A heat pump and a chiller use the same refrigeration cycle; the difference lies in which end of the cycle is put to use. A chiller's product is chilled water: it rejects the heat it takes from the water through its condenser. A heat pump's main product is heat: it delivers the energy it takes from the outside air to the building as hot water, and most models reverse the cycle to provide cooling in summer as well. For a building that needs both heating and cooling, a heat pump is usually the right starting point; for a production line that needs chilled water all year, or for a very large cooling load, a chiller is.
If you want to know the parts of a chiller and how it works in detail, see our sister company's article what a chiller is; here we focus on the differences that affect the choice.
Same cycle, different job
Both machines have four main components: evaporator, compressor, condenser and expansion valve. In the evaporator the refrigerant evaporates and absorbs heat; in the condenser it condenses and gives heat off. We explain the cycle step by step in our article what is a heat pump. The difference is which component is the "useful" side:
- In a chiller, the useful side is the evaporator. The unit produces chilled water, usually between 5 and 15 °C, for a building or a process; the heat at the condenser is rejected to the air or to tower water.
- In a heat pump, the useful side is the condenser. It produces water between 35 and 75 °C for underfloor heating, radiators and domestic hot water; the evaporator collects heat from the outside air.
That is also why efficiency goes by different names. For a chiller, cooling efficiency is expressed as EER; for a heat pump, heating efficiency as COP; their seasonal counterparts are SEER and SCOP. There is a simple link between them: the heat leaving the condenser is the sum of the heat absorbed in the evaporator and the electricity fed to the compressor. When the same cycle runs under the same conditions, and losses are ignored, the heating COP is exactly one more than the cooling EER. Example: under the same conditions, a cycle that provides 3 kW of cooling from 1 kW of electricity gives off about 4 kW of heat at its condenser.
What separates the designs: the temperatures they are built for
Using the same cycle does not mean the machines can replace each other. A chiller is designed to reject heat into hot summer air and to hold chilled water within a narrow band. With a winter kit, the commercial chiller units we supply run in outside air between −12 °C and +46 °C. In the industrial units, the process version holds the leaving water constant to ±0.5 °C; with glycol, −10 °C is standard, and the low-temperature version goes down to −30 °C.
A heat pump faces the opposite challenge: drawing heat from cold air in winter and raising water to a high temperature. This calls for solutions such as vapour injection compressors, economisers, cascade circuits and defrost control. In the AD series, the design point changes with the climate:
- Poyraz: 55 °C water at −7 °C outside air, R290
- Boran: 65 °C water at −25 °C outside air, R290 with vapour injection
- Vaha: 55 °C water at +2 °C outside air, tuned for cooling, R32
- Ayaz: 75 °C water at −30 °C outside air, R290 + R134a cascade
In cooling mode, a heat pump produces chilled water for fan coil and underfloor cooling circuits. Requirements such as ±0.5 °C precision, low temperatures with glycol or a process load that runs every hour of the year, however, are chiller territory. A chiller, in turn, does not heat in winter unless its heat pump version is chosen.
The building's water installation is part of this comparison too. Cooling with chilled water needs fan coils or an underfloor cooling circuit, and pipes well insulated against condensation; most existing buildings do not have this infrastructure. If such a building is to be cooled in summer with a reversible heat pump, either this installation is added or an indoor unit with refrigerant-based cooling, which cools through air conditioner indoor units, is chosen.
Reversible heat pump or chiller with heat recovery?
The two machines come closest where heating and cooling meet in the same project. There are two different approaches here.
Reversible heat pump
A single machine heats in winter, cools in summer and prepares domestic hot water all year. In homes, villas and commercial buildings with a significant heating load, it is the simplest solution: no boiler, fuel connection or flue is needed. At commercial scale, W series outdoor units are built in six capacities between 28 and 56 kW and grow by combination for larger needs; for greenhouses, housing developments and hotels, the Mega central system delivers 200–1,200 kW of heating and cooling from a single unit.
The heat from summer cooling need not be wasted either. The HİDREM indoor unit transfers the heat it takes from the rooms during cooling to the water in its tank; while cooling is running, the domestic hot water is heated without spending extra energy.
Chiller with heat recovery
In buildings where the cooling load dominates but hot water is needed at the same time, the chiller's condenser heat is recovered. The heat recovery or heat pump version of the commercial chiller units produces 55 °C hot water. Hotels, hospitals and food plants that use washing water are typical examples. The limit is clear as well: recovered heat exists only while the cooling is running; on a winter day with no cooling demand, hot water has to come from another source.
Waste heat does not always come from a chiller. At Çetin Civata, a system that recovers waste heat from the bolt production furnaces to heat the factory's social areas was completed and handed over. Finding out which heat a plant is wasting is a question that comes before choosing any machine.
Which one to choose, and when?
- Homes, villas and apartment buildings: mainly heating, with cooling in summer and hot water all year; a heat pump from the series that suits the climate. We explain how to choose the series and capacity in our article on heat pump selection.
- Hotels, schools, offices, housing estates and greenhouses: loads in both seasons; if the heating share is large, a reversible heat pump such as the W series or Mega; if heating comes from another source and cooling dominates, a chiller.
- Production lines, laboratories and data centres: chilled water all year, a narrow temperature band, redundancy; a chiller. We work through a capacity calculation in our chiller selection article.
- Cooling and hot water at the same time: a chiller with heat recovery, or an indoor unit such as HİDREM that uses the heat from cooling.
Climate also affects the decision. On the Mediterranean and Aegean coast cooling dominates, but heating is still needed in winter. In such a place, instead of installing a chiller and a boiler side by side, a heat pump tuned for cooling can do both jobs with one machine; the Vaha series was designed for this climate.
Scale and operation
Capacity ranges narrow the choice as well. AD heat pumps go from 12–16 kW for homes, through 20–56 kW for commercial outdoor units, up to 1,200 kW with Mega. On the chiller side there is a wide range, from 5 kW units serving a single machine to 2,000 kW industrial units; cooling loads at megawatt level are chiller territory.
On the operating side, the right comparison looks at how the same job is done in two ways. Doing the heating and cooling with one heat pump, compared with installing a chiller and a boiler separately, means a single installation and a building that burns no fuel on site. The electricity cost of heating depends on the COP, the outside air and the water temperature; we work this out with an example in our article on heat pump electricity consumption.
For your project
Share your project's heating and cooling loads, water temperatures and pattern of use through our quotation form, and we will assess together whether a heat pump, a chiller or both should be used. For maintenance and service after installation, we work with our sister company Aktek Elektromekanik.
