MEPworx – Point of Use Hot Water Heater

By Gary Mann

Local Water Heaters are not featured in MEPworx Appliance List by default because they are not specifically featured in the BS EN 806 Standard, but they can be added to your Public Health project.

To estimate the flow to the Water Heater, either calculate by summation, using Edit>Appliance list below, or as modelled by the red, Hot Water Entry Point (HW EP). See screenshot.

Use Display>Calculate & Display>Results, (Pipe F8) to determine the HW Loading units required to be supplied by the Cold Water (CW) pipe, e.g. 5 LUs, equating to 0.296 kg/s. (You could use the flow rate and insert as Continuous, but this would not allow for diversity).

Once the HW diversified demand is known, Insert>Special, so that the HW flow can be added to the CW via a Special Draw-Off. Be sure to input the “Highest Single Value” (in this case 2) as this ensures the correct graph-line is used to convert the Loading Units to a flow rate.

Tee this “Special” into the CW Supply by Inserting a CW Distribution Pipe, single-click the Draw-Off arrow and then double-click on CW pipe serving the appliances at the appropriate height level, to tee into this existing run.

The results of both Hot and Cold flows are summated and a suitable diversified flow rate (16 LUs or 0.486 kg/s) is obtained. This total flow through the CW supply now includes the diversified use of every Hot & Cold Draw-Off (Outlets).

N.B, Adding a Draw-Off into the “Appliance List” will distort the HSV from 2 to 5, resulting in an increased flow rate of 46%, Compare results above. So, using a “Special” is always preferable.

I hope you find this helpful, let me know if you have any suggestions for future topics.