If a calculation model for the generation of hot water is not based upon objectively verified values, it will not be possible to assess future building energy systems that are predominantly dimensioned around tap water for their overall energy performance.
The share of Domestic Hot Water (DHW) production in the total heat consumption of the building has increased. In new low-energy single family as well as multifamily buildings and the temperature of DHW is higher than the temperature for space-heating. Thus DHW production has become a dominant factor in heating systems for new buildings. The same is the case for the ‘deep’ renovation of existing buildings.
A good model is thus not only of importance for an optimal design and control, but also for deciding on the best concepts and for calculating calculate the energy performance of buildings.
Currently, the biggest challenge for every user of building and plant simulation is the large number of different simulation tools. Every simulation software has a main area of application and is optimized for this specific problem. Even software with a wide range of applications or specialized multi-physics software cannot calculate every problem in an accurate and efficient manner.
For policy purposes models (often commercially available) have been developed to calculate the energy performance of buildings required for building permits or commercial transactions. Climate, location and building specific components, often traditional for certain regions are the basis of these models, where it is expected that it will be difficult to make clear comparisons between those. Given the market of models already on the market, it does not make sense to develop an ‘own’ Annex 46 model.
Overall it is important to think in terms of complete system concepts. Even if the heat is produced with a high energy efficiency, high storage and/or distribution losses still remain unnecessary and eventually will cause a low overall system efficiency to the best generating apparatus. It is therefore important to consider the heat generators not only individually but to design a complete DHW concept with a critical view on performance, comfort and legionella prevention. If DHW is not included based on objectively verified values, it will not be possible to assess future systems that are predominantly dimensioned around tap water.
Future work
With new distribution systems in the market, especially in collective systems, adequate publicly available calculation models do not exist taking into account the latest innovations in domestic hot water technologies. More specifically a model should be developed that can be used for the different countries basically giving support to the existing formal legal calculation models.
A proposal has been done under Annex 46 but the required funding for the work was not available.
Annex Report on Calculation Models
The Annex has in its collaboration analysed the work done on Calculation Models for Heat Pump Water Heaters. The Final Report on this is available and can be downloaded.