- What are the benefits of heat recovery?
Recuperation - recovering heat from the exhaust air. A recuperator (plate heat exchanger) is a device that uses the heat of the air extracted from a space to heat the cool air brought in from outside. The extract and supply air are separated by a contact plate so that they do not mix and maximum heat transfer is guaranteed.
Recuperation unit - a ventilation device with a recuperator and fans, which ensures the removal of used air (air exhaled, containing odours from the kitchen, toilet, odours, smoke, humidity ...) outside the building and its replacement with fresh, heated (cooled in summer) air. So-called controlled ventilation with heat recovery ensures optimal use of the heat produced (and already paid for) with up to 97% efficiency. In summer, on the other hand, this ventilation can be used to cool the living space.
Another advantage of heat recovery ventilation is the hygiene aspects. Replacing the windows with new, tight windows with low noise transmission from the outside environment will prevent heat leakage and prevent noise emission, but they are so tight that they prevent any air from entering the room. The only solution to create an optimal climate is heat recovery. When using heat recovery, an additional advantage is the possibility of using filters to clean the air not only of dust but also of allergens. - Where can a heat recovery heat exchanger be used?
It can be used for all ventilated buildings for heat recovery.(i.e. residential buildings, shops, schools, buildings for sports and culture, kitchens and restaurants, agricultural buildings, in industrial halls and buildings, warehouses,........) - What airflows can heat recovery be used for and with what efficiency?
The efficiency of heat recovery defines how much heat can be transferred from waste air to fresh air in the heat exchanger. Standard cross-plate heat exchangers achieve a maximum efficiency of 60 to 70%, with this efficiency dropping to 50% at maximum flow. Today, the most used recuperators in units are the so-called counterflow (crossflow) recuperators, which reach an efficiency of up to 97%, but at maximum flow the efficiency can drop to 70%.
In addition to plate recuperators, there are also duct recuperators with an efficiency of 90 to 99%. They are complicated to manufacture and therefore more expensive.
Units with counterflow heat exchangers are currently used for flow rates up to approx. 15000 m3/h, units with crossflow heat exchangers up to approx. 30000 m3/h, separate recuperation crossflow heat exchangers (e.g. in assembled units) are used up to 150000 m3/h. - How high are the savings in heating costs?
30 to 50%. - What is the ratio of the cost of electricity to drive the fans to the heat gain?
Example: the heat gain at a flow rate of 100 m3/hr, with an outside temperature of 0 °C , a room temperature of 22 °C and a heat recovery efficiency of 90%, is 571 W. A small unit has an external heat gain of 51 W at 100 m3/hr at 100 Pa. The cost/benefit ratio is 1/9 to 1/13.
Example: the heat gain at a flow rate of 150 m3/h under the same conditions as in the previous example is 1020 W. A larger unit with DC motors with an input of 46 W is used, at this output the cost/benefit ratio is about 1/22. - What are the differences in heat exchangers?
Standard heat exchangers are plate heat exchangers. These can be cross-flow (less efficient) or counter-flow (more efficient). The airflow is between the plates, transferring heat in two directions. The plate area is limited, the plates can be of different materials, most commonly plastic or aluminium. Due to the thickness of the plates in the order of tenths of mm, the plate material has very little effect on the efficiency. In newer ducted recuperators, the air flows between the ducts, i.e. the heat transfer surface is doubled (heat transfer in four directions). - How does the air enter the apartment (RD)?
Fresh air is supplied through ED flex 75/63 ducts or flat ducts 200x50 or110x50, respectively, to the living areas (living room, bedroom, children's room, study). From there, the negative pressure infiltration (leaky internal doors) into the service areas with used exhaust air (kitchen, bathroom, toilet, cloakrooms, etc.). The fresh and exhaust air is supplied by fans in the heat recovery ventilation unit. - Where can a heat recovery unit be installed?
The most favourable installation is in an insulated space or basement, most often in a utility room, hobby room or boiler room. It can also be installed in the attic space (attic), but this location is unfavourable due to the lower temperature. When selecting the location, it is necessary to take into account the intake and exhaust of the unit, the length of the ducts, the noise of the unit (transmission of vibrations), the condensate drainage from the recuperator. - Isn't ventilation through a window healthier?
