Heat pumps are first classified by where they take their heat from: the outdoor air, the ground or water. The second distinction is how they deliver that heat to the building: through a water circuit (air-to-water) or directly to the indoor air (air-to-air). Add to these the construction of the unit (monobloc or split), hybrid systems that combine a heat pump with a boiler, and absorption units that run on heat instead of electricity. The most common type, and the one we manufacture under the AD brand, is the air source heat pump with a water circuit.
By heat source: air, ground, water
All types work with the same refrigerant cycle; we describe its steps in our article what is a heat pump. What defines the type is where the evaporator collects its heat. The temperature of that source in midwinter also decides how efficiently the unit works on the days when it is needed most.
Air source
A fan in the outdoor unit draws air across a finned coil, and the refrigerant takes up the heat in that air. No drilling, wells or large plot of land is needed; the unit stands in a garden, on a roof or on a balcony. Its weak point is that the source is coldest on exactly the days when the most heat is needed: as the outdoor air drops, capacity and efficiency fall, ice forms on the coil and the unit defrosts from time to time.
Solutions such as a vapour injection (EVI) compressor or a two-stage cascade circuit push that limit down. Among the AD series, Boran delivers its rated capacity at −25 °C and Ayaz at −30 °C; in other words, a correctly chosen air source unit can heat on its own even in an Eastern Anatolian winter.
Ground source
Ten to fifteen metres below the surface, the ground temperature is almost constant all year and roughly equal to the region's mean annual air temperature. A ground source system collects this heat through water with antifreeze circulating in vertical boreholes or in pipes laid horizontally. Because the source is warmer than the air in winter, efficiency stays high on cold days too, and no outdoor fan is needed. In return it needs drilling, land and permits; most of the initial investment goes into the ground side, and the number and depth of boreholes must be calculated from the thermal properties of the soil. The name "geothermal heat pump" usually refers to this system.
Water source
A lake, river, the sea or groundwater is usually milder than the outdoor air in winter, and its temperature changes slowly. Water source systems either take heat from that water through a heat exchanger or draw water from one well, use it and return it to another. Efficiency is high, but the approach cannot be used everywhere: the distance to the source, the quality and flow of the water, and the permit to use it are decisive. We cover boats and ships that use seawater as their source in our article on heat pumps on ships and boats.
By how heat reaches the building: air-to-water and air-to-air
An air-to-water heat pump transfers its heat into a water circuit. That water goes to underfloor heating, radiators, fan coils and the domestic hot water tank; the unit takes over the job of the boiler and can be connected to a boiler-based heating system. In summer the same circuit supplies chilled water to the fan coils or to underfloor cooling.
An air-to-air heat pump releases its heat directly into the room air. Domestic split air conditioners are technically exactly this: an air conditioner running in heating mode is a small air-to-air heat pump. It heats and cools quickly, but it does not make hot water, cannot feed underfloor heating and needs a separate indoor unit in every room. We compare the two for heating a home in our article air conditioner or heat pump.
There are also solutions that combine both approaches. The HİDREM indoor unit with direct-expansion cooling heats through the water circuit in winter and in summer sends refrigerant directly to wall-mounted air conditioner indoor units. In buildings without fan coil pipework, water-based heating and refrigerant-based cooling meet in one system this way, and the heat removed by cooling warms the water in the tank.
By construction: monobloc and split
In a monobloc unit the whole refrigerant circuit sits in the outdoor unit, and only water pipes enter the building. No refrigerant lines are run on site; the circuit arrives sealed from the factory. On the other hand, since water runs all the way to the outdoor unit, cold climates call for frost protection: glycol in the water, a frost protection valve or continuous circulation.
In a split unit there are refrigerant lines between the outdoor unit and a hydraulic unit indoors. The water circuit stays entirely inside the building, so the risk of freezing disappears; the pump, expansion vessel and heat exchanger sit in the cabinet of the indoor unit. AD's Poyraz, Boran and Vaha series work this way with the HİD / HİT, HİDRA or HİDREM indoor units, and the V series outdoor unit is also a split design. The Mega central system, by contrast, carries its shell-and-tube water heat exchanger in its own casing; the system water is connected directly to the unit.
Hybrid systems
A hybrid system usually runs a heat pump together with a gas boiler on the same heating system. The control uses the heat pump while the outdoor air is above a set temperature (the bivalent point) and switches to the boiler, or runs both, when it drops below. It is used as an intermediate solution in renovation projects that want to keep the existing boiler, or with old radiators that need very hot water. In return, two separate systems are installed and two separate energy connections are kept.
The word "hybrid" in the name of AD's Ayaz hybrid package heat pump means something else: there is no boiler in the package. Two refrigerant circuits work in series: the R290 circuit takes heat from the outdoor air, and the R134a circuit raises the water to 75 °C. The buffer tank and hydraulic components are inside the package. This gives water at radiator temperature even at −30 °C outdoors, without a boiler.
Absorption heat pumps
All the types described so far work with an electric compressor. An absorption heat pump does the compressor's job with heat: the refrigerant vapour is absorbed into a solution (in the absorber), the solution is pumped, and the vapour is driven out again by heating it in a generator. Lithium bromide with water and ammonia with water are the best known pairs. Electricity use is low, but a heat source is required, so the technology makes sense in large sites with natural gas, waste heat or district heating water. We explain the principle in detail in our article on the absorption heat pump.
Which type does AD make?
All AD heat pumps are air source units with a water circuit; they run on electricity with an inverter compressor. There are four climate series for homes: Poyraz for Marmara-type winters, Boran for harsh winters, Vaha for coastal climates and Ayaz for extreme cold, each in 12, 14 and 16 kW. For commercial buildings we build the 20–24 kW V series and the 28–56 kW W series outdoor units, and for large projects such as greenhouses and housing estates the 200–1,200 kW Mega central system. For companies that want to sell monobloc or split heat pumps under their own brand, we also offer OEM manufacturing.
Which type is right for you?
A project with land and a drilling budget that wants steady efficiency all year can consider a ground source system; a site next to a reliable water source, a water source system. A plant with plenty of waste heat brings absorption into the picture. For most other buildings, an air-to-water heat pump chosen for the climate is the shortest route to a result. We explain how the series and capacity are chosen in our article on heat pump selection, and you can send your project details through our contact page.
