The twin coil comes in many versions for. They are widely used in existing buildings where a heatrecovery for ventilated air in place. The reason is that the supply and drainage in a heatrecovery not need to be together. So conversion for the channels is not necessary.

Working Principle :

As mentioned, in the event that the supply and exhaust air is not brought together can be can be made of two elements system. This system consists of two elements (heater and economising), located respectively in the supply and drainage canal, via a closed circuit connected to each other. A built-circulation pump ensures the transport of the heat transport medium of the heat record of economising and handled by the heater. The entrances and drainage system can be totally separated. For freezing of the medium in the closed cycle, it is usually for this medium a water glycol solution at high temperatures or thermal oil. The twin coil system is usually governed by the medium flow on one of the elements vary. Heat Transfer for: gases (air). Help Medium: water glycol solution, thermal oil.

Aplication :

Two elements systems are used mainly for heat transfer between gas streams such flows is difficult, so only at great expense, can be brought together. As occurs with many existing buildings. The system is particularly suitable for the recovery of heat from the exhaust air and feeding on the fresh ventilated air to the building. The ventilated air with the discharge medium comprises a mixture of gases (eg boiler) and exhaust air has a large application. This is due to the good separation between the medium flows. Such a system is used in mechanically ventilated office buildings. Also it is applied in the manufacturing sector, focusing on heat recovery in industrial processes.


. great flexibility by separating supply and drainage (especially at existing situations);
. mixing of the air and afblaaslucht is completely excluded;
. practically unlimited capacity;
. Easy system adjustment capacity by liquid circuit;
. not own sound production;
. compact system requires little mounting space;
. medium leakage is totally excluded if the elements are in separate media processing units are built;
. simple system that demands little maintenance;
. also suitable for cold recovery;
. Easy installation in the channel system, which in existing circumstances, to realize
. no mixing again and drain medium.


. fluid exchange is not possible;
. relatively higher heat loss by long distance heat transfer;
. extra electricity consumption increased by an additional pump and air;
. more t.o.v. maintenance records related to exchange pump and system.


The choice of the intermediate medium is highly dependent on the temperature. For low temperatures, and between medium particularly water or freezing risk is present, a water glycol solution applied (common ratio water / glycol mixture 70/30). At high temperatures up to about 350 0C, then we think of industrial processes, in which thermal oil is applied. This has the property that remains liquid at high temperatures so low system pressures can be worked. The elements are basically standard batteries with the same selection options as the conventional heaters / chillers used in air conditioning cabinets. Batteries are typically constructed from copper tubes with aluminum fins. In an environment such as' wet areas' by condensation and / or aggressive condensate, it may be coated (pre-paint) strips or complete elements of copper or stainless steel be applied.


Normal pressure losses or the air on the elements are between 100 and 300 Pa, this velocity depends on the construction of the battery (strips distance, number of rows)

Profit current techniques. 40-60% :

The rate of return of the twin coil system is mainly dependent on the following factors:
1. Building Depth. When the yield is calculated from a twin coil system is calculated, the number of rows in the depth of the most decisive factor.
2. Impact medium. Each medium has a transfer coefficient.
3. Relative humidity (RH). As relative humidity increases, as a result, the yield increase.
In addition, other factors play a role such as:
. ratio exhaustair t.o.v. supplyair;
. medium speed.
The highest profits are achieved by :
low velocity,
high flow medium
large warming surface (deep block with small strips distance).
Profit are in these systems is between 40% and 60% (depending on dewpointendorsement in tail air, latent heat transfer).


Remarks :

Record changers come in many designs for. They are widely used in industrial and process air systems, where the installation under "extreme" conditions (polluted gases / liquids, high temperatures) to work. In addition, they are in another application well suited for comfort air boxes, simple ventilation systems with heat recovery.

