HIU SIZING / HIU COLD FEED SIZING / HIU SIMULATION HELP

Question

Good Morning Shane 
 
 I was hoping I might be able to avail of your expertise. 
 
 We are designing a large scale development 500+ apartments split in to Block A-H. The development will be comprised mainly of 1,2,3,4 bed apartments.
 
 
 Each apartment will have their own individual Heat Interface Unit unit for the production / Generation of hot water services. 
 
 I have being sizing the water services piping network using Hevacomp Netsy. Piping out individual appliances such as Basins Baths WC ect is ok. 
 
 Where we are having some difficulty is in the modelling the numerous HIU cold feeds. 
 
 It appears there is 2 different ways of entering the cold feed to the HIU. 
 
 Insert a special appliance and Enter the sum of the HWS Loading Units being generated by the HIU 
 Or 
 
 
 Insert a special appliance and Enter a continuous flow which is representative of the sum of the HWS Loading units 
 
 Either way is not a hundred percent correct and oversizes pipework in different parts of the network 
 
 
 When entering the HWS Lu the effect is to oversize the pipework nearest to the HIU. This appears to be caused by the way EN806 is structured so 10 Lu is seen as a single appliance with 10 Lu
 so the chart is read in such a way that 10 Lu is 1l/s (see chart below with line in red). 
 In reality the biggest single appliance connected the HIU is a bath so 10 Lu should be read against the single biggest appliance having 4 Lu which gives a figure of 0.52 l/s (see the
 chart below with line in blue) which is just over half of the other figure. 
 This effect is carried through to about 150 Lu which is when the branch lines on the below chart start to come together and totally disappears at 300 Lu which is when the branch lines
 coincide. 
 A typical apartment has approx. 25 Lu so this effect is very obvious on the pipework serving apartment groupings of 6 or less.
 
 The main system booster works out correctly though and the main distribution pipe from the booster. 
 
 
 
 
 If we convert the HIU HWS Lu to a continuous flow pipework at the HIU is correct but the distribution and riser pipework is massively oversized as the continuous flows are being summed together
 without diversity being applied. 
 So if we take a 2 bed apartment with 10 Lu on HWS generation as being the equivalent of 0.52l/s and we have a grouping of 6 apartments each with a HIU we have 3.12l/s + 1l/s (the diversified
 CWS flow) = 4.12l/s 
 whereas if done through loading units we would have 150Lu (with biggest appliance at 4 for a bath) which is approx. 1.2l/s from the chart. 
 The end result is an oversized booster set and primary pipework. 
 
 We have reviewed the previous topics on the forum but none seem to directly address this issue. 
 The nearest one we found was this post on cold feed to Hot water Systems
 https://communities.bentley.com/products/building/performance/w/building_performance__wiki/27598/including-hot-water-system-feed-in-your-cold-water-system 
 , 
 But this seems to be based on a single point of hot water generation in a system e.g. a central large capacity calorifier and not lots of smaller hot water generators spread over the water service network e.g.
 HIUs, Electric instantaneous water heaters, or individual calorfiers in each apartment . 
 
 
 I am wondering if you ( Hevacomp) have come up with a solution / work around to correctly simulate HIU&#8217;s within a piping network and how is this best achieved. 
 
 Your help and attention to this matter is greatly appreciated. 
 
 If it would suit you , myself and Daniel are free today if you would like to organise a conference call , where we could discuss the issue in more detail. 
 
 Best Regards 
 
 Seamus Murphy 
 Junior Mechanical Engineer 
 Homan O'Brien &#8226; Consulting Engineers 
 89 Booterstown Avenue Blackrock, Co. Dublin, A94 P2C2, Ireland. 
 Tel: +353 (01) 2056300 Fax: +353 (01) 2056301 
 Email: 
 seamus.muprhy@homanobrien.ie Web : www.homanobrien.ie 
 
 
 
 
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Shane Regan · Answer

Hi Seamus, 
 My first thoughts would be that modeling these may be somewhat outside the intended scope of BS806, as this is based on normal outlets, as you mention. So you may struggle to effectively model all components from the plant room, to HIU to outlets, in one single project. 
 You may need to consider modelling the system over two projects: 
 
 One to model the individual outlets in each apartment, where each HIU is entered as a System Marker. 
 The second to model the flow from the plant room (System Marker) to the HIU's, where the HIU's are entered as Special outlets (each with flow rate entered as calculated in results in step 1). 
 
 You would just need to export the results from each project to Excel and combine the relevant parts. This should mean that the diversity is taken into account at local level, and the pipework is not oversized at plant / HIU level. 
 Hopefully that helps, please let me know how you get on.