Ventilation through a window - uncomfortable, the intense intrusion will cause draughts and cold air in turn the danger of rapid cooling. The air is polluted with dust, there is a risk of allergic problems (pollen). Noise can penetrate through open windows. Continuous moisture removal is not ensured - danger of mould. Flowers must be removed from the windowsill, open windows can be damaged (by wind).
controlled ventilation with heat recovery - fresh heated air is supplied in controlled (smaller) quantities (no draughts), clean (filtered, no allergens), no noise pollution, with continuous moisture extraction, flowers can remain on the windows, no risk of damage to the windows.
Periodic window ventilation is only a substitute solution to provide the fresh air needed for human habitation. If we were to rely on windows alone, we would have to get up at night and briefly ventilate every 1 to 1.5 hours to maintain the microclimate .
- Does draughts occur with controlled ventilation?
Not. Fresh warm air is supplied in the specified amount needed to ventilate the apartment or house. The air velocity in the ventilated space is less than 0.1 m/s. - Is the ventilation device in continuous operation or is it better to use time-limited operation?
For continuous removal of odours from textiles and furniture, drying out a new house or to eliminate the risk of mould formation in high humidity, continuous ventilation is preferable. So-called basic ventilation is suitable for maintaining the required relative humidity set at an air exchange rate equal to 0.3 times the internal ventilated volume of the apartment or house. - What is the use of DC fans?
DCurrent motor fans used in EDV units have a significantly lower current consumption compared to conventional asynchronous motors, thus saving energy. - Is the noise from the fans generated in the ducts or also in the outlets?
The noise from the fans is attenuated in the unit , largely absorbed by the heat exchanger and filters. In the ductwork, the airflow velocity should be kept to a maximum of w = 3 m/s, in the outlet to w = 1.5 m/s. In the case of short ducting for the intake and exhaust of the heat recovery unit, it is necessary to use silencers and/or soundproof hoses. - How is noise transmission between rooms eliminated?
By branched parallel ducting (ED flex beam system). - Do all rooms have to be ventilated at the same time or can they also be switched?
The standard solution for controlled ventilation is to ventilate the whole room. If there is a requirement for time switching, this can be addressed in the system design by using motorised dampers in the supply air ductwork. This is called "zoning". - Will it be too warm in the bedroom when ventilating with heated fresh air?
At an average room temperature of 20 °C, the supply temperature is about 18 °C. The bedroom temperature is reduced when the heater is turned down or closed. The temperature in the bedroom drops below 18 °C due to heat loss through penetration (walls, window). It is also possible to ventilate the window briefly before going to bed. - Does the ducts get dirty during use and how are they cleaned?
Almost no dirt at all, the exhaust and supply air is cleaned with filters (at least two in the case of a ground register). Nevertheless, also for legislative reasons (e.g. after flooding), EDV systems are always with cleaning holes (manifolds, outlets). Cleaning is done mechanically with a brush (bristles or foam) on a plumbing pen or a nozzle with a compressed air hose. - How often are the filters in the unit changed?
The filters are changed according to the recommendations of the heat recovery unit manufacturer and with respect to local outdoor pollution (urban, rural). Generally, a change period of once every 2 to 6 months is prescribed. - Do you also supply pollen filters?
For allergy sufferers, EDV supplies a special electrostatic filter on request to capture fine pollen. - Will not the air be dry in winter with continuous ventilation?
Every home produces moisture. Moisture from short-term activities (cooking, bathing, etc.) is removed immediately from the operating rooms under controlled ventilation, so the permanent sources of moisture are more burdensome - evaporation from flowers, moisture production by people (one person produces 150 g of moisture per hour).
Specific humidity x (g/kg a.s.v.) indicates the mass of water vapour in 1 kg of dry air (a.s.v.).
Relative humidity rh (%) indicates the degree of saturation of air with water vapour (0 to 100%) at a given air temperature. The relative humidity in the heating season (winter) indoors is recommended to be kept between 30 and 50%.