Working Principle :

Operation Principle The heat exchanger system that relies on direct heat exchange between air and liquid flows (or combination) via heat conduction through the wall. The air / fluid flows in these exchangers are absolutely separated no fluid or mass transfer can take place between the supply and drainage medium. The tube exchangers, compared of the plate exchangers more volume in the same capacity. The wide choice of materials is possible by applying high temperatures and aggressive air. The capacity scheme using face or bypass valves regularly. The valves are on the front plate changer placed. It can also be used in case of heat to thaw the ice by no, or only a small part outside the plate exchanger to send. Heat Transfer suitable for gases and liquids.

Advantages: :

. good use in dirty air;
. suitable for high temperatures up to about 800 0C special performance;
. Air transfer about 100 0C fit;
. mixing with exhaust ventilation d.m.v. a by-pass;
. especially in small sizes relatively cheap;
. practically unlimited capacity;
. reliable and low maintenance due to the lack of moving parts (excluding any valves);
. the system is also suitable for cold recovery;
. possibility of series and parallel circuits;
. relatively small space requirement.

Disadvantages :

. leakage through the relatively many seams,
. entrances and drainage medium at the same place out;
. moisture transfer / hardly possible;
. system only through a circulation as possible;
. circulation structure is relatively much space.

Application :

In the implementation, several variations on the direction of medium flow; . crosses Room: Most recuperatoren are implemented as cross-flow plate heat exchanger. The cross section shape is prepared by a favorable price whole. This geometry creates a temperature in the outgoing flows across the width of the outflow channel. In most cases, cross-flow to heat for air heating including aluminum applied. Furthermore, this principle also applied in strips heat exchangers (gas / liquid). This kind of hot there is significant recovery in the utility sector. . Dual cross-flow: This is for example applied in convectierecuperatoren series. These often consist of a number of tube bundles that luchtzijdig series in a combustion gas are made. Double Cross Flow is also used to heat air in cabinets. See Figure 4. . By Power: plate changers in counter-flow design with high theoretical returns from cost considerations have hardly used (manufacture technically difficult to manufacture). The high efficiency (HR) recuperator. a laminar tegenstroomkanaalrecuperator and is very effective and relatively easy to make (mass). This recuperator is made solely for the housing. . DC: In a dc move the air in the same direction. If now the wall is very high, the exit temperatures of both streams equal and, at constant heat capacity flow, mid-temperature effect. This is usually applied to stralingsrecuperatoren. Heat transfer by radiation from a medium with shadowing direction has benefits - The speed of combustion gases does not affect the heat transfer, therefore no additional pressure loss. - In addition insensitive to polluted air. Coverage is primarily the manufacturing sector Record changers can be divided into heat transfer medium; . Gas for gas. This group is primarily for recovery of heat or cold from ventilated air . Liquid to gas. Heat exchangers for heating or cooling of ventilated air, for example CV residual water or wastewater. . Liquid to liquid. These are used for heat transfer equipment for heating, cooling, heat, hot water and related systems. Here we think of plants used in apartment buildings, hospitals, hotels, barracks, district heating and greenhouses.

Material :

As materials for the transfer of heat to ventilated air (usually plate heat exchangers) are aluminum,
steel and corrosion resistant surface treatment, stainless steel, glass, certain plastics and paper.
In the application of plastic need to be given, that no radiation damage can occur to the plastic plates.
The choice of material has great influence on the price and the lifetime of the device, but also the potential for cleaning and to use substances.

Resistance. :

For the heat recovery from ventilation air, the following applies.
Typical pressure losses are between 150 and 250 Pa,
this depends on the velocity and plate away.

The DC changer, and the effectiveness of this exchange is defined as the ratio between the temperature on the flow and the input temperatures. For a current exchange is effective up to 50% In cross-flow is a temperature efficiency of about 70% possible, counter-flow is around 75% possible in practice 60% is quite normal. The highest yields are achieved at low speed supply, small plate distances and large temperature differences in combination with moist air return. By series two crossflow dc are the returns to about 80% (see Figure 4). The yield for a number of conditions must be sought because dew point below the outlet air increases the efficiency. Note that the return depends on building size and volume flow of the heat regeneration .

