November 2016: Controllability Reviews: 100% significant flaws
Recent controllability reviews have all shown significant flaws in system design and control strategies. These include biomass systems with poor hydraulic design and sizing, heating circuits with poor header design and chilled water systems with fundamentally poor efficiency. The chilled water systems do comply with the latest Guide B, however, more efficient system design has been in use for decades.
One of the most concerning findings is the fundamental lack of understanding of sequence control systems. In many cases flow temperature sequence control was used where modulating gas fired boilers were also controlled on flow temperature via their inbuilt PID control loops. The sequence control will enable all the boilers but the individual boiler PID controls will unload the boilers on reducing demand before the sequence control, consequently the sequence control will be ineffective.
Where flow temperature sequence control is used for bivalent systems with biomass boilers, heat pumps or CHP in conjunction with gas fired boilers, the utilisation of the lead heat source will also often be compromised.
The above reviews included buildings which had not been accepted several years after completion, systems with biomass utilisation of 13% and buildings using nearly three times as much energy as predicted. There are many other factors that can affect building performance, but an early controllability review costing a few hundred pounds can make a significant difference to building performance and in some cases could have avoided long drawn out and very expensive contractual disputes.
Needless to say none of the above reviews are to be published as case studies, but my offer is still open to undertake a limited number of ‘desktop’ controllability reviews for free if I can publish them.
April 2014: Graham Smith is very pleased to advise he has been made a Fellow of CIBSE
CIBSE Journal December 2012 - Burning Issues The safe and efficient design of Biomass heating systems. Graham was one of the authors of this article in association with the other authors of CIBSE AM15.