In winter, at an outdoor temperature of -5 °C, the relative humidity is rh = 70% and the specific humidity is 1.8 g/m3. When heated to 20 °C, the water content in m3 remains the same and the relative humidity drops to about 12 %. However, if I replace this air with indoor air that is warm at 20 °C, with rh = 50%, and x = 8.2 g/m3, then without the moisture output from the occupants, the indoor humidity would drop from 50% to 37% in 1 hour. At a ventilation rate of 0.5 x internal volume/h the relative humidity dropped to below 20%. Therefore, with continuous ventilation at an intensity of I = 0.3/h the air will not be too dry. Therefore, permanent ventilation is set as the first stage of the fan speed control, and the impact (calculated) ventilation as the second stage (or third stage in the case of 3-speed control). - What is moisture recovery?
It is the use of a special heat recovery exchanger with a membrane instead of plates, which allows the transfer of moisture from the exhaust heat (by condensation on the cold surface of the membrane, absorption of water molecules into the membrane and transfer of water to the supply air on the other side of the membrane by evaporation). - Is there a possibility to heat (heating support) with controlled ventilation?
In controlled ventilation the outlet air temperature is about 18 °C. The air can be heated by a hot water or electric heating register to a maximum of 50 °C. Above this temperature, dust pyrolysis occurs, leading to respiratory diseases. The hygienically permissible outlet temperature from the outlets is 45 °C.
For an idea: if a 100 m3/hr batch of ventilation air is heated to 50 °C, 1010 W of heat is transferred by this amount. For 2 kW we need 200 m3/hr, but this amount is already disproportionately "drying" the building (see above). This shows that with controlled ventilation, the heating is insufficient even for passive houses. - Does bacteria form in the ventilation system?
Not. It is a fresh air supply device, filtered, dry, there is no risk of bacterial contamination. This can arise in air conditioning equipment with recirculating air operation. The waste air is exhausted to the outside and is perfectly separated from the fresh air. - Can I connect a cooker hood (kitchen extractor hood) to the system?
I cannot. Fume hoods have fans with a capacity of 250 to about 700 m3/h and at these speeds the grease filters are less efficient and the ducts and recuperator quickly become clogged with grease deposits and efficiency drops. The large amount of air from the hood (relative to the ventilation air) in itself reduces the efficiency of the heat recovery system because the heat exchanger is not sized for such a volume. The high amount of air from the hood fed to the exhaust air penetrates into the bathroom, toilet, etc. The solution is to use kitchen exhaust hoods with a grease trap and an activated carbon filter to trap odours. The remaining moisture that is not captured by the circulation hood can be extracted separately through the exhaust air circuit in a controlled ventilation system. - Can I connect a tumble dryer to the system?
Yes, if the tumble dryer has a good capture and separator for fabric dust and lint. - Can the recovery unit also be used for cooling?
Can, using a ground heat exchanger or using time-controlled night pre-cooling. - Can I install the unit myself?
Provided the appropriate instructions are provided by the manufacturer or installer (project documentation) or after EDV training, I can. However, please note that after installation, the system must be adjusted (EDV measuring equipment) and the end elements must be adjusted. - Can apartment buildings also be ventilated in this way?
Yes, decentrally by means of a small heat recovery unit in each apartment with supply and extract, usually from 2 central ducts in the shafts (cores) or centrally by means of an EDV system. - Do you recommend a ground heat exchanger?
A ground heat exchanger is an approx. 30 to 40 m long plastic pipe or hose (d = approx. 200 mm) buried approx. 1.5 to 2 m in the ground. The ground heat exchanger preheats the air from e.g. -10 °C to +2 °C and this air goes to the heat recovery exchanger, so that almost never air with a minus temperature is supplied and therefore no frost protection of the heat exchanger is necessary.
In summer the heat exchanger is used to cool the air, e.g. from 30 °C it reduces the temperature of the supply air to approx. 20 °C. In doing so, condensate is formed, so it is necessary to evaporate the ground heat exchanger and drain the condensate through a siphon to the sewer.