Heat Wheel


Heat recovery wheels with no moisture is called recuperative heat exchangers. Or fluid recovery is possible, depends on the surface of the heat wheel.

Working Principle.

The heat transfer in rotating heat exchangers occurs because of the turning of the rotating medium, the rotor, an interaction between the supply and drainage area. The system is a heat accumulative element in the form of a wheel, made of small aluminum tubes. The outgoing warm ventilated air by the aluminum tubes made by the temperature of the air to take. The spinning wheel, the tube through the incoming air. The fresh air by the heat of the tubes warmed up. The rotor in the amount of heat being stored away from the half revolution of the outlet air is then delivered to the supply air. The flow channels are thus in the opposite direction by alternating the supply and outlet air. In the summer of firms with the same cooling system used to warm the incoming air to cool with the relatively cool indoor air. The thickness of the heat wheel, often made of aluminum is, provides a significant capacity heat.

The heat wheel rotates at a speed ranging from 1 to about 10 revolutions per minute.
The speed of the heat wheel to vary and control the temperature of the air supply is kept fairly constant The regeneration is adjustable through the adjustment of the rotor speed. The corresponding Profit are for the temperature returns around 80%, depending on air flow. In addition, the moisture returns to about 70%, depending on the dew point. Maximum speed is the return in principle constant and independent of the air conditions. By varying the speed, for example, at part load, efficiency is not constant, see figure The reported efficiencies of suppliers are always at maximum speed. The return is dependent on the air flow ratio, the rotor composition (the finer the better) and the velocity.


. simple system by adjusting rotor speed;
. transfer of both sensible heat and moisture;
. high temperature ratio (high efficiency);
. self-cleaning effect by the laminar flow
no dust distribution on the rotor mass.


. supply and drain have to each other;
additional maintenance by moving parts;
. extra electricity;
. relatively large space, parallel preparation or influenced;
. dirty air to clean air (coil area shall reduce it).


The system is widely used in building, by a large capacity range and generally has a high efficiency for both air and moisture transfer. Also it is applied in the industrial sector aimed at heat recovery in certain industrial processes.


The pressure loss in the rotor between 150 and 250 Pa, depending on the flow and rotor construction.


The heat wheel is made up of alternating smooth and corrugated sheets with a thickness of + / - 0.08 mm. This method of construction created many small flow channels. This creates a large surface between the rotor material and flowing air. The choice of rotor material include depending on whether or not they wish to transfer fluid or the degree of corrosion, which is to be expected. Previously, an asbestos-containing filling of the rotor generally, this has now become a rarity. Today, many rotors constructed of aluminum foil. A hygroscopic low (eg LiCl) they can to bring them next sensible heat also latent heat transfer. Likewise, the aluminum wheels are equipped with anti-corrosion treatment. There are rotors made of a ceramic material and cellulose possible. We also used steel or plastic, in general, no moisture transfer. Not metal rotors (ceramics, etc.) are both perceived as a latent heat on their hygroscopic properties. Typical rotor diameters range between 0.5 and 5m, the rotor thickness is usually 20 cm (with ventilated air heat). The standard temperature range is up to about 2500 'C .

Heat Pump


Everywhere in our environment is heat present which is useless, because the temperature is too low. Examples include outdoor, ventilated air from buildings, water, waste heat from industry and the soil. With a heat pump it is possible to efficiently heat this value to a usable temperature level. Like a water pump water from a low to a high level pumps as "inflated" a heat pump heat from a low to a high temperature level, so the heat is useful. In winter the heat pump produces the main product so heat. As a by-product is cold. In summer the heat pump produces cold and heat as by-product. Energy by the cold and heat by-products are stored and later used effectively.

Working Principle.

