Apr 9

Air handling units AHU DEX S/M – a guarantee for high energy efficiency and air quality

  • April 9, 2015

хигиенна камераNowadays people spend most of their lives indoors. Each of us wants to live in a high quality environment that means better food, fresh water and clean air.

TANGRA has specialized more than 25 years in development and implementation of ventilation and air conditioning systems. Since 1994 we produce our own range of plate heat exchangers and we build them in the range of heat recovery ventilation units. This was the dawn of these systems in Europe and today they are accepted as standard worldwide. Our series of heat recovery units TANGRA EVB and the air handling units TANGRA AHU were the first products with an integrated heat recovery that we produced.

To upgrade the air handling units range was a logical step in our growth.

The ambition to be among the innovators in the industry and to provide our partners with superior quality and highly efficient solutions is leading for us. This led to the development and implementation of a new series of air handling units with two stage heat recovery. The first stage is a plate or rotary heat exchanger and the second is an integrated heat pump module. These are the two series TANGRA AHU DEX S/M (plug&play solution).

The fuel prices are rising constantly. The investments for energy efficiency in the last few years were orientated to better insulations and new windows systems for the building in order to reduce energy losses. But those improvements have transformed our houses into a thermos. Without a fresh air the life in this well insulated thermos is impossible.

In order to achieve a higher efficiency while we supply the building with warmed and cooled air during the summer and winter season we created the new series of air handling units TANGRA AHU DEX S/M with an integrated heat pump. The M modification is a monoblock type with integrated indoor and outdoor (monoblock) unit while the S modification is with integrated indoor unit and a separated outdoor unit (split type). (See fig. 1)

Fig. 1


The units are ready to install and there is no need of an additional energy source to ensure the heating and cooling of the fresh air. All units are factory tested in our laboratory.
The only thing our partners need to do is to install and start the system.

A traditional ventilation or air-conditioning system consists of an air handling unit and an additional energy source such as heat pump or chiller and a boiler for hot water. Those additional energy sources are installed to ensure the supply of hot and cold water for the thermal sections in the air handling units. But to install such a system, it takes time. That means a several working hours to design a project that includes all those features. After that we need a variety of specialists to install all the components. At the end, we need to run and synchronize three different systems. All those factors make the system very complicated and expensive.

treeAir handling units with an integrated heat pump TANGRA AHU-DEX S/M: high efficient solution for all year round operation.

The air handling units TANGRA AHU DEX offer two stages of heat recovery. The first stage is a plate or regenerative heat exchanger and the second is a heat pump module working on direct expansion that is responsible for the additional air heating or cooling.
The first stage is the passive heat recovery. This is a plate heat exchanger with heat recovery efficiency between 50 and 85%. The customers can choose between our standard series heat exchangers REC AL/AL+ (up to 65%) or the high efficient series REC HiE (up to 85%). All the exchangers meet the requirements of Eurovent EN 308 that proves their efficiency. It is also possible to build a rotary heat exchanger with efficiency up to 75%. 3
The active stage is done by an integrated heat pump module. As we already mentioned those heat pump modules could be as monoblock (M) or as a split (S) units. In AHU DEX M the heat pump is fully integrated into the air handling unit. That means the fresh air is directly chilled or warmed by refrigerant in the cooling coil while the condenser and the compressors are situated in the discharge air section. Due to technical reasons this system allows only a partial recirculation of the fresh air. The models TANGRA AHU DEX S offer also an integrated refrigerant coil while the heat pump is a separated module installed near the air handling unit. The system allows working with 100% recirculated air.

TANGRA AHU DEX M uses a high efficiency Copeland compressor with inverter and electronic tree-way valve. The inverter allows to control the compressor capacity from 10 to 100%, depending on the temperature requirements. A study shows that during a year the heat pump works at full capacity only about 5-6% of the time. With this type of regulation, we could increase the system efficiency and reduce the running costs. Thus system lifetime is also increased when the compressor does not work at its full capacity.

OLYMPUS DIGITAL CAMERAAir transportation is done with high efficient direct driven plug fans with frequency inverters. They are compact and more efficient compared to the belt-driven centrifugal fans. The frequency inverters provide more opportunities for regulation that leads to significant running cost optimizations even if the fan works on 100% of its capacity. All those facts make them a reliable, safety and energy efficient solution for the modern air handling units.


контролерTANGRA’s air handling units TANGRA AHU DEX M/S come fully equiped automation and control. A special PLC controller deals with all electrical components such as the electronic valves, compressor and fan inverters. A specially developed software, by TANGRA, manages the work of the unit during the summer and winter mode. The unit’s capacity is controlled according to an assigned temperature and could be managed according the to moment’s needs. The interrated PLC controller allows an upgrades. It also could be connected to a BMS or an external PC and provides air quality control and monitoring in order to satisfy the customers needs.

When should one choose an air handling unit with heat recovery and an integrated heat pump?

izborThe main purpose of these units is ventilation in buildings (supply of fresh air and discharge the exhausted one). When the inside air characteristics (CO2, VOC, relative humidity, gasses, etc.) change, the air handling units automatically change the ratio between fresh and recirculation air. This leads to saving of energy.
Some common types of buildings that could use those units are:

– Trade centers
– Office buildings
– Municipal buildings
– Indoor swimming pools
– Industrial buildings

10 reasons why we should choose an air handling unit with heat pump TANGRA AHU DEX S/M.

  1. Supply enough quantity of fresh filtered air to the inhabitants with only one unit. This fresh filtrated air is heated during the winter and cooled during the summer.
  2. High annual energy efficiency thanks to a two stage heat recovery.
  3. High COP/EER efficiency of the heat pump, due to the heat recovery.
  4. Various opportunities for air flow regulation, according to the needs of the project for fresh air, temperature and humidity. (CO2, rH, VOC, etc.)
  5. Flexible inverter heat pump control 10%-100%, depending on the necessary temperature and moment load.
  6. Decrease of the sum for initial investment as a consequence of the lack of additional cooling and heating plant.
  7. Esthetic and compact solution – Air handling unit and heat pump – all in one unit.
  8. Easy to install and control – plug and play system. No need for additional pipe or duct connections.
  9. Factory tested and with proven quality.
  10. The air handling units TANGRA AHU are certified by TÜV Rheinland.


Last but not least those Air Handling Units benefit:

– Building owners by reducing the annual bills for heating, cooling and ventilation.
– Designer by saving time for planning and designing additional air and pipe systems that support the air handling units
– Installers by delivering and installing one unit instead of several units.
– Facility managers and maintenance personnel by maintaining a single unit instead of two or three different installations.

TANGRA AHU’s DEX M/S are supplied in modules for easy transportation and installation. When TANGRA AHU DEX M is already installed it only needs to be connected to the electrical system and it is ready to use. TANGRA AHU DEX S requires an additional connection between the unit and the external heat pump before the initial start.

The advantages of using an air handling unit with two stage heat recovery are significant reduction of the running costs and the decreasing environmental impact.


Иван Армянов Управител ТрО K.L Пламен Бенев Ел. & КиП и А
Ivan Armianov
Управител ТрО
Kolyo Lekov
Plamen Benev
Ел. & КиП и А



National Service Telephone:
0887 73 73 75