator ensuring heat exchange between the removed air, and fresh air. When considering the purchase of such a device, it should be noted that devices with cross-flow exchangers are the most popular on the market due to the investment and operating costs and profitability of use in small buildings., such as single-family houses. The use of ventilation heat recovery in large cubature buildings requires not only quite a costly investment in equipment, but also the ventilation installation itself is expensive. For this reason, modern ventilation heat recovery systems, specially selected at the building design stage, are increasingly used in such facilities.