Feedback This month, Readers Discuss Direct-fired water heating, why gas may not be the best option at home, and good management practice Coming to a head With reference to the CPD article on direct-fired water heating (CIBSE Journal, March 2015), I have concerns that the illustrative schematic in Figure 1 which appears to be following the schematics in KS14: Energy efficient heating can create unwanted problems if not carefully implemented. Work undertaken for AM15: Biomass heating included an investigation into the design of low loss headers, which resulted in the Talking Headers article (CIBSE Journal, February 2014) and Section 8.3 of AM15. This investigation and my experience of investigating poorly performing heating systems has shown that pressurising a low loss header should be avoided unless the velocity on the header is so low that primary-secondary is comfortable, flexible and easy to install; and ground and air source heat pumps are now readily available for the domestic market. Putting two utilities in the road is not efficient and generates more maintenance, which causes mass inconvenience. Two meters, two distribution systems, two sets of safety devices gas isnt winning too many votes here. This leaves cost and perception as the things we need to change if we are to build homes that will optimise the gradual decarbonisation of our electricity grid. Geoffrey Palmer, Grontmij interactions are avoided. I have identi fied several instances where the installation of excess boiler capacity is masking poor hydronic design, which becomes apparent only when attempting to optimise boiler plant on the primary side of a low loss header. Modern low water content gas boilers have a typical internal resistance of between 10kPa and 30kPa, so the primary pump has to develop this pressure. While gas boiler manufacturers have divided views over whether it matters if the pump is on the primary or secondary loop of their boilers, once a low loss header is included, the pump should preferably be on the return to the boilers. If a circuit with low water content boilers has a primary pump on the flow, and the velocity on the header is too high, many problems can result, including primary- Micro-management There is much to agree with in Jackie Portmans article (Giving building services design the attention it deserves, CIBSE Journal, February 2015). However, I disagree with her assertion that a new profession of design manager is required. OK, on larger projects where the work has to be divided up but what is needed is somebody who has been a services designer, but who is senior enough secondary circuit interactions and partial reverse flow up the header, making circuit balancing problematic. The configurations in KS15 have been in existence for a very long time, and would have been developed when boilers had a low internal hydronic resistance with the load circuits having a higher resistance so pumps were, correctly, placed on the flow from the boiler. I believe the era of low water content, high-resistance boilers operating into low loss headers necessitates a review of CIBSE advice on hydronic configurations, including the many publications containing such schematics. The new CIBSE Guide B1 is currently being updated to reflect the above findings. David Palmer lower water content boilers and certainly not appropriate where there is significant pressure drop in the header. Such traditional header systems can also challenge the effective use of condensing boilers, as discussed in the presentation by Simon Mitchell at www.cibseashrae.org Technical editor Tim Dwyer FCIBSE replies: The simplified sketch of the traditional boiler with a true low loss header in the CPD is typical of many legacy systems but, as David has correctly highlighted, this might be unsuitable for newer, Living without gas Technological innovation has allowed us to generate synthetic gas from waste products to deliver into the grid. However, gas is still a finite resource, so why is it that low-grade requirements, such as heating new homes, still rely on this highgrade fuel? If we put on our utopian glasses and wind the clock forward, we will find an electricity network fuelled by renewable, low carbon and highly efficient energy. So why do gas cookers and gas boilers still have a place in new homes? Modern induction hobs are cleaner, quicker and have almost no local waste heat; electric ovens provide multiple programmes to suit any chef, can be self-cleaning and efficient; underfloor heating to get the respect and trust of those doing the design, and who is not worried about simply monitoring what has happened and where additional effort is required. In short, good direction is preferable to overly concentrated management. In the case of a smaller project, involving fewer staff, the designer is really the only person who can be competent to manage what they do. Within all this lies the truth that HVAC (and other building services) design time is unpredictable at the beginning of a project, and depends on the project, the client, and the architect and structural engineer. There is a statistical-mean design time based on building type, area, servicing and project cost, but it is only a mean and these factors are variable for quite some time into the run of a project. Statistics may show that particular firms of architects, and particular types of building, cause extended design times, but the inexactitude remains. This vexes graduates of certain MBA courses, who have not designed services (or anything at all), and means many of them will never understand sub-plots such as HVAC design being less predictable than that of almost all the other professions. Thus, this type of manager is not suited to interfering with the design process. At risk of infringing copyright, Det Supt Pullman, in the TV series New Tricks, exemplifies how good direction and minimal management of old but vastly experienced and technically competent staff gets results. One could also criticise a too intellectual approach that treats design concepts and elements as discrete, self-contained and, therefore, programmable entities, whereas they often have unnoticeable strings attached that may unexpectedly link with other design professions. John Moss, consultant, building performance and systems, Arup CIBSE Journal welcomes readers letters, opinions, news stories, events listings, and proposals for articles. Please send all material for possible publication to: editor@cibsejournal.com, or write to Alex Smith, editor, CIBSE Journal, CPL, 275 Newmarket Road, Cambridge, CB5 8JE, UK. We reserve the right to edit all letters.