Calculation Models for Hot Water Systems

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, 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 while the temperature of DHW is higher than the temperature for space-heating. Thus DHW production is becoming a dominant factor in heating systems for new buildings. This is also the case for the ‘deep’ renovation of existing buildings.

A good model is not only of importance for an optimal design and control, but also for deciding on the best concepts and calculating the energy performance of buildings, which is in many countries a legal issue for a building or renovation permit and for building energy labels.

Currently, a challenge for users of calculation models is the large number of different available often commercial software tools on the market. For policy purposes models 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. However studying these models Domestic Hot Water is often handled as a default value not taking into account the differences in energy usage and the innovative technologies in the market.

Given the market of models already on the market, it does make sense to develop a model that can support the already existing models.

Overall it is important to think in terms of complete system concepts. Even if heat is generated with a high energy efficiency other aspects in the system like storage and distribution losses can cause a low overall system efficiency. It is important to consider the heat generators not only individually but to design a complete Domestic Hot Water concept with a critical view on performance, comfort and legionella prevention. Geelen et al presented his analyses at the 11th IEA Heat Pump Conference.

If Domestic Hot Water 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. A model should be developed that can be used for the different countries basically giving support to the existing formal legal calculation models.

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.