Ability will be refitting their London Showroom. This is used to showcase and demonstrate its ranges of Fan Coil Units, Heat Recovery Units and Twin / Single Fan Units. It will also be used for training and CPDs. The facility itself is...

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Chilled Beams Vs Fan Coil Units

A new study conducted by EDSL (Environmental Design Solutions Ltd) has been published - 10th July 2014. This relooks at the comparative energy efficiency of Fan Coils and Chilled Beams. This report has not been rewritten or adjusted by any Fan Coil Manufacturer, it is as it was issued by EDSL. The upshot is that in a 'Like for Like' system, Fan Coils can be just as efficient as a chilled beam, not 17% less efficient as the CBCA report would have had you believe. When you then consider (Fan Coil Only) features such as Unoccupied Setbacks and Ability Multi Room FCUs, Fan Coils are going to be more efficient and certainly more flexible!

Please follow this link to see the report

 

 

Our Previous Web Page on the CBCA Report

We are seeing a number of articles resulting from a recent independent energy modelling study undertaken by EDSL on behalf of the CBCA (Chilled Beam and Ceiling Association) in the UK which purports to show typical energy reductions in the region of 20% for chilled beams against EC VAV Fan Coils and up to 40% against traditional VAV solutions - So that is pretty unequivocal then!

However, through the wonders of the internet we (and many others) have obtained copies of the document in advance of the official release and we (and many others) think that this document needs to be strongly challenged.

The deficiency with this ‘Sales Document’ is that as it steps thought the various scenarios, every single time it arrives at an ‘inconvenient truth’ in support of the fan coil it stops short of further explanation. Consequently, by the time you get to the end you are convinced that chilled beams are the more efficient system without realising you have only heard half the story.

Before reading the detail of why the chilled beam report is considered by many to be flawed, it should be noted that a new, more balanced study has just been financed and approved by the Fan Coil Unit manufacturers association within FETA. The study results and report is expected Feb / March 2014. Those results will be published on this site.

A brief synopsis of the problems with the report:-

The efficiency benefits attributed to the beams are as a result of running the beams at elevated water temperatures (14-17C) whereas the fan coils have only been modelled at 6-12C. It is true to say that chilled beams use (can only use) elevated water temperatures and can so benefit from the better chiller COPs that affords. What the report does not suggest once is that fan coil units can of course also use the same elevated temperatures and so would also get the same beneficial chiller COP’s. To have had overall balance the report should have had at least one comparison between a beam and a fan coil both operating at the same water condition. Remember, at least with fan coils a designer has the freedom to choose the water temperatures he considers most appropriate, with beams that opportunity is not there.

The air handling unit specific fan power (SFP). Active beams require more system pressure to operate and will therefore, without question have a higher SFP than both the passive chilled beam and FCU systems - is this alluded to? No! When using Active Chilled beams it becomes much more difficult to make the AHU SFP comply with limiting factors in the current building regulations and if correct values were used for the different systems much of the reported gains attributed to the Active Chilled beam would not apply.

While the report refers to the fan coils as VAV fan coils over and over, the specific fan power of the fans used in the fan coil study appears to be a constant 0.25W/(l/s). Most fixed speed fan coils as installed will be drawing more in the region of 0.2 W/(l/s) and with a VAV strategy in place will for the most part be drawing far less than that. If the VAV SFP values used accounted for the VAV strategy, then the fan energy reported for a year would be far less.

Ability welcomes meaningful studies on systems, products and methods that will constructively help us advance the building services industry. However, this document does not yet in our view fall into that category. Remember, this study has not been based on any new chilled beam technology, it is simply an attempt to put a new slant on our existing understanding of the relative merits of beams and fan coils.

If we have misinterpreted some of the data and made an inaccurate observation then we apologise. However, that would kind of reinforce the fact that there is a lack of any detail on the fan coil side of the evaluation to allow readers (such as ourselves) to make reasoned judgement.