Sustainable cooling systems: surface cooling vs. air conditioning

Cooling systems for sustainable indoor climate comfort

Both new build and renovation projects today are very much focussed on energy efficiency. The challenge here is to create a sustainable building that also offers year-round comfort. With the right heating and cooling system it’s easy to comply, provided that it’s matched to the building and its occupants needs.

A popular solution, for example, is to complement a radiator heating system with an active cooling system such as an air conditioning. Yet, fan convectors or radiant systems with panel or floor heating and cooling can be an interesting option as well. Let’s look at the pros and cons of each system.

Air conditioning

The primary reason why people install AC systems is their high cooling performance. An air con can also include an air filter function, which removes pollutants from the air to improve the indoor air quality. Moreover, air conditioning is a very reliable way to control humidity, which decreases the risk of damp, mould or harmful bacteria. In some cases air conditioning can also be used for heating, but this requires certain conditions to be met.

Find out when heating with an air conditioner is a good choice

Although air conditioning provides high comfort levels, it also has a relatively high energy consumption. Furthermore, it often contains refrigerants that have a rather low lifespan and a negative impact on the environment. So the challenge for both manufacturers and end-users is to move towards a more sustainable implementation.

In its report on the future of cooling⁽¹⁾, the International Energy Agency (IEA) touches upon the subject and pleads for end users to opt for more efficient air conditioners. They state that the average efficiency of air conditioners sold today is less than half of what is typically available on the shelves – and one third of best available technology. According to their Efficient Cooling Scenario, effective policies can double average AC efficiency and reduce cooling energy demand by 45% compared to the Reference Scenario.

Surface cooling

A floor or panel system doesn’t take up valuable wall space or produce any noise. Thanks to the radiant heating or cooling there is also no dust circulation or draught. Additionally, such a system can easily be combined with user-friendly controls like our Unisenza range to set different temperatures for different rooms. This optimises comfort for the occupants and reduces energy consumption as unoccupied rooms are not unnecessarily heated or cooled.

Moreover, only a few additional components are required to convert our surface heating systems into surface heating and cooling. As a rule, a 2-pipe system is used, in which the same pipe system and the same components can be used for heating and cooling as for pure heating. This means that the already high level of comfort and living quality of a Purmo surface heating system can be increased even further without a great deal of additional material and expense.

In principle, a distinction is made between active and passive cooling in surface cooling, depending on the cold water generation.

• Passive cooling: mainly water/water, brine/water and in rare cases air/water heat pump systems are used for this. With passive cooling, the ground or groundwater is usually used as a regenerative cooling source. In the case of cooling, the corresponding temperature level is transferred directly to the system water with a heat exchanger.
  
• Active cooling: this requires energy to drive a chiller or a reversible heat pump. A refrigerant circulating in the chiller extracts excess heat from the system water to be cooled via an evaporator. The principle corresponds to that of a refrigerator, just in larger dimensions. The achievable cooling capacity depends on the cold water temperature and the effective transfer area of the cooling surface in the room. It is mainly limited by the dew point temperature. Even if the calculated cooling load and the planned room temperature are not reached, the room temperatures can be reduced by a few degrees, which results in a significant comfort advantage compared to buildings that are not cooled.

A downside of surface cooling systems is that their maximum cooling performance is limited by the surface area of the room. Moreover, for optimal operation, the formation of condensation should be prevented. This means that any areas which come into contact with warm outside air, such as windows, doors, vents, etc. must be sealed off properly.

Fan convectors

Just like radiant systems, fan convectors, such as the iVector S2, are a great match for low temperature heating systems and can be used for both heating and cooling when coupled with a reversible heat pump. Moreover, they are not so much influenced by the available surface area so that their output can be tailored more specifically to the full heating and cooling needs.

On the other hand, fan convectors do require some wall space and need to be dimensioned sufficiently large to ensure the fans don’t need to run at their highest setting most of the time. That would increase both energy consumption and noise levels.

Comparing different cooling systems

Within the SCoolS (Sustainable Cooling Systems) project, researchers at the Thomas More University of Applied Science and the Belgian Building Research Institute set up several simulations. Using these simulations, they examined the performance of sustainable cooling systems and compared them with air conditioning as a reference in comfort (best) and energy usage (highest). As expected, active air-cooling systems can provide good comfort in 98% of studied cases with a cooling power of 50 W/m². At 15 to 30 W/m², the more sustainable systems with surface cooling and fan convectors can, however, provide similar comfort in 80% of the cases.

The simulations also show that when sustainable cooling systems, such as surface cooling or fan convectors, are applied there is a drastic reduction in energy usage compared to classic active cooling systems. This is, however, on condition that their control is adapted to the building and the occupants’ needs. On top of that, there needs to be a large enough margin between the set-point and the lower comfort temperature level, so the highest capacity demands can be buffered in the system and in the building.⁽²⁾

Sustainable cooling systems: the full picture

Whenever the choice between the different cooling systems discussed above is on the table, it’s important to look at the full picture. This means taking into account both heating and cooling, but also the features of the building and daily activities of its occupants. For example, is there enough surface area available for cooling to provide sufficient comfort? If so, then underfloor cooling or a panel system is certainly a good option that’s both flexible and energy-efficient. However, in case of a high occupancy rate, for example, it might be better choose a cooling system with fan convectors or an air conditioner that can be better tailored to the cooling demand.

Sources
1. https://www.iea.org/reports/the-future-of-cooling
2. https://www.duurzamekoeling.be/uploads/1/0/2/1/102130926/8-180-21_wuyts.pdf