How do you model WWHRS in DSM? (IES VE, TAS, Apache HVAC)

An explanation of how to model WWHRS in DSM: Using known work-arounds

WWHRS is native to SBEM and works in a similar way to SAP (see here for SBEM 5.6a guidance for modelling WWHRS)

If you are modelling using Dynamic Simulation Modeling (DSM) then WWHRS can be directly inputted via the IES VE Apache HVAC tool.

Unfortunately, however, to model WWHRS where the IES VE Apache HVAC tool is not available, in ‘standard’ DSM packages a ‘work-around’ needs to be applied.

IES VE - WWHRS is implemented in their Apache HVAC tool and a user can configure the system there: click here for ApacheHVAC modelling guidance.

Where the Apache tool is not available, some users have opted for ‘workarounds’ to incorporate the impact of WWHRS within their DSM models. Recoup can offer justifiable project-based calculations, demonstrating kWh or % DHW energy savings, which can then be incorporated into your model (Please contact technical@recoup.co.uk for calculation tools)

Either via:

DHW energy reduction / Hot water volume reduction or
an ‘artificial’ increase in DHW plant efficiency or
an ‘artificial’ increase in incoming CWM temperature.

1. Energy Reduction or DHW volume reduction, due to the presence of WWHRS

If you are installing WWHRS in a scenario where multiple showers are present and DHW is provided from a centralised source. Then it is likely that you will be required to design the WWHRS as System B.

Pipe HEX System B

System B, simply reduces the volume of hot water required per shower use. Therefore, the WWHRS System efficiency (which can be calculated specifically for any given project) can be translated as a direct percentage reduction in the volume of DHW required per shower use (see example calculation sheet below). Therefore, if you know how much DHW is attributed to the showers in your project or scheme, you can reduce this DHW volume by the percentage shown (orange cells, below) or as a direct energy reduction (yellow cells).

Screenshot WWHRS Hotel energy example calculation (150 rooms)

(Above) Example 150-bed Hotel calculation:

Recoup Pipe HEX installed as System B (1no Pipe per 2no showers)

The 43.2% reduction calculated in the example above is purely down to using less DHW per shower. Therefore, you can either, estimate how much DHW is attributed to showering at the site, (either in kWh or as a total annual volume) and then reduce this by 43.2%

2. Artificially increase the efficiency of the DHW plant

Manually increasing the system efficiency of the DWH plant, will reduce the kWh required to produce DHW. You can, therefore, increase the DHW plant efficiency, to the point that the kWh required to produce DHW is, reduced by the energy reduction as shown in the calculation (yellow box)

3. Adjust mean cold water inlet temperature

Another method that can be used to reduce the energy required to produce DHW (and align it with the calculation model provided by Recoup) is to adjust the temperature of the incoming cold water feed to the DHW plant. The area to edit this is usually found in the DHW Supply and return temps tab (eg below):

DHW supply and return temp tabs-2

Hopefully, this gives you justifiable options to enable WWHRS to be incorporated into your project. We are always more than happy to discuss individual projects over Teams, and you can book a Teams call directly into the technical team calendar here: Book a Teams Call

Note:

Another problem with most of these DSM software tools (other than not directly allowing for WWHRS) is that they don’t always allow for the proportion of DHW for showering to be separated from other DHW uses in a particular model. However, usually a specifier or energy modeller will make assumptions of how much energy DHW showering would require (without WWHRS).

If you have calculated how much DHW is attributed to showering, then Recoup can use these figures (rather than shower occupancy and usage assumptions) to tie the WWHRS calculation we produce directly in to the energy usage within your DSM model. (Please contact technical@recoup.co.uk for calculation tools)