The physics is well known that pressure and evaporation temperature a relationship with each other. Low pressure, low evaporation temperature. From this property is heat pump process or cold process used. These electric heat pump, called compression heat pump system is shown schematically shows a closed loop with four lines attached to the evaporator (1), compressor (2), the condenser (3) and an expansion valve (4). Evaporator and condenser are heat exchangers, the compressor is a pump: a piston pump or a screw pump. The cycle called a refrigerant circulates, the heat transports. In the evaporator the refrigerant evaporates at low temperature and low pressure absorption of heat (eg from a water or air). The compressor pumps, under absorption of mechanical energy (here provided by an electric motor), the vapor from the evaporator to the condenser. This condenses the refrigerant at high pressure and high temperature, and capable of heat (the sum of heat evaporator and compressor work) to the surroundings (central heating installation, boiler or air heating). Then the refrigerant flows on a throttle valve back to the evaporator.

The three main types :

Electric heat pump. In most heat pumps, the compressor using powered electricity.
This common type is used to heat homes and other buildings.

Gas-fired heat pumps. This is the compressor directly by a gas powered or through a so-called absorption process with a burner / generator combination.

In the industry are very different species, like mechanical vapor compression, thermal vapor compression and heat transformer

Application :

In local systems, it is useful in a limited number of spaces as central heating and cooling need not be profitable or not present. For central systems, it is only suitable for smaller buildings. In addition, heat pumps for cooling of the ventilated air in buildings, known as integrated refrigerating. There have to be said that the application of a heat pump in an air box is not widely used because the investment and maintenance costs are relatively high compared to the payback period.

Advantages :

. converts the normally untapped environmental and energy waste into usable energy;
. environmental friendly;
. very suitable for swimming pools related to dehumidify;
. covered by subsidy and tax schemes;
. means renewable energy with high efficiency;
. has a high reliability and long life;
. emissions of harmful substances that cause the greenhouse effect is 40% lower than that of an HR-boiler.

Disadvantages :

. relatively high maintenance and inspection costs;
. capital intensive;
. relatively small temperatures bridge;
. many high quality and sensitive techniques;
. high internal pressures, reduced potential for wear.

Resistance :

The pressure losses due to the recuperative heat exchanger, evaporator and condenser is about 150 to 300 Pa.
This depends on the size of the system, the velocity and dehumidify.

Materials :

Electric heat pumps The refrigerant that is currently used mostly propane (R-290) or HFC (chlorine free), or a fluorocarbon CH2FCF3 which are environmentally friendly cold means. To give an idea of the press device, to the refrigerant R-290 is at a low temperature 0'C pressure pl of 5 bar, and a high temperature 50'C pressure of 18 bar. R-134.

Absorption changer :

Typical mixtures are water / ammonia (ammonia refrigerant) and lithiumbromide / water (refrigerant water). The material of the evaporator and the condenser is dependent on both the properties of the intermediate medium in closed circuit and through media. Depending on these properties such as temperature conditions, and stainless steel is widely used at high temperatures and pressures (industrial processes). In ventilation applications in, for example, utility buildings, the material of the pipes usually copper (possibly even a surface) and the aluminum strips are widely used. The pipes can be fitted with an internal porous layer to improve the transport medium.

Profit :

For the production of useful heat with a heat pump is energy needed. This energy is required for compressing the vapor and driving energy. How efficient it is, is expressed with the English term Coefficient Of Performance (COP). This is the ratio between the useful power and heat pump supplies the necessary power supply. This is the efficiency of the heat pump. Then for the Dutch heating season with an average outdoor temperature of 4.8 'C and an average inside temperature of 17.3 'C and 50% efficiency a COP of 3.0. The smaller the temperature difference between the heat source and heat users, the better the efficiency (COP). This COP is the ratio between the obtained usable heat and power supply. A heat pump with a COP of 3, so 1 part power supply (eg electricity) needed to 3 parts to produce useful heat. The efficiency is then 300% The COP of the current generation of heat is between 1 and 5. It varies by type and also the temperature level of heat

Guidelines for the COP of heat pumps in homes and buildings are:
The electric heat pump: 2.5 to 5.0
The gas engine heat pump: 1.2 to 2
The absorption heat pump: 1 to 1.5