Using water as a cooling medium

Selling points for water-based air conditioning

Air conditioning systems available on the market can essentially be divided into two groups:

1. DX or direct evaporation systems
2. Chilled water systems

Cooling is generated identically with both systems. Heat is absorbed in each case in a refrigeration circuit containing refrigerant and thus cooling is generated. The visible components do not differ very much outwardly from each other.

However, there is a major difference between the two systems: refrigerant is reduced to the minimum possible level in chilled water systems. Large volumes of refrigerant are pumped through the entire building in DX or direct evaporation systems.

Benefits of chilled water systems

Discover below why the quantity of refrigerant used needs to be kept as low as possible:

1. Minimum possible volume of refrigerant

Refrigerants are needed in all cooling systems. However, the quantity of refrigerant needs to be kept as low as possible for various reasons. The refrigerant R410A is commonly used in air conditioning systems. If 1 kg of this is released into the atmosphere, the resulting greenhouse effect is comparable to heating a home for 8 -10 months or driving a mid-sized car for around 16,500 km. The legislator has recognised this and implemented what is known as the F-Gas Regulation to ban certain refrigerants and seriously limit others in future. This will significantly increase the price of refrigerant, a factor that could become noticeable when a system needs to be serviced or repaired.

Discover more about the new refrigerant regulation to limit climate change here

2. Reduction of potential leaks

The pipework of direct evaporation systems contains refrigerant throughout the entire building. Great care needs to be taken to ensure that the pipework is leak-tight when connecting up the pipework. The legislator has therefore made it mandatory for plant operators (generally the users) to have an annual leak inspection carried out by a certified professional. This increases to twice yearly, depending on the volume (above approx. 25 kg). Each and every connection of the pipework needs to be checked for leaks. With chillers, this only affects the circuit inside the outdoor unit, while it affects all indoor units and the entire pipework of direct evaporation systems. Operators face penalties of up to €50,000 for non-compliance with this legislation. The likelihood of a leak in a small cooling circuit a few metres in length (chillers) is much less compared to extensively ramified pipework several hundred metres in length (with direct evaporation systems).

3. Water is not harmful to health

Water is an ideal medium for energy transmission. There are many reasons for this: it is cheap, easily available, non-toxic, non-flammable or non-explosive, has no impact on the environment and does not cause a greenhouse effect. These are not properties you can ascribe to refrigerants. Apart from the above resulting greenhouse effect, recently introduced refrigerants (e.g. R32) are flammable or explosive. EN 378-1 regulates the arrangements that need to be put in place in these rooms to prevent choking hazards. In class A spaces, (e.g. hotels, supermarkets, restaurants, homes etc.), a certain maximum threshold of refrigerant per room volume may not be exceeded. Gas detectors may need to be installed.

4. Water is flexible

Water supply offers almost unlimited options when an air conditioning system is subsequently installed, even into new buildings. While only one manufacturer’s equipment and one type of product range can be used with a refrigerant network, water systems enable solar systems, gas heating systems and other renewable heating systems, as well as various cooling systems, to be combined. They can also be flexibly extended and replaced in future. As has happened on several occasions in the past with direct evaporation systems, the only option was to replace the entire system (even including all pipework) when a product range was discontinued or the refrigerant had to be replaced by law.

5. Made-to-measure efficiency

As is clear from point 4, the efficiency and thus the energy costs of air conditioning with water-based systems can be freely selected and altered as required in future with the addition of many systems (e.g. free cooling). Studies of existing systems, including studies by the independent Ashrae association, have also shown that even simple chilled water systems are at least equivalent to direct evaporation systems in terms of efficiency.

Comparison: Chilled water system vs. direct evaporation

Office building – small system

• Ground floor
• 4 offices
• Required cooling output: 8 kW
• Length of pipework: approx. 40 m

Office building – mid-sized system

• Ground floor
• 3 meeting rooms
• 1 training room up to 30 persons
• Offices for a total of 50 - 60 people
• Required cooling output: 40 kW
• Length of pipework: approx. 120 m