Underfloor Cooling: Cool alternative to air con!
Underfloor cooling is becoming increasingly popular among clients and consultants chasing low SAP and high BREEAM ratings for their buildings, writies Malcolm Morgan, senior development engineer, Rehau. In schools, hospitals and buildings where large expanses of glazing are an issue, it has the potential to become the default alternative to air conditioning.
Compared with air conditioning, underfloor cooling provides a comfort cooling effect with no draughts, no high air speeds or cold spots and reduced risk of Sick Building Syndrome. Crucially, of course, it is also a low energy, low carbon solution with both low capital and low running costs.
As a pioneer in this UK market, Rehau is responding, in particular, to the demands of Building Bulletins to cool buildings efficiently where the building temperature is expected to exceed 28ºC for 120 hours (as stated in CIBSE Environmental Design Guide A and Building Bulletin 101) and anticipating the proposed changes to Part L of the Building Regulations.
Underfloor cooling can be used with chiller units but operates efficiently with heat pump systems or direct with ground source energy probes extracting the heat via a heat exchanger. This means it is available day or night, whatever the weather, day or night. A heat pump system is ideally matched to modern low temperature underfloor systems and it is possible to reverse the cycle and essentially get cooling for free.
Although the PE-Xa pipework and installation method are the same for both underfloor heating and cooling, it is important to consider that the cooling element is designed into the building from the outset especially as there are different pipework spacing requirements. Effectively, the underfloor pipework becomes an indoor coil and can be considered as the evaporator in a refrigeration process in the sense that it is going to be used to absorb the heat from inside the enclosed space and as such requires greater heat transfer. Once this is achieved, the controls need to be capable of automatically changing from heating to cooling and of controlling the dew point when in cooling mode.
Pipe spacing is recommended at between 200 mm and 300 mm for underfloor heating but 150 mm for underfloor cooling which obviously has implications on the amount of pipe required for each installation, but still means the capital cost is low when compared with chillers, ahus and air conditioning.
Recent high profile installations by Rehau include the new £45 million West London Audi centre, built alongside the elevated section of the M4 in West London. As well as 1500m2 of underfloor heating, the building includes more than 500m2 of underfloor cooling installed instead of ahus in the glazed areas of the building to counter the predicted solar gain.
Also new is Wyke College in Hull where around 2000m2 of underfloor heating/cooling is operating direct with ground source energy probes providing comfort cooling for students.
Rehau has the ability to design a system using its in-house design team and a network of partners trained to install its systems, so it can manage the project from design to commissioning.
However, what gives Rehau its competitive advantage in underfloor cooling is its controls, which enable a system to switch automatically from heating to cooling. These controls are compatible with nearly all BMS systems and utilise MODBUS-based open protocol.
The Rehau controls manage the output cooling function so that the dewpoint is not reached and the risk of condensation is eliminated. On an installation where there are large expanses of metal present, this was essential.
Similarly, it eliminates the risk of condensation sometimes seen beneath floor coverings and means that, for end users, there are fewer limitations on the use of carpets with a Rehau system.
I confidently predict underfloor cooling will become a mainstream solution in the UK, just as underfloor heating has done during the past 20 years.
8 May 2010