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Maximizing comfort and efficiency with underfloor cooling

Ventilation systems, fans, air conditioning or evaporative coolers are quite popular cooling solutions. Yet underfloor cooling is also an interesting option in certain cases. Unfortunately, experience tells us that HVAC professionals and end consumers know little about underfloor cooling and it is occasionally perceived as ineffective. Our experts are happy to help clear up that misconception with straightforward information and practical tips on how to maximize comfort and efficiency with underfloor cooling.
underfloor cooling comfort and efficiency

Underfloor cooling vs. air conditioning

Before addressing more detailed aspects of underfloor cooling, it’s important to look at how it compares to other, more well-known cooling systems. In fact, you cannot easily compare underfloor cooling to air conditioning for example since it’s almost technically impossible to achieve comparatively low room temperatures at high outdoor temperatures. Air conditioning actively cools the room air and can lower the indoor temperature up to 15°C. Underfloor cooling, on the other hand, provides passive cooling by absorbing heat through the floor and lowers the room temperature 3 to 5°C compared to an uncooled room.

“Most of the times underfloor cooling is used in a combined system where underfloor heating is the main functionality and cooling is a support option. The cooling is an added benefit since all the system components, such as pipes, manifold, wiring centre and thermostat, are already installed. If you then have a reversible heat pump or heat pump with an outside collector you enjoy cooling at no additional cost whereas air conditioning will raise your energy bill”, says Olaf Kloetzel, Product Manager Radiant Heating and Cooling at Purmo. Especially with the right system components, it’s very easy to combine comfort and efficiency with an underfloor heating and cooling system. Our Unisenza controls range, for example, includes various thermostats and a wiring centre suitable for both heating and cooling, allowing users to combine multiple functionalities in one system and enjoy indoor climate comfort year-round.

In certain projects, such as office buildings, underfloor cooling is also sometimes used as base cooling. The free cooling energy is used on a base level and allows for a reduced configuration of the active cooling system because it only needs to cover the peak cooling demand.


Underfloor cooling planning and design

“One of the reasons underfloor cooling is sometimes perceived as inefficient, is inadequate planning and design”, says Jente Witters, HVAC Systems specialist at Purmo Group. “It’s important to set the optimal flow for both heating and cooling in order to maximise the floor output and absorption. Especially in modern, well-insulated buildings, you need a slightly higher flow for cooling. So it’s best to plan the worst-case heating scenario in an attempt to keep the circulating water volume of the individual heating circuits as high as possible by minimising the flow temperatures.”

Olaf adds: “In addition, the installation distances of the pipes are generally smaller in case of a heating and cooling system. Whereas a distance of 150 to 200 mm is sufficient for a regular underfloor heating system, a distance of 100 to 150 mm is better in case of a combined floor heating and cooling system.”

To determine the cooling capacity of the individual circuits, the standard calculation is usually reversed based on the water quantities designed for the heating mode and the available cold-water temperatures in the cooling mode. If a cooling load calculation of the building or room is available, a statement can be made about the room temperatures to be expected in the cooling mode. However, due to costs reasons, a separate cooling load calculation is usually not carried out so the cooling capacity is used to check whether the temperature falls below the dew point at any point and condensation forms on the floor.

In case you have questions about the design or planning of an underfloor heating and cooling system, the Purmo calculation department is at your disposal.

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Underfloor cooling controls

A second issue that Jente regularly comes across is related to the humidity sensor. To prevent condensation on the floor surface, the water circulation in the system must not fall below a certain temperature. Therefore, a humidity sensor is used to constantly measure the temperature and humidity of the room air and control the cooling water temperature. “To get the most accurate readings, it would be best to place the humidity sensor in a reference room. In practice, however, the sensor is generally installed on the manifold, which in turn is often placed in a technical room that also houses the boiler. Consequently, there is more moisture in the room air and the cooling system is unable to reach its full potential because it shuts down as soon as the sensor measures condensation in that room.”

When using the Unisenza wired control system, this issue can be largely remedied by installing a Unisenza floor sensor in every room. You can then measure the floor temperature and set a minimum surface temperature of 18 to 20°C, which should prevent condensation on the floor most of the time. This also allows for easy zone control which increases indoor climate comfort and helps to save energy at the same time.

Read more about heating and cooling with zone temperature control

We are aware, however, that this is not a foolproof solution as a floor sensor only measures the surface temperature and not the real dew point. In case of very humid weather conditions, there is still a risk of surpassing the dewpoint. The humidity sensor therefore remains a must.

To offer our customers the best possible solutions, we continue to improve and expand our product range. For this particular application, for example, a wireless RF control system including room thermostats equipped with a humidity sensor would be better suited. This would consider humidity levels in every individual room and facilitate system control on a room-by-room basis. We are happy to confirm that such a solution is in the pipeline as an addition to our Unisenza Plus range. When combined with the latest version of the Unisenza Plus app, it will be possible to easily set up dew point control and enjoy optimal efficiency of the underfloor cooling system at all times.



As we have highlighted above, underfloor cooling is not equivalent to active cooling systems such as air conditioning or evaporative coolers. It is however, an automatic, user-friendly cooling system that offers great benefits at a very low cost. When planning underfloor cooling, only a few key points need to be taken into account, such as the highest possible water volume and a reduced installation distance of the pipes. The low costs and minor efforts combined with the increase in indoor climate comfort and energy efficiency make underfloor cooling a very interesting alternative to consider for a variety of applications.

Should you have any questions about the design or implementation of an underfloor cooling system for your project(s), please don’t hesitate to get in touch. We will be happy to offer tailored advice.

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