I came across a scenario that I feel using below approach advised by Hevacomp to add hot water cylinder to CWS would almost double the real CWS incoming supply/or booster set.
The attached approach ignores the diversity occurs at the point of sanitary fittings, which would only allow a fixed flow rate of the combined hot and cold water supply. By adding a continuous flow, the pipework will see the peak hot water demand as a single outlet constantly satisfied. I would think the correct way to add hot water cylinder feed by CWS, is to add max flow rate and 0 loading units (screen shot as below). That way, the pipework would be property size and flow rate would be accurately estimated.
Hi Shane,
Thanks for the comments. We are not intending to use a collective loading units to represent hot water cylinder but proposed to use the "Max Flow rate" (with no loading units). I believe this might be the most accurate way to hot/cold bending tap application. And this is just to cross check our approach and ensure there is nothing we missed. We understand that if we use 0LUs and maximum flow, then the system will not use the coninous flow as you advised in your comments? But only size the pipe adequate to cope with maximum flow
The problem occurs when sizing the CWS pipework, when we would have to take account of the maximum cold water flow rate so the diversity can not be allowed. if there is a continuous flow for the hot water cylinder, then the pipework will be sized to allow the base continuous flow for the hot water cylinder whilst sizing the CWS pipe based on the BS806 Loading units approach. For example using the "continuous flow" approach, if there is a wash hand basin and a hot water cylinder to serve it, which has a LUs as 2 (0.2l/s). The CWS pipe to this WHB will be sized on LU=2 (0.2l/s). Additionally the hot water cylinder will receive the same LU=2 (0.2l/s). Therefore the total CWS pipework to serve this whb will be sized for 2LUs+0.15l/s continuous flow. Whilst we know the maximum flow rate for this WHB would be 0.2l/s only, and 2LUs if this will be taken into account with other water outlets. In reality, the tap will be set as 0.2l/s, within which this 0.2l/s could completely come from CWS, or partially come from heated by hot water cylinder (still 0.2l/s from CWS afterall)
Our approach as mentioned on the initial post for above mentioned application, would be to assume there is no additional LUs associated to the CWS pipework (as more CWS to serve the hot water, the less CWS to serve the outlets, as the flow rate to each outlet are assumed to be fixed). There will be maximum flow assigned to the outlet representing the hot water cylinder taken from HWS netsys to allow for adequate pipework to cover the maximum flow rate.
It would be appreciated if we can have the comments on above, as if we deviate from what we have been advised from software provider, it may reduce our confidence of using this approach or make it difficult being approved by our Clients.
Thanks,
Shidan
ShidanFurther to my colleagues comments:Using zero loading units with maximum flow is exactly the same as setting Continuous flow.
The method to set up your system should be:
Calculate your HWS system. This will consider diversity and generate a required flow rate for the HWS cylinder.Add a special outlet on the CWS system to represent the HWS cylinder. Set this to Continuous Flow, with the required flow rate derived from the HWS system. Other outlets should be set with flow rates and loading units, so that diversity can be considered. Sizing systems with Blender taps still need to consider they could be fully CWS or fully HWS supplied. Regards,
Duncan Brown